Strengthened glass with ultra deep depth of compression

Abstract

To provide strengthened glass materials having improved survivability, when subjected to relatively deep flaws and / or tensile stresses caused by contact with hard / sharp surfaces.SOLUTION: A glass article made from alkali aluminosilicate has: a thickness t ranging from 0.4 mm to 1.5 mm; and a compressive region having a compressive stress CSs in a range from about 400 MPa to about 1200 MPa at a surface of the glass article. The compressive region extends from the surface of the glass article to a depth of compression DOC and has a compressive stress profile, wherein 0.1 t≤DOC≤0.25 t. The compressive stress profile comprises: a. a first portion b extending from the surface of the glass article to a first depth ranging from 3 μm to 15 μm below the surface and having a slope mb; and b. a second portion c extending from the second depth ranging from 3 μm to 15 μm to the depth of compression DOC and having a slope mc.SELECTED DRAWING: Figure 3

Description

Priority

[0001] This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Patent Application No. 62 / 073252, filed October 31, 2014, the contents of which are relied upon and incorporated herein by reference in their entirety. This application is a divisional application of Japanese Patent Application No. 2023-150779, filed on September 19, 2023. Japanese Patent Application No. 2023-150779 is a divisional application of Japanese Patent Application No. 2020-166791, filed on October 1, 2020. [Technical Field]

[0002] The present disclosure relates to chemically strengthened glass articles. More particularly, the present disclosure relates to chemically strengthened glass having a deep compressive surface layer. [Background technology]

[0003] Tempered glass is widely used in electronic devices as cover plates or windows for portable or mobile electronic communication and entertainment devices such as mobile phones, smartphones, tablets, video players, information terminal (IT) devices, laptop computers, and other applications. Summary of the Invention [Problem to be solved by the invention]

[0004] As tempered glass is increasingly utilized, it has become more important to develop tempered glass materials with improved survivability, especially when exposed to relatively deep scratches and / or tensile stresses caused by contact with hard / sharp surfaces. [Means for solving the problem]

[0005] Provided is a chemically strengthened glass article having at least one deep compressive layer extending from a surface of the article to a compression depth DOC of at least about 125 μm within the article. In one embodiment, the compressive stress profile includes one linear segment or portion extending from the surface to the compression depth DOC. Alternatively, the compressive stress profile may include an additional portion extending from the surface to a relatively shallow depth and a linear portion extending from the shallow depth to the compression depth.

[0006] Accordingly, one embodiment of the present disclosure is a glass article having a thickness t, the glass article having a compressive stress CS of at least about 120 MPa at a surface thereof. s The present invention provides a glass article having an underlying compressed region extending from a surface to a compression depth DOC, where 0.1 t≦DOC≦0.25 t, and having a compressive stress profile extending from the surface to a depth d a extends to a slope of m a a first portion a having a depth d a is equal to the compression depth, and -0.4MPa / μm ≥ m a ≧−3.0 MPa / μm. In some embodiments, the portion a is linear or substantially linear.

[0007] Another aspect of the present disclosure is to provide an alkali aluminosilicate glass comprising at least about 4 mol% P2O5 and 0 mol% to about 4 mol% B2O3, where 1.3 < [(P2O5 + R2O) / M2O3] ≤ 2.3, M2O3 = Al2O3 + B2O3, and R2O is the sum of all monovalent cation oxides present in the alkali aluminosilicate glass. The alkali aluminosilicate glass is ion-exchanged and has a thickness t and a compression zone. The compression zone has a compressive stress CS at the surface of the glass ranging from about 100 MPa to about 400 MPa. s , which extends from the surface to a compression depth DOC, where 0.1·t≦DOC≦0.25·t. This compression region has a compressive stress profile. The compressive stress profile is aextends to a slope of m a where the depth d a is equal to the compression depth DOC, and -0.4MPa / μm ≥ m a ≧−3.0 MPa / μm. In some embodiments, the portion a is linear or substantially linear.

[0008] Yet another aspect of the present disclosure is to provide a glass article having a thickness t and a compressed region, the compressed region having a compressive stress CS at a surface of the glass article in the range of about 400 MPa to about 1200 MPa. s , extending from the surface to a compression depth DOC, where 0.1 t≦DOC≦0.25 t. The compression zone has a compressive stress profile that is: b extends to a slope of m b A first portion b having a thickness of 1000 MPa / μm or more (wherein −40 MPa / μm or more) b ≥-200MPa / μm); and approximately d c extends from the compression depth DOC and has a gradient m c a second substantially linear portion c having a thickness of 0.4 MPa / μm or more; c ≧-3.0MPa / μm).

[0009] These and other aspects, advantages, and salient features will become apparent from the following detailed description, the accompanying drawings, and the appended claims. [Brief explanation of the drawings]

[0010] [Figure 1] Schematic cross-sectional view of a chemically strengthened glass article [Figure 2] Schematic diagram showing the compressive stress profile obtained by the single-step ion exchange process [Figure 3] 1) a photographic graphic depiction of a tempered glass article exhibiting frangible behavior upon breakage, and 2) a tempered glass article exhibiting non-frangible behavior upon breakage. [Figure 4a]1) a photographic graphic depiction of a tempered glass article exhibiting frangible behavior upon breakage, and 2) a tempered glass article exhibiting non-frangible behavior upon breakage. [Figure 4b] A photographic graphic depiction showing a tempered glass sheet exhibiting break-resistant behavior upon cracking. [Figure 5a] 1 is a schematic cross-sectional view of an embodiment of an apparatus used to perform the inverted ball on sandpaper (IBoS) test described in this disclosure. [Figure 5b] Schematic cross-sectional view showing the dominant mechanism of failure due to the introduction of damage in bending that typically occurs in tempered glass articles used in portable or handheld electronic devices. [Figure 5c] Schematic cross-sectional view showing the dominant mechanism of failure due to the introduction of damage in bending that typically occurs in tempered glass articles used in portable or handheld electronic devices. [Figure 5d] 1 is a flow diagram of a method for performing IBoS testing on the device described herein. [Figure 6] Schematic cross-section of a ring-on-ring device DETAILED DESCRIPTION OF THE INVENTION

[0011] In the following description, like reference characters refer to like or corresponding parts throughout the several views shown in the drawings. It is also understood that, unless otherwise specified, terms such as "upper," "lower," "outer," "inner," and the like are words of convenience and should not be considered limiting terms. Furthermore, whenever a group is described as comprising at least one of a group of elements and combinations thereof, it is understood that the group may comprise, consist essentially of, or consist of any of those listed elements, either individually or in combination with one another. 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 may consist of any of those listed elements, either individually or in combination with one another. Unless otherwise specified, ranges of values, when recited, include both the upper and lower limits of the range, as well as any ranges therebetween. As used herein, unless otherwise specified, nouns are intended to refer to "at least one" or "one or more" objects. It is also understood that the various features disclosed in this specification and in the drawings may be used in any and all combinations.

[0012] As used herein, the terms "glass article" and "glass articles" are used in the broadest sense to include any object made wholly or partially from glass. Unless otherwise specified, all glass compositions are expressed in mole percent (mol%) and all ion exchange bath compositions are expressed in weight percent (wt%).

[0013] Please note that the terms "substantially" and "about" may be used herein to express the inherent degree of uncertainty that may contribute to any quantitative comparison, value, measurement, or other representation. These terms are also used herein to express the degree to which a quantitative representation may vary from the stated standard without changing the basic functionality of the subject matter at issue. Thus, a glass that is "substantially free of MgO" is one in which MgO is not actively added or batched into the glass, but may be present as a contaminant in very small amounts, e.g., 0.1 mol % or greater.

[0014] Referring to the drawings generally, and Figure 1 in particular, it will be understood that the illustrations are for purposes of describing particular embodiments and are not intended to limit the scope of the disclosure or the appended claims thereto. The drawings are not necessarily drawn to scale, and certain features and certain views of the drawings may be shown exaggerated in scale or schematic form for clarity and conciseness.

[0015] As used herein, the terms "depth of layer" and "DOL" refer to the depth of the compacted layer as determined by surface stress meter (FSM) measurements using a commercially available instrument such as the FSM-6000.

[0016] As used herein, the terms "depth of compression" and "DOC" refer to the depth at which the stress in the glass changes from compressive to tensile. At the DOC, the stress crosses from positive (compressive) to negative (tensile) and therefore has a value of zero.

[0017] As used herein, unless otherwise specified, compressive stress (CS) and central tension (CT) are expressed in megapascals (MPa), depth of layer (DOL) and depth of compression (DOC) are expressed in micrometers (μm), where 1 μm = 0.001 mm, and thickness t is expressed herein in millimeters, where 1 mm = 1000 μm.

[0018] As used herein, unless otherwise specified, the term "fracture" means that a crack propagates through the entire thickness and / or surface of a substrate when the substrate is dropped or impacted by an object.

[0019] According to common scientific conventions in the art, compression is represented as a negative (<0) stress and tension is represented as a positive (>0) stress. However, throughout this description, to better visualize the compressive stress profiles described herein, compressive stress Cs will be represented as a positive or absolute value - i.e., Cs = |Cs|, as set forth herein, and central tension or tensile stress will be represented as a negative value.

[0020] As used herein, "slope (m)" refers to the gradient of a section or portion of a stress profile that closely approximates a straight line. The major slope is defined as the average slope for a region well approximated by a straight line section. These are regions where the absolute value of the second derivative of the stress profile is less than the ratio of the first derivative and about half the depth of the region, as defined by equation (4) below. For example, for a steep, shallow section of a stress profile near the surface of a strengthened glass article, a substantially linear section is one where the absolute value of the second derivative of the stress profile at each point is less than the absolute value of the local gradient of the stress profile divided by the depth at which the absolute value of the stress changes by two times. Similarly, for a deeper profile section within the glass, a linear portion of the section is a region where the local second derivative of the stress profile has an absolute value less than the absolute value of the local gradient of the stress profile divided by half the DOC.

[0021] For typical stress profiles, this restriction on the second derivative ensures that the slope varies relatively slowly with depth and can therefore be used to define regions of slope that are reasonably well defined and important for stress profiles that are considered favorable for drop performance.

[0022] The stress profile as a function of depth x is

[0023]

number

[0024] and the first derivative of the stress profile with respect to depth is given by

[0025]

number

[0026] Then, the second derivative is

[0027]

number

[0028] This becomes:

[0029] The shallow section is at depth d s If the profile extends to about 1 / 2, the straight portion of the profile must be

[0030]

number

[0031] This is the area where

[0032] The deep section extends to a depth of about DOC or a depth of d d or in conventional terms, to a depth DOL, the straight portion of the profile

[0033]

number

[0034] This is the area where

[0035] The latter equation is also valid for one-compartment stress profiles obtained by a single ion exchange in salts containing only one alkali ion other than the ions replaced in the glass for chemical strengthening.

