Non-fragile stress distribution with high stress area for improved fracture resistance

Abstract

In one or more embodiments, a chemically strengthened glass-based article includes a first major surface and an opposing second major surface defining a thickness t of the glass article; a stress profile [sigma] (x) extending through the thickness t of the glass article; a first compressive stress layer extending to a first depth DOC1 of greater than about 0.15 t; a second compressive stress layer extending from the second major surface to a second depth of compression DOC2 less than or equal to DOC1; and a central tension zone positioned between the first compressive stress layer and the second compressive stress layer and including a peak tension PT and a tension zone width BTZ spanning DOC1 to tDOC2. In an embodiment, the following criteria are satisfied: wherein DOC = DOC1 and is the slope of the stress profile sigma (x) at DOC; ; and wherein TA is the tension area, defined as follows.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 450,276, filed March 6, 2023, entitled “Non-Frangible Stress Profiles With High Stress Area For Improved Fracture Resistance,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] This specification generally relates to chemically strengthened glass-based products, and more specifically, to non-fragile chemically strengthened glass-based products. Background Technology

[0004] Chemically strengthened glass is widely used as cover glass for mobile devices, touch-enabled displays, and the like. Generally, non-fragile ion-exchange glass is preferred for touchscreen devices to reduce the risk of injury to users from small glass particles ejected during self-accelerated, highly fragmented fracture, a condition characterized by high brittle stress. This situation often arises from a combination of excessive compressive stress in the surface layer of the glass substrate and excessive tensile stress in the central tension zone balancing the substrate. There is a continuous need to impart the desired stress distribution to the glass substrate through strengthening, thereby providing the glass with good mechanical and fracture properties for various applications, including cover glass applications. Summary of the Invention

[0005] Many electronic devices, such as smartphones, tablets, portable media players, personal computers, and cameras, incorporate cover glass that serves as a display cover and may also include touch functionality. Through strengthening processes such as ion exchange, the cover glass of electronic devices exhibits significantly enhanced fracture resistance. Such strengthening processes provide the cover glass with a compressive stress layer extending from the outer surface to the depth of finite compression (DOC). The compressive stress in the compressive stress layer is balanced by a central tension zone located between the compressive stress layers.

[0006] When a portable device is dropped onto a hard surface, the cover glass exhibits two main failure modes. One mode is flexural failure, caused by the bending of the glass when the device is subjected to a dynamic load from an impact with the hard surface. The other mode is abrupt contact failure, caused by damage to the glass surface. Impacts between the glass and rough, hard surfaces such as asphalt or granite can result in noticeable dents on the glass surface. These dents become failure sites on the glass surface, from which cracks may originate and propagate.

[0007] In general, the deeper the DOC and the greater the compressive stress in the compressive layer, the more the cover glass will be able to withstand drops onto hard surfaces, especially rough surfaces, as defects introduced into the surface of the cover glass will be less likely to penetrate the compressive stress layer and enter the central tension zone where they can propagate cracks, thereby negatively impacting the use of the device. However, given that in some cases surface defects can penetrate the compressive stress layer, the cover glass is preferably non-fragile, in part to reduce the risk of injury to the user from small glass particles that can be ejected during self-accelerating high-fragmentation cracking that can occur under highly fragile stress conditions. Moreover, as the fragility of the cover glass is determined in part by the magnitude and distribution of tensile stress in the central tension zone, care must be taken when designing the compressive stress layer so as not to result in a balanced central tension zone with a fragile stress profile. Thus, there is a continuing need for chemically strengthened glass-based articles that exhibit both improved resistance to cracking and non-fragility.

[0008] One driver of fragility is the tensile strain energy (TSE) of the glass-based article. It has been found that, in order to produce a deep compressive stress layer while avoiding fragility, the tension area, i.e., the tensile stress integrated across the thickness of the central tension zone, should be maximized relative to an acceptable TSE level. The acceptable TSE level is determined based on the fracture toughness of the glass-based article, and the actual TSE is proportional to the square tensile stress integrated across the thickness of the central tension zone. As the TSE is proportional to the depth integral of the square tensile stress, and where the tension area, i.e., the force of the compressive stress in the balanced compressive layer, is only the depth integral of the tensile stress (and not the square), a more uniform distribution of tensile stress in the central tension zone will maximize the tension area relative to a given TSE (set according to the acceptable level discussed above).

[0009] The present disclosure provides non-fragile chemically strengthened glass-based articles with improved resistance to cracking by incorporating a compressive stress layer with both a high DOC and a high magnitude of stress deep in the compressive stress layer. The focus of the present disclosure is to increase the deep compressive stress level of any fixed material parameter (e.g., fracture toughness) such that the performance improvements associated with the present disclosure can add to any performance improvements based on improving material properties. Moreover, it should be understood that the concepts disclosed herein with respect to non-fragile stress profiles can be implemented in articles of different thicknesses, different numbers and combinations of stages (e.g., fully amorphous glass or glass with precipitated crystalline phases), and different compositions (e.g., free of Li). Finally, while the glass-based articles discussed herein are generally planar, the concepts discussed can also be applied to non-planar articles.

[0010] According to a first aspect of the disclosure, a chemically strengthened glass-based article includes: a first major surface and an opposing second major surface defining a thickness t of the glass article; a stress profile σ(x), where x extends through the thickness t of the glass article in a direction normal to the first and second major surfaces; a first compressive stress layer extending from the first major surface to a first compressive depth DOC1 greater than about 0.15t; a second compressive stress layer extending from the second major surface to a second compressive depth DOC2 less than or equal to DOC1; and a central tension zone positioned between the first and second compressive stress layers and including a peak tension PT and a tension zone width (BTZ) spanning DOC1 to t - DOC2, wherein:

[0011] ,

[0012] where DOC = DOC1 and is a slope of the stress profile σ(x) at DOC; and

[0013] ,

[0014] where TA is a tension area defined by:

[0015] .

[0016] The second aspect can include the first aspect, wherein the chemically strengthened glass-based article has a greater than 140 MPa.

[0017] The third aspect can include any of the preceding aspects, wherein the chemically strengthened glass-based article has a greater than 900 MPa.

[0018] The fourth aspect can include any of the preceding aspects, wherein the chemically strengthened glass-based article has a peak tension PT greater than 90 MPa.

[0019] The fifth aspect can include any of the preceding aspects, wherein the chemically strengthened glass-based article has a peak tension PT greater than where K IC is a fracture toughness of the glass article at a location x peak corresponding to the peak tension PT in the central tension zone.

[0020] The sixth aspect can include any of the preceding aspects, wherein the chemically strengthened glass-based article has a thickness t between 0.4 mm and 0.77 mm.

[0021] The seventh aspect can include any of the preceding aspects, wherein the composition of the chemically strengthened glass-based article includes less than 3 mol% Li20, and the glass article has a fracture toughness K peak in the central tension zone at a location x IC greater than or equal to 0.720 .

[0022] The eighth aspect can include any of the first through sixth aspects, wherein the composition of the chemically strengthened glass-based article includes Li20 in an amount ranging from about 3.0 mol% to about 7.5 mol%, and the glass article has a fracture toughness K peak in the central tension zone at a location x IC greater than or equal to 0.810 .

[0023] The ninth aspect can include any of the first through fifth aspects, wherein the composition of the chemically strengthened glass-based article includes Li20 in an amount ranging from about 7.5 mol% to about 11 mol%, and the glass article has a fracture toughness K peak in the central tension zone at a location x IC greater than or equal to 0.850 .

[0024] The tenth aspect can include any of the first through fifth aspects, wherein the composition of the chemically strengthened glass-based article includes Li20 in an amount ranging from about 11 mol% to about 13 mol%, and the glass article has a fracture toughness K peak in the central tension zone at a location x IC greater than or equal to 0.870 .

[0025] The eleventh aspect can include any of the first through fifth aspects, wherein the composition of the chemically strengthened glass-based article includes greater than about 13 mol% Li20; and the glass article has a fracture toughness K peak in the central tension zone at a location x IC greater than or equal to 0.950 .

[0026] The twelfth aspect can include any of the preceding aspects, wherein the stress profile s(x) in the central tension zone, when fit to Equation I,

[0027] (Equation I),

[0028] has a best fit value of the power coefficient p that exceeds 2.75, where xpeak is the location in the central tension zone corresponding to the peak tension PT.

[0029] The thirteenth aspect can include any of the preceding aspects, wherein the power coefficient p is no more than 20.

[0030] The fourteenth aspect can include any of the preceding aspects, wherein the chemically strengthened glass-based article comprises a fragility factor no more than wherein is the fracture toughness of the glass article in the central tension zone at a location x peak corresponding to the peak tension PT, and wherein:

[0031] ,

[0032] where σ is the stress profile σ(x).

[0033] The fifteenth aspect can include any of the preceding aspects, wherein .

[0034] The sixteenth aspect can include any of the preceding aspects, wherein the DOC is greater than or equal to 0.190t.

[0035] The seventeenth aspect can include any of the preceding aspects, wherein the chemically strengthened glass-based article comprises a surface compressive stress CS at each of the first major surface and the second major surface, the surface compressive stress CS satisfying the relationship I:

[0036] (relationship I).

[0037] The eighteenth aspect can include any of the preceding aspects, wherein the stress profile σ(x) of the chemically strengthened glass-based article exhibits a spike at the first major surface and the second major surface, and a knee stress CS SP at a location DOL k satisfies the relationship II:

[0038] (relationship II).

[0039] The nineteenth aspect can include any of the preceding aspects, wherein the chemically strengthened glass-based article satisfies the following criteria:

[0040] ,

[0041] wherein is the greater of 4 µm and 0.01t.

[0042] ​The twentieth aspect can include any of the preceding aspects, wherein the stress profile σ(x) of the chemically strengthened glass-based article exhibits a sharp peak at the first and second major surfaces and a knee stress CS at a depth DOL SP k wherein a portion of the stress profile σ(x) between the DOL SP and the DOC includes a negative second derivative.

[0043] According to a first aspect of the disclosure, a chemically strengthened glass-based article includes: a first major surface and an opposing second major surface defining a thickness t of the glass article; a stress profile σ(x), where x extends through the thickness t of the glass article in a direction normal to the first and second major surfaces; a first compressive stress layer extending from the first major surface to a first compressive depth DOC1 greater than about 0.15t; a second compressive stress layer extending from the second major surface to a second compressive depth DOC2 less than or equal to DOC1; and a central tension zone positioned between the first and second compressive stress layers and including a peak tension PT and a tension zone width (BTZ) spanning DOC1 to t - DOC2, wherein:

[0044] ,

[0045] where DOC = DOC1 and is a slope of the stress profile σ(x) at the DOC; and

[0046] ,

[0047] where TA is a tension area defined by:

[0048] .

[0049] The second aspect can include the first aspect, wherein the peak tension PT of the chemically strengthened glass-based article is greater than 140 MPa.

[0050] The third aspect can include any of the preceding aspects, wherein the peak tension PT of the chemically strengthened glass-based article is greater than 900 MPa.

[0051] The fourth aspect can include any of the preceding aspects, wherein the peak tension PT of the chemically strengthened glass-based article is greater than 90 MPa.

[0052] The fifth aspect can include any of the preceding aspects, wherein the peak tension PT of the chemically strengthened glass-based article is greater than where K IC is a fracture toughness of the glass article at a location x peak corresponding to the peak tension PT in the central tension zone.​​​

[0053] The sixth aspect can include any of the preceding aspects, wherein the chemically strengthened glass-based article has a thickness t between 0.4 mm and 0.77 mm.

[0054] The seventh aspect can include any of the preceding aspects, wherein the composition of the chemically strengthened glass-based article includes less than 3 mol% Li20, and the glass article has a fracture toughness Kic in a location x in the central tension zone corresponding to the peak tension PT that is greater than or equal to 0.720. peak IC .

[0055] The eighth aspect can include any of the first through sixth aspects, wherein the composition of the chemically strengthened glass-based article includes Li20 in an amount ranging from about 3.0 mol% to about 7.5 mol%, and the glass article has a fracture toughness Kic in a location x in the central tension zone corresponding to the peak tension PT that is greater than or equal to 0.810. peak IC .

[0056] The ninth aspect can include any of the first through sixth aspects, wherein the composition of the chemically strengthened glass-based article includes Li20 in an amount ranging from about 7.5 mol% to about 11 mol%, and the glass article has a fracture toughness Kic in a location x in the central tension zone corresponding to the peak tension PT that is greater than or equal to 0.850. peak IC .

[0057] The tenth aspect can include any of the first through sixth aspects, wherein the composition of the chemically strengthened glass-based article includes Li20 in an amount ranging from about 11 mol% to about 13 mol%, and the glass article has a fracture toughness Kic in a location x in the central tension zone corresponding to the peak tension PT that is greater than or equal to 0.870. peak IC .

[0058] The eleventh aspect can include any of the first through sixth aspects, wherein the composition of the chemically strengthened glass-based article includes greater than about 13 mol% Li20; and the glass article has a fracture toughness Kic in a location x in the central tension zone corresponding to the peak tension PT that is greater than or equal to 0.950. peak IC .

[0059] The twelfth aspect can include any of the preceding aspects, wherein the stress profile s(x) in the central tension zone, when fit to Equation I, has a peak tension PT that is greater than or equal to 0.720.​​​​​​​​​​

[0060] (Equation I)

[0061] The best-fit value has a power coefficient p greater than 2.75, where x peak This refers to the position in the central tension zone corresponding to the peak tension PT.

[0062] The thirteenth aspect may include any of the aforementioned aspects, wherein the power coefficient p does not exceed 20.

[0063] The fourteenth aspect may include any of the foregoing aspects, wherein chemically strengthened glass-based articles include no more than Fragility factor ,in x represents the position of the glass product in the central tension zone corresponding to the peak tension PT. peak The fracture toughness in, and where:

[0064] ,

[0065] Where σ represents the stress distribution σ(x).

[0066] The fifteenth aspect may include any of the foregoing aspects, wherein .

[0067] The sixteenth aspect may include any of the foregoing aspects, wherein DOC is greater than or equal to 0.190t.

[0068] The seventeenth aspect may include any of the foregoing aspects, wherein the chemically strengthened glass substrate article includes surface compressive stress CS at each of the first primary surface and the second primary surface, the surface compressive stress CS satisfying relation I:

[0069] (Relation I).

[0070] The eighteenth aspect may include any of the foregoing aspects, wherein the stress distribution σ(x) of the chemically strengthened glass substrate exhibits peaks at the first and second principal surfaces, and the peak depth DOL SP Inflection point stress CS k Satisfying relation II:

[0071] (Relationship II).

[0072] The nineteenth aspect may include any of the foregoing aspects, wherein the chemically strengthened glass-based articles meet the following criteria:

[0073] ,

[0074] in 4 pm and the larger of 0.01t.

[0075] The twentieth aspect can include any of the preceding aspects, wherein the stress profile s(x) of the chemically strengthened glass-based article exhibits a spike at the first and second major surfaces and a inflection point stress CS SP at the spike depth DOL k wherein a portion of the stress profile s(x) between DOL SP and DOC includes a negative second derivative.

[0076] According to a twenty-first aspect of the disclosure, a chemically strengthened glass-based article includes: a first major surface and an opposing second major surface defining a thickness t of the glass article; a stress profile s(x), where x extends through the thickness t of the glass article in a direction normal to the first and second major surfaces; a first compressive stress layer extending from the first major surface to a first compressive depth DOC1 greater than about 0.15t; a second compressive stress layer extending from the second major surface to a second compressive depth DOC2 less than or equal to DOC1; and a central tension zone positioned between the first and second compressive stress layers and including a peak tension PT and a tension zone width (BTZ) spanning DOC1 to t - DOC2, wherein:

[0077] ,

[0078] where DOC = DOC1 and is a slope of the stress profile s(x) at DOC; and

[0079] ; and

[0080] ,

[0081] where TA is a tension area defined by:

[0082] .

[0083] The twenty-second aspect can include the twenty-first aspect, wherein the peak tension PT is greater than 90 MPa.

[0084] The twenty-third aspect can include the twenty-first aspect, wherein the peak tension PT is greater than 115 MPa.

[0085] The twenty-fourth aspect can include the twenty-first aspect, wherein the peak tension PT is greater than 125 MPa.

[0086] The twenty-fifth aspect can include any of the twenty-first through twenty-fourth aspects, wherein:

[0087] ,

[0088] where K IC is the fracture toughness of the glass-based article at a location x peak corresponding to the peak tension PT in the central tension region.

[0089] A twenty-sixth aspect can include the twenty-fifth aspect, wherein .

[0090] A twenty-seventh aspect can include the twenty-fifth aspect, wherein .

[0091] A twenty-eighth aspect can include any of the twenty-first through twenty-seventh aspects, wherein the thickness t of the glass-based article is between 0.4 mm and 0.77 mm.

[0092] A twenty-ninth aspect can include any of the twenty-first through twenty-seventh aspects, wherein the thickness t of the glass-based article is between 0.43 mm and 0.68 mm.

[0093] A thirtieth aspect can include any of the twenty-first through twenty-ninth aspects, wherein the composition of the glass-based article includes less than 3 mol% Li20, and wherein the fracture toughness K peak of the glass-based article at a location x IC corresponding to the peak tension PT in the central tension region is greater than or equal to 0.720 .

[0094] A thirty-first aspect can include any of the twenty-first through twenty-ninth aspects, wherein the composition of the glass-based article includes Li20 in an amount ranging from about 3.0 mol% to about 7.5 mol%, and wherein the fracture toughness K peak of the glass-based article at a location x IC corresponding to the peak tension PT in the central tension region is greater than or equal to 0.810 .

[0095] A thirty-second aspect can include any of the twenty-first through twenty-ninth aspects, wherein the composition of the glass-based article includes Li20 in an amount ranging from about 7.5 mol% to about 11 mol%, and wherein the fracture toughness K peak of the glass-based article at a location x IC corresponding to the peak tension PT in the central tension region is greater than or equal to 0.850 .

[0096] The thirty-third aspect may include any one of aspects twenty-one to twenty-nine, wherein the composition of the glass-based article includes an amount of Li₂O in the range of about 11 mol% to about 13 mol%, and wherein the position x of the glass-based article in the central tension region corresponding to the peak tension PT is... peak Fracture toughness K IC Greater than or equal to 0.870 .

[0097] The 34th aspect may include any one of aspects 21 to 29, wherein the composition of the glass-based article includes more than about 13 mol% Li2O, and wherein the position x of the glass-based article in the central tension region corresponding to the peak tension PT is... peak Fracture toughness K IC Greater than or equal to 0.950 .

[0098] The thirty-fifth aspect may include any one of aspects twenty-one to thirty-four, wherein the stress distribution σ(x) in the central tension region, when fitted to equation I,

[0099] (Equation I)

[0100] The best-fit value has a power coefficient p greater than 2.4, where x peak This refers to the position in the central tension zone corresponding to the peak tension PT.

[0101] The thirty-sixth aspect may include the thirty-fifth aspect, in which the best-fit value of the power coefficient p exceeds 2.75.

[0102] The thirty-seventh aspect may include the thirty-fifth aspect, where the best-fit value of the power coefficient p exceeds 3.2.

[0103] The thirty-eighth aspect may include any one of the thirty-fifth to thirty-seventh aspects, wherein the power coefficient p does not exceed 20.

[0104] The thirty-ninth aspect may include any one of aspects 21 to 38, and further include no more than Fragility factor ,in x represents the position of the glass-based product in the central tension zone corresponding to the peak tension PT. peak The fracture toughness in, and where:

[0105] ,

[0106] Where σ represents the stress distribution σ(x).

[0107] The fortieth aspect may include the thirty-ninth aspect, among which .

[0108] The forty-first aspect can include any of aspects twenty-first through forty- first, wherein the DOC is greater than or equal to 0.190t.

[0109] The forty-second aspect can include any of aspects twenty-first through forty- first, wherein the DOC is greater than or equal to 0.200t.

[0110] The forty-third aspect can include any of aspects twenty-first through forty- first, wherein the DOC is greater than or equal to 0.210t.

[0111] The forty-fourth aspect can include any of aspects twenty-first through forty- third, wherein the surface compressive stress CS at each of the first major surface and the second major surface is greater than 110 MPa.

[0112] The forty-fifth aspect can include any of aspects twenty-first through forty- fourth, wherein the stress profile σ(x) exhibits a spike at the first major surface and the second major surface, and a knee stress CS SP at a spike depth DOL k satisfies the relationship II:

[0113] (relationship II).

[0114] The forty-sixth aspect can include the forty-fifth aspect, wherein the knee stress CS SP at the spike depth DOL k is less than or equal to .

[0115] The forty-seventh aspect can include the forty-fifth aspect, wherein the knee stress CS SP at the spike depth DOL k is less than or equal to .

[0116] The forty-eighth aspect can include any of aspects forty-fifth through forty- seventh, wherein:

[0117] ,

[0118] wherein is the greater of 4 µm and 0.01t.