[0036] The linear segment is

[0037]

number

[0038] where d represents the relative depth of the region, shallow or deep.

[0039] The slope m of the linear section of the compressive stress profile described herein is given as the absolute value of the slope dσ / dx - i.e., m as given herein is equal to |dσ / dx|. More specifically, the slope m represents the absolute value of the slope of a profile in which the compressive stress generally decreases as a function of increasing depth.

[0040] Described herein are glass articles that are chemically strengthened by ion exchange to achieve a defined compressive stress profile and therefore survivability when dropped from a defined height onto a hard abrasive surface.

[0041] Compressive stress CS and depth of layer DOL are stress profile parameters that have been used for many years to enable quality control of chemical strengthening. Compressive stress CS provides an estimate of surface compression, an important parameter that correlates well with the amount of stress that needs to be applied to fracture a glass article, especially when the glass is substantially free of deep mechanical flaws. Depth of layer DOL is a function of the amount of stress that is applied to the larger (strengthening) cations (e.g., Na). + K + K in the middle of exchanging + ) is used as an approximate measure of penetration depth, with a larger DOL correlating well with a deeper compressive layer, which protects the glass by preventing deeper scratches and preventing breakage due to scratches under conditions of relatively small externally applied stress.

[0042] Even with slight to moderate bending of a glass article, the bending moment is generally linear with depth from the surface, producing a stress distribution with maximum tensile stress on the outside of the bend, maximum compressive stress on the inside of the bend, and zero stress at the so-called neutral plane, which is usually internal. For tempered glass articles, this bending-induced constant gradient stress distribution adds to the tempered stress profile to produce a net stress profile in the presence of external (bending) stress.

[0043] The net stress profile in the presence of bending-induced stress generally has a different compression depth DOC than the compression depth DOC from the stress profile without bending. In particular, outside the bend, the compression depth DOC is reduced in the presence of bending. If the quenched stress profile has a relatively small stress gradient at a smaller depth than the DOC near the DOC, the DOC can actually be significantly reduced in the presence of bending. In the net stress profile, the tips of moderately deep flaws may be exposed to tension, while the tips of the same flaws would typically be blocked in the stress region of the quenched profile without bending. Therefore, these moderately deep flaws can grow during bending and lead to failure.

[0044] Bending stresses are also important during drop testing. During mechanical vibration and wave propagation through the glass article, regions of localized, time-dependent stresses are created. As the drop height increases, the glass article experiences higher time-dependent stresses during contact with the floor surface, as well as during post-contact vibrations. Therefore, some fracture failure will occur due to excessive post-contact tensile stresses at the tip of relatively shallow flaws that would normally be harmless in the presence of tempering without these time-dependent stresses.

[0045] This disclosure describes a range of gradients that provides a good compromise between the performance of glass articles during drop and bend tests. The preferred ranges will, in some cases, be dictated or limited in part by the capabilities and limitations of stress measurement instruments (e.g., FSM-6000 stress meters, etc.) for collecting and interpreting the spectra associated with these profiles for quality control purposes during manufacturing. Not only the depth of layer (DOL), but also the gradient of the stress profile (due to the gradient of the refractive index profile associated with the stress profile) affects the ability to resolve specific lines in the combined spectrum and, therefore, effectively control product quality.

[0046] Ion exchange is commonly used to chemically strengthen glass. In one particular example, alkali cations in a source of alkali cations (e.g., a molten salt, or "ion exchange" bath) are exchanged with smaller alkali cations in the glass to create a layer under compressive stress (CS) near the surface of the glass. For example, potassium ions from the cation source are often exchanged for sodium ions in the glass. The compressive layer extends from the surface to a depth within the glass.

[0047] An illustrative cross-sectional view of a planar ion-exchanged glass article is shown in FIG. 1. The glass article 100 has a thickness t, a first surface 110, and a second surface 112. In some embodiments, the thickness t of the glass article 100 is at least 0.15 mm and up to (i.e., less than or equal to) about 2.0 mm, or up to about 1.0 mm, or up to about 0.7 mm, or up to about 0.5 mm. While the embodiment shown in FIG. 1 depicts the glass article 100 as a flat, planar sheet or plate, the glass article 100 may have other shapes, such as a three-dimensional shape or another non-planar shape. The glass article 100 has a first compressed region 120 extending from the first surface 110 into the bulk of the glass article 100 to a depth of compression (DOC) d1. In the embodiment shown in FIG. 1, the glass article 100 also has a second compressed region 122 extending from the second surface 112 to a second depth of compression (DOC) d2. The glass article 100 also has a central region 130 extending from d1 to d2. The central region 130 is under a tensile stress, referred to as the central tension or center tension (CT), which has a maximum value at the center of the central region 130. The tensile stress in region 130 balances or opposes the compressive stress Cs in regions 120 and 122. The depths d1, d2 of the first and second compressed regions 120, 122 protect the glass article 100 from the propagation of scratches introduced by sharp impacts to the first and second surfaces 110, 112 of the glass article 100, while the compressive stress Cs minimizes the tendency of scratches to grow and propagate through the depths d1, d2 of the first and second compressed regions 120, 122.

[0048] The tempered glass articles described herein have a maximum compressive stress CS of at least about 150 megapascals (MPa). s In some embodiments, the maximum compressive stress CS s is at least 100 MPa, in other embodiments at least 140 MPa, and in some embodiments up to about 400 MPa. In some embodiments, the maximum compressive stress CS sHowever, in other embodiments, the maximum compressive stress C.S. s may be located in a compressed region (120, 122) at a depth below the surface of the glass article. Each compressed region (120, 122) extends from the surface of the glass article to a compression depth DOC (d1, d2) of at least about 95 micrometers (μm) to about 250 μm. In some embodiments, the DOC is in the range of from about 100 μm, and in other embodiments, in the range of from about 140 μm to about 190 μm. The compression depth DOC (d1, d2) may be expressed in terms of the thickness t of the glass article 100. In some embodiments, 0.1·t≦DOC≦0.25·t, and in other embodiments, 0.12·t≦DOC≦0.22·t.

[0049] The compressive stress varies as a function of depth below the surface of the strengthened glass article, resulting in a compressive stress profile in the compressed region. In some embodiments, the compressive stress profile is substantially linear with respect to depth below the surface in the compressed region, as shown generally in Figure 2. In Figure 2, the compressive stress behaves substantially linearly with respect to depth below the surface, resulting in a compressive stress profile in the compressed region. s The gradient m in MPa / μm is the intercept of the vertical y(CS) axis at a A line a having a value of 0. The CS profile a intercepts the x-axis at the compression depth DOC. At this point, the total stress (tension + compression) is zero. Below DOC, the glass article is under tension CT and reaches a median CT. In one non-limiting example, there may be a small region where the tension varies from 0 to a maximum (in absolute value) tension equal to CT, and a region where the tension is substantially constant and equal to CT.

[0050] In some embodiments, the substantially linear portion of the compressive stress profile a of the glass articles described herein has a slope m within a specified range. a In FIG. 2, for example, the slope m of the line a a is between the upper bound δ1 and the lower bound δ2; i.e., δ2 ≦ m a In some embodiments, the slope m ais in the range of about -0.4 MPa / μm to about -3.0 MPa / μm. In some embodiments, -0.7 MPa / μm≧m a ≧−2.7 MPa / μm, in other embodiments, −1.0 MPa / μm≧m a ≧−2.0 MPa / μm, in other embodiments, −1.5 MPa / μm≧m a ≧-2.7MPa / μm. slope m a has such values ​​and the compression depth DOC is at least about 95 μm, the resistance of the tempered glass to at least one type of failure mode (e.g., very deep puncture) that would be common in field failure of a particular equipment design is particularly advantageous.

[0051] In other embodiments, the compressive stress profile is a combination of multiple substantially linear functions, as shown generally in Figure 3. As shown in Figure 3, the compressive stress profile has a first section or portion b and a second section or portion c. The first portion b is located at a depth d from the tempered surface of the glass article. b The first part b exhibits a substantially linear behavior up to the slope m b and y-intercept CS s The second part of the compressive stress profile, c, extends to approximately the depth d b extends from the compression depth DOC and has a gradient m c The depth d b Compressive stress CS(d b )teeth,

[0052]

number

[0053] In some embodiments, the depth d b is in the range of about 3 μm to about 8 μm; i.e., 3 μm≦d b In other embodiments, 3 μm≦d b In yet another embodiment, 3 μm≦d b ≦15μm.

[0054] Those skilled in the art will recognize that the present disclosure is not limited to compressive stress profiles consisting of only two distinct sections. Instead, the compressive stress profile may include additional segments. In some embodiments, the different linear sections or segments of the compressive stress profile are defined by the slope of the profile from a first slope to a second slope (e.g., m b From m c ) may be connected by a transition region (not shown).

[0055] As shown in Figure 3, the slope of part b of the compressive stress profile is much steeper than the slope of part c; i.e., |m b |>>|m c This corresponds to a condition where a compressive stress profile with a "spike" on the surface of the glass article is created by multiple ion exchange processes occurring in succession to provide the surface with sufficient compressive stress to withstand the introduction or growth of several impact-induced flaws.

[0056] In some embodiments, the compressive stress profiles b and c of the glass articles described herein each have a slope m within a specified range. b and m c In FIG. 3, for example, the slope m of the line / first portion b b is between the upper boundary δ3 and the lower boundary δ4, and the slope m of the line / second part c c is between the upper boundary δ5 and the lower boundary δ6; i.e., δ3 ≥ m b ≥ δ4 and δ5 ≥ m c ≧δ6. In some embodiments, −40 MPa / μm≧m b ≥-200MPa / μm, and -0.7MPa / μm ≥ m c ≧−2.0 MPa / μm. In some embodiments, −40 MPa / μm≧m b ≧−120 MPa / μm, and in some embodiments, −50 MPa / μm≧m b ≧−120 MPa / μm. In some embodiments, the gradient m cis in the range of about -0.4 MPa / μm to about -3.0 MPa / μm. In some embodiments, -0.7 MPa / μm≧m c ≧−2.7 MPa / μm, in other embodiments, −1.0 MPa / μm≧m c ≧−2.0 MPa / μm, in other embodiments, −1.5 MPa / μm≧m c ≥-2.7MPa / μm.

[0057] Compressive stress CS and depth of compressive layer (referred to as "depth of layer" or DOL) are measured using means known in the art, including, but not limited to, surface stress measurement (FSM) using commercially available instruments such as the FSM-6000 manufactured by Luceo Co., Ltd. (Tokyo, Japan). Methods for measuring compressive stress and depth of layer are described in ASTM 1422C-99, entitled "Standard Specification for Chemically Strengthened Flat Glass," and ASTM 1279.19779, 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 by reference in their entireties. Surface stress measurement relies on accurate measurement of the stress optical coefficient (SOC), which is related to the birefringence of the glass. The stress-optical coefficient is then measured by methods known in the art, such as the fiber and four-point bend method, and the bulk cylinder 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 by reference in their entirety.

[0058] The relationship between C and central tension C in some embodiments is given by the formula

[0059]

number

[0060] where t is the thickness of the glass article in micrometers (μm). In various parts of this disclosure, central tension CT and compressive stress CS are expressed herein in megapascals (MPa), thickness t is expressed in either micrometers (μm) or millimeters (mm), and depth of layer DOL is expressed in micrometers (μm) or millimeters (mm) according to the notation of t.

[0061] For tempered glass articles in which the compressive stress layer extends to greater depths within the glass, the FSM technique can suffer from contrast issues that affect the observed DOL values. At deeper DOL values, the contrast between the TE and TM spectra becomes inadequate, and therefore calculating the difference between the TE and TM spectra—and therefore determining the DOL—will be more difficult. Furthermore, the FSM software analysis cannot determine the compressive stress profile (i.e., the variation of compressive stress as a function of depth within the glass). Furthermore, the FSM technique cannot determine the depth of layers resulting from ion exchange of specific elements, such as, for example, ion exchange of sodium with lithium.

[0062] The DOL determined by FSM is a relatively good approximation of the depth of compression (DOC) when the DOL is a small fraction r of the thickness t and the refractive index profile has a depth distribution that is reasonably well approximated by a simple linear truncated profile. When the DOL is a significant fraction of the thickness, such as DOL ≥ 0.1 t, the DOC is often significantly smaller than the DOL. For example, in the ideal case of a linear truncated profile, the relationship DOC = DOL(1 - r) applies, where r = DOL / t.

[0063] Most TM and TE profiles have a curvature near the bottom of the refractive index profile, so that the relationship between DOC and DOL may be somewhat more complicated, but in general, the ratio DOC / DOL decreases as r increases. For some profile shapes, it is even possible for DOC≧DOL, especially when r<0.02.

[0064] Larger (strengthening) cations introduced by ion exchange (e.g., K + If the concentration profile of ) has two sections, one closest to the surface with a substantially higher concentration and one extending to greater depths with a substantially lower concentration, the DOL found by FSM will be significantly smaller than the total depth of chemical intrusion of the larger ion. This is in contrast to the case of a simple one-section diffusion profile, where the DOL gives a good estimate of chemical intrusion. In a two-section profile, the DOL can be larger or smaller than the DOL, depending on the depth and stress parameters of the profile, as well as the thickness.

[0065] When tempered glass is subjected to low external stresses, the flaws that cause fracture have depths that correlate better with the DOC rather than the DOL. The reason DOL has been successfully used as a high-value parameter for chemical strengthening is that for simple, one-piece stress profiles, DOL correlates well with DOC. Moreover, for many years, DOL has generally been less than 0.1 t, and for the most part, less than 0.05 t, so DOC and DOL are similar. Therefore, for conventional chemically strengthened glass, DOL has correlated well with the depth of strength-limiting flaws.

[0066] With the increasing importance of thinner coverglass (e.g., with a thickness of less than 0.5 mm) and the introduction of deeper and more complex stress profiles aimed at improving drop performance while maintaining high strength under high-stress tests such as ring-on-ring (ROR), abrasive ring-on-ring (AROR), and four-point bending (4PB), the depth of layer (DOL) deviates significantly from the compression depth (DOC). The crack-inducing flaws under low external stress conditions occur at depths shallower than the DOL but coincide with the DOC.

[0067] To more accurately determine the depth of compression (DOC) and compressive stress profile for strengthened glass articles, the techniques described below were developed.

[0068] In U.S. Patent Application No. 13 / 463,322 of the same title, filed May 3, 2012 by Rostislav V. Roussev et al. (hereinafter "Roussev I"), which claims priority to U.S. Provisional Patent Application No. 61 / 489,800, filed May 25, 2011, entitled "Systems And Methods for Measuring the Stress Profile of Ion-Exchanged Glass," two methods are disclosed for obtaining detailed and accurate stress profiles (stress as a function of depth) of tempered or chemically strengthened glass. Spectra of coupled optical modes for TM and TE polarizations are collected by a prism coupling technique and used in combination to obtain detailed and accurate TM and TE refractive index profiles. TM (z) and n TE (z). In one embodiment, the detailed refractive index profile is obtained from the mode spectrum using the inverse Wenzel-Kramers-Brillouin (IWKB) method. The contents of the prior application are incorporated herein by reference in their entirety.

[0069] In another embodiment, the detailed refractive index profile is obtained by fitting the measured mode spectrum to a numerically calculated spectrum of a predetermined functional form that describes the shape of the refractive index profile, and obtaining the parameters of the functional form from the best fit. The detailed stress profile S(z) is calculated from the difference between the obtained TM and TE refractive index profiles by using known values ​​of the stress optical coefficient (SOC).

[0070]

number

[0071] Due to the small value of SOC, the birefringence n TM (z)-n TE (z) is the refractive index n TM (z) and n TE (z) is a relatively small fraction (typically on the order of 1%) of the modal effective refractive index. To obtain a stress profile that is not significantly distorted by noise in the measured modal spectrum, it is necessary to determine the modal effective refractive index with an accuracy on the order of 0.00001 RIU (refractive index unit). The method disclosed in Roussev I further includes techniques applied to the raw data to ensure such high accuracy of the measured modal refractive index despite noise and / or insufficient contrast in the collected TE and TM mode spectra or images of the mode spectra. Such techniques include noise averaging, filtering, and curve fitting to find the locations of extrema corresponding to the modes with sub-pixel resolution.

[0072] Similarly, U.S. Patent Application No. 14 / 033,954, filed September 23, 2013, by Rostislav V. Roussev et al., which claims priority to U.S. Provisional Patent Application No. 61 / 706,891, filed September 28, 2012, entitled "Systems and Methods for Measuring Birefringence in Glass and Glass-Ceramics" (hereinafter "Roussev II"), discloses apparatus and methods for optically measuring birefringence on the surfaces of glasses and glass-ceramics, including opaque glasses and glass-ceramics. Unlike Roussev I, in which separate modal spectra are identified, the method disclosed in Roussev II relies on a thorough analysis of the angular intensity distributions for TM and TE light reflected at the prism-sample interface in a prism-coupled measurement format. The contents of the prior application are incorporated herein by reference in their entirety.

[0073] In another disclosed method, the derivatives of the TM and TE signals are determined after applying some combination of the signal processing techniques described above. The positions of the maximum derivatives of the TM and TE signals are obtained with sub-pixel resolution, and the surface birefringence is proportional to the spacing between these two maxima, with coefficients determined as described above by the device parameters.

[0074] Related to the requirement for accurate intensity extraction, the device includes several enhancements, such as a light-scattering surface (static diffuser) adjacent to or on the prism entrance surface to improve the angular uniformity of the illumination, a moving diffuser for speckle reduction when the light source is coherent or partially coherent, and a light-absorbing coating on portions of the input and output faces of the prism as well as on the sides of the prism to reduce parasitic background that tends to distort the intensity signal. Additionally, the device may include an infrared light source to enable measurement of opaque materials.

[0075] Furthermore, Roussev II discloses the extinction coefficients of the samples studied and the wavelength ranges that can be measured using the described method and apparatus enhancements. s λ<250πσ s where α s is the optical attenuation coefficient at the measurement wavelength λ, and σ s is the expected value of stress to be measured with the precision typically required for practical applications. This wide range allows practically important measurements to be obtained at wavelengths where high optical attenuation makes conventional measurement methods inapplicable. For example, Roussev II discloses successful measurements of stress-induced birefringence in opaque white glass-ceramics at a wavelength of 1550 nm, where the attenuation is greater than about 30 dB / mm.

[0076] Although some issues were noted above with the FSM technique at deeper DOL values, FSM is still a useful conventional technique that can be utilized with the understanding that there may be an error range of up to ±20% at deeper DOL values. As used herein, the terms "depth of layer" and "DOL" refer to DOL values ​​calculated using the FSM technique, while the terms "compaction depth" and "DOC" refer to the depth of the compacted layer determined by the method described in Roussev I and II.

[0077] As previously mentioned, the glass article may be chemically strengthened by ion exchange. In this process, ions at or near the surface of the glass are replaced—or exchanged—with larger ions, usually having the same valence or oxidation state. In those embodiments in which the glass 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 typically Na. + (Li + is present in the glass), K + , Rb + , and C.S. + Alternatively, the monovalent cations in the surface layer are Ag +The cations may be replaced with monovalent cations other than alkali metal cations, such as:

[0078] The ion exchange process is generally carried out by immersing the glass article in a molten salt bath containing larger ions to be exchanged for smaller ions in the glass. Those skilled in the art will recognize that the parameters of the ion exchange process, including but not limited to the bath composition and temperature, immersion time, number of immersions of the glass in the salt bath(s), use of multiple salt baths, and additional steps such as annealing and rinsing, generally depend on the composition of the glass and the desired layer depth and compressive stress of the glass resulting from the tempering operation. As an example, ion exchange of an alkali metal-containing glass would be carried out by immersion in at least one molten bath containing salts of larger alkali metal ions, such as, but not limited to, nitrates, sulfates, and chlorides. The temperature of the molten salt bath typically ranges from about 380°C to about 450°C, while the immersion time ranges from about 15 minutes to about 40 hours. However, temperatures and immersion times different from those described above may also be used.