[0119] The forty-ninth aspect can include any of aspects twenty-first through forty- eighth, wherein the stress profile σ(x) exhibits a spike at the first major surface and the second major surface, and a knee stress CS SP at a spike depth DOL k , and wherein the stress profile σ(x) exhibits a knee stress CS SPA portion of the disclosure comprises negative second order derivatives.

[0120] The fifty-first aspect can include any of aspects twenty-first through forty-ninth, wherein .

[0121] The fifty-first aspect can include any of aspects twenty-first through forty-ninth, wherein .

[0122] The fifty-second aspect can include any of aspects twenty-first through forty-ninth, wherein .

[0123] The fifty-third aspect can include any of aspects twenty-first through fifty-second, wherein .

[0124] The fifty-fourth aspect can include any of aspects twenty-first through fifty-second, wherein .

[0125] The fifty-fifth aspect can include any of aspects twenty-first through fifty-second, wherein .

[0126] The fifty-sixth aspect can include any of aspects twenty-first through fifty-fifth, wherein .

[0127] The fifty-seventh aspect can include any of aspects twenty-first through fifty-fifth, wherein .

[0128] The fifty-eighth aspect can include any of aspects twenty-first through fifty-fifth, wherein .

[0129] The fifty-ninth aspect can include any of aspects twenty-first through fifty-eighth, wherein the surface compressive stress CS at each of the first major surface and the second major surface is greater than 550 MPa.

[0130] The sixtieth aspect can include any of aspects twenty-first through fifty-eighth, wherein the surface compressive stress CS at each of the first major surface and the second major surface is greater than 725 MPa.

[0131] The sixty-first aspect can include any of aspects twenty-first through sixtieth, wherein the chemically strengthened glass-based article comprises an amorphous microstructure that is substantially free of crystals or crystallites.

[0132] The sixty-second aspect can include any of aspects twenty-first through sixty-first, wherein the chemically strengthened glass-based article comprises a fracture toughness of less than or equal to 1.0 .

[0133] The sixty-third aspect can include any of aspects twenty-first through sixty- first, wherein the chemically strengthened glass-based article is a glass-ceramic material comprising an amorphous phase and a crystalline phase.

[0134] The sixty-fourth aspect can include any of aspects twenty-first through sixty- first or the sixty-third aspect, wherein the chemically strengthened glass-based article comprises a fracture toughness greater than or equal to 1.2

[0135] The sixty-fifth aspect can include any of aspects twenty-first through sixty-fourth, wherein the chemically strengthened glass-based article is formed by subjecting a glass-based substrate to an ion exchange treatment, and wherein the glass-based substrate comprises: greater than or equal to 50 mol% and less than or equal to 75 mol% Si02; greater than or equal to 10 mol% and less than or equal to 25 mol% AI2O3; greater than or equal to 1 mol% and less than or equal to 11 mol% B2O3; greater than or equal to 1 mol% and less than or equal to 10 mol% Na20; and greater than or equal to 5 mol% and less than or equal to 15 mol% Li20, wherein the molar concentration of Li20 in the glass-based substrate is greater than the molar concentration of Na20 in the glass-based substrate.

[0136] The sixty-sixth aspect can include any of aspects twenty-first through sixty-fifth, wherein the chemically strengthened glass-based article is formed by subjecting a glass-based substrate to an ion exchange treatment, and wherein the glass-based substrate comprises Li20 in an amount of 7.0 to 15.0 mol%.

[0137] The sixty-seventh aspect can include any of aspects twenty-first through sixty-sixth, wherein the chemically strengthened glass-based article is formed by subjecting a glass-based substrate to an ion exchange treatment, and wherein the glass-based substrate comprises a molar ratio of Li20 to Na20 greater than or equal to 2.0.

[0138] According to a sixty-eighth aspect of the disclosure, a chemically strengthened glass-based article comprises: a first major surface and an opposing second major surface defining a thickness t of the glass-based article, wherein the thickness t is less than or equal to 0.52 mm; a stress profile s(x), wherein x extends through the thickness t of the glass-based article in a direction normal to the first and second major surfaces; a first compressive stress layer extending from the first major surface to a first compressive depth DOC1 greater than about 0.15t; a second compressive stress layer extending from the second major surface to a second compressive depth DOC2 less than or equal to DOC1; and a central tension zone positioned between the first and second compressive stress layers and comprising a peak tension PT and a tension zone width BTZ spanning DOC1 to t - DOC2, wherein:

[0139] ,​

[0140] where DOC = DOC1and is the slope of the stress profile σ(x) at DOC;

[0141] ; and

[0142] ,

[0143] where TA is the tension area, defined by:

[0144] .

[0145] The sixty-ninth aspect can include the sixty-eighth aspect, wherein the peak tension PT is greater than 115 MPa.

[0146] The seventieth aspect can include the sixty-eighth aspect, wherein the peak tension PT is greater than 125 MPa.

[0147] The seventy-first aspect can include any of the sixty-eighth through seventieth aspects, wherein the stress profile σ(x) in the central tension zone, when fit to Equation I,

[0148] (Equation I),

[0149] has a best fit value of the power coefficient p that exceeds 2.4, where x peak is the location in the central tension zone corresponding to the peak tension PT.

[0150] The seventy-second aspect can include any of the sixty-eighth through seventieth aspects, wherein the stress profile σ(x) in the central tension zone, when fit to Equation I,

[0151] (Equation I),

[0152] has a best fit value of the power coefficient p that exceeds 2.75, where x peak is the location in the central tension zone corresponding to the peak tension PT.

[0153] The seventy-third aspect can include any of the sixty-eighth through seventy-second aspects, wherein the stress profile σ(x) exhibits a spike at the first and second major surfaces and an inflection stress CS SP at a spike depth DOL k , and wherein a portion of the stress profile σ(x) between DOL SP and DOC comprises a negative second derivative.

[0154] The seventy-fourth aspect can include any of the sixty-eighth through seventy-third aspects, wherein DOC is greater than or equal to 0.190t.

[0155] The seventy-fifth aspect can include any of aspects sixty-eighth through seventy-third, wherein the DOC is greater than or equal to 0.200t.

[0156] The seventy-sixth aspect can include any of aspects sixty-eighth through seventy-third, wherein the DOC is greater than or equal to 0.210t.

[0157] According to a seventy-seventh aspect of the disclosure, a chemically strengthened glass-based article includes: a first major surface and an opposing second major surface defining a thickness t of the glass-based article, wherein the thickness t is from about 0.43 mm to about 0.68 mm; a stress profile σ(x), wherein x extends through the thickness t of the glass-based article in a direction normal to the first and second major surfaces; a first compressive stress layer extending from the first major surface to a first compressive depth DOC1 that is greater than about 0.19t; a second compressive stress layer extending from the second major surface to a second compressive depth DOC2 that is less than or equal to DOC1; and a central tension zone positioned between the first and second compressive stress layers and including a peak tension PT and a tension zone width BTZ spanning DOC1 to t - DOC2, wherein: the peak tension PT is greater than 95 MPa; the stress profile σ(x) in the central tension zone, when fit to Equation I,

[0158] (Equation I),

[0159] has a best fit value of the power coefficient p that exceeds 2.4, wherein DOC = DOC1 and x peak is a location in the central tension zone corresponding to the peak tension PT; and the stress profile σ(x) exhibits a spike at the first and second major surfaces and a spike depth DOL SP at an inflection point stress CS k satisfies relationship II:

[0160] (Relationship II)

[0161] wherein DOC = DOC1 and is a slope of the stress profile σ(x) at DOC.

[0162] The seventy-eighth aspect can include the seventy-seventh aspect, wherein the thickness t is less than or equal to 0.52 mm.

[0163] The seventy-ninth aspect can include the seventy-seventh or seventy-eighth aspect, wherein the peak tension PT is greater than 103 MPa.

[0164] According to an eightieth aspect of the disclosure, a method of making a chemically strengthened glass-based article includes exposing a glass-based substrate to a molten salt bath to form a chemically strengthened glass-based article, wherein: a temperature of the molten salt bath is less than a strain point of the glass-based substrate by no more than 110 °C, wherein the strain point of the glass-based substrate is determined by fiber elongation; the chemically strengthened glass-based article includes a first major surface and an opposing second major surface defining a thickness t of the glass-based article; and an ion exchange treatment time is selected such that the chemically strengthened glass-based article includes: a stress profile σ(x), where x extends through the thickness t of the glass-based article in a direction normal to the first and second major surfaces; a first compressive stress layer extending from the first major surface to a first compressive depth DOC1 that is greater than about 0.15t; a second compressive stress layer extending from the second major surface to a second compressive depth DOC2 that is less than or equal to DOC1; and a central tension zone positioned between the first and second compressive stress layers and including a peak tension PT and a tension zone width BTZ spanning DOC1 to t - DOC2, wherein:

[0165] ,

[0166] where DOC = DOC1 and is a slope of the stress profile σ(x) at DOC;

[0167] ; and

[0168] ,

[0169] where TA is a tension area defined by:

[0170] .

[0171] An eighty-first aspect can include the eightieth aspect, wherein the temperature of the molten salt bath is from 455 °C to 490 °C.

[0172] An eighty-second aspect can include the eightieth or eighty-first aspect, wherein the ion exchange treatment time is from 2 to 4 hours.

[0173] An eighty-third aspect can include any of the eightieth through eighty-second aspects, wherein the glass-based substrate includes: greater than or equal to 50 mol% and less than or equal to 75 mol% SiO2; greater than or equal to 10 mol% and less than or equal to 25 mol% Al2O3; greater than or equal to 1 mol% and less than or equal to 11 mol% B2O3; greater than or equal to 1 mol% and less than or equal to 10 mol% Na2O; and greater than or equal to 5 mol% and less than or equal to 15 mol% Li2O, wherein a molar concentration of Li2O in the glass-based substrate is greater than a molar concentration of Na2O in the glass-based substrate.

[0174] The eighty-fourth aspect can include any of the eightieth through eighty-third aspects, wherein the glass-based substrate comprises Li20 in an amount of 7.0 to 15.0 mol%.

[0175] The eighty-fifth aspect can include any of the eightieth through eighty-fourth aspects, wherein the glass-based substrate comprises a molar ratio of Li20 to Na20 that is greater than or equal to 2.0.

[0176] Additional features and advantages of the chemically strengthened glass-based articles described herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art who practice the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0177] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments described herein and, together with the description, serve to explain principles and operations of the claimed subject matter. BRIEF DESCRIPTION OF DRAWINGS

[0178] Figure 1 is a schematic cross-sectional view of a chemically strengthened glass-based article;

[0179] Figure 2a schematically depicts a strengthened glass-based article 1) exhibiting a brittle behavior upon breakage; and 2) exhibiting a non-brittle behavior upon breakage;

[0180] Figure 2b schematically depicts a strengthened glass-based article exhibiting a non-brittle behavior upon breakage;

[0181] Figure 3 is a graph showing a stress profile of a glass-based article, the stress profile approximated as a power profile with different power coefficients p, where tension (y-axis) is plotted as a function of depth (x-axis);

[0182] Figure 4 is a graph showing stress profile attributes and (y-axis) as a function of power coefficient p (x-axis);

[0183] Figure 5 is a graph showing stress profile attributes (x-axis) as a function of power coefficient p (x-axis); and

[0184] Figure 6to show stress distribution profiles according to the power coefficient p (x-axis) showing the stress distribution properties 、 and (y-axis);

[0185] Figure 7 to show the average retardation (in degrees) (y-axis) as a function of depth (x-axis) for a chemically strengthened glass-based article of the present disclosure measured according to the SLP-2000 stress profile characterization method;

[0186] Figure 8 to show the average retardation (in degrees) (y-axis) as a function of depth (x-axis) for a comparative example measured according to the SLP-2000 stress profile characterization method;

[0187] Figure 9 to show the symmetric and antisymmetric components of the average retardation curve of Figure 7 and the fitted power model for the antisymmetric component, with the origin of the symmetric and antisymmetric components located at the midplane between the retardation turning points where the stress crosses zero (changes between tension and compression);

[0188] Figure 10 to show the symmetric and antisymmetric components of the average retardation curve of Figure 8 and the fitted power model for the antisymmetric component, with the origin of the symmetric and antisymmetric components located at the midplane between the retardation turning points where the stress crosses zero (changes between tension and compression);

[0189] Figure 11 to show the residuals between the antisymmetric component of the average retardation of Figure 7 and its fitted power model;

[0190] Figure 12 to show the residuals between the antisymmetric component of the average retardation of Figure 8 and its fitted power model;

[0191] Figure 13 to show the stress profile of the fitted power model for a chemically strengthened glass-based article, the average retardation curve of which is shown in Figure 7 where the tension (y-axis) is plotted as a function of depth (x-axis); and

[0192] Figure 14 to show the stress profile of the fitted power model for a comparative example, the average retardation curve of which is shown in Figure 8 where the tension (y-axis) is plotted as a function of depth (x-axis).

[0193] Reference will now be made in detail to various embodiments, some of which are illustrated in the accompanying drawings. Wherever possible, the same or like reference numbers will be used throughout the drawings to refer to the same or like parts. DETAILED DESCRIPTION

[0194] Reference will now be made in detail to various embodiments of strengthened glass-based articles having a non-fragile stress profile. Particular reference will be made herein to various embodiments of chemically strengthened glass-based articles and methods of making the same with reference to the accompanying drawings.

[0195] With general reference to the drawings and specific reference to Figure 1 It is to be understood that the drawings are for purposes of describing particular embodiments and are not intended to limit the present disclosure or the appended claims. The drawings are not necessarily to scale, and certain features and certain views of the drawings can be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.

[0196] Before several exemplary embodiments are described, it is to be understood that the present disclosure is not limited to the details of construction or process steps set forth in the present disclosure. The present disclosure provided herein can have other embodiments and can be practiced or carried out in various ways.

[0197] The present disclosure describes chemically strengthened glass-based articles comprising: a first major surface and an opposing second major surface defining a thickness t of the glass-based article; a stress profile σ(x), where x extends through the thickness t of the glass-based article in a direction normal to the first and second major surfaces; a first compressive stress layer extending from the first major surface to a first compressive depth DOC1 greater than about 0.15t; a second compressive stress layer extending from the second major surface to a second compressive depth DOC2 less than or equal to DOC1; and a central tension zone positioned between the first and second compressive stress layers and comprising a peak tension PT and a tension zone width BTZ spanning DOC1 to t - DOC2,

[0198] wherein:

[0199] where DOC = DOC1 and is a slope of the stress profile σ(x) at DOC;

[0200] ; and

[0201] where TA is a tension area defined by:

[0202] .

[0203] Without wishing to be bound by theory, it is believed that the chemically strengthened glass-based articles described herein having the above combination of stress distribution attributes exhibit improved fracture toughness while avoiding fragility. This is achieved by modifying the stress distribution in the central tension zone to achieve an increased tension area for a given tensile strain energy selected to avoid making the glass-based article fragile in terms of its fracture toughness. The increased tension area TA permits a deeper DOC and high level of compressive stress in the compressive layer while keeping the glass-based article non-fragile. However, the present disclosure also describes chemically strengthened glass-based articles having stress distributions that are modified, for example, relative to the above combination of stress distribution attributes, in order to account for variations in the composition and thickness of the glass-based article, while similarly aiming to improve fracture toughness while avoiding fragility.

[0204] Reference throughout this specification to "one embodiment", "certain embodiments", "various embodiments", "one or more embodiments" or "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of the phrases, for example, "in one or more embodiments", "in certain embodiments", "in various embodiments", "in one embodiment", or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment, or only to one embodiment. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments.

[0205] In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that, unless otherwise specified, terms such as "top", "bottom", "outward", "inward", and the like are words of convenience and are not to be construed as limiting terms. In addition, whenever a group is described as comprising at least one of a group of elements and combinations thereof, it is understood that the group can comprise, consist essentially of, or consist of any number of those elements recited, either individually or in combination with each other. Similarly, whenever a group is described as consisting of at least one of a group of elements or combinations thereof, it is understood that the group can consist of any number of those elements recited, either individually or in combination with each other. Unless otherwise specified, in describing the various embodiments, ranges of values are inclusive of the recited range limits and any ranges therebetween.

[0206] As used herein, unless otherwise specified, the indefinite articles "a", "an", and corresponding definite article "the" mean "at least one" or "one or more". It is also to be understood that the various features disclosed in the specification and in the figures can be used in any and all combinations.

[0207] As used herein, the term "about" means quantities, dimensions, formulations, parameters and other quantities and characteristics are not and need not be exact, but can be approximated and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and other factors that are expected to be within the scope of one of ordinary skill in the art. When the term "about" is used in reference to a range or endpoint of a range, the disclosure herein shall be understood to encompass the specific value or endpoint referred to. Whether or not the numerical value or endpoint of a range is expressly recited as being "about," the numerical value or endpoint of the range is intended to include both embodiments "about" the recited value or endpoint and embodiments exactly at the recited value or endpoint. It is further understood that each endpoint of a range is effective as both an open and a closed boundary.

[0208] Definitions and Measurement Techniques

[0209] The terms "glass-based article" and "glass-based substrate" are used to include any object that is made wholly or partly of glass, including glass-ceramics (including amorphous and crystalline phases). As utilized herein, "glass-based substrate" refers to a shaped substrate that can subsequently undergo a strengthening process to form a "glass-based article." The glass-based substrates according to one or more embodiments can be selected from the group consisting of soda-lime silicate glass, alkali-aluminosilicate glass, alkali-containing borosilicate glass, alkali-containing aluminoborosilicate glass, and alkali-containing glass-ceramics.

[0210] A "glass-ceramic" includes a material produced by controlled crystallization of a glass. One or more nucleating agents such as titanium oxide (Ti02), zirconium oxide (Zr02), sodium oxide (Na20), and phosphorous oxide (P205) can be added to the glass-ceramic composition to promote uniform crystallization. In some embodiments, the glass-based articles described herein can exhibit an amorphous microstructure and can be substantially free of crystals or crystallites. In other words, in some embodiments, the glass-based articles described herein can not include a glass-ceramic material. In some embodiments, the glass-based articles described herein can include a glass-ceramic material. Thus, the terms "glass-based article" and "glass-based articles" are used in their broadest sense to include any object made wholly or partly of glass.

[0211] The "base composition" is the chemical composition of the substrate prior to any ion exchange (IOX) treatment. That is, the base composition is not doped with any ions from the IOX. When the IOX treatment conditions are such that the ions supplied to the IOX do not diffuse to the center of the substrate, the composition at the center of the glass-based article that has been treated by the IOX is close to or the same as the base composition. In one or more embodiments, the center composition at the center of the glass-based article includes the base composition. The "base composition" can also be referred to herein as the "glass composition."

[0212] It should be noted that the terms "substantially" and "about" can be used herein to denote an amount that can vary from a stated reference by an acceptable degree of error. These terms also can be used herein to denote an amount that can differ from a stated reference by an amount that is not materially significant to the subject matter at issue. Thus, for example, a glass-based article that is "substantially free of MgO" is a glass-based article in which MgO has not been added or formulated into the glass-based article, but can be present in trace amounts (e.g., < 0.1 mol %) as a contaminant.

[0213] Unless otherwise specified, all compositions are expressed in terms of mole percent (mol %). The terms "0 mol %," and "free" when used to describe the concentration and / or absence of a particular constituent ingredient in a glass composition and the resulting glass-based article means that the constituent ingredient is not present in the glass composition and the resulting glass-based article.

[0214] As used herein, the term "fracture toughness (K IC )" denotes the ability of a glass-based article to resist fracture. The fracture toughness of a non-strengthened glass-based article is measured, for example, prior to ion exchange (IOX) treatment of the glass-based article, to yield a K IC value that is characteristic of the glass-based substrate prior to ion exchange. The fracture toughness test method described herein is not applicable to glass that has been exposed to an ion exchange treatment. However, a fracture toughness measurement performed on the same glass (e.g., a glass-based substrate) prior to ion exchange treatment in accordance with that described herein is relevant to the fracture toughness after ion exchange treatment, and is therefore used as such. Reddy, K. P. R. et al., "Fracture Toughness Measurement of Glass and Ceramic Materials Using Chevron-Notched Specimens", J. Am. Ceram. Soc., 71 [6], C-310-C-313 (1988) discloses a chevron notched short bar (CNSB) method for measuring K IC values, with the exception that Y* mare calculated using Equation 5 of Bubsey, R. T., et al., "Closed-Form Expressions for Crack-Mouth Displacement and Stress Intensity Factors for Chevron-Notched Short Bar and Short Rod Specimens Based on Experimental Compliance Measurements", NASA Technical Memorandum 83796, pp. 1-30 (October 1992). The double torsion method and grips for measuring K IC values are described in Shyam, A. and Lara-Curzio, E., "The double-torsion testing technique for determination of fracture toughness and slow crack growth of materials: A review", J. Mater. Sci., 41, pp. 4093-4104, (2006). The double torsion measurement method generally yields K IC values that are slightly higher than the chevron notch short bar method. Unless otherwise specified, all fracture toughness values are measured by the chevron notch short bar (CNSB) method.