[0079] Additionally, non-limiting examples of ion exchange processes in which glass is immersed in multiple ion exchange baths with washing and / or slow cooling steps between immersions include U.S. Patent No. 8,561,429, entitled "Glass with Compressive Surface for Consumer Applications," issued October 22, 2013, by Douglas C. Allan et al., which claims priority from U.S. Provisional Patent Application No. 61 / 079,995, filed July 11, 2008, in which glass is strengthened by immersion in multiple successive ion exchange treatments in salt baths of different concentrations; and U.S. Patent No. 8,561,429, entitled "Dual Stage Ion Exchange for Chemical Strengthening of Glass," filed July 29, 2008, in which glass is strengthened by ion exchange, in which a first bath is diluted with effluent ions followed by immersion in a second bath having a lower concentration of effluent ions than the first bath. No. 8,312,739 to Christopher M. Lee et al., entitled "Ultra-High-Performance Glass," issued on November 20, 2012. The contents of U.S. Patent Nos. 8,561,429 and 8,312,739 are incorporated herein by reference in their entirety.

[0080] For example, compressive stress is created by chemically strengthening a glass article by the ion exchange process described above, in which a plurality of first metal ions in an outer region of the glass 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 metal ions has a second ionic radius. The second ionic radius is larger than the first ionic radius, and the presence of the larger second alkali metal ions in the outer region creates compressive stress in the outer region.

[0081] At least one of the first metal ion and the second metal ion is an alkali metal ion. The first ion may be an ion of lithium, sodium, potassium, or rubidium. The second metal ion may be an ion of one of sodium, potassium, rubidium, or cesium, provided that the ionic radius of the second alkali metal ion is larger than the ionic radius of the first alkali metal ion.

[0082] In some embodiments, glass is strengthened in a single-step ion-exchange process to produce the compressive stress profile shown in FIG. 2. Typically, the glass is immersed in a molten salt bath containing a salt of a larger alkali metal cation. In some embodiments, the molten salt bath contains or consists essentially of a salt of a larger alkali metal cation. However, small amounts of salts of smaller alkali metal cations may be present in the bath—in some embodiments, less than about 10% by weight, in some embodiments, less than about 5% by weight, and in other embodiments, less than about 2% by weight. In other embodiments, the salts of smaller alkali metal cations may comprise at least about 30% by weight, or at least about 40% by weight, or from about 40% to about 75% by weight of the ion-exchange bath. This single-step ion-exchange process may be carried out at a temperature of at least about 400°C, and in some embodiments, at least about 440°C, for a time sufficient to achieve the desired depth of compression (DOC). In some embodiments, the single-step ion-exchange process may be carried out for at least about 8 hours, depending on the bath composition.

[0083] In another embodiment, glass is strengthened by a two-step or dual ion-exchange process to produce the compressive stress profile shown in FIG. 3. In the first step of this process, the glass is ion-exchanged in the first molten salt bath described above. After the first ion-exchange is complete, the glass is immersed in a second ion-exchange bath. The second ion-exchange bath is different from—i.e., separate from—the first bath, and in some embodiments, has a different composition. In some embodiments, the second ion-exchange bath contains only salts of larger alkali metal cations, although in some embodiments, small amounts (e.g., ≦2% by weight; ≦3% by weight) of smaller alkali metal cations may also be present in the bath. Furthermore, the immersion time and temperature of the second ion-exchange step may be different from those of the first ion-exchange step. In some embodiments, the second ion-exchange step is performed at a temperature of at least about 350°C, and in other embodiments, at least about 380°C. The duration of the second ion-exchange step is determined based on the desired depth d of the shallow section. a The period of time is sufficient to achieve this, and in some embodiments may be 30 minutes or less. In other embodiments, the period is 15 minutes or less, and in some embodiments, ranges from about 10 minutes to about 60 minutes.

[0084] The second ion exchange bath is different from the first ion exchange bath because the second ion exchange step is directed to delivering a different concentration of larger cations, or in some embodiments, entirely different cations, to the alkali aluminosilicate glass article than the first ion exchange step. In one or more embodiments, the second ion exchange bath may include at least about 95 wt. % of a potassium composition, delivering potassium ions to the alkali aluminosilicate glass article. In certain embodiments, the second ion exchange bath may include about 98 wt. % to about 99.5 wt. % of a potassium composition. While the second ion exchange bath can include only at least one potassium salt, the second ion exchange bath may, in yet other embodiments, include 0-5 wt. % or about 0.5-2.5 wt. % of at least one sodium salt, e.g., NaNO3. In an exemplary embodiment, the potassium salt is KNO3. In yet other embodiments, the temperature of the second ion exchange step may be 380°C or higher.

[0085] The purpose of the second ion exchange step is to create a "spike" increase in compressive stress in the region immediately adjacent to the surface of the glass article, as represented by portion b of the stress profile shown in FIG. 3.

[0086] The glass articles described herein may comprise or consist essentially of any glass that is chemically strengthened by ion exchange. In some embodiments, the glass is an alkali aluminosilicate glass.

[0087] In one embodiment, the alkali aluminosilicate glass comprises, or consists essentially of, at least one of alumina and boron oxide, and at least one of alkali metal oxides and alkaline earth metal oxides, where −15 mol%≦(R2O+R'O−Al2O3−ZrO2)−B2O3≦4 mol%, where R is one of Li, Na, K, Rb, and Cs, and R' is at least one of Mg, Ca, Sr, and Ba. In some embodiments, the alkali aluminosilicate glass comprises, or consists essentially of, about 62 mol% to about 70 mol% SiO, 0 mol% to about 18 mol% AlO, 0 mol% to about 10 mol% BO, 0 mol% to about 15 mol% LiO, 0 mol% to about 20 mol% NaO, 0 mol% to about 18 mol% KO, 0 mol% to about 17 mol% MgO, 0 mol% to about 18 mol% CaO, and 0 mol% to about 5 mol% ZrO. In some embodiments, the glass comprises alumina and boron oxide, and at least one alkali metal oxide, where −15 mol%≦(R2O+R'O−Al2O3−ZrO2)−B2O3≦4 mol%, where R is one of Li, Na, K, Rb, and Cs, and R' is at least one of Mg, Ca, Sr, and Ba, and 10≦Al2O3+ B2O3+ZrO2≦30 and 14≦R2O+R'O≦25, the silicate glass comprising or consisting essentially of 62-70 mol% SiO2, 0-18 mol% Al2O3, 0-10 mol% B2O3, 0-15 mol% Li2O, 6-14 mol% Na2O, 0-18 mol% K2O, 0-17 mol% MgO, 0-18 mol% CaO, and 0-5 mol% ZrO2.This glass is described in U.S. patent application Ser. No. 12 / 277,573, filed Nov. 25, 2008, by Matthew J. Dejneka et al., entitled "Glasses Having Improved Toughness And Scratch Resistance," which both claim priority to U.S. Provisional Patent Application Ser. No. 61 / 004,677, filed Nov. 29, 2007, and U.S. Patent No. 8,652,978, filed Aug. 17, 2012, by Matthew J. Dejneka et al., entitled "Glasses Having Improved Toughness And Scratch Resistance," both of which claim priority to U.S. Provisional Patent Application Ser. No. 61 / 004,677, filed Nov. 29, 2007. The contents of all of the above-cited documents are incorporated herein by reference in their entirety.

[0088] In another embodiment, the alkali aluminosilicate glass comprises, or consists essentially of, about 60 mol% to about 70 mol% SiO, about 6 mol% to about 14 mol% AlO, 0 mol% to about 15 mol% BO, 0 mol% to about 15 mol% LiO, 0 mol% to about 20 mol% NaO, 0 mol% to about 10 mol% KO, 0 mol% to about 8 mol% MgO, 0 mol% to about 10 mol% CaO, 0 mol% to about 5 mol% ZrO, 0 mol% to about 1 mol% SnO, 0 mol% to about 1 mol% CeO, less than about 50 ppm AsO, and less than about 50 ppm SbO, where 12 mol%≦LiO+NaO+KO≦20 mol%, and 0 mol%≦MgO+CaO≦10 mol%. In some embodiments, the alkali aluminosilicate glass comprises, or consists essentially of, 60-70 mol% SiO, 6-14 mol% AlO, 0-3 mol% BO, 0-1 mol% LiO, 8-18 mol% NaO, 0-5 mol% KO, 0-2.5 mol% CaO, greater than 0 mol% to 3 mol% ZrO, 0-1 mol% SnO, and 0-1 mol% CeO, where 12 mol% < LiO + NaO + KO < 20 mol%, and the silicate glass contains less than 50 ppm AsO. In some embodiments, the alkali aluminosilicate glass comprises, or consists essentially of, 60-72 mol% SiO, 6-14 mol% AlO, 0-3 mol% BO, 0-1 mol% LiO, 0-20 mol% NaO, 0-10 mol% KO, 0-2.5 mol% CaO, 0-5 mol% ZrO, 0-1 mol% SnO, and 0-1 mol% CeO, where 12 mol% < LiO + NaO + KO < 20 mol%, and the silicate glass contains less than 50 ppm AsO and less than 50 ppm SbO.This glass is described in U.S. Patent No. 8,158,543, entitled "Fining Agents for Silicate Glasses," filed February 25, 2009, to Sinue Gomez et al., which claims priority to U.S. Provisional Patent Application No. 61 / 067,130, filed February 26, 2008; U.S. Patent No. 8,431,502, entitled "Silicate Glasses Having Low Seed Concentration," filed June 13, 2012, to Sinue Gomez et al.; and U.S. Patent No. 8,623,776, entitled "Silicate Glasses Having Low Seed Concentration," filed June 19, 2013, to Sinue Gomez et al., all of which claim priority to U.S. Provisional Patent Application No. 61 / 067,130, filed February 26, 2008. The contents of all of the foregoing references are incorporated herein by reference in their entirety.

[0089] In another embodiment, the alkali aluminosilicate glass comprises SiO and NaO, and the glass is heated to a temperature T at which the viscosity of the glass is 35 kilopoise (kP). 35kp and the temperature T at which zircon decomposes to form ZrO2 and SiO2. 分解 But, T 35kp In some embodiments, the alkali aluminosilicate glass comprises, or consists essentially of, about 61 mol% to about 75 mol% SiO, about 7 mol% to about 15 mol% AlO, 0 mol% to about 12 mol% BO, about 9 mol% to about 21 mol% NaO, 0 mol% to about 4 mol% KO, 0 mol% to about 7 mol% MgO, and 0 mol% to about 3 mol% CaO. This glass is described in U.S. Patent No. 8,802,581, entitled "Zircon Compatible Glasses for Down Draw," filed August 10, 2010, by Matthew J. Dejneka et al., which claims priority to U.S. Provisional Patent Application No. 61 / 235,762, filed August 29, 2009. The contents of the foregoing patents and applications are incorporated herein by reference in their entirety.

[0090] In another embodiment, the alkali aluminosilicate glass contains at least 50 mol% of SiO2 and at least one modifier selected from the group consisting of alkali metal oxides and alkaline earth metal oxides, where [(Al2O3 (mol%) + B2O3 (mol%)) / (Σ alkali metal modifiers (mol%))] > 1. In some embodiments, the alkali aluminosilicate glass contains, or consists essentially of, from about 50 mol% to about 72 mol% of SiO2, from about 9 mol% to about 17 mol% of Al2O3, from about 2 mol% to about 12 mol% of B2O3, from about 8 mol% to about 16 mol% of Na2O, and from 0 mol% to about 4 mol% of K2O. In some embodiments, the glass contains, or consists essentially of, at least 58 mol% of SiO2, at least 8 mol% of Na2O, from 5.5 mol% to 12 mol% of B2O3, and Al2O3, where [(Al2O3 (mol%) + B2O3 (mol%)) / (Σ alkali metal modifiers (mol%))] > 1, Al2O3 (mol%) > B2O3 (mol%), 0.9 < R2O / Al2O3 < 1.3. This glass claims priority to U.S. Provisional Patent Application No. 61 / 235767, filed Aug. 21, 2009, and is described in U.S. Patent No. 8,586,492, entitled "Crack And Scratch Resistant Glass and Enclosures Made Therefrom," filed Aug. 18, 2010, by Kristen L. Barefoot et al., and in U.S. Patent Application No. 14 / 082847, entitled "Crack And Scratch Resistant Glass and Enclosures Made Therefrom," filed Nov. 18, 2013, by Kristen L. Barefoot et al. The entire contents of the previously cited documents are hereby incorporated by reference in their entirety.

[0091] In another embodiment, the alkali aluminosilicate glass comprises SiO2, Al2O3, P2O5, and at least one alkali metal oxide (R2O), where 0.75 < [(P2O5 (mol %) + R2O (mol %)) / M2O3 (mol %)] < 1.2, where M2O3 = Al2O3 + B2O3. In some embodiments, the alkali aluminosilicate glass comprises, or consists essentially of, about 40 mol% to about 70 mol% SiO, 0 mol% to about 28 mol% B2O3, 0 mol% to about 28 mol% Al2O3, about 1 mol% to about 14 mol% P2O5, and about 12 mol% to about 16 mol% R2O, and in specific embodiments, comprises, or consists essentially of, about 40 mol% to about 64 mol% SiO, 0 mol% to about 8 mol% B2O3, about 16 mol% to about 28 mol% Al2O3, about 2 mol% to about 12 mol% P2O5, and about 12 mol% to about 16 mol% R2O. This glass is described in U.S. Patent Application No. 13 / 305,271, entitled "Ion Exchangeable Glass with Deep Compressive Layer and High Damage Threshold," filed November 28, 2011, by Dana C. Bookbinder et al., which claims priority to U.S. Provisional Patent Application No. 61 / 417,941, filed November 30, 2010. The contents of the prior application are incorporated herein by reference in their entirety.

[0092] In yet another embodiment, the alkali aluminosilicate glass comprises at least 50 mol% SiO2 and at least about 11 mol% Na2O and has a surface compressive stress of at least about 900 MPa. In some embodiments, the glass further comprises Al2O3 and at least one of B2O3, K2O, MgO, and ZnO, where -340 + 27.1 · Al2O3 - 28.7 · B2O3 + 15.6 · Na2O - 61.4 · K2O + 8.1 · (MgO + ZnO) ≥ 0 mol%. In certain embodiments, the glass comprises, or consists essentially of, about 7 mol% to about 26 mol% Al2O3, 0 mol% to about 9 mol% B2O3, about 11 mol% to about 25 mol% Na2O, 0 mol% to about 2.5 mol% KO, 0 mol% to about 8.5 mol% MgO, and 0 mol% to about 1.5 mol% CaO. This glass is described in U.S. Patent Application No. 13 / 533,298, filed June 26, 2012, by Matthew J. Dejneka et al., entitled "Ion Exchangeable Glass with High Compressive Stress," which claims priority to U.S. Provisional Patent Application No. 61 / 503,734, filed July 1, 2011. The contents of the prior application are incorporated herein by reference in their entirety.

[0093] In other embodiments, the alkali aluminosilicate glass is ion-exchangeable and comprises at least about 50 mol% SiO2, at least about 10 mol% R2O (where R2O includes Na2O), Al2O3, and B2O3, where B2O3-(R2O-Al2O3)≥3 mol%. In some embodiments, the glass comprises at least about 50 mol% SiO2, at least about 10 mol% R2O (where R2O includes Na2O), Al2O3, and from 3 mol% to 4.5 mol% B2O3, where Al2O3 (mol%)<R2O (mol%) and B2O3 (mol%)-(R2O (mol%)-Al2O3 (mol%))≥3 mol%. In certain embodiments, the glass comprises at least about 50 mol% SiO2, from about 9 mol% to about 22 mol% Al2O3, from about 3 mol% to about 10 mol% B2O3, from about 9 mol% to about 20 mol% Na2O, from 0 mol% to about 5 mol% K2O, at least about 0.1 mol% MgO, ZnO, or a combination thereof, and optionally at least one of CaO, BaO, and SrO, or consists essentially of, with 0≤MgO≤6 mol%, 0≤ZnO≤6 mol%, and 0 mol%≤CaO+SrO+BaO≤2 mol%. When ion-exchanged, such glass has, in some embodiments, a Vickers crack initiation threshold of at least about 10 kgf (about 98 N). Such glass is both a continuation application of U.S. Patent Application No. 13 / 903433, filed May 28, 2013, by Matthew J. Dejneka et al., titled "Zircon Compatible, Ion Exchangeable Glass with High Damage Resistance," which claims priority to U.S. Provisional Patent Application No. 61 / 653489, filed May 31, 2012, and is described in the specification of U.S. Patent Application No. 14 / 197658, filed May 28, 2013, by Matthew J. Dejneka et al., titled "Zircon Compatible, Ion Exchangeable Glass with High Damage Resistance." The contents of these applications are hereby incorporated by reference in their entirety.

[0094] In some embodiments, the glass comprises at least about 50 mol% SiO, at least about 10 mol% RO (R0 includes NaO), AlO, and B0, where -0.5 mol%≦AlO(mol%)−R0(mol%)≦2 mol%, and B0(mol%)−(R0(mol%)−AlO(mol%))≧4.5 mol%. In other embodiments, the glass has a zircon decomposition temperature equal to the temperature at which the viscosity of the glass exceeds about 40 kpoise, and comprises at least about 50 mol% SiO, at least about 10 mol% RO (R0 includes NaO), AlO, and B0, where B0(mol%)−(R0(mol%)−AlO(mol%))≧4.5 mol%. In yet another embodiment, the glass is ion-exchanged, has a Vickers crack initiation threshold of at least about 30 gkf (about 294 N), and comprises at least about 50 mol% SiO, at least about 10 mol% RO (R0 includes NaO), AlO, and B0, where -0.5 mol%≦AlO(mol%)−R0(mol%)≦2 mol%, and B0(mol%)−(R0(mol%)−AlO(mol%))≧4.5 mol%. Such glasses are described in U.S. Patent Application No. 13 / 903,398, filed May 28, 2013, by Matthew J. Dejneka et al., entitled “Ion Exchangeable Glass with High Damage Resistance,” which claims priority from U.S. Provisional Patent Application No. 61 / 653,485, filed May 31, 2012. The contents of these applications are incorporated herein by reference in their entireties.

[0095] In certain embodiments, the alkali aluminosilicate glass comprises at least about 4 mol% P2O5, where (M2O3 (mol%) / R x O (mol%) < 1, where M2O3 = Al2O3 + B2O3, R xO is the sum of monovalent and divalent cation oxides present in the alkali aluminosilicate glass. In some embodiments, the monovalent and divalent cation oxides are selected from the group consisting of Li2O, Na2O, KO, Rb2O, Cs2O, MgO, CaO, SrO, BaO, and ZnO. In some embodiments, the glass has 0 mol% B2O3. In some embodiments, the glass is ion-exchanged to a depth of at least about 10 μm and contains at least about 4 mol% P2O5, where 0.6<[(MO3(mol%) / R x O (mol %)] < 1.4 or 1.3 < [(P2O5 + R2O) / M2O3] ≤ 2.3, where M2O3 = Al2O3 + B2O3, R x where PO is the sum of monovalent and divalent cation oxides present in the alkali aluminosilicate glass, and R2O is the sum of monovalent cation oxides present in the alkali aluminosilicate glass. In one embodiment, the glass comprises at least about 4 mol% PO and 0 mol% to about 4 mol% BO, where 1.3 < [(PO + R2O) / MO] ≤ 2.3, where MO = Al2O + BO, and R2O is the sum of monovalent cation oxides present in the alkali aluminosilicate glass. In some embodiments, the glass is lithium-free and contains about 40 mol% to about 70 mol% SiO, about 11 mol% to about 25 mol% Al2O, about 4 mol% to about 15 mol% PO, about 13 mol% to about 25 mol% Na2O, and about 13 mol% to about 30 mol% R x 0, from about 11 mol% to about 30 mol% M2O3, from 0 mol% to about 1 mol% K2O, from 0 mol% to about 4 mol% B2O3, and 3 mol% or less of at least one of TiO2, MnO, Nb2O5, MoO3, Ta2O5, WO3, ZrO2, Y2O3, La2O3, HfO2, CdO, SnO2, Fe2O3, CeO2, As2O3, Sb2O3, Cl, and Br, wherein 1.3<[(P2O5+R2O) / M2O3]≦2.3, wherein R xwhere M2O3 = Al2O3 + B2O3, and R2O is the sum of the alkali metal oxides, alkaline earth metal oxides, and transition metal monoxides present in the glass; MO = Al2O3 + B2O3; and RO is the sum of the monovalent cation oxides present in the glass. This glass is described in U.S. patent application Ser. No. 13 / 678,013, entitled "Ion Exchangeable Glass with High Crack Initiation Threshold," filed Nov. 15, 2012, by Timothy M. Gross, and U.S. Patent No. 8,756,262, entitled "Ion Exchangeable Glass with High Crack Initiation Threshold," filed Nov. 15, 2012, both of which claim priority to U.S. Provisional Patent Application Ser. No. 61 / 560,434, filed Nov. 16, 2011. The contents of the foregoing patents and patent applications are incorporated herein by reference in their entireties.