[0215] As described herein, the modulus of elasticity (also known as Young's modulus) and shear modulus of the glass-based articles are provided in gigapascals (GPa) and are measured according to ASTM C623. As described herein, the Poisson's ratio is also measured according to ASTM C623.

[0216] As used herein, the term "strain point" refers to the temperature at which the viscosity of the glass composition is 1 x 1014.5poise, as measured according to ASTM C598. 14.68 .

[0217] As used herein, the term "annealing point" or "effective annealing temperature" refers to the temperature at which the viscosity of the glass composition is 1 x 1010.5poise, as measured according to ASTM C598. 13.18 .

[0218] As used herein, the term "softening point" refers to the temperature at which the viscosity of the glass composition is 1 x 1010.5poise, as measured according to the parallel plate viscosity method, which measures the change in thickness of a 10 7.6 mm diameter disk of glass as a function of temperature. 7 mm diameter disk of glass as a function of temperature.9 The viscosity of the inorganic glass is similar to ASTM C1351M.

[0219] As used herein, the term "softening point" refers to the temperature at which the viscosity of the glass composition is 1,000,000 poise as measured according to ASTM C97.

[0220] As described herein, the terms "linear coefficient of thermal expansion" and "CTE" can be measured according to ASTM E228-85 over a temperature range of 25°C to 300°C, and are expressed in units of "x 10 −6 / °C". As used herein, the term "low temperature CTE" or "LTCTE" refers to the CTE of the glass composition measured at a specific temperature in the range of 50°C to 500°C. As used herein, the term "high temperature CTE" or "HTCTE" refers to the CTE of the glass composition at the minimum temperature (T 11 ) at which the glass has a viscosity of 10 11 The CTE is measured by digital image correlation, which determines the thermal expansion and instantaneous coefficient of thermal expansion of the glass composition as it is cooled through the glass transition region at a cooling rate of 2°C / s.

[0221] As described herein, the density is measured by the buoyancy method of ASTM C693-93.

[0222] As described herein, the refractive index is measured according to ASTM E1967.

[0223] The "stress profile" is a plot of the stress across the thickness of the glass-based article as a function of depth. A compressive stress region, in which the article is under compressive stress, extends from the first surface to a depth of compression (DOC) of the article. A central tension region extends from the DOC and includes a region of the glass-based article under tensile stress.

[0224] As used herein, the terms "depth of compression" and "DOC" refer to the depth within the glass at which the stress changes from compressive to tensile. At the DOC, the stress changes from a positive (compressive) stress to a negative (tensile) stress and thus has a value of zero. However, when used with the term "tensile", the stress in the central tension region can be expressed as a positive value.

[0225] "Surface spike" refers to a region of the stress profile in which the compressive stress decreases rapidly from a maximum value at the surface to a depth of typically about 15 to 20 pm below the surface, followed by a less rapid decrease to the point at which the stress transitions from compressive to tensile stress.

[0226] The "knee" of the stress profile is the region of the article having a surface spike where the slope of the stress profile transitions from steep (spike region) to shallow (deep region). The steep portion of the stress profile extending from the surface into the glass-based article is referred to as the "spike." The knee can refer to the transition region over the depth span where the slope changes. The knee compressive stress (CS k ) is defined as the compressive stress value of the CS profile extrapolated to the depth of layer (DOL sp ) of the spike. DOL sp refers to the depth of the knee and can be measured by surface stress meter using known methods (see U.S. Patent No. 11 / 402,366 entitled "Methods of Characterizing Ion-Exchanged Chemically Strengthened Gasses Containing Lithium").

[0227] A non-zero metal oxide concentration that varies from a first surface to a depth of layer (DOL) relative to the metal oxide or along at least a substantial portion of the thickness (t) of the article indicates that a stress is created in the article due to ion exchange. The variation in the concentration of the metal oxide can be referred to herein as a concentration gradient of the metal oxide. A metal oxide that has a non-zero concentration and varies from the first surface to the DOL or along a portion of the thickness can be described as creating a stress in the glass-based article. The concentration gradient or variation of the metal oxide is created by chemically strengthening the glass-based substrate, where a plurality of first metal ions in the glass-based substrate are exchanged with a plurality of second metal ions.

[0228] As used herein, the terms "depth of exchange," "depth of layer (DOL)," "chemical depth of layer," and "depth of chemical layer" are used interchangeably and generally describe the depth at which ion exchange facilitated by an ion exchange process (IOX) occurs for a particular ion. DOL refers to the depth within a glass-based article (i.e., the distance from a surface of the glass-based article to an interior region thereof) at which ions of a metal oxide or alkali metal oxide (e.g., metal ions or alkali metal ions) diffuse into the glass-based article at which point the concentration of the ions reaches a minimum value as determined by glow discharge-optical emission spectroscopy (GD-OES). In some embodiments, the DOL is given as the depth of exchange of the slowest or largest ion introduced by the ion exchange (IOX) process.

[0229] Figure 1 A cross-sectional schematic of a chemically strengthened glass-based article is shown in FIG. 1. The glass-based article 100 has a thickness t, a first surface 110, and a second surface 112. While not shown, the glass-based article 100 can include a third surface and a fourth surface.Figure 1 The embodiments shown in the FIGS. depict the glass-based article 100 as a flat, planar sheet or pane, but the glass-based article can have other configurations, such as a three-dimensional shape or other non-planar configuration. The glass-based article 100 has a first compressive stress layer 120 extending from the first surface 110 into the bulk of the glass-based article 100 a compressive depth DOC1. In the embodiments shown in the FIGS., the first compressive stress layer 120 has a compressive stress CS1. The glass-based article 100 also has a second compressive stress layer 122 extending from the second surface 112 to a second compressive depth DOC2. In the embodiments shown in the FIGS., the second compressive stress layer 122 has a compressive stress CS2. In embodiments, DOC2 is less than or equal to DOC1. The glass-based article 100 also has a central tension region 130 extending from DOC1 to DOC2. The central tension CT refers to the tensile stress in the middle of the central tension region 130, which, when DOC1 and DOC2 are equal, corresponds to 0.5 x t. The peak tension PT refers to the maximum tensile stress in the central tension region 130. It is common for CT and PT to be the same, but this is not a requirement. Figure 1 In the embodiments shown in the FIGS., the glass-based article 100 also has a second compressive stress layer 122 extending from the second surface 112 to a second compressive depth DOC2. In embodiments, DOC2 is less than or equal to DOC1. The glass-based article 100 also has a central tension region 130 extending from DOC1 to DOC2. The central tension CT refers to the tensile stress in the middle of the central tension region 130, which, when DOC1 and DOC2 are equal, corresponds to 0.5 x t. The peak tension PT refers to the maximum tensile stress in the central tension region 130. It is common for CT and PT to be the same, but this is not a requirement.

[0230] The tensile stress in the central tension region 130 balances or offsets the compressive stress of the stress layers 120 and 122. The compressive depths DOC1, DOC2 of the first compressive stress layer 120 and the second compressive stress layer 122 protect the glass-based article 100 from defects introduced by a sharp impact from propagating to the first surface 110 and the second surface 112 of the glass-based article 100, while the magnitude of the compressive stress minimizes the likelihood of the defect penetrating the depths DOC1, DOC2 of the first compressive stress layer 120 and the second compressive stress layer 122.

[0231] CT and PT values can be measured using a scattered light polariscope (SCALP), such as a SCALP-05 portable scattered light polariscope. Stress profiles and depth of compression (DOC) can be measured using a refracted near field (RNF) method or SCALP. When measuring stress profiles using the RNF method, the peak tension PT value provided by SCALP is utilized in the RNF method. Specifically, the stress profile measured by RNF can be force balanced and calibrated to the peak tension PT value provided by SCALP measurements. The RNF method is described in U.S. Patent No. 8,854,623, entitled “Systems and methods for measuring a profile characteristic of a glass sample,” which is incorporated herein by reference in its entirety. Specifically, the RNF method includes placing a glass article adjacent to a reference block; generating a polarization-switched light beam that switches between orthogonal polarizations at a rate of 1 Hz to 50 Hz; measuring an amount of power in the polarization-switched light beam; and generating a polarization-switched reference signal, wherein the measured amount of power in each of the orthogonal polarizations is within 50% of each other. The method further includes transmitting the polarization-switched light beam through the glass sample and the reference block into different depths of the glass sample, then relaying the transmitted polarization-switched light beam to a signal photodetector using a relay optical system, the signal photodetector generating a polarization-switched detector signal. The method also includes dividing the detector signal by the reference signal to form a normalized detector signal, and determining a profile characteristic of the glass sample from the normalized detector signal.

[0232] As used herein, CS refers to the peak compressive stress in a glass-based article, which for many embodiments is the surface compressive stress, i.e., the compressive stress as the first and second surfaces 110, 112. Thus, unless otherwise specified, CS refers to the surface compressive stress. However, in embodiments, the chemical strengthening process can be designed such that the peak compressive stress CS is not at the surface of the glass-based article, but is actually embedded within the glass-based article. In some embodiments, the relationship between the peak compressive stress CS and the peak tension PT can be approximated by the following expression:

[0233]

[0234] In various portions of the disclosure, the peak tension PT and the maximum compressive stress CS are expressed in megaPascals (MPa), the thickness t is expressed in micrometers (pm) or millimeters (mm), and the depth of compression DOC is expressed in micrometers (pm).

[0235] The stress profile attributes of the compressive stress layer, including the surface compressive stress CS, the depth of compression DOC (for non-lithium glasses), and the sharpness of the peak DOL can be measured using those methods known in the art.SP Such means include, but are not limited to, film stress measurement (FSM) using commercially available instruments such as FSM-6000 stress meter manufactured by Luceo Corporation (Tokyo, Japan), and methods of measuring compressive stress and depth of compression described in ASTM 1422C-99 entitled “Standard Specification for Chemically Strengthened Flat Glass” and ASTM 1279.1977 9 entitled “Standard Test Method for Non-Destructive Photoelastic Measurement of Edge and Surface Stresses in Annealed, Heat-Strengthened, and Fully-Tempered Flat Glass”, the contents of which are incorporated herein in their entirety. Surface stress measurement relies on accurate measurement of the stress optical coefficient (SOC), which is related to the birefringence of the glass. SOC is in turn measured by methods known in the art such as the fiber method and the four-point bend method, both of which are described in ASTM Standard C770-98(2008) entitled “Standard Test Method for Measurement of Glass Stress-Optical Coefficient”, the contents of which are incorporated herein in their entirety, and the bulk cylinder method.

[0236] The stress profile properties of the compressive stress layer can be measured using a prism coupling instrument similar to the FSM-6000 but with additional wavelength options to provide preferred measurement windows as described in U.S. Patent No. 11,448,595 entitled “Prism-Coupling Systems and Methods with Improved Intensity Transition Position Detection and Tilt Compensation” issued September 20, 2022, the entirety of which is incorporated herein by reference.

[0237] For strengthened glass-based articles in which the compressive stress layer extends to a greater depth within the glass, the FSM technique can suffer from contrast issues, affecting the observed DOC values. At greater DOC values, the contrast between the transverse electric (TE) and transverse magnetic (TM) spectra can be insufficient, thus making it more difficult to calculate the difference between the TE and TM spectra and to determine the DOC. In addition, the FSM technique cannot determine the compressive stress profile (i.e., the variation of the compressive stress within the glass as a function of depth). Further, the FSM technique cannot determine the depth of the layer resulting from ion exchange of certain elements, such as lithium.

[0238] The techniques described below have been developed to more accurately determine the depth of compression (DOC) and the compressive stress profile for strengthened glass-based articles.

[0239] In U.S. Patent Application No. 13 / 463,322, filed May 3, 2012, by Rostislav V. Roussev et al., entitled "Systems And Methods for Measuring the Stress Profile of Ion- Exchanged Glass" (hereinafter "Roussev I") and claiming priority to U.S. Provisional Patent Application No. 61 / 489,800, filed May 25, 2011, of the same title, two methods for extracting the detailed and accurate stress profile (stress as a function of depth) of ion-exchanged glass are disclosed. The TM and TE polarized bound optical mode spectra are collected via prism coupling technique and used in their entirety to obtain detailed and accurate TM and TE refractive index profiles n TM (z) and n TE (z). The contents of the above application are incorporated herein by reference in their entirety.

[0240] In one embodiment, the detailed refractive index profile is obtained from the mode spectra by using the inverse Wenzel-Kramer-Brillouin (IWKB) method.

[0241] In another embodiment, the detailed refractive index profile is obtained by fitting the measured mode spectra to a numerically calculated spectrum in the form of a predefined function describing the shape of the refractive index profile and obtaining the parameters of the function form from the best fit. The detailed stress profile S(z) is calculated from the difference of the recovered TM and TE refractive index profiles using the known value of the stress optical coefficient (SOC):

[0242]

[0243] Due to the small value of the SOC, the birefringence n TM (z) - n TE (z) are both refractive indices nTM (z) and n TE a fraction (typically about 1%) of any one of (z). Obtaining a stress profile that is not significantly distorted by noise in the measured mode spectrum requires determining the mode effective index with a precision of about 0.00001 RIU. The method disclosed in Roussev I further includes techniques applied to the raw data to ensure that the measured mode index has this high precision despite the presence of noise and / or poor contrast in the collected TE and TM mode spectra or mode spectrum images. These techniques include noise averaging, filtering, and curve fitting, while finding the location of the extreme value corresponding to the mode at sub-pixel resolution.

[0244] Similarly, Rostislav V. Roussev et al. in U.S. Patent Application No. 14 / 033,954, filed September 23, 2013, entitled "Systems and Methods for Measuring Birefringence in Glass and Glass-Ceramics" (hereinafter "Roussev II") and claiming priority to U.S. Provisional Application No. 61 / 706,891, filed September 28, 2012, of the same title, disclose apparatus and methods for optically measuring birefringence on the surface of glass and glass-ceramics, including opaque glass and glass-ceramics. Unlike Roussev I, where discrete mode spectra are identified, the method disclosed in Roussev II relies on careful analysis of the angular intensity distribution of the TM and TE light reflected at the prism-sample interface in a prism-coupling measurement configuration. The contents of the above-identified application are incorporated herein by reference in their entirety.

[0245] Accordingly, the correct assignment of the reflected light intensity versus angle is significantly more important in Roussev II than in conventional prism-coupling stress measurements, where only the location of discrete modes is sought. To this end, the methods disclosed in Roussev I and Roussev II include techniques for normalizing the intensity spectra, including normalization to a reference image or signal; correcting for non-linearities of the detector; averaging multiple images to reduce image noise and speckle; and applying digital filtering to further smooth the intensity of the angular spectrum. In addition, a method includes forming a contrast signal that is subjected to additional normalization to correct for fundamental differences in shape between the TM and TE signals. The above-described method relies on achieving two signals that are nearly identical, and determining the mutual shift of the signals with sub-pixel resolution by comparing the portions of the signals that contain the steepest regions. The birefringence is proportional to the mutual shift, with a coefficient that is determined by the apparatus design, including the prism geometry and refractive indices, the focal length of the lens, and the pixel pitch on the sensor. The stress is determined by multiplying the measured birefringence by a known stress-optic coefficient.

[0246] In another method, after applying some combination of the above signal conditioning techniques, the derivatives of the TM and TE signals are determined. The locations of the maxima of the derivatives of the TM and TE signals are obtained at sub-pixel resolution, and the birefringence is proportional to the separation of the two maxima, with the coefficient determined from the device parameters as described above.

[0247] In connection with the requirements for correct intensity extraction, the device includes several enhancements, such as the use of light scattering surfaces (static diffusers) next to or on the prism entrance surface to improve the angular uniformity of the illumination, the use of moving diffusers to reduce speckle when the light source is coherent or partially coherent, and the use of light absorbing coatings on parts of the input and output faces of the prism and on the prism sides to reduce spurious backgrounds that tend to distort the intensity signal. In addition, the device can contain an infrared light source to enable measurements on non-transparent materials.

[0248] Further, Roussev II discloses the wavelength range and attenuation coefficient of a sample under investigation, where measurements can be enhanced by the described method and device. The range is given by a s λ < 250 π σ s where a s is the optical attenuation coefficient at the measurement wavelength λ, and a s is the expected value of the stress to be measured with the accuracy typically required in practical applications. This wide range allows obtaining measurements of practical importance at wavelengths where the previously existing measurement methods are not applicable due to the large optical attenuation. For example, Roussev II discloses the successful measurement of the stress-induced birefringence of a non-transparent white glass-ceramic at a wavelength of 1550 nm, where the attenuation is greater than about 30 dB / mm.

[0249] In embodiments, a scattered light photoelastic stress meter (SLP) or SLP in combination with FSM can be used to measure the stress distribution of the chemically strengthened glass-based articles disclosed herein. Commercial SLP meters include SLP-1000 and SLP-2000 manufactured by Orihara Industrial Co. However, custom measurement systems can also be used to measure the stress distribution properties. In some cases, custom measurement systems can be able to provide more accurate measurements than commercially available systems.

[0250] It should be noted that in utilizing a commercial grade device to measure the properties of the stress distribution of a glass-based article, it can be necessary to take several measurements, such as ten measurements, and average the retardation data for subsequent analysis and extraction of various properties of interest discussed in more detail below.

[0251] Base Composition of Glass-Based Articles

[0252] In embodiments of the glass-based articles disclosed herein, Si02 is the largest constituent, and thus, Si02 is the primary constituent of the glass network formed from the composition of the glass-based substrate. Pure Si02 has a relatively low CTE and is free of alkalis. However, pure Si02 has a high melting point. Thus, if the concentration of Si02 in the composition of the glass-based substrate is too high, the formability of the glass composition can be reduced because a higher concentration of Si02 increases the difficulty of melting the glass, which in turn adversely affects the formability of the glass. In embodiments, the composition of the glass-based substrate can include 50.0 to 75.0 mol % Si02. In embodiments, the composition of the glass-based substrate can include 50.0 to 70.0 mol % Si02. In embodiments, the composition of the glass-based substrate can include 55.0 to 65.0 mol % Si02. In embodiments, the composition of the glass-based substrate can include 57.0 to 63.0 mol % Si02. In embodiments, the concentration of Si02 in the composition of the glass-based substrate can be in the following ranges: 50.0 to 70.0 mol %, 50.0 to 67.0 mol %, 50.0 to 65.0 mol %, 50.0 to 63.0 mol %, 50.0 to 60.0 mol %, 55.0 to 70.0 mol %, 55.0 to 67.0 mol %, 55.0 to 65.0 mol %, 55.0 to 64.0 mol %, 55.0 to 63.0 mol %, 55.0 to 62.0 mol %, 55.0 to 61.0 mol %, 55.0 to 60.0 mol %, 55.0 to 59.0 mol %, 56.0 to 70.0 mol %, 56.0 to 67.0 mol %, 56.0 to 65.0 mol %, 56.0 to 64.0 mol %, 56.0 to 63.0 mol %, 56.0 to 62.0 mol %, 56.0 to 61.0 mol %, 56.0 to 60.0 mol %, 56.0 to 59.0 mol %, 57.0 to 70.0 mol %, 57.0 to 67.0 mol %, 57.0 to 65.0 mol %, 57.0 to 64.0 mol %, 57.0 to 63.0 mol %, 57.0 to 62.0 mol %, 57.0 to 61.0 mol %, 57.0 to 60.0 mol %, 57.0 to 59.0 mol %, or 65.0 to 75.0 mol %, or any and all sub-ranges formed from any one of these endpoints.

[0253] The base compositions or glass-based articles described herein can further include AI2O3. Similar to SiO2, AI2O3 can act as a glass network former. AI2O3 can increase the viscosity of the composition of the glass-based substrate due to its tetrahedral coordination in the glass melt formed from the composition of the glass-based substrate. If the amount of AI2O3 is too high, the formability of the composition of the glass-based substrate can decrease. However, when the concentration of AI2O3 is balanced with respect to the concentration of SiO2 and the concentration of alkali oxides in the composition of the glass-based substrate, AI2O3 can lower the liquidus temperature of the glass melt. Lowering the liquidus temperature enhances the liquidus viscosity and improves the compatibility of the composition of the glass-based substrate with certain forming processes, such as fusion forming processes. In embodiments, the composition of the glass-based substrate can include 10.0 to 25.0 mol % AI2O3. In embodiments, the composition of the glass-based substrate can include 14.0 to 20.0 mol % AI2O3. In embodiments, the composition of the glass-based substrate can include 15.0 to 19.0 mol % AI2O3. In embodiments, the concentration of AI2O3 in the composition of the glass-based substrate can be in the following ranges: 10.0 to 25.0 mol %, 10.0 to 23.0 mol %, 10.0 to 20.0 mol %, 10.0 to 19.0 mol %, 10.0 to 18.0 mol %, 12.0 to 25.0 mol %, 12.0 to 23.0 mol %, 12.0 to 20.0 mol %, 12.0 to 19.0 mol %, 12.0 to 18.0 mol %, 13.0 to 25.0 mol %, 13.0 to 23.0 mol %, 13.0 to 20.0 mol %, 13.0 to 19.0 mol %, 13.0 to 18.0 mol %, 14.0 to 25.0 mol %, 14.0 to 23.0 mol %, 14.0 to 20.0 mol %, 14.0 to 19.0 mol %, 14.0 to 18.0 mol %, 15.0 to 25.0 mol %, 15.0 to 23.0 mol %, 15.0 to 20.0 mol %, 15.0 to 19.0 mol %, 15.0 to 18.0 mol %, 16.0 to 25.0 mol %, 16.0 to 23.0 mol %, 16.0 to 20.0 mol %, 16.0 to 19.0 mol %, 16.0 to 18.0 mol %, 17.0 to 25.0 mol %, 17.0 to 23.0 mol %, 17.0 to 20.0 mol %, 17.0 to 19.0 mol %, or 17.0 to 18.0 mol %, or any and all sub-ranges formed from any of these endpoints.In embodiments, the concentration of AI2O3 in the composition of the glass-based substrate can be greater than or equal to 10.0 mol %, greater than or equal to 11.0 mol %, greater than or equal to 12.0 mol %, greater than or equal to 13.0 mol %, greater than or equal to 14.0 mol %, greater than or equal to 15.0 mol %, greater than or equal to 16.0 mol %, or greater than or equal to 17.0 mol %.