[0096] In other embodiments, the alkali aluminosilicate glass comprises about 50 mol% to about 72 mol% SiO, about 12 mol% to about 22 mol% AlO, up to about 15 mol% BO, up to about 1 mol% PO, about 11 mol% to about 21 mol% NaO, up to about 5 mol% KO, up to about 4 mol% MgO, up to about 5 mol% ZnO, and up to about 2 mol% CaO. In some embodiments, the glass comprises about 55 mol% to about 62 mol% SiO, about 16 mol% to about 20 mol% AlO, about 4 mol% to about 10 mol% BO, about 14 mol% to about 18 mol% NaO, about 0.2 mol% to about 4 mol% KO, up to about 0.5 mol% MgO, up to about 0.5 mol% ZnO, and up to about 0.5 mol% CaO, and the glass is substantially free of PO. In some embodiments, NaO + KO - AlO ≦ 2.0 mol%, and in certain embodiments, NaO + KO - AlO ≦ 0.5 mol%. In some embodiments, BO - (NaO + KO - AlO) > 4 mol%, and in certain embodiments, BO - (NaO + KO - AlO) > 1 mol%. In some embodiments, 24 mol% < RAlO4 < 45 mol%, and in other embodiments, 28 mol% < RAlO4 < 45 mol%, where R is at least one of Na, K, and Ag. This glass is described in U.S. Provisional Patent Application No. 61 / 909,049, by Matthew J. Dejneka et al., entitled "Fast Ion Exchangeable Glasses with High Indentation Threshold," filed November 26, 2013, the contents of which are incorporated herein by reference in their entirety.

[0097] In some embodiments, the glasses described herein are substantially free of at least one of arsenic, antimony, barium, strontium, bismuth, and compounds thereof. In other embodiments, the glasses may contain up to about 0.5 mol% Li2O, or up to about 5 mol% Li2O, or in some embodiments, up to about 10 mol% Li2O. In other embodiments, these glasses are substantially free of Li2O.

[0098] In some embodiments, the glasses described herein, when ion-exchanged, are resistant to the introduction of flaws by sharp or sudden impacts. Accordingly, these ion-exchanged glasses exhibit Vickers crack initiation thresholds of at least about 10 kilograms force (kgf) and up to about 50 kgf (about 490 N). In certain embodiments, these glasses exhibit Vickers crack initiation thresholds of at least 20 kgf (about 196 N), and in some embodiments, at least about 30 kgf (about 294 N).

[0099] The glasses described herein, in some embodiments, are downdrawable by processes known in the art, such as slot draw, fusion draw, and redraw, and have a liquidus viscosity of at least 130 kpoise. In addition to the compositions listed above, a variety of other ion-exchangeable alkali aluminosilicate glass compositions may also be used.

[0100] The tempered glass described herein is contemplated as being suitable for a variety of two-dimensional and three-dimensional shapes and applications, and is contemplated to have a variety of thicknesses. In some embodiments, the thickness of the glass article ranges from about 0.1 mm to about 1.5 mm. In some embodiments, the thickness of the glass article ranges from about 0.1 mm to about 1.0 mm, and in certain embodiments, from about 0.1 mm to about 0.5 mm.

[0101] Tempered glass articles may be defined by their central tension, CT. In one or more embodiments, the tempered glass articles described herein have a CT≦150 MPa, or a CT≦125 MPa, or a CT≦100 MPa. The central tension of the tempered glass is related to the fragile behavior of the tempered glass article.

[0102] In another aspect, a method for manufacturing a strengthened glass article having at least one compressive stress layer extending from a surface of the strengthened glass article to a compression depth DOC of at least about 125 μm is provided. The method includes, in some embodiments, a single-step ion exchange process in which the alkali aluminosilicate glass article is immersed in a first ion exchange bath at a temperature greater than 400° C. for a sufficient time such that the compressive stress layer has a compression depth of at least about 100 MPa, and in other embodiments, at least about 140 MPa and up to about 400 MPa, after the ion exchange step.

[0103] The actual immersion time in the ion exchange bath will depend on factors such as the temperature and / or composition of the ion exchange bath, the diffusivity of cations within the glass, and other factors. Therefore, various durations of ion exchange are contemplated. When potassium cations from the ion exchange bath are exchanged for sodium cations in the glass, the bath typically contains potassium nitrate (KNO). Here, the ion exchange step may be carried out for a period of at least 5 hours in some embodiments. A longer ion exchange period for the ion exchange step will correlate with a higher sodium ion content in the first ion exchange bath. In some embodiments, a desired sodium ion content in the first ion exchange bath may be achieved by including at least about 30% by weight, or in some embodiments, at least about 40% by weight, of a sodium compound, such as sodium nitrate (NaNO). In some embodiments, the sodium compound comprises about 40% to about 60% by weight of the first ion exchange bath. In exemplary embodiments, the first ion-exchange step is carried out at a temperature of about 440°C or greater, and in some embodiments, up to about 500°C.

[0104] After the first ion exchange step has been performed, the strengthened glass article will have a maximum compressive stress (CS) of at least about 100 MPa, in other embodiments at least 140 MPa, and in some embodiments up to about 400 MPa. This first ion exchange step achieves a depth of compressed layer / compression depth DOC after the first ion exchange step of about 100 μm to about 200 μm, and in some embodiments, about 140 μm to about 200 μm.

[0105] In some embodiments, after the ion exchange process described above, the surface is etched to a depth d of at least about 3 μm. bA second ion exchange step may be performed by immersing the alkali aluminosilicate glass article in a second ion exchange bath at a temperature of at least 350°C and up to about 450°C for a time sufficient to produce a shallow steep section having a gradient of 0.01% (FIG. 3). In some embodiments, the second ion exchange bath differs in composition and / or temperature from the first ion exchange bath. The second ion exchange step achieves a compressive stress at the surface of at least about 400 MPa and up to about 1200 MPa.

[0106] The second ion-exchange step is a relatively rapid ion-exchange step that produces a "spike" of compressive stress near the surface of the glass, as shown in Figure 3. In one or more embodiments, the second ion-exchange step may be carried out for a period of up to about 30 minutes, in other embodiments up to about 15 minutes, and in some embodiments ranging from about 10 minutes to about 60 minutes.

[0107] The second ion exchange step involves delivering different ions to the alkali aluminosilicate glass article than those provided by the first ion exchange step. Thus, the composition of the second ion exchange bath is different from that of the first ion exchange bath. In some embodiments, the second ion exchange bath comprises at least about 95% by weight of a potassium composition (e.g., KNO) that delivers potassium ions to the alkali aluminosilicate glass article. In certain embodiments, the second ion exchange bath may comprise about 98% to about 99.5% by weight of the potassium composition. While the second ion exchange bath can comprise only a potassium salt(s), the second ion exchange bath may, in further embodiments, comprise up to about 2% by weight, or from about 0.5% to about 1.5% by weight of a sodium composition, such as, for example, NaNO. In further embodiments, the temperature of the second ion exchange step may be 390°C or higher.

[0108] The frangible behavior is characterized by at least one of: the breaking of the tempered glass article (e.g., plate or sheet) into multiple small pieces (e.g., 1 mm or less); the number of shards formed per unit area of ​​the glass article; multiple cracks branching from an initial crack in the glass article; the violent ejection of at least one shard up to a predetermined distance (e.g., about 5 cm, or about 2 inches) from the original location; and any combination of prior fracture (size and density), crack formation, and ejection behavior. As used herein, the terms "frangible behavior" and "frangibility" refer to those aspects of violent or forceful cracking of a tempered glass article without any external constraint, such as a coating, adhesive layer, etc. While coatings, adhesive layers, etc. may be used with the tempered glass articles described herein, such external constraints are not used in determining the frangible or frangible behavior of the glass article.

[0109] Examples of frangible and non-frangible behavior of tempered glass articles upon point impact with a score needle having a sharp tungsten carbide (WC) tip are shown in Figures 4a and 4b. The point impact test used to determine frangible behavior involves an apparatus that delivers a force to the surface of the glass article that is just sufficient to release the internal stored energy present within the tempered glass article. That is, the point impact force is sufficient to initiate at least one new crack on the surface of the tempered glass sheet and propagate the crack through the region of compressive stress CS (i.e., depth of layer) into the region under central tension CT. The impact energy required to initiate or impart a crack to the tempered glass sheet depends on the compressive stress CS and depth of layer DOL of the article, and therefore on the conditions under which the sheet was tempered (i.e., the conditions used to temper the glass by ion exchange). Alternatively, each ion-exchanged glass plate shown in Figures 13a and 13b was subjected to a sharp dart-shaped indenter (e.g., a score needle with a sharp WC point) sufficient to propagate a crack into the inner region of the plate, where the inner region was under tensile stress. The force applied to the glass plate is just enough to reach the beginning of the interior region, thus allowing the energy to initiate the crack to come from the tensile stress within the interior region, rather than from the dart impact force on the exterior surface. The extent of ejection may be determined, for example, by centering the glass sample on a grid, impacting the sample, and using the grid to measure the ejection distance of individual pieces.

[0110] Referring to Figure 4a, glass plate a can be classified as fragile. Specifically, glass plate a fractured into numerous small pieces that were expelled, showing a large degree of crack branching from the initial crack that produced the small pieces. Approximately 50% of the pieces were less than 1 mm in size, and it is estimated that approximately 8 to 10 cracks branched from the initial crack. As can be seen in Figure 4a, approximately 5 cm of glass fragments were expelled from the original glass plate a. Glass articles that exhibit any of the three criteria described above (i.e., numerous crack branching, expulsion, and extreme cracking) are classified as fragile. For example, if a glass only exhibits excessive branching but does not exhibit expulsion or extreme cracking as described above, the glass would still be characterized as fragile.

[0111] Glass plates b, c (Figure 4b), and d (Figure 4a) are not classified as fragile. For each of these samples, the glass sheet fractured into a small number of large fragments. For example, glass plate b (Figure 4b) fractured into two large fragments without any crack branching; glass plate c (Figure 4b) fractured into four fragments after branching from the initial crack into two cracks; and glass plate d (Figure 4a) fractured into four fragments after branching from the initial crack into two cracks. Based on the lack of ejected fragments (i.e., no glass fragments were forcibly ejected more than 2 inches (approximately 5 cm) from their original position), the absence of visible fragments 1 mm or smaller in size, and the minimal amount of observed crack branching, samples b, c, and d are classified as not fragile or not substantially fragile.

[0112] Based on the foregoing, a fragility index (Table 1) can be constructed to quantify the degree of fragile or non-fragile behavior of a glass, glass-ceramic, and / or ceramic article upon impact by another object. Indexes ranging from 1 for non-fragile behavior to 5 for extremely fragile behavior were assigned to describe different levels of fragility or non-fragility. Using the index, fragility can be characterized in terms of a number of parameters: 1) the percentage of the population of fragments with a diameter (i.e., largest dimension) of less than 1 mm ("fragile size" in Table 1); 2) the percentage of fragments per unit area of ​​the sample (in this case, cm 2 ) the number of fragments formed per impact ("Fragment Density" in Table 1); 3) the number of cracks that branched off from the initial crack formed during impact ("Crack Branching" in Table 1); and 4) the percentage of the population of fragments ejected during impact that were more than about 5 cm (or about 2 inches) from their original location ("Ejection" in Table 1).

[0113] [Table 1]

[0114] A fragility index is assigned to a glass article if it meets at least one of the criteria associated with a particular index value. Alternatively, if a glass article meets criteria between two specific levels of fragility, the article may be assigned a fragility index range (e.g., a fragility index of 2 to 3). A glass article may be assigned the highest fragility index value as determined from the individual criteria listed in Table 1. In many cases, it is impossible to ascertain the value of each criterion listed in Table 1, such as the percentage of fragments ejected more than 5 cm from their original position or the fragment density. Therefore, different criteria are considered individual surrogate measures of fragility behavior and fragility index, such that glass articles that fall within one criterion level are assigned corresponding degrees of fragility and fragility index. A glass article is classified as fragile if its fragility index based on any of the four criteria listed in Table 1 is 3 or greater.

[0115] Applying the previous fragility index to the samples shown in Figures 13a and 13b, glass plate a fractured into numerous ejected small pieces, demonstrating a large degree of crack branching from the initial crack that resulted in the small pieces. Approximately 50% of the pieces were less than 1 mm in size, and it is predicted that approximately 8 to 10 cracks branched from the initial crack. Based on the criteria listed in Table 1, glass plate a would have a fragility index between approximately 4 and 5, classifying it as having moderate to high fragility.

[0116] Glass articles having a fragility index of less than 3 (low fragility) may be considered non-fragile or substantially non-fragile. Glass plates b, c, and d each have no fragments less than 1 mm in diameter, no numerous branches from the initial crack formed upon impact, and no fragments ejected more than 5 cm from their original position. Glass plates b, c, and d are not fragile and therefore have a fragility index of 1 (non-fragile).

[0117] As discussed above, the observed difference in behavior between glass plate a, which exhibited frangible behavior, and glass plates b, c, and d, which exhibited non-frangible behavior in Figures 4a and 4b, may be due to differences in central tension C T among the tested samples. The possibility of such frangible behavior is a consideration in the design of various glass products, such as cover plates or windows for displays for portable or mobile electronic devices, such as mobile phones and entertainment devices, as well as information terminal (IT) devices, such as laptop computers. Furthermore, such frangible behavior limits the maximum compressive layer depth DOL and compressive stress C S that can be designed into or imparted to the glass article.

[0118] Thus, the tempered glass articles described herein, in some embodiments, exhibit a fragility index of less than 3 when subjected to a point impact sufficient to break the tempered glass article. In other embodiments, tempered glass articles that are not fragile may achieve a fragility index of less than 2 or less than 1.

[0119] The tempered glass articles described herein exhibit improved fracture resistance when subjected to repeated drop tests, the purpose of which is to characterize the performance of such glass articles in normal use as display windows or cover plates for handheld electronic devices such as mobile phones, smartphones, and the like.

[0120] The concept of a typical ball drop test currently in use is shown in FIG. 5a. The ball drop test assembly 250 includes a solid, rigid substrate 212, such as a granite slab, and a steel ball 230 of a predetermined mass and diameter. A glass sample 220 is secured to the substrate 212, and a piece of abrasive paper 214 with a desired grit is placed on the top surface of the glass sample 220 opposite the substrate 212. The abrasive paper 214 is placed on the glass sample 220 so that the rough side 214a of the abrasive paper contacts the top surface 222 of the glass sample 220. A steel ball 230 is allowed to freely drop from a predetermined height h onto the abrasive paper 214. The top surface 222 or compression side of the glass sample 220 contacts the rough side 214a of the abrasive paper 214, introducing a crack into the surface of the top / compression side 222. The height h is gradually increased until either a maximum height is reached or the glass sample cracks.

[0121] The previously described ball drop test 250 does not represent the true behavior of glass when dropped onto and contacts a rough surface. Instead, the faces of glass are known to bend outward under tension, rather than inward under compression as shown in Figure 5a.

[0122] The inverted ball on sandpaper (IBoS) test is a dynamic component-level test that mimics the dominant mechanism of failure due to damage introduction and bending that typically occurs in tempered glass articles used in portable or handheld electronic devices, as shown schematically in Figure 5c. In the field, damage introduction occurs at the top surface of the glass (a in Figure 5c). Cracks initiate at the top surface of the glass, and the damage penetrates the compression layer (b in Figure 5c), or the crack propagates from the top surface bending or from central tension (c in Figure 5c). This IBoS test is designed to simultaneously introduce damage to the surface of the glass and apply bending under dynamic loading.

[0123] The IBoS testing apparatus is shown schematically in FIG. 5b. The apparatus 200 includes a test stand 210 and a ball 230. The ball 230 is a rigid or solid ball, such as a stainless steel ball. In one embodiment, the ball 230 is a 10 mm diameter, 4.2 gram stainless steel ball. The ball 230 is dropped directly onto the glass sample 218 from a predetermined height h. The test stand 210 includes a solid base 212 made of a hard, rigid material, such as granite. An abrasive-covered sheet 214 is placed on top of the solid base 212, with the abrasive-covered surface facing upward. In some embodiments, the sheet 214 is abrasive paper with a 30-grit surface, and in other embodiments, a 180-grit surface. The glass sample 218 is held in place on the sheet 214 by a sample holder 215 so that an air gap 216 exists between the glass sample 218 and the sheet 214. An air gap 216 between the glass sheet 214 and the glass sample 218 allows the glass sample 218 to bend upon impact of the ball 230 on the polished surface of the sheet 214. In one embodiment, the glass sample 218 is clamped at all corners to constrain bending only to the point of impact of the ball and ensure repeatability. In some embodiments, the sample holder 215 and test stand 210 are adapted to accommodate sample thicknesses up to about 2 mm. The air gap 216 ranges from about 50 μm to about 100 μm. Adhesive tape 220 may be used to cover the top surface of the glass sample to collect debris in the event of breakage of the glass sample 218 upon impact of the ball 230.

[0124] A variety of materials may be used as the abrasive surface. In one particular embodiment, the abrasive surface is abrasive paper, such as silicon carbide or alumina abrasive paper, industrial abrasive paper, or any abrasive known to those skilled in the art to have comparable hardness and / or sharpness. In some embodiments, abrasive paper with 30 grit is used, as it has a known range of grain sharpness, a more consistent surface topography than concrete or asphalt, and a grain size and sharpness that produces the desired level of surface damage to the sample.

[0125] In one embodiment, a method 300 for performing an IBoS test using the previously described apparatus 200 is shown in FIG. 5d. In step 310, a glass sample (218 in FIG. 5d) previously described and secured in a sample holder 215 is placed in a test stand 210 such that a gap 216 is formed between the glass sample 218 and the sheet 214 having an abrasive surface. Method 300 assumes that the sheet 214 having an abrasive surface has already been placed in the test stand 210. However, in some embodiments, the method may include placing the sheet 214 in the test stand 210 with the abrasive surface facing upward. In some embodiments (step 310a), adhesive tape 220 is applied to the top surface of the glass sample 218 before securing the glass sample 218 to the sample holder 215.

[0126] In step 320, a solid ball 230 of predetermined mass and size is dropped from a predetermined height h onto the top surface of the glass sample 218 so that the ball 230 impacts the top surface approximately at the center of the top surface (i.e., within 1 mm, or within 3 mm, or within 5 mm, or within 10 mm of the center). After the impact in step 320, the extent of damage to the glass sample 218 is determined (step 330). As previously stated, the term "crack" as used herein means that a crack propagates through the entire thickness and / or surface of a substrate when the substrate is dropped or impacted by an object.

[0127] In test method 300, the polished surfaced sheet 214 may be replaced after each drop to avoid the "aging" hardening that has been observed with repeated use of other types of drop test surfaces (e.g., concrete or asphalt).

[0128] Various predetermined drop heights, h, and increments are commonly used in the test method 300. The test may, for example, initially use a minimum drop height (e.g., about 10-20 cm). This height may then be increased for successive drops by either a specified increment or a variable increment. The test 300 stops once the glass sample 218 breaks or cracks (step 331). Alternatively, the drop test method 300 may stop when the drop height, h, reaches a maximum drop height (e.g., about 80 cm) without the glass breaking, or step 320 may be repeated at that maximum height until cracking occurs.

[0129] In some embodiments, the IBoS test method 300 is performed only once on each glass sample 218 at each predetermined height h. However, in other embodiments, multiple tests may be performed on each sample at each height.

[0130] If cracking of the glass sample 218 occurs (step 331 in FIG. 5d), the IBoS test 300 ends (step 340). If no cracking is observed upon dropping the ball at a predetermined drop height (step 332), the drop height is increased by a predetermined increment, e.g., 5, 10, or 20 cm (step 334), and steps 320 and 330 are repeated until either cracking of the sample is observed (step 331) or the maximum test height is reached without the sample cracking (step 336). Once either step 331 or 336 is reached, the test method 300 ends.

[0131] When performing the inverted ball on sandpaper (IBoS) test described above, the damage resistance of the previously described tempered glass may be expressed in terms of "survival rate" when a ball is dropped onto the glass surface from a height of 100 cm. For example, a tempered glass article is said to have a 60% survival rate when dropped from a given height if three out of five identical (or nearly identical) samples (i.e., having nearly the same composition and, when tempered, having nearly the same CS and DOC or DOL) survive the IBoS test without breaking.

[0132] To determine the survival rate of a tempered glass article when dropped from a predetermined height using the IBoS test method and apparatus described above, at least five identical (or nearly identical) samples of tempered glass (i.e., having nearly the same composition and nearly the same CS and DOC or DOL) are tested, although a greater number of samples (e.g., 10, 20, 30, etc.) may be tested to increase the confidence level of the test results. Each sample is dropped once from a predetermined height (e.g., 80 cm) and visually (i.e., with the naked eye) examined for evidence of cracking (crack formation and propagation throughout the entire thickness and / or surface of the sample). If no cracks are observed after the drop, the sample is considered to have "survived" the drop test. Survival is determined to be the percentage of the sample population that survived the drop test. For example, if seven samples out of a group of ten samples did not break when dropped from a predetermined height, the survival rate of the glass would be 70%.