[0254] The composition of the glass-based substrate can further include B2O3. B2O3 can be added to the composition of the glass-based substrate as a network former, thereby reducing the meltable and formable properties of the glass-based substrate. In embodiments, the composition of the glass-based substrate can include 1.0 to 11.0 mol % B2O3. In embodiments, the composition of the glass-based substrate can include 2.0 to 10.0 mol % B2O3, 3.0 to 9.0 mol % B2O3, 4.0 to 8.0 mol % B2O3, 5.0 to 7.0 mol % B2O3. In embodiments, the concentration of B2O3 in the composition of the glass-based substrate can be greater than or equal to 0.5 mol %, greater than or equal to 1.0 mol %, greater than or equal to 1.5 mol %, greater than or equal to 1.0 mol %, greater than or equal to 2.0 mol %, greater than or equal to 2.0 mol %, greater than or equal to 2.5 mol %, greater than or equal to 3.0 mol %, greater than or equal to 3.5 mol %, or greater than or equal to 4.0 mol %.

[0255] The composition of the glass-based substrate can further include Li20. The effect of Li20 on fracture toughness is discussed above. In addition, the addition of lithium in the glass allows for better control of the ion exchange process and further reduces the softening point of the glass. In embodiments, the composition of the glass-based substrate can include 5.0 to 15.0 mol% Li20. In embodiments, the composition of the glass-based substrate can include 5.0 to 10.0 mol% Li20. In embodiments, the composition of the glass-based substrate can include 6.0 to 9.0 mol% Li20. In embodiments, the concentration of Li20 in the composition of the glass-based substrate can be in the range of 5.0 to 15.0 mol%, 5.0 to 10.0 mol%, 5.0 to 9.0 mol%, 5.0 to 8.5 mol%, 5.0 to 8.0 mol%, 6.0 to 15.0 mol%, 6.0 to 10.0 mol%, 6.0 to 9.0 mol%, 6.0 to 8.5 mol%, 6.0 to 8.0 mol%, 6.0 to 7.5 mol%, 6.0 to 7.0 mol%, 6.5 to 15.0 mol%, 6.5 to 10.0 mol%, 6.5 to 9.0 mol%, 6.5 to 8.5 mol%, 6.5 to 8.0 mol%, 7.0 to 15.0 mol%, 7.0 to 10.0 mol%, 7.0 to 9.0 mol%, 7.0 to 8.5 mol%, 7.0 to 8.0 mol%, 7.5 to 15.0 mol%, 7.5 to 10.0 mol%, 7.5 to 9.0 mol%, or 7.5 to 8.5 mol%, or any and all sub-ranges formed by any of these endpoints. In embodiments, the concentration of Li20 in the composition of the glass-based substrate can be less than or equal to 15.0 mol%, less than or equal to 10.0 mol%, less than or equal to 9.5 mol%, less than or equal to 9.0 mol%, less than or equal to 8.5 mol%, or less than or equal to 8.0 mol%. In embodiments, the glass-based substrate includes greater than or equal to 9 mol% Li20, greater than or equal to 10 mol% Li20, greater than or equal to 10.5 mol% Li20, greater than or equal to 11 mol% Li20, greater than or equal to 11.5 mol% Li20, or greater than or equal to 12 mol% Li20.

[0256] The composition of the glass-based substrate described herein can further include an alkali metal oxide other than Li20, such as Na20. Na20 contributes to the ion exchangeability of the composition of the glass-based substrate, and also increases the melting point and improves the formability of the composition of the glass-based substrate. However, if too much Na20 is added to the composition of the glass-based substrate, the CTE can be too low, and the melting point can be too high. Thus, in embodiments, the concentration of Li20 present in the composition of the glass-based substrate is greater than the concentration of Na20 present in the composition of the glass-based substrate. In embodiments, the composition of the glass-based substrate can include 0.5 to 15.0 mol% Na20. In embodiments, the composition of the glass-based substrate can include 1.0 to 10.0 mol% Na20. In embodiments, the composition of the glass-based substrate can include 1.0 to 2.0 mol% Na20. In embodiments, the composition of the glass-based substrate can include 1.0 to 3.0 mol% Na20.

[0257] The composition of the glass-based substrate described herein can further include an alkali metal oxide other than Li20 and Na20, such as K20. K20 promotes ion exchange and increases the DOC. However, the addition of K20 can make the CTE too low and the melting point too high. In embodiments, the composition of the glass-based substrate can include 0.0 to 1.0 mol% K20. In embodiments, the composition of the glass-based substrate can include 0.0 to 0.5 mol% K20. In embodiments, the composition of the glass-based substrate can include 0.0 to 0.4 mol% K20. In embodiments, the concentration of K20 in the composition of the glass-based substrate can be in the range of 0.0 to 1.0 mol%, 0.0 to 0.5 mol%, 0.0 to 0.4 mol%, 0.0 to 0.3 mol%, 0.0 to 0.2 mol%, or 0.0 to 0.1 mol%, or any and all sub-ranges formed by any of these endpoints. In embodiments, the composition of the glass-based substrate can include less than or equal to 1.0 mol% K20, less than or equal to 0.5 mol% K20, less than or equal to 0.4 mol% K20, less than or equal to 0.3 mol% K20, less than or equal to 0.2 mol% K20, or less than or equal to 0.1 mol% K20.

[0258] The compositions of the glass-based substrates described herein can further include MgO. MgO lowers the viscosity of the glass, which enhances formability, strain point, and Young’s modulus, and can improve ion exchangeability. However, when too much MgO is added to the composition of the glass-based substrate, the density and CTE of the composition of the glass-based substrate increases. In embodiments, the concentration of MgO in the composition of the glass-based substrate can be in the range from 0.0 to 5.0 mol %, 0.0 to 4.5 mol %, 0.0 to 4.0 mol %, 0.0 to 3.5 mol %, 0.0 to 3.0 mol %, 0.0 to 2.5 mol %, 0.0 to 2.0 mol %, 0.0 to 1.5 mol %, 0.5 to 5.0 mol %, 0.5 to 4.5 mol %, 0.5 to 4.0 mol %, 0.5 to 3.5 mol %, 0.5 to 3.0 mol %, 0.5 to 2.5 mol %, 0.5 to 2.0 mol %, 0.5 to 1.5 mol %, 1.0 to 5.0 mol %, 1.0 to 4.5 mol %, 1.0 to 4.0 mol %, 1.0 to 3.5 mol %, 1.0 to 3.0 mol %, 1.0 to 2.5 mol %, 1.0 to 2.0 mol %, or 1.0 to 1.5 mol %, or any and all sub-ranges formed from any of these endpoints. In embodiments, the concentration of MgO is less than or equal to 5.0 mol %, less than or equal to 4.5 mol %, less than or equal to 4.0 mol %, less than or equal to 3.5 mol %, less than or equal to 3.0 mol %, less than or equal to 2.5 mol %, less than or equal to 2.0 mol %, or less than or equal to 1.5 mol %. In embodiments, the concentration of MgO in the composition of the glass-based substrate can be greater than 0.0 mol % to less than or equal to 3.0 mol %, greater than 0.0 mol % to less than or equal to 2.5 mol %, greater than 0.0 mol % to less than or equal to 2.0 mol %, or greater than 0.0 mol % to less than or equal to 1.5 mol %.

[0259] The compositions of the glass-based substrates described herein can further include CaO. CaO lowers the viscosity of the glass, which enhances formability, strain point, and Young’s modulus, and can improve ion exchangeability. However, the density and CTE of the composition of the glass-based substrate increase when too much CaO is added to the composition of the glass-based substrate. In embodiments, the concentration of CaO in the composition of the glass-based substrate can be 0.0 to 5.0 mol %, 0.0 to 4.0 mol %, 0.0 to 3.5 mol %, 0.0 to 3.0 mol %, 0.0 to 2.5 mol %, 0.0 to 2.0 mol %, 0.0 to 1.5 mol %, 0.0 to 1.0 mol %, 0.0 to 0.5 mol %, 0.0 to 0.1 mol %, 0.5 to 5.0 mol %, 0.5 to 4.0 mol %, 0.5 to 3.5 mol %, 0.5 to 3.0 mol %, 0.5 to 2.5 mol %, 0.5 to 2.0 mol %, 0.5 to 1.5 mol %, 0.5 to 1.0 mol %, 1.0 to 5.0 mol %, 1.0 to 4.0 mol %, 1.0 to 3.5 mol %, 1.0 to 3.0 mol %, 1.0 to 2.5 mol %, 1.0 to 2.0 mol %, 1.5 to 5.0 mol %, 1.5 to 4.0 mol %, 1.5 to 3.5 mol %, 1.5 to 3.0 mol %, 1.5 to 2.5 mol %, 1.5 to 2.0 mol %, 2.0 to 5.0 mol %, 2.0 to 4.0 mol %, 2.0 to 3.5 mol %, 2.0 to 3.0 mol %, 2.0 to 2.5 mol %, 2.5 to 5.0 mol %, 2.5 to 4.0 mol %, 2.5 to 3.5 mol %, or 2.5 to 3.0 mol %, or any and all sub-ranges formed from any of these endpoints. In embodiments, the concentration of CaO in the composition of the glass-based substrate can be less than or equal to 0.1 mol %. In embodiments, the concentration of CaO in the composition of the glass-based substrate can be greater than 0.0 mol % to less than 0.1 mol %. In embodiments, the composition of the glass-based substrate can be substantially free or free of CaO.

[0260] The compositions of the glass-based substrates described herein can further include ZnO. In embodiments, the concentration of ZnO in the composition of the glass-based substrate can be greater than 0.0 mol % to less than or equal to 3.0 mol %.

[0261] The compositions of the glass-based substrates described herein can further include one or more fining agents. In embodiments, the fining agent can include, for example, Sn02. In embodiments, the concentration of Sn02in the composition of the glass-based substrate can be 0.0 to 1.0 mol%, 0.0 to 0.5 mol%, 0.0 to 0.4 mol%, 0.0 to 0.3 mol%, 0.0 to 0.2 mol%, or 0.0 to 0.1 mol%, or any and all sub-ranges formed from any of these endpoints. In embodiments, the concentration of Sn02in the composition of the glass-based substrate can be less than or equal to 0.1 mol%. In embodiments, the concentration of Sn02in the composition of the glass-based substrate can be in a range from greater than 0.0 mol% to less than or equal to 0.1 mol%, from greater than 0.0 mol% to less than or equal to 0.5 mol%, or from greater than 0.0 mol% to less than or equal to 1.0 mol%. In embodiments, the composition of the glass-based substrate can be substantially free or free of Sn02.

[0262] The base composition of the glass-based articles disclosed herein can include additional elements and / or oxides depending on the particular properties desired. For example, Ti02may be added to increase the UV absorption of the composition of the glass-based substrate. Those skilled in the art will appreciate that it is possible to add additional components to the composition without departing from the concepts disclosed herein relating to the stress profile imparted to the glass-based article via the strengthening process.

[0263] In embodiments, the glass-based substrate can include: greater than or equal to 50 mol% and less than or equal to 75 mol% Si02; greater than or equal to 10 mol% and less than or equal to 25 mol% AI2O3; greater than or equal to 1 mol% and less than or equal to 11 mol% B2O3; greater than or equal to 1 mol% and less than or equal to 10 mol% Na20; and greater than or equal to 5 mol% and less than or equal to 15 mol% Li20, wherein the molar concentration of Li20 in the glass-based substrate is less than the molar concentration of Na20 in the glass-based substrate.

[0264] In embodiments, the glass-based substrate includes a molar ratio of Li20 to Na20 that is greater than or equal to 1.0, greater than or equal to 1.5, greater than or equal to 2.0, greater than or equal to 2.5, greater than or equal to 3.0, greater than or equal to 3.5, greater than or equal to 4.0, greater than or equal to 4.5, greater than or equal to 5.0, greater than or equal to 5.5, greater than or equal to 6.0, greater than or equal to 6.5, greater than or equal to 7.0, greater than or equal to 7.5, greater than or equal to 8.0, greater than or equal to 8.5, greater than or equal to 9.0, greater than or equal to 9.5, or greater than or equal to 10.0.

[0265] Ion Exchange Treatment

[0266] As stated above, the glass-based articles can be chemically strengthened by an ion exchange treatment. In this process, ions at or near the surface of the glass are replaced with or exchanged for larger ions of the same valence or oxidation state. In those embodiments where the glass-based article comprises, consists essentially of, or consists of an alkali-aluminosilicate glass, the ions in the surface layer of the glass and the larger ions are monovalent alkali metal cations, such as Li + (Na +、 K +、 Rb + and Cs + . Alternatively, the monovalent cations in the surface layer can be replaced by monovalent cations other than alkali metal cations, such as Ag + and the like.

[0267] The ion exchange process is typically carried out by immersing the glass-based article in a molten salt bath containing the larger ions to be exchanged for the smaller ions in the glass. Those skilled in the art will appreciate that the parameters of the ion exchange process, including but not limited to bath composition and temperature, immersion time, the number of immersions of the glass in one or more salt baths, the use of multiple salt baths, and additional steps such as annealing, washing, and the like, are generally determined based on the composition of the glass and the depth of layer and compressive stress of the glass required for the strengthening operation. As an example, ion exchange of an alkali-containing glass can be achieved by immersion in at least one molten bath containing a salt of the larger alkali ion, such as, but not limited to, nitrates, sulfates, and chlorides. The temperature of the molten salt bath is generally in the range of about 380 °C to about 450 °C or to about 460 °C, while the immersion time is in the range of about 15 minutes to about 40 hours. However, temperatures and immersion times different from those described above can also be used. For example, those skilled in the art will appreciate that the thickness of the glass-based substrate to be subjected to the ion exchange treatment can be considered in selecting the temperature of the molten salt bath and the immersion time of the ion exchange treatment.

[0268] In addition, non-limiting examples of ion exchange processes in which the glass is immersed in multiple ion exchange baths with washing and / or annealing steps between immersions are described in U.S. Patent No. 8,561,429 to Douglas C. Allan et al., issued October 22, 2013, entitled "Glass with Compressive Surface for Consumer Applications" and claiming priority to U.S. Provisional Patent Application No. 61 / 079,995, filed July 11, 2008, in which the glass is strengthened by ion exchange treatment with multiple, sequential immersions in salt baths of different concentrations; and U.S. Patent No. 8,312,739 to Christopher M. Lee et al., issued November 20, 2012, and entitled "Dual Stage Ion Exchange for Chemical Strengthening of Glass" and claiming priority to U.S. Provisional Patent Application No. 61 / 084,398, filed July 29, 2008, in which the glass is strengthened by ion exchange in a first bath, dilution with efflux ions, and subsequent immersion in a second bath having a lower concentration of efflux ions than the first bath. The contents of U.S. Patent Nos. 8,561,429 and 8,312,739 are incorporated herein by reference in their entirety.

[0269] The compressive stress is generated by chemically strengthening the glass-based article, for example, by the ion exchange process previously described herein, in which a plurality of first metal ions in an outer region of the glass-based article are exchanged with a plurality of second metal ions, such that the outer region comprises the plurality of second metal ions. Each of the first metal ions has a first ionic radius, and each of the second alkali metal ions has a second ionic radius. The second ionic radius is greater than the first ionic radius, and the presence of the larger second alkali metal ions in the outer region generates a compressive stress in the outer region.

[0270] At least one of the first metal ions and the second metal ions is an alkali metal ion. The first ion can be an ion of lithium, sodium, potassium, and rubidium. The second metal ion can be an ion of one of sodium, potassium, rubidium, and cesium, with the proviso that the second alkali metal ion has a larger ionic radius than the first alkali metal ion.

[0271] As used herein, the term "penetration depth of sodium ions after ion exchange" refers to the depth within the glass-based article (i.e., the distance from the surface of the glass-based article to the interior region thereof) at which sodium ions introduced by the ion exchange process have diffused into the glass-based article at which point the concentration of sodium ions reaches a minimum, as determined by glow discharge-optical emission spectroscopy (GD-OES).

[0272] As used herein, the term "penetration depth of potassium ions after ion exchange" refers to the depth within the glass-based article (i.e., the distance from the surface of the glass-based article to an interior region thereof) at which potassium ions introduced by the ion exchange process have diffused into the glass-based article at which point the concentration of potassium ions reaches a minimum, as determined by GD-OES.

[0273] As mentioned above, the present disclosure relates to chemically strengthened glass-based articles that are strengthened so as to achieve a deep DOC and a high compressive stress level in the compressive layer, while also meeting the requirement of non-fragility. However, in order to obtain a stress profile of a strengthened glass-based article that is capable of achieving these features, several hurdles must be overcome. For example, the ability to induce a stress profile with a high DOC can be hindered by a limited concentration of the outward diffusing ion species, as the required ion exchange diffusion rate often depends on the concentration of the outward diffusing ion species. Thus, a limited concentration of the outward diffusing ion species can limit the ability to induce stress in the glass. Exemplary ion exchange processing methods that overcome some of these challenges are discussed in greater detail herein.

[0274] Non-Brittle

[0275] As discussed above, the strength of a glass-based article that experiences tensile stress depends largely on the depth of a sharp defect extending from the surface into the glass.

[0276] During service, the cover glass of an electronic device can come into contact with a rough surface, thereby creating defects of varying depths, including significant depths that approach and even exceed 100 micrometers (pm). In order to effectively prevent breakage due to relatively deep defects, it is desirable to have a DOC as high as possible. In addition, during a drop event, considerable stress can be generated in the cover glass, particularly near the contact site. The compressive stress in the compressive layer can offset the tensile stress generated during a drop event. Thus, when the magnitude of the compressive stress in the compressive layer is high, the level of protection can be further improved. Therefore, in order to provide a cover glass with improved fail-safe protection, a strengthened glass-based article with a deep DOC and a high compressive stress level in the compressive layer is desirable.

[0277] The glass-based articles described herein are non-fragile glass-based articles. It has become increasingly common for manufacturers of electronic devices having cover glasses to require that the cover glasses be non-fragile. The non-fragile glass-based articles described herein do not exhibit fragile behavior (also referred to herein as "fragility").

[0278] Fragility behavior is the result of a glass-based article storing enough strain energy that the glass-based article breaks into multiple parts (e.g., more than three) and several branches occur. In a glass-based article that is thermally tempered, laminated, or chemically strengthened (e.g., strengthened by ion exchange), sufficient energy is generated when the compressive stress in the surface or outer region of the glass-based article balances the tensile stress in the center of the glass-based article, causing crack branching, ejection, expulsion, or "throwing" of small glass particles from the article, and potentially, fragility behavior. The speed at which this ejection occurs is a result of the large amount of tensile energy stored in the glass-based article.

[0279] Fragility behavior can be characterized by at least one of the following: a strengthened glass-based article (e.g., a sheet or a pane) breaking into multiple small pieces (e.g., < 1 mm); the number of fragments formed per unit area of the glass-based article; a plurality of cracks branching from an initial crack in the glass-based article; at least one fragment being ejected violently from its original location to a specified distance (e.g., about 5 cm, or about 2 inches); and a combination of any of the foregoing breaking (size and density), cracking, and ejection behavior. As used herein, the terms "fragility behavior" and "fragility" refer to a violent or energetic breaking pattern of a strengthened glass-based article in the absence of any external constraints (e.g., coating layers, adhesive layers, etc.). While coating layers, adhesive layers, etc. can be used in conjunction with the strengthened glass-based articles described herein, such external constraints are not used to determine the fragility or fragility behavior of the glass-based article.

[0280] A non-fragile glass-based article can be made from a glass composition that is strengthened by one or more strengthening processes configured to impart a desired stress profile in the glass composition, such as the glass compositions and strengthening processes disclosed herein. In some embodiments, the strengthening processes can include one or more ion exchange processes. In such embodiments, the glass composition from which the non-fragile glass-based article is made is an ion exchangeable glass composition. As used herein, "ion exchangeable" means that the glass composition, or a glass-based article comprising the composition, is capable of exchanging a first cation located at or near the surface of the substrate with a second cation of the same valence. The first cation can be a sodium ion. The second cation can be an ion of one of potassium, rubidium, and cesium, provided that the second cation has a larger ionic radius than the first cation. The first cation is present in the glass composition in the form of its oxide (e.g., Na20). As used herein, "ion-exchanged glass-based article" or "chemically strengthened glass-based article" means that the glass-based article has undergone at least one ion exchange process that exchanges a cation located at or near the surface of the glass with a cation of the same valence. In some embodiments, the strengthening processes can include one or more thermal tempering processes. In some embodiments, the strengthening processes can include one or more annealing processes.

[0281] Figure 2a and 2b Examples of brittle and non-brittle behavior of tempered glass substrates under point impact with a sharp indenter are shown. The point impact test for determining brittle behavior includes a device that delivers a force to the surface of the glass substrate with just sufficient force to release the internally stored energy within the substrate. That is, the point impact force is sufficient to form at least one new crack at the surface of the tempered glass sheet and extend the crack through the compressive stress layer into a region under tension. The impact energy required to generate or activate a crack in the tempered glass sheet depends on the compressive stress in the compressive stress layer and the depth of compression (DOC) of the article, and therefore also on the strengthening conditions of the sheet (i.e., the conditions used for strengthening the glass by ion exchange). Otherwise, Figure 2a and 2b Each ion-exchange glass plate shown is subjected to contact with a sharp dart indenter (e.g., a SiC indenter), sufficient to propagate a crack into the inner region of the plate, which is under tensile stress. The force applied to the glass plate is just sufficient to reach the initiation point in the inner region, thus causing the energy driving the crack to originate from the tensile stress in the inner region, rather than from the force of the dart impact on the outer surface. For example, the extent of ejection can be determined by placing the glass sample at the center of a grid, impacting the sample, and using the grid to measure the ejection distance of individual pieces.

[0282] refer to Figure 2a The glass plate can be classified as fragile. Specifically, the glass plate fragments into multiple ejected small pieces, exhibiting numerous branching cracks from the initial crack to produce these small pieces. Approximately 50% of the fragments are smaller than 1 mm, and it is estimated that about 8 to 10 cracks branch from the initial crack. The glass pieces are also ejected from the original glass plate a by about 5 cm, such as... Figure 2a As seen above, glass-based articles exhibiting any of the three criteria described above (i.e., multiple crack branches, ejection, and extreme breakage) are classified as brittle. For example, if glass only exhibits excessive branching but not the ejection or extreme breakage described above, then the glass is still characterized as brittle.

[0283] Glass plates b and c ( Figure 2b ) and d ( Figure 2a The glass plates were classified as non-fragile. In each of these samples, the glass had broken into a few large pieces. For example, glass plate b ( Figure 2b The glass plate (c) broke into two large pieces without any branching cracks. Figure 2b The glass plate d broke into four pieces, with two cracks branching from the initial crack; and the glass plate d ( Figure 2a) into four pieces with two cracks branching from the initial crack. Samples b, c, and d were classified as non- or substantially non-frangible based on the absence of ejected fragments (i.e., no glass pieces were ejected a distance of more than 2 inches from their original location with force), the absence of visible fragments having a size of 1 mm or less, and the minimum amount of crack branching observed.

[0284] Stress Profile of Compressive Stress Layer

[0285] The chemically strengthened glass-based articles of the present disclosure exhibit improved resistance to fracture and non-frangibility in a combined manner by having a stress profile (induced by a particular chemical strengthening process) with certain attributes that are believed to result in these mechanical properties. These attributes are described in detail below.

[0286] In glass-based articles exhibiting surface peaks, the surface peaks consume a substantial portion of the compressive stress area to protect the glass-based article from relatively lower penetration, but result in lower compressive stress levels at the depth of the compressive stress layer (for the same compressive stress area) where the tip of a deep flaw can exist. Thus, the protective effect of surface peaks is not very useful in preventing damage from deep flaws. This is especially true when the surface compressive stress is too concentrated such that near-surface facets of a crack (e.g., a flaw) do not separate during a bending event with an externally applied tensile stress.

[0287] Two compressive layer parameters of glass-based articles according to embodiments of the present disclosure include a deep compressive stress area (CSA deep ) and an average deep compressive stress in the compressive region not including surface peaks (CSA ). Without being bound by any particular theory, it is believed that as these attributes of the stress profile increase, the resistance to fracture relative to deep flaws (from tens of pm to depths exceeding 100 pm) improves.

[0288] These two parameters of the deep compressive stress region are defined as follows:

[0289]

[0290] where σ(x) refers to the stress profile, DOC refers to the depth of the compressive stress layer (i.e., the depth at which the stress transitions from compressive to tensile), and DOL spis the depth of the inflection point (i.e., the depth at which the slope of the stress profile transitions from steep (corresponding to a surface spike) to shallow). These parameters can be used to assess the fracture resistance of a glass-based article relative to a deep defect having a sharp end at a depth comparable to the DOC. In the context of the present disclosure, reference to the DOC, i.e., as opposed to DOC1 or DOC2, refers to the depth of compression DOC1. However, in the context in which "DOC" is used in reference to the second compressive layer, it refers to the depth of compression of the second compressive stress layer.

[0291] The stress intensity factor is a more refined strengthening parameter that can well predict the increase in fracture resistance on a rough surface compared to previously known glass-based articles:

[0292]

[0293] where c is the target defect depth, is a crack shape factor typically assumed to be 1.12, σ(x) is the stress profile, and g(x) is the Green's function, which depends on the particular case (see Vincenzo M. Sglavo and Luca Larentis, "Flaw-insensitive ion-exchanged glass: I, Theoretical Aspects", Journal of the American Ceramic Society, 84 [8], 1827-31 (2001)). The Green's function representing most of the cases of interest is, for a crack extending from the surface and normal to the surface, under an externally applied tensile stress that is approximately constant along the crack span and normal to the crack:

[0294]

[0295] In particular, the value of corresponding to a defect depth c equal to the DOC can be represented by:

[0296]

[0297] After setting the crack shape factor to 1.12 and inputting the above-mentioned Green's function approximation, the stress intensity factor is:

[0298]

[0299] It has been found that, since the stress profile obtained by diffusion typically has a continuous and mainly monotonic character, these three parameters ( , and each of which is suitable for assessing the protection afforded by the stress profile induced by chemical strengthening against defects having various relatively large depths (e.g., about 0.5 DOC to DOC, and even slightly beyond DOC). As these parameters increase, it is believed that the glass-based article will exhibit stronger protection against penetration of defects deep into the compressive layer. The parameters may allow for more accurate assessment of the protection afforded to glass-based articles having small to moderate thicknesses (0.4 mm to 0.7 mm), as deeper defects tend to have defect depths comparable to DOC. Nonetheless, the calculation requires a bit more work in order to avoid the pole associated with the point x = DOC, which is the upper limit of the integral. This can be done by performing a limit analysis of the integral near the pole. Alternatively, a similar good parameter can be chosen that avoids this slight complication altogether, allowing the integral to be evaluated directly numerically, e.g., :

[0300]

[0301] It has been found that the above parameters, which represent different stress profile attributes of the deep compressive zone, allow for effective comparison of the projected fracture resistance of different generations of high DOC stress profiles during drop on rough surfaces for any chosen specific thickness. This is largely because the DOC / thickness ratio of the Li glass profile is roughly the same (force balance sets maximum DOC for conventional chemical strengthening of Li-based glasses) since DOC is essentially maximized for thicknesses below about 0.8 mm. DOC is typically about 20% of the thickness, but in some cases it is slightly less or greater, depending on the specifics of the process (single or double ion exchange), the glass composition and its interaction with the concentration dependence of the diffusion coefficient, and the extent of stress relaxation. Furthermore, and (or ) can be normalized to account for the slight variations in the DOC / thickness ratio, as follows:

[0302]

[0303] and

[0304]

[0305] where N stands for "normalized" and the normalization is chosen to be relative to DOC of 0.2t so that the normalized and have similar values to the average compressive stress and the actual , as DOC will be about 0.2t as usual.

[0306] It has been found that glasses having higher fracture toughness can exhibit a sharper tension zone (p < 2), higher PT, and thus, advantageously, , the value of (Equation 3), (Equation 4), and (Equation 7) are higher. Without wishing to be bound by theory, it is believed that this is due in part to a lower Na / Li ratio in the glass-based substrate.

[0307] In embodiments, when the composition of the glass-based article includes less than 3 mol% Li20, the fracture toughness K peak of the glass-based article at a location x IC corresponding to the peak tension PT in the central tension zone 130 can be greater than or equal to 0.720 In embodiments, when the composition of the glass-based article includes Li20 in an amount in a range from about 3.0 mol% to about 7.5 mol%, the fracture toughness K peak of the glass-based article at a location x IC corresponding to the peak tension PT in the central tension zone 130 can be greater than or equal to 0.810 In embodiments, when the composition of the glass-based article includes Li20 in an amount in a range from about 7.5 mol% to about 11 mol%, the fracture toughness K peak of the glass-based article at a location x IC corresponding to the peak tension PT in the central tension zone 130 can be greater than or equal to 0.850 In embodiments, when the composition of the glass-based article includes Li20 in an amount in a range from about 11 mol% to about 13 mol%, the fracture toughness K peak of the glass-based article at a location x IC corresponding to the peak tension PT in the central tension zone 130 can be greater than or equal to 0.870 In embodiments, when the composition of the glass-based article includes Li20 in an amount greater than about 13 mol% Li20, the fracture toughness K peak of the glass-based article at a location x IC corresponding to the peak tension PT in the central tension zone 130 can be greater than or equal to 0.950 .

[0308] In embodiments, the fracture toughness K IC of the glass-based article can be greater than or equal to 1.0 , greater than or equal to 1.05 , greater than or equal to 1.1 , greater than or equal to 1.15 , greater than or equal to 1.2 or greater than or equal to 1.2 In embodiments where the glass-based article is in an amorphous phase substantially free of crystallites, the fracture toughness K IC may be less than or equal to 1.1 less than or equal to 1.05 less than or equal to 1.0 less than or equal to 0.95 less than or equal to 0.90 or less than or equal to 0.85 .

[0309] It has been recognized that the DOL should be increased in at least three situations of interest relative to a glass-based article that has been ion exchanged to have surface peaks sp the level of deep compressive stress disposed between the DOL and the DOC: (i) cover glasses having high fracture toughness and reduced thickness (primarily 0.4 mm to 0.6 mm, more typically up to 0.65 mm or 0.7 mm, and as low as 0.35 mm or 0.30 mm); (ii) cover glasses having shaped edges of locally reduced or further reduced thickness (2.5D shaped edges); and (iii) 3D shaped cover glasses, particularly cover glasses having reduced thickness (e.g., 0.4 mm to 0.6 mm).

[0310] In the case of thin or 3D shaped cover glasses, higher deep compressive stress is particularly important due to the tendency to create more local bending and thus higher local bending stresses upon contact. For glass-based articles including 2.5D shaped edges, the stress profile can have a higher deep compressive stress level in the thicker, wider regions of the sheet to achieve a higher deep compressive stress level for at least one relevant stress component in the 2.5D edge of the sheet where the thickness is reduced, thus reducing the risk of fracture upon a contact event on the 2.5D edge.

[0311] As discussed above, it is difficult to increase the deep compressive stress level beyond current state-of-the-art without making the glass brittle, because an increase in deep compressive stress will be accompanied by an increase in tensile stress in the central tension zone 130, which results from the force balance between the integrated compressive stress and the integrated tensile stress. Unless the glass-based substrate has a fairly high fracture toughness, this increase in tensile stress will result in a brittle strengthened glass article. Transparent glass-ceramics have been invented that have substantially better fracture toughness than typical cover glasses, and have actually been successfully brought to market, but the cost of current glass-ceramic covers is significantly higher than glass covers because the glass-ceramics require additional processing steps and are more costly to process overall (e.g., more expensive polishing). The focus of the present disclosure is to increase the deep compressive stress level of any fixed material strength parameter, such that the resulting performance improvement will be additive relative to any performance improvement based on increasing the material's mechanical properties (e.g., fracture toughness).

[0312] Stress Profile of Central Tensile Zone

[0313] While the primary goal of the present disclosure is to increase the deep compressive stress level in the compressive zone, an important aspect of the present disclosure involves increasing the tension area and / or average tension in the tension zone without increasing the tensile stress energy. This is because of the importance of tensile stress energy as a driver of brittleness. Thus, one primary aspect of the strengthened glass-based articles of the present disclosure is to deliberately shape the stress distribution in the tension zone to achieve a more uniform distribution of a particular target high DOC (e.g., greater than or substantially greater than 15% of the thickness). One goal of the present disclosure is to improve the fracture resistance of low to moderate thickness modern cover glasses. Such cover glasses typically need to have a high DOC to thickness ratio.

[0314] The tensile stress profile needs to be relatively uniform because the tensile strain energy (TSE) is proportional to the depth integral of the square of the tensile stress over the central tension zone, while the tension area TA (which, by force balance, is equal to the compressive stress area) is simply the depth integral of the tensile stress over the central tension zone. Thus, for a fixed TA, a less uniform stress profile will increase the TSE, and vice versa. Since the fragility imposes an upper limit on the TSE, the present disclosure seeks to increase TA by improving the uniformity of the tensile stress profile in the tension zone. Another reason to focus first on the tension zone is that it is relatively easy to measure the stress profile deep inside the Li-based glass using scattered light polarization measurements (SLP). In fact, the measurement of the stress profile in the tension zone of Li-based glasses is typically much more accurate than in the compression zone because the compression zone is close to the surface and strong surface scattering corrupt the data collected for the near-surface region. A second reason to more accurately extract the stress in the tension zone is that the resolution of scattered light polarization measurements is limited, which leads to a loss of accuracy in regions where the absolute value of the profile has a high second derivative. Typically, the Li glass stress profile has a higher absolute value second derivative in the compression zone at the bottom of the spike and at some deeper locations.

[0315] While the tension zone stress profile properties are particularly applicable to Li-based glasses, they can be equally applicable to Na-based glasses. However, for Na-based glasses, the inverse Wenzel-Kramer-Brillouin (IWKB) method discussed above provides an alternative method to directly obtain accurate stress profiles in the compression zone, provided that the glass surface is flat and the profile is not too deep so that it is possible to correctly resolve the fringes in the prism coupling spectrum corresponding to the deep modes and obtain their effective refractive index with high accuracy.

[0316] It is counter-intuitive to pursue a more uniform tension profile in the tension zone in order to increase the deep compression level while avoiding fragility. In fact, the prior art profiles with the most uniform tension zone have a substantially flat tension zone, e.g., the one-step profiles in the traditional soda-alumino-silicate glasses (Gorilla® Glasses 1, 2 and 3) have a DOC / t < 0.08, and most commonly a DOC / t < 0.06, where the average tension nearly the same as the peak tension PT (which typically occurs at the mid-plane of the substrate). It has been disclosed that for profiles with a significantly larger ratio DOC / t and a less pronounced uniform distribution in the tension zone, their tension energy fragility limit is significantly higher. However, the present disclosure describes that it is possible to increase the deep compression stress level in the compressive stress layer by increasing the DOC and utilizing a more uniform tensile stress profile in the tension zone, without increasing the tension strain energy TSE and the corresponding probability of fragility.

[0317] The tensile area (TA) of the stress profile is the depth integral of the tensile stress over the tensile zone of the glass-based article. The central tensile zone 130 is defined by the space spanning the DOC of the compressive stress layer on one side of the glass-based article to the DOC of the compressive stress layer on the opposite side of the glass-based article. The tensile area TA is calculated according to the following equation:

[0318]

[0319] where DOC1 and DOC2 are the depths of compression from the opposite surfaces of the glass-based article, and σ is the stress in MPa. When the in-plane dimensions of the glass-based article are each several orders of magnitude larger than the thickness of the glass-based article, TA is also equal to the sum of the stress areas of the compressive layers on both sides of the central tensile zone 130. Unless otherwise specified, the stress and / or energy values of the equations described herein are positive values. In other words, both compressive and tensile stresses and energies are expressed as positive values, i.e., absolute values.

[0320] One method of ensuring that a chemically strengthened glass-based article is not brittle is to limit the tensile zone brittleness factor K t while taking into account the fracture toughness of the glass-based substrate undergoing chemical strengthening. The brittleness factor K t is defined as follows:

[0321]

[0322] In embodiments, the glass-based article can have a brittleness factor K of no more than 0.5. where KIC peak is the fracture toughness of the glass article at a location x corresponding to the peak tension PT in the central tensile zone 130. In embodiments, the glass-based article can have a brittleness factor K of no more than 0.5. .

[0323] It has been found that the maximum non-brittleness PT varies approximately in proportion to the inverse of the square root of the thickness. Thus, in embodiments, the PT of a glass-based article induced via chemical strengthening can be set based on the inverse of the square root of the thickness. In embodiments, the peak tension PT of a glass-based article can be set to be greater than where A is equal to 2.5, 2.6, 2.7, 2.8, or 2.9. In embodiments, A is equal to 3.0, 3.1, 3.2, 3.25, 3.3, or 3.35.

[0324] In embodiments, the peak tension PT of the glass-based article is greater than 90 MPa, greater than 92 MPa, greater than 95 MPa, greater than 100 MPa, greater than 103 MPa, greater than 108 MPa, greater than 110 MPa, greater than 113 MPa, or greater than 115 MPa. In embodiments, the peak tension PT of the glass-based article is greater than 105 MPa. In embodiments, the peak tension PT of the glass-based article is greater than 120 MPa, greater than 125 MPa, or greater than 130 MPa.

[0325] In embodiments, the thickness t of the glass-based article can be in the range from about 0.4 mm to about 0.77 mm, or from about 0.43 mm to about 0.68 mm. In embodiments, the thickness t of the glass-based article can be greater than or equal to 0.40 mm or greater than or equal to 0.43 mm. In embodiments, the thickness t of the glass-based article can be less than or equal to 0.77 mm or less than or equal to 0.68 mm. In embodiments, the thickness t of the glass-based article is less than or equal to 0.52 mm.

[0326] The shape of the stress profile in the tension zone can be approximated by a power shape profile as follows:

[0327]

[0328] where x is the depth from the surface of the glass-based article, t is the thickness of the glass-based article, and p is the power coefficient of the stress profile, where p is close to 2 (parabolic profile), but slightly higher (about 2.1). Equation 14 only closely approximates the stress in the tension zone, i.e. , and extrapolating Equation 14 outside the tension zone will do a good job of representing the stress profile in the compression zone, especially far from the DOC. Figure 3 A plot of Equation 14 is shown with different power coefficients p (in the range from 1.2 to 20). Figure 3 The DOC in Equation 14 is fixed at 0.12 mm (20% of a 0.6 mm thickness). Also, Figure 3 The stress profile plotted in Equation 14 has a tension zone factor of 1.45 (Equation 13). Figure 1 Each of the stress profiles in Equation 14 has the same tension energy, but different tension areas TA (Equation 12).

[0329] It is convenient to use an appropriate model for the stress profile in the tension zone to illustrate methods of improving stress profile properties, and to enable accurate measurements of stress profile properties even in cases where the measured retardation is relatively noisy, and for glass-based articles containing and The same is true for the stress profile properties. In fact, the approximate distribution shape in the tension zone can be obtained by differentiating the polynomial fit of the retardation curve, but low order polynomials tend to not fit complex distributions well, while high order polynomials tend to fit a lot of noise. For symmetric tension zone distributions, the power profile introduced in Equation 14 above provides a good fitting model for distributions with varying degrees of tension uniformity. The power coefficient p can be thought of as a degree of uniformity, where a low level of p corresponds to a less uniform tension assignment, and a higher level of p corresponds to a more uniform assignment. Strictly speaking, when p tends to infinity, the tension zone is always perfectly flat. In practice, p cannot be too high for a diffuse distribution that tends to be continuous and gradually varying with a finite slope.

[0330] In embodiments, the stress profile of the glass-based article, when fit to Equation 14, has a best fit value of the power coefficient p that is greater than or equal to 2.75, greater than or equal to 2.8, greater than or equal to 2.85, greater than or equal to 2.9, greater than or equal to 3.0, greater than or equal to 3.1, or greater than or equal to 3.2. In embodiments, the stress profile of the glass-based article, when fit to Equation 14, has a best fit value of the power coefficient p that is no more than 20. In embodiments, the stress profile of the glass-based article, when fit to Equation 14, has a best fit value of the power coefficient p that is more than 2.35, more than 2.4, more than 2.45, more than 2.5, more than 2.55, more than 2.6, more than 2.65, or more than 2.7.

[0331] Average tension in the tension zone TA is the ratio between the tension zone width (BTZ), which is t - 2DOC for symmetric distributions.

[0332] Several different properties of the stress profile can be used to assess the degree of uniformity of the tensile stress assignment. Some of the most generally applicable properties, regardless of the assignment shape, include the following ratios:

[0333]

[0334] where BTZ represents "tension zone width." In embodiments, for glass-based articles of the present disclosure, the stress distribution attribute shown in Equation 16 can be set to 0.735 or greater. In embodiments, the stress distribution attribute shown in Equation 16 can be greater than or equal to 0.700, greater than or equal to 0.705, greater than or equal to 0.710, greater than or equal to 0.715, greater than or equal to 0.720, greater than or equal to 0.725, greater than or equal to 0.730, greater than or equal to 0.735, greater than or equal to 0.740, greater than or equal to 0.745, greater than or equal to 0.750, greater than or equal to 0.755, greater than or equal to 0.760, greater than or equal to 0.765, greater than or equal to 0.770, greater than or equal to 0.775, greater than or equal to 0.780, greater than or equal to 0.785, greater than or equal to 0.790, greater than or equal to 0.795, or greater than or equal to 0.800.

[0335] Figure 4 A plot of the non-dimensional stress distribution attribute as a function of the power coefficient p (x-axis) and (y-axis) is shown. Figure 4 It is indicated that when most of the failures are caused by the formation of defects extending to a depth similar to, preferably not significantly exceeding, the DOC and by stresses, it can be advantageous to design a stress distribution with as high a p as possible.

[0336] Other ratios associated with the improvement of the stress distribution under non-frangibility constraints incorporate the tension zone frangibility factor and (proportional to the tension energy):

[0337]

[0338] With the increase of each of the stress distribution attributes shown above, the amount of compression in the compressive stress layer will also be permitted to increase, given a level of tensile strain energy.

[0339] Figure 5 The non-dimensional stress distribution attribute shown in Equation 19 is shown, where the power coefficient p varies from 1 to 20. For a fixed tension zone width (e.g., a fixed DOC), the distributions with higher p have higher stress area. It is noted that when the ratio is not allowed to vary, the stress distribution attribute and is related to a constant, and thus can be considered equivalent in this case. As the distribution of the tension zone tends towards a perfect rectangular distribution, the stress distribution attribute will get arbitrarily close to 1. It can be seen from Figure 5 that For p = 1.2 to 0.866, for p = 1.6 to 0.899, and for p = 2 to 0.913. When the diffusion coefficient can be considered approximately constant over the range of diffusant concentration represented in the profile, and when the profile has diffused long enough to reach a maximum or near-maximum DOC, the profile for p = 2 (parabolic) approximates well the profile that is experimentally possible. Depending on the diffusion time or diffusion length, such profiles also approach or exceed the peak tension PT. From Figure 5 It can be seen, for example, that increasing p to more than 2.4, for the same factor, obtains a higher TA. The rate at which the TA benefit is obtained is higher when the value of p is lower, and decreases as p increases. Thus, most of the benefit will be obtained when increasing p from about 2 or less to 3, 4, or 5, without significantly reducing .

[0340] Furthermore, recognizing again the importance of high DOC for fracture resistance on rough surfaces, the present disclosure defines a stress profile parameter indicative of increased deep compressive stress level that also explicitly accounts for the increase in DOC:

[0341]

[0342] and in dimensionless form:

[0343]

[0344] explicitly accounts for the increase in DOC and includes the stress profile property of the ratio of TA to or includes:

[0345]

[0346] For flat portions of the glass-based article away from the edge, the evaluation of the above stress profile properties is less adequate. Furthermore, for 2.5D geometries, the ratio of the flat (and thicker) portion of the sheet away from the 2.5D edge may not be as important as in the case of non-2.5D geometries, as it is very important to strengthen the 2.5D edge region. Thus, while all of the above tension zone stress profile properties can be applied to increase the fracture resistance of glass-based articles having 2.5D edges, in most cases focusing on stress profile properties that do not explicitly include will result in higher performance in the 2.5D context than focusing on the corresponding stress profile properties that include Of course, some minimum value of may be imposed when maximizing the stress profile properties without DOC to ensure that performance is not degraded by completely ignoring the importance of DOC.

[0347] In embodiments, the glass-based article can have a DOC greater than or equal to 0.150 t, greater than or equal to 0.160 t, greater than or equal to 0.170 t, greater than or equal to 0.180 t, greater than or equal to 0.190 t, or greater than or equal to 0.200 t. In embodiments, the glass-based article can have a DOC greater than or equal to 0.205 t or greater than or equal to 0.210 t.

[0348] Another set of tension zone stress profile attributes that more directly relate to the deepest stress level in the compression zone incorporate the slope of the stress profile at the DOC, as a high slope at the DOC of the stress profile generated by the diffusion indicates compression stresses in the region of the compression layer closest to the DOC. The slope at the DOC can be calculated as follows:

[0349]

[0350] And the associated stress profile attributes are:

[0351]

[0352] Figure 6 Plots of the stress profile attributes , and (y-axis) as a function of the power coefficient p (x-axis). Figure 6 show how these stress profile attributes show a significant rate of increase even at high values of the power coefficient p. This significant rate of increase is driven by the growth of the slope at the DOC, evaluated on the inside of the tension zone. These stress profile attributes continue to grow even at high values of p, indicating that high p profiles have an additional significant benefit for strengthening deep defects, with the tip close to but preferably not exceeding the DOC.

[0353] Combining the stress profile attributes of the DOC and / or thickness and the slope at the DOC include:

[0354]

[0355] In embodiments, the glass-based article can have a greater than or equal to 140 MPa. In embodiments, the glass-based article can have a The compressive stress CS can be greater than or equal to 160 MPa, greater than or equal to 175 MPa, greater than or equal to 190 MPa, greater than or equal to 200 MPa, greater than or equal to 210 MPa, greater than or equal to 220 MPa, greater than or equal to 230 MPa, greater than or equal to 240 MPa, greater than or equal to 250 MPa, greater than or equal to 260 MPa, or greater than or equal to 265 MPa. In an embodiment, the surface compressive stress CS can be greater than or equal to 100 MPa or greater than or equal to 110 MPa. In an embodiment, the surface compressive stress CS can be less than or equal to... Less than or equal to or less than or equal to The high values ​​of the aforementioned stress distribution properties indicate that the glass-based article has a high level of compressive stress deep within the compressive stress layer. In embodiments, the surface compressive stress CS may be greater than or equal to 500 MPa, greater than or equal to 550 MPa, greater than or equal to 600 MPa, greater than or equal to 650 MPa, greater than or equal to 675 MPa, greater than or equal to 700 MPa, greater than or equal to 725 MPa, greater than or equal to 750 MPa, greater than or equal to 775 MPa, or greater than or equal to 800 MPa.

[0356] In embodiments where the glass-based article includes a compression peak at the surface, the inflection point compressive stress CS k (The deeper portion of the CS distribution is at the peak depth (DOL)) sp The extrapolated compressive stress at the point () can be greater than or equal to 100 MPa or greater than or equal to 110 MPa. In embodiments where the glass-based article includes a compressive peak at the surface, the inflection point compressive stress CS k Can be less than or equal to Less than or equal to or less than or equal to .

[0357] In embodiments where the glass-based article includes a compression peak at the surface, the peak depth DOL SP It can be greater than or equal to zero and less than or equal to the upper limit DOL. ul DOL ul It is the larger of 4 µm and 0.01t.

[0358] In embodiments where the glass-based article includes compression spikes at the surface, DOL SP A portion of the stress distribution between the stress and the DOC can include negative curvature. Extremely high DOC / t ratios (e.g., above 0.19 and 0.20) are achieved while simultaneously exhibiting high p and One method for calculating the value is by utilizing inflection points (DOL). SP) a negative curvature in a sub-region of the compressive stress region occurring somewhere between the DOC, while limiting the diffusion length to prevent Na20 enrichment in the mid-plane. This negative curvature in the compressive stress profile occurs at a depth somewhat beyond the depth of the peak (i.e., toward the center of the glass sample), e.g., only a few microns and quite far from the DOC, especially in the depth region below about 50 to 60 μιη from the surface, the limited resolution of the SLP-2000 measurement and the delayed distortion caused by surface scattering and convolution effects make it complicated to determine the presence of a negative curvature from the SLP-2000 measurement alone. On the other hand, based on accurate measurements of the tension zone boundary and the slope of the stress profile at the DOC, as well as the inflection point stress CS k , decay prism coupling (EPC) measurements (e.g., FSM-6000), it can be demonstrated that some stress profiles contain a negative compressive stress curvature. Considering that the value CS k approximately occurs at the depth of the peak DOL SP , if the compressive stress profile beyond the depth of the peak in the compressive region is a straight line to the DOC, and the second derivative across the entire depth span is equal to zero, then the following equation holds: .

[0359] Here, it should be apparent that if , then there must be a sub-region between DOL SP and the DOC where the absolute value of the slope of the compressive stress profile is less than the slope at the DOC, which means that as the depth increases, the slope of the compressive stress profile becomes more negative (higher in absolute value) as it approaches the DOC. If the slope of the compressive stress profile (i.e., the first derivative) becomes more negative as it approaches the DOC, then this means that at those points where it becomes more negative, its second derivative is negative, as is its curvature (curvature is proportional to the second derivative, and the proportionality constant is always positive).

[0360] Furthermore, since for the cases of interest in this disclosure, the condition DOL SP << DOC holds, the condition will tend to indicate the presence of a sub-region of negative second derivative of the compressive stress profile in the region between DOL SP and the DOC. Moreover, it should be noted that in practice there is a small transition region around the depth DOL SP where the compressive stress has a strong positive second derivative associated with the transition of the compressive stress from the high negative slope in the peak to a much smaller slope (negative or otherwise) immediately after the peak. When both the TM and TE total internal reflection (TIR) transitions are in the preferred measurement window, the CS k value detected by prism coupling tends to correspond to a point on the compressive stress profile that occurs in the small transition region of strong positive second derivative, and thus the measured CS kThe values tend to be slightly higher than the values extrapolated directly from the slope (first derivative) of the deeper sub-zone immediately after the transition zone. In other words, if the distribution were strictly a straight line from slightly deeper than DOL SP to DOC, then the measured value of CS k would tend to be slightly higher than . Thus, it is possible, and even common, that if the bulk of the deeper compressive stress zone is essentially a straight line, then there is only a small negative second derivative at a depth slightly beyond DOL SP , and also a measured CS value that is slightly higher than k . On the other hand, if CS k is significantly higher than , then the likelihood of a sub-zone of negative second derivative of compressive stress in the compressive stress zone between DOL SP and is greatly reduced. In summary, having CS k similar to or less than indicates that the compressive stress distribution beyond DOL SP contains a sub-zone of negative second derivative, and ensures that the compressive stress assignment is not too heavy closer to the surface, but has considerable compressive stress at greater depths. This is even more true when the measured value of CS k is significantly lower than , such as at least lower than .

[0361] Higher CS k is strongly associated with higher resistance to breakage during system drop tests on rough surfaces such as sandpaper, at least when the DOC is nearly maximized. The inventive stress distributions in this disclosure tend to have high levels of CS k , which is strongly associated with high slope at DOC, resulting from the preferred shape for the central tensile zone. At the same time, the especially preferred inventive distributions are those that also satisfy: , and further more preferably satisfy , or , and especially , to ensure that a considerable portion of the compressive stress area is placed at greater depths of the distribution, since at such greater depths, greater amounts of compressive stress have a more significant and positive impact on the retention strength of deeper flaws. At the same time, to ensure that CS k is high, preferred embodiments also have a relatively high , such as higher than 140 MPa, preferably higher than 170 MPa, and especially preferred higher than 190 MPa (the higher the better, as long as the DOC is sufficient to cover most of the flaws expected to occur during service).

[0362] In embodiments, the stress distribution property of the glass-based article may be greater than or equal to 700 MPa, greater than or equal to 800 MPa, greater than or equal to 850 MPa, greater than or equal to 900 MPa, greater than or equal to 970 MPa, greater than or equal to 1000 MPa, greater than or equal to 1040 MPa, greater than or equal to 1100 MPa, or greater than or equal to 1120 MPa. In embodiments, the stress distribution property shown in Equation 40 can be greater than or equal to 0.2 MPa / µm or greater than or equal to 0.3 MPa / µm. In embodiments, the stress distribution property shown in Equation 40 can be greater than or equal to 0.325 MPa / µm, greater than or equal to 0.350 MPa / µm, greater than or equal to 0.375 MPa / µm, greater than or equal to 0.400 MPa / µm, greater than or equal to 0.425 MPa / µm, greater than or equal to 0.450 MPa / µm, or greater than or equal to 0.475 MPa / µm.

[0363] It is expressly contemplated that the increase in DOC, the ratio of TA to or and also the stress distribution property at the DOC of the slope can include:

[0364]

[0365] The stress distribution property (Equation 15), (Equation 16), (Equation 23), (Equation 24), (Equation 30), (Equation 31), (Equation 41), and (Equation 42) (which do not include or ) are particularly convenient to measure accurately using the scattered light photoelastic (SLP) technique, as they are generally insensitive to the centering calibration error. This is because the calibration error tends to cancel out in the ratio and because each of the variables in the stress distribution property can be measured directly from the retardation curve obtained from the SLP measurement, except for the thickness, which can be measured separately with a micrometer with very high precision. In fact, an independent thickness direct measurement using a micrometer can be used to verify the depth calibration of the SLP measurement, and thus to ensure the accuracy of the other terms, such as , , and The retardation curve is a plot showing the retardation between transverse magnetic (TM) and transverse electric (TE) polarized light as a function of depth as the laser beam traverses the sample thickness in an SLP measurement. The retardation can be measured directly by looking at points along the laser beam with a camera, and by mapping these points to depth and plotting retardation versus depth the curve is obtained.

[0366] In particular, parameters of the stress profile properties can be obtained directly from the retardation curve as follows:

[0367] • The difference between the highest and lowest values of retardation in the retardation curve, e.g., the retardation difference between the two points where the stress profile crosses zero. • The maximum slope of the retardation curve between the locations of the minimum and maximum retardation.

[0368] • The difference in depth between the points of minimum and maximum retardation.

[0369] • The distance from the surface to the nearest minimum or maximum retardation value. • The second derivative of the retardation at the location of the maximum retardation (coinciding with the zero-crossing of the stress profile) or minimum retardation (coinciding with the zero-crossing of the stress profile).

[0370] • The second derivative of the retardation at the location of the maximum retardation (coinciding with the zero-crossing of the stress profile) or minimum retardation (coinciding with the zero-crossing of the stress profile).

[0371] • The second derivative of the retardation at the location of the maximum retardation (coinciding with the zero-crossing of the stress profile) or minimum retardation (coinciding with the zero-crossing of the stress profile).

[0372] While , and depend on the calibration of the instrument, the stress profile properties (Equation 15), (Equation 16), (Equation 23), and (Equation 24) do not depend on the calibration and are therefore not sensitive to moderate calibration errors. In particular,

[0373]

[0374] where is the measured retardation as a function of depth x in radians, degrees, or nanometers.

[0375]

[0376] and

[0377]

[0378] ​​​​​Experimental delay curves often contain noise, which can increase the uncertainty of the measured quantities, especially in cases involving derivatives of the delay (e.g. and Thus, it is highly preferred to use an SLP apparatus with a shorter wavelength (violet) and noise reduction means (e.g. laser spot suppression) to start with a relatively good signal-to-noise ratio. Furthermore, if the noise is still such that the uncertainty of the measured quantities is higher than a few percent, then a fit of the delay curve or parts thereof should be applied to obtain a more accurate estimate of , and or Finally, as discussed above for commercial grade SLP apparatuses, it can be necessary to take several measurements, e.g. ten measurements, and average the delay data for subsequent analysis and extraction of various properties of interest.

[0379] SLP-2000 Stress Profile Characterization Method

[0380] From the above discussion, the stress profile properties of the embodiments described herein can be measured using the SLP-2000 stress profile characterization method. The SLP-2000 stress profile characterization method utilizes a commercial SLP-2000 manufactured by Orihara Industrial Co. with a working light source (laser) wavelength of 405 nm. To address the laser spot noise (which can be too high by default to accurately determine the underlying distribution shape by a single measurement) of the spatial distribution of light intensity in the laser beam image, the SLP-2000 stress profile characterization method involves taking ten measurements, with the glass sample being rotated or linearly shifted between each measurement. Each of the ten measurements produces a different spot noise pattern, which drives a different delay noise pattern on the delay curve. After all ten measurements are completed and the delay curves are saved, an average delay curve is obtained, which is characterized by a significant reduction in noise relative to the delay noise of the individual delay curves.

[0381] If the glass sample is rotated between each measurement, then different delay noise patterns can be achieved by covering a cumulative rotation angle range of 180 degrees and a roughly equal angular spacing between successive orientations (e.g., roughly 20 degrees / rotation). However, if multiple measurements are not taken at exactly the same sample location and orientation, then a greater cumulative rotation angle range and / or different rotation increments can be implemented, which can result in the same noise pattern persisting even after averaging. If the glass sample is linearly shifted between each measurement, then it should be shifted by about 100 pm (roughly the diameter of the 405 nm laser) between each measurement, so that ten measurements involve a cumulative linear shift of about 1 mm. However, as with the sample rotation method, a greater cumulative linear shift and / or different linear shift increments can be implemented as long as multiple measurements are not taken at exactly the same sample location and orientation.

[0382] To ensure the accuracy of the measured delay curves, the SLP-2000 should be calibrated according to the calibration procedure provided by the manufacturer. This involves providing the SLP-2000 software with the accurate values of the prism refractive index at the measurement wavelength (provided by the manufacturer) and the measured glass refractive index, as well as the accurate value of the stress optical coefficient (SOC) of the measured glass at the measurement wavelength. It is also important to supply the SLP-2000 software with the correct calibration coefficients for each calibration sample at the measurement wavelength when using the depth calibration sample (“depth standard glass”) and the stress calibration sample (“stress standard glass”) provided by the manufacturer. In the 2018 version of the SLP-2000 software, three calibration coefficients are provided, one for depth correction (“DOL_zero”) and two for stress correction, surface stress correction, and deep stress correction (“CS correction” and “deep stress correction”, respectively). In order for the delay curves of the central tension zone to accurately represent the depth integral of the stress distribution in the tension zone, the deep stress correction calibration coefficient needs to be equal or approximately equal to the surface stress correction calibration coefficient. Otherwise, applying the deep stress correction calibration coefficient results in a distorted stress distribution. In addition, when the deep stress correction calibration coefficient is not set to the same value as the surface stress correction calibration coefficient, the shape of the resulting stress distribution varies depending on the depth to which the deep stress correction refers (the deep stress correction value should be applied at a particular depth). Therefore, it is preferable to keep the deep stress correction calibration coefficient the same as the surface stress correction calibration coefficient (i.e., “deep stress correction” = “CS correction”) to avoid unexpected distortion of the distribution.

[0383] For the SLP-2000 instrument used by the inventors, depth calibrations were performed using deep calibration samples with depth correction factors very close to 1, typically between 0.99 and 1.0, so the inventors kept the value of the depth correction factor at 1. Surface compressive stress calibrations applied over multiple days had an average value in the range of about 1.038 to about 1.048. Each of these calibration values was obtained after 10 measurements on the calibration sample, and the average of the 10 surface compressive stress values was taken as the calibration measurement. The inventors set the surface stress correction calibration factor to 1.04. In addition, the deep stress correction calibration factor was set to the same value as the surface stress correction calibration factor, since the relative symmetric stress profile is due to the delay curve.

[0384] The SLP-2000 stress profile characterization method described herein permits accurate and repeatable measurements of the average delay curve of a glass sample, which measurements are subjected to post-processing procedures described below to extract the properties of the corresponding stress profile of the glass sample. Thus, in addition to the measurement techniques and calibration procedures described above, the SLP-2000 stress profile characterization method involves the following post-processing procedures to extract the properties of the corresponding stress profile of the glass sample.

[0385] Figure 7 The average delay curve of Example 7 is presented, and is referred to below to facilitate discussion of the post-processing procedures utilized by the SLP-2000 stress profile characterization method. Figure 7 The horizontal axis represents the spatial coordinate along the depth dimension of the glass sample, and is approximately equal to the depth measured from the surface within the accuracy of the precision specification of the DOC (typically equivalent to ± 5 pm) in identifying the precise location of the surface of the glass sample on the delay curve. The vertical axis shows the measured delay (phase difference) between the transverse electric and transverse magnetic polarization states, in degrees. The continuous line represents the average delay of the ten measurements. The two dashed lines, one approaching the local peak value of the delay and the other approaching the local valley value, represent a local 4thorder polynomial fit used to determine the more precise location of the delay peak and valley values at sub-pixel resolution. The 4thorder polynomial fit is based on delay data spanning between the outer 32 microns (i.e., in the corresponding compressive stress layer) and the inner 51 microns (i.e., in the central tension zone). The locations of the peak and valley values are obtained as the local minima / local maxima of the corresponding 4thorder local polynomial fit, evaluated on a dense depth grid with a depth spacing of 0.05 microns.

[0386] The x-coordinates of the maxima and minima of the retardation curve represent the locations where the sign of the stress changes, e.g., from compressive to tensile, or vice versa. When measured relative to the nearest surface of the sample, these locations represent the corresponding depths of compression (DOC) relative to the nearest surface. The breadth of the tension zone, BTZ, is determined as the difference between the x-locations corresponding to the maxima (peaks) and minima (valleys) of the retardation curve.

[0387] It is noted that if the angle of incidence of the laser beam inside the sample, measured relative to an orientation normal to the large surface of the sample, is greater than about 80 degrees, there can be a small deviation between the locations of the peaks and valleys of the retardation curve and the locations where the sign of the stress changes. Thus, at very high beam angles, especially well above 80 degrees, the effects of slightly different beam bending for transverse electric and transverse magnetic waves can result in the need for more complex analysis to maintain high accuracy of the stress profile measurements (see Siim Hodemann et al., "Gradient scattered light method for non-destructive stress profile determination in chemically strengthened glass", Journal of Materials Science, 51 : 5962-5978 (2016)).

[0388] The peak tension, PT, is determined by fitting each of the ten individual retardation curves using a 6thorder polynomial fit provided by the SLP-2000 software, thereby limiting the fit region to be inside the glass sample, excluding the outermost 70 to 80 microns on both sides of the glass sample. The peak tension, PT, for each measurement is determined by calculating the maximum slope of the 6thorder polynomial fit between the minimum and maximum retardation locations. It has been determined that although the retardation noise in the individual measurements is relatively high, averaging the peak tensions, PT, of the ten measurements for different sample orientations results in a value that is nearly the same as that obtained by averaging the retardation data of the ten retardation curves and then performing a 6thorder fit on the average retardation curve to calculate the peak tension, PT. Thus, to determine the peak tension, PT, of the stress profile, it is only necessary to average the peak tensions, PT, of the ten measurements for slightly different orientations or positions using the 6thorder polynomial fit utility in the SLP-2000 software as set forth above.

[0389] Next, the average retardation curve is decomposed into symmetric and antisymmetric components, with the decomposition plane (symmetry plane) chosen as the midpoint between the locations of the peaks and valleys of the retardation curve (see Figure 7). When a symmetric stress model is used to obtain a retardation model for fitting the retardation curves, the retardation model will produce an anti-symmetric retardation about the thickness through axis centered on the midpoint or midplane (centered on the point / plane means that the zero value of the axis lies in the midplane). This decomposition is performed because, even after performing the averaging of the individual retardation curves described above to mitigate noise in the retardation data, obtaining an accurate fit to the improved retardation can still be limited by certain distortions in the retardation curves that can be caused by systematic errors in the measurement setup, asymmetries in the actual stress distribution, and / or some warping of the glass sample. For more information on the decomposition of the retardation curves, see U.S. Patent No. 11,105,561, entitled “Hybrid Systems and Methods for Characterizing Stress in Chemically Strengthened Transparent Substrates,” issued August 31, 2021, the entirety of which is incorporated herein by reference (see column 32, lines 33-67).

[0390] Next, the antisymmetric component of the average retardation curve is non-linearly fitted based on the integral form of the power model provided in Equation 14, using the tension zone width, BTZ, and the peak tension, PT, as model input parameters, and restricting the fitting region to a sub-region within the interior of the glass sample. The sub-region contains the entire tension zone, but does not include at least the outermost 50 microns on both sides of the sample, as it is well known that the retardation in the outermost 50 microns cannot directly and accurately represent the depth integral of the stress profile due to the effects of various distortions, which are beyond the scope of the present discussion. Furthermore, depending on the scattering intensity of the sample-prism interface bonding oil (liquid, fluid), the sample-back cover interface bonding oil, and the refractive index mismatch between the oil and the glass, the oil and the prism, and the surface roughness of the glass sample and the prism, the focusing conditions of the beam, the rate of change of stress with depth, the rate of change of stress slope with depth, and the thickness of the sample, there is some non-negligible difference between the retardation in the depth range of 50 to 110 microns and the assumed perfect retardation that is perfectly proportional to the depth integral of the stress at the corresponding depths in the range. The difference (or error) generally decreases with increasing depth, and is generally small enough at a depth of 110 microns, unless the surface roughness is very significant and causes very bright surface scattering, thereby destroying the retardation signal corresponding to the relatively larger depths. Fitting the retardation signal at depths significantly smaller than the compression depth does not improve the accuracy of the fitted representation of the tension zone retardation. Therefore, to ensure accurate measurement of important aspects of the tension zone stress profile (e.g., shape), it is preferable to rely on fitting a small portion of the tension zone and the compression zone closest to the compression depth. To obtain a more accurate value of the slope at DOC, the fitting region extends at least 15 microns into the compression stress layer on both sides of the central tension zone.

[0391] The antisymmetric integral of the symmetric stress power distribution model used to fit the antisymmetric component of the experimental retardation curve gives, in terms of the optimization parameters and is given in the form

[0392]

[0393] where the optimization parameters and correspond to the retardation slope produced by the central tension and the distribution shape parameter p, whose coordinate z corresponds to the coordinate through the thickness, representing the signed distance from the midplane between the peak and valley values of the retardation, positive on one side of the plane and negative on the other.

[0394] The non-linear fitting routine used with the power model of the tension zone stress is the function ‘nlinfit’ for scientific numerical computation in the Matlab and Octave software engines. Figure 9The integral power distribution model of Equation 14 is shown fitting the antisymmetric component of the average retardation curve of Example 7, where the vertical dashed lines indicate the boundaries of the fitting region. Figure 11 The residual between the antisymmetric component of the average retardation and its fitted power distribution model is shown, where the absolute value of the residual does not exceed 1.5 degrees. From Figure 9 and 11 It can be seen that the power distribution provided by Equation 14 accurately represents the stress distribution of the central tension zone of the chemically strengthened glass-based articles of the present disclosure. Figure 13 The associated stress distribution of the fitted power model of Example 7 is shown, where the vertical dashed lines indicate the boundaries of the fitting region. The tension area TA, the slope of the stress distribution at the DOC and the fragility factor K t .

[0395] The thickness of the glass sample is measured using a micrometer. For a stress distribution that is symmetric about the central plane of the glass sample, it is assumed that DOC1 and DOC2 are equal (DOC1 = DOC2 = DOC), and the DOC is determined by subtracting the tension zone width BTZ from the thickness and dividing by 2. However, for a substantially asymmetric stress distribution, DOC1 and DOC2 can be determined using the SLP-2000 data.

[0396] Compressive Stress Layer Characterization Method

[0397] As described above, the stress distribution properties of the compressive stress layer of the embodiments described herein can be measured using prism-coupling instruments similar to the FSM-6000, but with additional options for the operating wavelength to provide a preferred measurement window, described in U.S. Patent No. 11,448,595, issued September 20, 2022, entitled “Prism-Coupling Systems and Methods with Improved Intensity Transition Position Detection and Tilt Compensation,” the entirety of which is incorporated herein by reference. The compressive stress layer characterization methods of the present disclosure are performed in accordance with U.S. Patent Nos. 11,448,595 and 11,703,500, issued July 18, 2023, entitled “Methods of characterizing ion-exchanged chemically strengthened glasses containing lithium,” and U.S. Patent No. 11,703,500, the entirety of which are incorporated herein by reference. Such methods can measure the compressive inflection point stress CS k, spike depth DOL SP and surface compressive stress CS. In performing the CS k measurement, the wavelength must be chosen such that there is no resonance near the TIR transition for both TE and TM polarizations.

[0398] Surface compressive stress CS is obtained using fringes spectrum at 365 nm and extrapolated from the surface refractive index using the assumption that the depth (point of inflection) of the refractive index profile from the surface to the second mode (fringes) is linear. In this approximation, the surface refractive index is equal to the effective refractive index of the first mode plus 1.317 times the effective refractive index separation between the first and second modes.

[0399] The present disclosure introduces a number of stress profile attributes that are helpful in characterizing the nature of the stress profile imparted via one or more ion exchange processes. Without wishing to be bound by theory, it is believed that the stress profile attributes described herein, and the associated limits and ranges, will result in a glass-based article that exhibits improved fracture resistance while avoiding fragility. The following sections of the present disclosure provide exemplary ion exchange process methods that can be used to achieve the desired stress profile attributes described herein. The exemplary ion exchange process methods are followed by examples of chemically strengthened glass-based articles of the present disclosure.

[0400] Exemplary Ion Exchange Method :

[0401] For Na-based glasses:

[0402] First Method : Ion exchange in a K-rich bath such that the surface concentration of K20 in the glass is increased by at least 5 mol%, preferably more or significantly more. Ion exchange is performed until near the target DOC / t ratio. The surface concentration is chosen such that the glass reaches near the fragility limit at near the DOC / t ratio. A modest heat treatment is then performed which further increases the DOC and slightly reduces the tensile strain energy due to the increase in DOC and the decrease in uniformity of the tension zone. Then, if needed, a short spike step in a K-rich bath is performed to complete the profile with high surface CS.

[0403] Second Method:(for further higher p and higher slope at DOC): ion exchange in a K-rich bath to increase the surface concentration of K20 beyond 5 mol%, preferably significantly. Ion exchange is performed until near the target ratio DOC / t, and the glass is brought into the fragile regime, but with extra care to avoid partial breakage during chemical strengthening. A moderate heat treatment is then performed to increase the DOC to the target value, which will slightly decrease the power coefficient p and slightly decrease the slope at DOC. If a buried peak is preferred, a short ion exchange in a bath with a mixture of Na and K ions can be performed after the heat treatment to decrease the surface concentration of K20, resulting in a buried peak. In some cases, the heat treatment step prior to the K20 reduction ion exchange step can be omitted. After any such combination of heat treatment and K reduction steps, the glass-based article should be in the non-fragile regime. Finally, if a surface spike is desired, a short ion exchange in a K-rich bath can be performed to increase the surface concentration and surface CS. The size of the spike needs to be adjusted according to the tension energy budget to avoid fragility.

[0404] Third Method : high temperature ion exchange in a first K-rich bath. The temperature is high enough to enable strong stress relaxation. In this way, at least until the DOC is not very close to target, the profile can be prevented from deepening, avoiding that its tension energy rises to the fragility limit. Optionally, a short to moderate heat treatment is then performed to further increase the DOC to the target DOC. A short ion exchange in a second K-rich bath is then performed to increase the surface concentration and surface CS. If the surface K20 concentration increase in the first K-rich bath is significantly lower when compared to the second K-rich bath, then the heat treatment step can not be needed. The choice of using a heat treatment step depends on the target of maximum degree optimization of the profile.

[0405] For Li20-containing glasses with relatively high Li20 content (e.g., more than 7 mol% Li20, but preferably more than 8 or 9 mol% Li20):

[0406] First Method: At sufficiently high temperatures, ion exchange is performed to activate significant stress relaxation in the compressive region of the glass having a high Li20 content, preferably greater than 8 mol%. In cases where the fracture toughness of the glass-based substrate is relatively high and a certain limit surface stress is required to prevent overstress failure of shallow flaws, a single step ion exchange in a mixed bath (KNO3 and NaNO3) can be used. Ion exchange is stopped when the DOC is sufficient. The temperature is chosen such that the stress relaxation is just sufficient to boost the DOC while the tension zone uniformity has not yet been degraded (e.g., when p is still above 2.4), but not so high that the tension can be unnecessarily reduced to well below the fragility limit. For a glass-based substrate of 0.55 mm thickness having composition 1 (see Table 1), a suitable ion exchange bath can contain 8 to 9.5 wt% NaNO3, 90.5 to 92 wt% KNO3. The glass-based substrate should be properly pre-heated prior to ion exchange, which should be performed at about 470°C for about 2.5 to 2.75 hours. This ion exchange procedure will result in a stress profile with a DOC similar to that produced using a 0.7 wt% LiNO3 / 9 wt% NaNO3 / 90.3 wt% KNO3 bath composition, a bath temperature of 450°C, and a treatment time of 5 hours. If the glass is somewhat fragile, a small amount of LiNO3 (0.1 to 0.3 wt%) can be added to the bath to reduce the TSE. The final profile will have a larger stress area than the one recorded for the process conditions for the non-fragile case. The stress profile attributes discussed above can be progressively enhanced by further increasing the IOX temperature, reducing the treatment time, and slightly increasing the NaNO3 content of the bath at the expense of KNO3 and LiNO3. For example, for a glass-based substrate of 0.55 mm thickness having composition 1, it can be advantageous to use an IOX temperature of 480°C and a treatment time of 2.05 to 2.25 hours, with a bath having 9 to 11 wt% NaNO3, less than 0.3 wt% LiNO3, and the balance KNO3. At 490°C, a suitable time would be 1.7 to 1.87 hours, and it can be necessary to further slightly increase the NaNO3 content of the bath.

[0407] The first method, based on activating an appropriate amount of stress relaxation, increasing the NaNO3 content of the bath, and reducing the treatment time, can be applicable to some glasses having a composition similar to composition 1, with a high content of Li20 (10.7 mol%) and non-linear diffusion properties, which are well suited to allow very high PT and DOC profiles. However, this method can have limited utility for glasses with a lower Li20 content (about 8 mol%), and a moderate Li20 / Na20 ratio, which is not conducive to achieving very high PT and very high DOC.

[0408] Second Method: The second method is to use a multi-step ion exchange process where the first step provides a Na2O composition near the surface so that the glass becomes fragile in the first ion exchange step when the DOC is close to the target DOC. Subsequently, in the second step, a surface spike is formed with KNO3 where the influx of Na ions is strongly or completely suppressed or even reversed in the second step (by adding an appropriate amount of Li ions in the second step bath). Thus, in the second step, the TSE of the distribution is reduced (mostly together with the PT) while the DOC is slightly increased and the inflection stress CS k is very significantly reduced. The second step is short enough so that the slope at the DOC is only slightly reduced relative to the slope after the first step. An optional short heat treatment step can be inserted between the first and second steps as long as the heat treatment step is small enough to avoid significantly reducing the slope at the DOC and reducing the p parameter of the distribution (e.g., significantly reducing the tension uniformity of the tension zone).

[0409] Third Method : This method involves a two-stage ion exchange process where the stress relaxation is enhanced in the first stage. In this case, the stage one IOX temperature is increased substantially so that significant stress relaxation is activated (e.g., somewhere between 100°C and 20°C below the glass strain point). The first stage ion exchange is performed until the DOC is close to the target DOC (but not quite reached). After the first stage, the glass is either slightly above the fragility limit or very close to the fragility limit. The second stage has little or no Na ion influx into the glass and primarily forms a spike. If necessary, the second stage can extract some Na ions from the glass by supplying an appropriate relatively low content of Li ions to the bath which will exchange with the Na ions. As with the second method described above, the vast majority of the cations in the second stage bath are K ions. For glasses with low content of Li2O (about 8 mol%) and where the molar concentrations of Li2O and Na2O in the base glass are comparable, performing the first stage at a higher temperature can allow for concentration partitioning so that a higher DOC is achieved because some of the undesirable aspects of non-linear diffusion can be mitigated.

[0410] Fourth Method : In the fourth method, part of the process to form the deep part of the stress profile (which creates the high tension area and high DOC) is split into two steps. The first of the two steps is a short ion exchange at very high temperature with strong stress relaxation. In this step, the weight gain is kept below about 65% of the total weight gain. The remaining ion exchange step (one or two steps are added depending on the surface CS, DOC and CS k combination desired) is performed at a significantly lower temperature to limit further stress relaxation.

[0411] Examples

[0412] Exemplary compositions of glass-based substrates capable of being chemically strengthened to meet one or more objectives of the present disclosure are provided in Table 1 below, and are referred to herein as "Composition 1."

[0413] * Although not shown in Table 1, Composition 1 includes about 0.1 mol% Sn02.

[0414] Properties of a glass-based substrate having Composition 1 are shown in Table 2:

[0415]

[0416] The inventive stress profiles of Examples 1-8 of the present disclosure were obtained using a glass-based substrate having Composition 1. The glass-based substrate having Composition 1 was manufactured on a roll manufacturing platform and polished to obtain a high surface quality. As a result, the fictive temperature of the glass was significantly higher than that of an annealed glass of the same composition, but the difference in fictive temperature relative to the annealed glass was not as high as the difference in fictive temperature between a fusion-formed glass sheet and an annealed glass sheet of the same composition. The elevated fictive temperature of the rolled glass sheet having Composition 1 relative to the annealed glass was associated with: a higher diffusivity of alkali ions participating in the chemical strengthening ion exchange; a slightly higher rate of stress relaxation; and a slightly lower network dilatancy (e.g., less expansion and stress per unit ion exchange). Thus, if the methods described in the present disclosure for implementing the inventive stress profiles were to be applied to an annealed version of the glass or a similarly composed glass made by the float process, then a modest adjustment to the IOX procedure can be needed, such as increasing the diffusion time to compensate for the smaller diffusivity of the annealed glass and / or adding some LiN03 to the bath to lower the central tension of the annealed glass to prevent it from becoming fragile. If the diffusion time is not increased, then the annealed glass can not reach the preferred high DOC.

[0417] A substitute adjustment for annealed glass and float glass is to increase the ion exchange temperature by between about 8°C and 20°C, depending on how large the difference between the roll sheet fictive temperature and the annealed glass fictive temperature is. In most cases, this approach requires increasing the temperature by between about 10°C and 15°C. The advantage of this approach is that it reduces the ion exchange processing time and causes all the stress profile attributes to develop in the right direction to match the roll glass implementation because (i) the stress relaxation accelerates with the diffusivity at higher temperatures, and (ii) the diffusivity of K ions increases more than the diffusivity of Na ions. Of course, a combination of modest temperature increase and addition of small amounts of LiNO3to the bath is also an acceptable approach to implement the target profile in annealed glass without making it fragile. The specific times and temperatures utilized in the following description for a glass-based substrate having composition 1 also apply to the fictive temperature of roll glass.

[0418] Examples 1-8 in this disclosure were produced by performing single-step ion exchange (SIOX) on a glass-based substrate having composition 1. One key aspect of the SIOX-based implementation is the use of a mixed bath that provides both Na and K ions, the former to control the compressive stress profile in the deep portion of the compressive stress layer, and the latter to control the compressive stress profile in the spike of the compressive stress layer. Another key aspect of the SIOX-based implementation is a relatively high bath temperature to activate a non-negligible amount of stress relaxation during ion exchange. In addition, another key aspect of the SIOX-based implementation is to keep the ion exchange processing time within a very narrow window, enabling the combination of high DOC with stress relaxation, but without significantly altering the Na concentration in the deepest portion of the sample around the neutral plane, so that a high power coefficient p of the stress profile is achieved despite the high DOC.

[0419] With respect to the activation of stress relaxation, the strain point and the annealing point of the glass are relevant, as are the fictive temperatures. The strain point of the glass used in the inventive examples in this disclosure is about 563°C, as measured by the fiber elongation method of ASTM C336-71 (2015), or about 567°C, as estimated by the beam bending viscosity (BBV) measurement. The annealing point at fiber elongation is about 607°C, and the annealing point at BBV is about 612°C. The inventive examples in this disclosure use ion exchange temperatures of at least 455°C and up to 490°C. It should be noted that further inventive examples can be produced at higher ion exchange temperatures, where the ion exchange time will be further shortened, and the bath will shift to a higher Na / K ratio. The resulting profile will still have the inventive combination of properties of a zone of tension and a deep compression zone, with the main difference being that the surface compressive stress CS will be slightly smaller than in the examples with ion exchange temperatures in the range of 455°C to 490°C.

[0420] In embodiments, the ion exchange temperature used to implement the inventive stress profile should not be less than a temperature corresponding to about 110 °C below the glass strain point (measured by the fiber elongation method of ASTM C336-71 (2015)), and preferably not less than a temperature corresponding to about 107 °C below the glass strain point. In cases where it is particularly desirable to increase the negative curvature of the compressive region, the ion exchange temperature should be increased significantly to a range corresponding to 40 to 90 °C below the strain point, with the understanding that (i) as the difference relative to the strain point decreases, it is necessary to increase the Na / K ratio of the bath to achieve a high compressive stress integral, and (ii) the surface compressive stress CS will decrease. If it is also critical for the application to have a high surface compressive stress CS, then a two-step process can be required in order to combine the higher negative second derivative of the deep portion of the profile with a high stress area and a high surface stress.

[0421] Furthermore, when the target product thickness is significantly smaller (e.g., 0.3 to 0.4 mm), it can be useful to use an ion exchange temperature closer to the strain point, in a range of less than 40 °C from it. Indeed, in some cases it is particularly important to maximize the DOC in such thin glass while achieving as high a compressive stress integral as possible. The shorter diffusion times required for small thicknesses can work very effectively at higher rates of stress relaxation. In general, thinner glasses have higher flakiness in terms of peak tension, so the combination of small thickness and high ion exchange temperature will generally also require an increase in the Na / K ratio in the ion exchange bath.

[0422] In examples of the present disclosure, the ion exchange time is selected in a manner that ensures that the composition of the center of the glass article does not change significantly or at all due to ion exchange, while also achieving a high DOC, in all cases exceeding 19% of the thickness, in most cases exceeding 20% of the thickness, and in some cases exceeding 21% of the thickness. The relatively narrow range of diffusion times that achieve this condition is identified by optimization following (i) selection of a target temperature to activate sufficient stress relaxation; and (ii) determination of the diffusion properties of the glass to alkali ion exchange at the target temperature.

[0423] Example 9 of the disclosure was produced by performing double step ion exchange (DIOX) on a glass-based substrate made on a roll press manufacturing platform, having composition 1, and a thickness of 0.502 mm after polishing and before ion exchange. In step one, the pre-heated sample was ion exchanged in a bath having 20% by weight NaNCb and 80% KNCb, with a standard addition of 0.5% silicic acid, at 500 °C for 0.67 hours. Subsequently, in a second step, the sample was ion exchanged in a bath comprising about 9% NaNCb and 91% KNCb, with a standard addition of 0.5% silicic acid, at 460 °C for 0.8 hours. After this process, the sample had a central tension of 130.8 MPa, a tension zone width of about 104 microns or 20.7% of the thickness, a surface compressive stress CS of 750 MPa, a DOL SP of about 4.2 pm, a CS k of about 256 MPa at 405 nm, a tension area of about 28.7 MPa*mm, and a p- coefficient of the distribution shape of about 3.2. The distribution was characterized by , and . As with most of the inventive examples in the disclosure, it was also characterized by a sub-zone of the negative second derivative of CS in the compressive zone.

[0424] While both step 1 and step 2 in this two-step example were within 110 °C of the strain point, the additional flexibility afforded by extending to two-step ion exchange allowed the implementation of inventive embodiments having a sub-zone of the negative second derivative of the CS distribution, without significant activation of stress relaxation even at lower temperatures. In this approach, the negative second derivative was obtained by strictly limiting the flow-in of Na ions in the second step when compared to the first step, by using a second step bath with a much lower Na / K ratio than the first step bath, for example with a molar ratio of NaNCb / (NaNCb + KNCb) in the second step that is 10 times lower than the first bath, or even more than 10 times lower. In this case, the design space for the ion exchange process can be reduced compared to the case of high ion exchange temperatures, since the glass is required to be non-fragile after both the first step and the second step to avoid glass shards contaminating the ion exchange equipment when a sample occasionally breaks during production.

[0425] An ion exchange procedure for Composition 2 is now provided that achieves the inventive stress profile of the present disclosure. The strain point of Composition 2 is very high, reaching 592 °C. The fracture toughness of Composition 2 is in the range 0.74 to 0.87 MPaVm. An example of using a single step high temperature ion exchange to produce the inventive stress profile on a glass-based substrate having Composition 2 can be obtained using a bath having between 8% and 20% NaNCb, and ion exchanging the annealed glass substrate having a thickness of 0.6 mm at 490 °C (i.e., within 110 °C of the strain point) for 0.6 to 0.75 hours.

[0426] With a two step ion exchange, the inventive stress profile with higher surface compressive stress CS than the case of 600 MPa can be obtained, including using a lower temperature than 490 °C. For example, in the case of 0.6 mm, step 1 of ion exchange is at 460 °C in a bath having 20% NaNCb / 80% KNCb by weight using immersion for 1 hour, followed by step 2 at 430 °C in a bath having 4% NaNCb and 96% KNCb by weight for 0.3 hours.

[0427] For the case of a glass having the same composition and having a slightly higher fictive temperature formed on a roll press platform, for the 1 step method, the salt bath NaNCb content should be increased from the range of 8% to 20% to the range of 12% to 25%, and the ion exchange time should be reduced by 2 / 3, so that the ion exchange time is 0.4 to 0.5 hours at 490 °C. For the two step method, the step 1 bath NaNCb content is increased to 25% with KNCb reduced to 75%. The step 1 ion exchange time is reduced to 70% of the ion exchange time of the annealed glass, or 0.7 hours at 460 °C. To maintain the high surface compressive stress CS, step 2 uses 4% NaNCb / 96% KNCb, at 430 °C for 0.2 hours.

[0428] The bath composition and ion exchange temperature ranges for Composition 2 are very similar to Composition 1, but there are significant differences in the percentage of the different components. However, since Composition 2 has a higher diffusivity than Composition 1, the ion exchange processing times are significantly less than for Composition 1.

[0429] Table 3 provides the IOX processing parameters for Examples 1-8, each of which is a chemically strengthened glass-based article prepared by a process of chemically strengthening a glass-based substrate having Composition 1 according to the methods described herein.

[0430]

[0431] Table 4 provides the thickness and stress profile properties for Examples 1-8.

[0432]

[0433]

[0434]

[0435]

[0436] The stress distribution properties of chemically strengthened glass-based articles in Examples 1 to 8 provided in Table 4 above demonstrate a uniform tensile stress distribution in the central tension zone, which can increase the amount of compressive stress in the compressive stress layer while avoiding brittleness. To illustrate the difference between the inventive stress distribution of this disclosure and stress distributions not incorporating the content of this disclosure (i.e., strengthened glass articles found in the prior art), Figure 8 , 10 Tables 12 and 14 show the average delay curves, power model fit, power model residuals, and stress distributions corresponding to the fitted power model for the comparative examples, respectively. Figure 13 The stress distribution of Inventive Example 7 shown in the figure is similar to Figure 14 Comparing the stress distributions of the comparative examples shown, the increased tensile area provided by the uniform tensile stress distribution in Example 7 can be observed. Furthermore, as described above, a uniform tensile stress distribution is required because the tensile strain energy (TSE) is proportional to the square of the tensile stress over the depth integral in the central tension region, while the tension area TA (which, according to force balance, is equal to the compressive stress area) is merely the depth integral of the tensile stress over the central tension region (i.e., not the square). Therefore, for a fixed TA, a less uniform stress distribution leads to an increase in TSE. Since fragility imposes an upper limit on TSE, the increased TA of the embodiments described herein allows for an increase in the compressive stress level in the compressive stress layer while maintaining the non-fragile nature of the chemically strengthened glass substrate.

[0437] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Therefore, this specification is intended to cover modifications and variations to the various embodiments described herein, provided that such modifications and variations fall within the scope of the appended claims and their equivalents.

Claims

1. A chemically strengthened glass-based product, comprising: The first primary surface and the opposite second primary surface define the thickness t of the glass substrate article; Stress distribution σ(x), where x extends through the thickness t of the glass substrate in a direction perpendicular to the first main surface and the second main surface; A first compressive stress layer extends from the first main surface to a first compression depth DOC1 greater than approximately 0.15t; A second compressive stress layer extends from the second main surface to a second compressive depth DOC2 that is less than or equal to DOC1; as well as The central tension zone is located between the first compressive stress layer and the second compressive stress layer, and includes the peak tension PT and the tension zone width BTZ spanning from DOC1 to t−DOC2. in: ， Where DOC = DOC1 and Let σ(x) be the slope of the stress distribution at DOC; ;and ， Where TA is the tension area, defined as follows: 。 2. The chemically strengthened glass substrate article according to claim 1, wherein the peak tension PT is greater than 90 MPa.

3. The chemically strengthened glass substrate article according to claim 1, wherein the peak tension PT is greater than 115 MPa.

4. The chemically strengthened glass substrate article according to claim 1, wherein the peak tension PT is greater than 125 MPa.

5. The chemically strengthened glass-based article according to any one of claims 1 to 4, wherein: ， Where K IC The position x of the glass-based article in the central tension zone corresponding to the peak tension PT. peak Fracture toughness in the middle.

6. The chemically strengthened glass-based article according to claim 5, wherein... .

7. The chemically strengthened glass substrate article according to claim 5, wherein... .

8. The chemically strengthened glass-based article according to any one of claims 1 to 7, wherein the thickness t of the glass-based article is between 0.4 mm and 0.77 mm.

9. The chemically strengthened glass matrix article according to any one of claims 1 to 7, wherein the thickness t of the glass matrix article is between 0.43 mm and 0.68 mm.

10. The chemically strengthened glass-based article according to any one of claims 1 to 9, wherein: The glass-based product comprises less than 3 mol% Li₂O; and The glass-based article is located at position x in the central tension region corresponding to the peak tension PT. peak Fracture toughness K IC Greater than or equal to 0.720 .

11. The chemically strengthened glass-based article according to any one of claims 1 to 9, wherein: The glass-based article comprises an amount of Li₂O ranging from about 3.0 mol% to about 7.5 mol%. The glass-based article is located at position x in the central tension region corresponding to the peak tension PT. peak Fracture toughness K IC Greater than or equal to 0.810 .

12. The chemically strengthened glass-based article according to any one of claims 1 to 9, wherein: The glass-based article comprises an amount of Li₂O ranging from about 7.5 mol% to about 11 mol%; and The glass-based article is located at position x in the central tension region corresponding to the peak tension PT. peak Fracture toughness K IC Greater than or equal to 0.850 .

13. The chemically strengthened glass-based article according to any one of claims 1 to 9, wherein: The glass-based article comprises an amount of Li₂O ranging from about 11 mol% to about 13 mol%; and The glass-based article is located at position x in the central tension region corresponding to the peak tension PT. peak Fracture toughness K IC Greater than or equal to 0.870 .

14. The chemically strengthened glass-based article according to any one of claims 1 to 9, wherein: The glass-based article comprises more than about 13 mol% Li₂O; and The glass-based article is located at position x in the central tension region corresponding to the peak tension PT. peak Fracture toughness K IC Greater than or equal to 0.950 .

15. The chemically strengthened glass matrix article according to any one of claims 1 to 14, wherein the stress distribution σ(x) in the central tension region, when fitted to Equation I, (Equation I) The best-fit value has a power coefficient p greater than 2.4, where x peak This refers to the position within the central tension zone that corresponds to the peak tension PT.

16. The chemically strengthened glass matrix article according to claim 15, wherein the best-fit value of the power coefficient p exceeds 2.

75.

17. The chemically strengthened glass matrix article according to claim 15, wherein the best-fit value of the power coefficient p exceeds 3.

2.

18. The chemically strengthened glass matrix article according to any one of claims 15 to 17, wherein the power coefficient p does not exceed 20.

19. The chemically strengthened glass-based article according to any one of claims 1 to 18, further comprising not more than Fragility factor ,in The position x of the glass-based article in the central tension zone corresponding to the peak tension PT. peak The fracture toughness in, and where: ， Where σ represents the stress distribution σ(x).

20. The chemically strengthened glass matrix article according to claim 19, wherein... .

21. The chemically strengthened glass-based article according to any one of claims 1 to 20, wherein the DOC is greater than or equal to 0.190t.

22. The chemically strengthened glass-based article according to any one of claims 1 to 20, wherein the DOC is greater than or equal to 0.200t.

23. The chemically strengthened glass-based article according to any one of claims 1 to 20, wherein the DOC is greater than or equal to 0.210t.

24. The chemically strengthened glass substrate article according to any one of claims 1 to 23, wherein the surface compressive stress CS at each of the first main surface and the second main surface is greater than 110 MPa.

25. The chemically strengthened glass matrix article according to any one of claims 1 to 24, wherein the stress distribution σ(x) exhibits peaks at the first main surface and the second main surface, and the peak depth DOL SP Inflection point stress CS k Satisfying relation II: (Relationship II).

26. The chemically strengthened glass matrix article of claim 25, wherein the peak depth DOL SP The inflection point stress CS at the location k Less than or equal to .

27. The chemically strengthened glass substrate article of claim 25, wherein the peak depth DOL SP The inflection point stress CS at the location k Less than or equal to .

28. The chemically strengthened glass-based article according to any one of claims 25 to 27, wherein: ， in It is the larger of 4 µm and 0.01t.

29. The chemically strengthened glass matrix article according to any one of claims 1 to 28, wherein the stress distribution σ(x) exhibits peaks at the first primary surface and the second primary surface, and the peak depth DOL. SP Inflection point stress CS k And wherein the stress distribution σ(x) in DOL SP The portion between DOC includes the negative second derivative.

30. The chemically strengthened glass-based article according to any one of claims 1 to 29, wherein: 。 31. The chemically strengthened glass-based article according to any one of claims 1 to 29, wherein: 。 32. The chemically strengthened glass-based article according to any one of claims 1 to 29, wherein: 。 33. The chemically strengthened glass-based article according to any one of claims 1 to 32, wherein: 。 34. The chemically strengthened glass-based article according to any one of claims 1 to 32, wherein: 。 35. The chemically strengthened glass-based article according to any one of claims 1 to 32, wherein: 。 36. The chemically strengthened glass-based article according to any one of claims 1 to 35, wherein: 。 37. The chemically strengthened glass-based article according to any one of claims 1 to 35, wherein: 。 38. The chemically strengthened glass-based article according to any one of claims 1 to 35, wherein: 。 39. The chemically strengthened glass substrate article according to any one of claims 1 to 38, wherein the surface compressive stress CS at each of the first main surface and the second main surface is greater than 550 MPa.

40. The chemically strengthened glass substrate article according to any one of claims 1 to 38, wherein the surface compressive stress CS at each of the first main surface and the second main surface is greater than 725 MPa.

41. The chemically strengthened glass matrix article according to any one of claims 1 to 40, wherein the chemically strengthened glass matrix article comprises an amorphous microstructure that is substantially free of crystals or microcrystals.

42. The chemically strengthened glass-based article according to any one of claims 1 to 41, wherein the chemically strengthened glass-based article comprises less than or equal to 1.0 Fracture toughness.

43. The chemically strengthened glass-based article according to any one of claims 1 to 40, wherein the chemically strengthened glass-based article is a glass-ceramic material comprising an amorphous phase and a crystalline phase.

44. The chemically strengthened glass-based article according to any one of claims 1 to 40 or 43, wherein the chemically strengthened glass-based article comprises a thickness greater than or equal to 1.

2. Fracture toughness.

45. The chemically strengthened glass-based article according to any one of claims 1 to 44, wherein the chemically strengthened glass-based article is formed by subjecting a glass-based substrate to ion exchange treatment, and wherein the glass-based substrate comprises: Greater than or equal to 50 mol% and less than or equal to 75 mol% SiO2; Greater than or equal to 10 mol% and less than or equal to 25 mol% Al2O3; Greater than or equal to 1 mol% and less than or equal to 11 mol% of B2O3; Greater than or equal to 1 mol% and less than or equal to 10 mol% Na2O; as well as The molar concentration of Li2O in the glass substrate is greater than or equal to 5 mol% and less than or equal to 15 mol%, wherein the molar concentration of Li2O in the glass substrate is greater than the molar concentration of Na2O in the glass substrate.

46. ​​The chemically strengthened glass substrate article according to any one of claims 1 to 45, wherein the chemically strengthened glass substrate article is formed by subjecting a glass substrate to ion exchange treatment, and wherein the glass substrate comprises Li2O in an amount of 7.0 to 15.0 mol%.

47. The chemically strengthened glass substrate article according to any one of claims 1 to 46, wherein the chemically strengthened glass substrate article is formed by subjecting a glass substrate to ion exchange treatment, and wherein the glass substrate comprises a molar ratio of Li2O to Na2O greater than or equal to 2.

0.

48. A chemically strengthened glass-based article, comprising: A first primary surface and an opposing second primary surface define the thickness t of the glass substrate article, wherein the thickness t is less than or equal to 0.52 mm; Stress distribution σ(x), where x extends through the thickness t of the glass substrate in a direction perpendicular to the first main surface and the second main surface; A first compressive stress layer extends from the first main surface to a first compression depth DOC1 greater than approximately 0.15t; A second compressive stress layer extends from the second main surface to a second compressive depth DOC2 that is less than or equal to DOC1; as well as The central tension zone is located between the first compressive stress layer and the second compressive stress layer, and includes the peak tension PT and the tension zone width BTZ spanning from DOC1 to t−DOC2. in: ， Where DOC = DOC1 and Let σ(x) be the slope of the stress distribution at DOC; ;and ， Where TA is the tension area, defined as follows: 。 49. The chemically strengthened glass substrate article according to claim 48, wherein the peak tension PT is greater than 115 MPa.

50. The chemically strengthened glass substrate article according to claim 48, wherein the peak tension PT is greater than 125 MPa.

51. The chemically strengthened glass matrix article according to any one of claims 48 to 50, wherein the stress distribution σ(x) in the central tension region, when fitted to Equation I, (Equation I) The best-fit value has a power coefficient p greater than 2.4, where x peak This refers to the position within the central tension zone that corresponds to the peak tension PT.

52. The chemically strengthened glass matrix article according to any one of claims 48 to 50, wherein the stress distribution σ(x) in the central tension region, when fitted to Equation I, (Equation I) The best-fit value has a power coefficient p greater than 2.75, where x peak This refers to the position within the central tension zone that corresponds to the peak tension PT.

53. The chemically strengthened glass matrix article according to any one of claims 48 to 52, wherein the stress distribution σ(x) exhibits peaks at the first primary surface and the second primary surface, and the peak depth DOL. SP Inflection point stress CS k And wherein the stress distribution σ(x) in DOL SP The portion between DOC includes the negative second derivative.

54. The chemically strengthened glass-based article according to any one of claims 48 to 53, wherein the DOC is greater than or equal to 0.190t.

55. The chemically strengthened glass-based article according to any one of claims 48 to 53, wherein the DOC is greater than or equal to 0.200t.

56. The chemically strengthened glass-based article according to any one of claims 48 to 53, wherein the DOC is greater than or equal to 0.210t.

57. A chemically strengthened glass-based article, comprising: A first primary surface and an opposing second primary surface define the thickness t of the glass substrate article, wherein the thickness t is about 0.43 mm to about 0.68 mm; Stress distribution σ(x), where x extends through the thickness t of the glass substrate in a direction perpendicular to the first main surface and the second main surface; A first compressive stress layer extends from the first main surface to a first compression depth DOC1 greater than approximately 0.19t; A second compressive stress layer extends from the second main surface to a second compressive depth DOC2 that is less than or equal to DOC1; as well as The central tension zone is located between the first compressive stress layer and the second compressive stress layer, and includes the peak tension PT and the tension zone width BTZ spanning from DOC1 to t−DOC2. in: The peak tension PT is greater than 95 MPa; The stress distribution σ(x) in the central tension region, when fitted to equation I, (Equation I) The best-fit value has a power coefficient p greater than 2.4, where DOC = DOC1 and x peak The position in the central tension zone corresponding to the peak tension PT; and The stress distribution σ(x) exhibits peaks at the first and second main surfaces, and the peak depth DOL SP Inflection point stress CS k Satisfying relation II: (Relationship II) Where DOC = DOC1 and Let σ(x) be the slope of the stress distribution at DOC.

58. The chemically strengthened glass substrate article according to claim 57, wherein the thickness t is less than or equal to 0.52 mm.

59. The chemically strengthened glass matrix article according to claim 57 or claim 58, wherein the peak tension PT is greater than 103 MPa.

60. A method of manufacturing a chemically strengthened glass matrix article, the method comprising exposing a glass matrix substrate to a molten salt bath to form the chemically strengthened glass matrix article, wherein: The temperature of the molten salt bath is no more than 110°C below the strain point of the glass substrate, wherein the strain point of the glass substrate is determined by fiber elongation; and Select the ion exchange treatment time such that the chemically strengthened glass-based article comprises: The stress distribution σ(x) extends through the thickness t of the glass substrate in a direction perpendicular to the first and second main surfaces; A first compressive stress layer extends from the first main surface to a first compression depth DOC1 greater than approximately 0.15t; A second compressive stress layer extends from the second main surface to a second compression depth DOC2 that is less than or equal to DOC1; and The central tension zone is located between the first compressive stress layer and the second compressive stress layer, and includes the peak tension PT and the tension zone width BTZ spanning from DOC1 to t−DOC2. in: ， Where DOC = DOC1 and Let σ(x) be the slope of the stress distribution at DOC; ;and ， Where TA is the tension area, defined as follows: 。 61. The method of claim 60, wherein the temperature of the molten salt bath is 455°C to 490°C.

62. The method according to claim 60 or claim 61, wherein the ion exchange treatment time is 2 to 4 hours.

63. The method according to any one of claims 60 to 62, wherein the glass substrate comprises: Greater than or equal to 50 mol% and less than or equal to 75 mol% SiO2; Greater than or equal to 10 mol% and less than or equal to 25 mol% Al2O3; Greater than or equal to 1 mol% and less than or equal to 11 mol% of B2O3; Greater than or equal to 1 mol% and less than or equal to 10 mol% Na2O; as well as The molar concentration of Li2O in the glass substrate is greater than or equal to 5 mol% and less than or equal to 15 mol%, wherein the molar concentration of Li2O in the glass substrate is greater than the molar concentration of Na2O in the glass substrate.

64. The method according to any one of claims 60 to 63, wherein the glass substrate comprises Li₂O in an amount of 7.0 to 15.0 mol%.

65. The method according to any one of claims 60 to 64, wherein the glass substrate comprises a molar ratio of Li2O to Na2O greater than or equal to 2.0.

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