[0133] The tempered glass articles described herein also exhibit improved surface strength when subjected to abrasive ring-on-ring (AROR) testing. The strength of the material is defined as the stress at which fracture occurs. The abrasive ring-on-ring test is a surface strength measurement for testing flat glass specimens, and ASTM C1499-09(2013), entitled "Standard Test Method for Monotonic Equibiaxial Flexural Strength of Advanced Ceramics at Ambient Temperature," serves as the basis for the abrasive ring-on-ring ROR test methodology described herein. The contents of ASTM C1499-09 are incorporated herein by reference in their entirety. In one embodiment, the glass specimens are abraded with 90-grit silicon carbide (SiC) particles delivered to the glass sample using the method and apparatus described in Annex A2, entitled "Abrasion Procedures," of ASTM C158-02(2012), entitled "Standard Test Methods for Strength of Glass by Flexure (Determination of Modulus of Rupture)," prior to ring-on-ring testing. The contents of ASTM C158-02, and particularly Annex 2, are incorporated herein by reference in their entirety.

[0134] Prior to ring-on-ring testing, the surface of the glass sample is polished as described in ASTM C158-02, Annex 2, using the apparatus shown in Figure A2.1 of ASTM C158-02 to standardize and / or control the surface defect condition of the sample. The abrasive is blown onto the sample surface with a load of 15 psi (approximately 103 kPa) using 304 kPa (44 psi) air pressure. After the airflow is established, the abrasive is blown onto the sample surface with a load of 15 psi (approximately 103 kPa). After the airflow is established, the abrasive is blown onto the sample surface with a load of 15 psi (approximately 103 kPa) using 304 kPa (44 psi) air pressure. After the airflow is established, the abrasive is blown onto the sample surface with a load of 15 psi (approximately 103 kPa) using 304 kPa (44 psi) air pressure. After the abrasive is blown onto the sample surface with a load of 15 psi (approximately 103 kPa), the abrasive is blown onto the sample surface with a load of 15 psi (approximately 103 kPa) using 304 kPa (44 psi) air pressure. After the abrasive is blown onto the sample surface with a load of 15 psi (approximately 103 kPa) using 304 kPa (44 psi) air pressure, ... 3 of abrasive is placed in the funnel and the sample is sandblasted for 5 seconds after the introduction of the abrasive.

[0135] For ring-on-ring testing, a glass specimen having at least one polished surface 412 is placed between two concentric rings of different sizes to determine its equibiaxial bending strength (i.e., the maximum stress the material can sustain when subjected to bending between two concentric rings), as shown schematically in Figure 6. In the ring-on-ring polishing configuration 400, a polished glass specimen 410 is supported by a support ring 420 having a diameter D2. A load cell (not shown) applies a force F to the surface of the glass specimen by a loading ring 430 having a diameter D1.

[0136] The diameter ratio D1 / D2 of the load ring to the support ring will be in the range of about 0.2 to about 0.5. In some embodiments, D1 / D2 is about 0.5. The load and support rings 430, 420 should be concentrically aligned to within 0.5% of the support ring diameter D2. The load cell used for testing should be accurate to within ±1% at any load within the selected range. In some embodiments, testing is performed at a temperature of 23±2°C and a relative humidity of 40±10%.

[0137] For the design of the instrument, the radius r of the protruding surface of the load ring 430 is h / 2≦r≦3h / 2, where h is the thickness of the specimen 410. The load and support rings 430, 420 are generally made of a material with a hardness of HR c Made from hardened steel >40. ROR instruments are commercially available.

[0138] The objective failure mechanism of the ROR test is to observe cracks in the specimen 410 originating from the surface 430a within the loading ring 430. Cracks occurring outside of this region—i.e., between the loading ring 430 and the support ring 420—are excluded from data analysis. However, due to the thinness and high strength of the glass specimen 410, large deflections exceeding half the specimen thickness h can be observed. Therefore, it is not uncommon to observe a high percentage of cracks originating from below the loading ring 430. Without knowing the stress development both inside and below the ring (gathered via strain gauge analysis) and the point of failure initiation for each specimen, stress cannot be accurately calculated. Therefore, the ROR test focuses on the maximum load at failure as the measured response.

[0139] The strength of glass depends on the presence of surface flaws. However, because glass strength is statistical in nature, the tendency for flaws of a given size to be present cannot be accurately predicted. Therefore, a Weibull probability distribution is commonly used as a statistical representation of the data obtained.

[0140] While exemplary embodiments have been set forth for purposes of illustration, the foregoing description should not be deemed a limitation on the scope of the disclosure or the appended claims. Accordingly, various modifications, applications, and alternatives will occur to those skilled in the art without departing from the scope of the disclosure or the appended claims.

[0141] Preferred embodiments of the present invention will be described below in detail.

[0142] Embodiment 1 In a glass article, a compressive stress CS at the surface of the glass article is in the range of about 100 MPa to about 400 MPa. s the compressed region extending from the surface to a compression depth DOC and having a compressive stress profile, where 0.1 t≦DOC≦0.25 t, and the compressive stress profile extends from the surface to a depth d a extends to a slope of m a a portion a having a depth d ais equal to the compression depth DOC, and -0.4MPa / μm≧m a A glass article having a hardness of ≧−3.0 MPa / μm.

[0143] Embodiment 2 2. The glass article of claim 1, wherein the compression depth DOC is in the range of about 95 μm to about 250 μm.

[0144] Embodiment 3 3. The glass article of claim 2, wherein the compression depth DOC is in the range of about 100 μm to about 190 μm.

[0145] Embodiment 4 2. The glass article of claim 1, wherein 0.12·t≦DOC≦0.22·t

[0146] Embodiment 5 2. The glass article of claim 1, wherein the glass article has a thickness t in the range of about 0.15 mm to about 2.0 mm.

[0147] Embodiment 6 The gradient m a 2. The glass article of claim 1, wherein the modulus of elasticity is in the range of about −0.7 MPa / μm to −2.7 MPa / μm.

[0148] Embodiment 7 The gradient m a 2. The glass article of claim 1, wherein the modulus of elasticity is in the range of about -1.5 MPa / μm to -2.7 MPa / μm.

[0149] Embodiment 8 2. The glass article of claim 1, wherein the glass article is made from an alkali aluminosilicate glass.

[0150] Embodiment 9 9. The glass article of claim 8, wherein the alkali aluminosilicate glass comprises up to about 10 mol% LiO.

[0151] Embodiment 10 9. The glass article of claim 8, wherein the alkali aluminosilicate glass comprises at least about 4 mol% P2O5 and 0 mol% to about 4 mol% B2O3, where 1.3<[(P2O5+R2O) / M2O3]≦2.3, M2O3=Al2O3+B2O3, and R2O is the sum of monovalent cation oxides present in the alkali aluminosilicate glass.

[0152] Embodiment 11 9. The glass article of claim 8, wherein the glass is lithium-free.

[0153] Embodiment 12 an alkali aluminosilicate glass comprising at least about 4 mol% P2O5 and 0 mol% to about 4 mol% B2O3, wherein 1.3<[(P2O5+R2O) / M2O3]≦2.3, M2O3=Al2O3+B2O3, and R2O is the sum of monovalent cation oxides present in said alkali aluminosilicate glass; a. the alkali aluminosilicate glass is ion-exchanged and has a thickness t and a compressed region, the compressed region having a compressive stress CS at a surface of the alkali aluminosilicate glass in the range of about 100 MPa to about 400 MPa; s and b. the compressed region extends from the surface to a compression depth DOC, and 0.1 t≦DOC≦0.25 t; c. the compressed region has a compressive stress profile, the compressive stress profile extending from the surface to a depth d a extends to a slope of m a a portion a having a depth d a is equal to the compression depth DOC, and -0.4MPa / μm≧m a ≧-3.0MPa / μm, Alkali aluminosilicate glass.

[0154] Embodiment 13 13. The alkali aluminosilicate glass of claim 12, wherein the glass is lithium-free.

[0155] Embodiment 14 The glass is comprised of about 40 mol % to about 70 mol % SiO, about 11 mol % to about 25 mol % AlO, about 4 mol % to about 15 mol % PO, about 13 mol % to about 25 mol % NaO, about 13 mol % to about 30 mol % R x 0, from about 11 mol% to about 30 mol% M2O3, from 0 mol% to about 1 mol% K2O, from 0 mol% to about 4 mol% B2O3, and up to 3 mol% of one or more of TiO2, MnO, Nb2O5, MoO3, Ta2O5, WO3, ZrO2, Y2O3, La2O3, HfO2, CdO, SnO2, Fe2O3, CeO2, As2O3, Sb2O3, Cl, and Br, wherein 1.3<[(P2O5+R2O) / M2O3]≦2.3, wherein R x 13. The alkali aluminosilicate glass of embodiment 12, wherein O is the sum of alkali metal oxides, alkaline earth metal oxides, and transition metal monoxides present in the glass, MO = AlO + BO, and RO is the sum of monovalent cation oxides present in the glass.

[0156] Embodiment 15 13. The alkali aluminosilicate glass of embodiment 12, wherein the compression depth DOC is in the range of about 95 μm to about 250 μm.

[0157] Embodiment 16 16. The alkali aluminosilicate glass of embodiment 15, wherein the compression depth DOC is in the range of about 100 μm to about 190 μm.

[0158] Embodiment 17 13. The alkali aluminosilicate glass of embodiment 12, wherein 0.12·t≦DOC≦0.22·t

[0159] Embodiment 18 13. The alkali aluminosilicate glass of embodiment 12, wherein the thickness ranges from about 0.1 mm to about 2.0 mm.

[0160] Embodiment 19 The gradient m a13. The alkali aluminosilicate glass of embodiment 12, wherein the tensile strength is in the range of about −0.7 MPa / μm to −2.7 MPa / μm.

[0161] Embodiment 20 The gradient m a 13. The alkali aluminosilicate glass of embodiment 12, wherein the tensile strength is in the range of about −1.5 MPa / μm to −2.7 MPa / μm.

[0162] Embodiment 21 a glass article having a thickness t and a compressive stress CS at a surface of the glass article in the range of about 400 MPa to about 1200 MPa; s the compressed region extending from the surface to a compression depth DOC and having a compressive stress profile having: a. a depth d below the surface from the surface b extends to a slope of m b a first portion b having a thickness of 1000 MPa / μm or more, b ≥-200MPa / μm; and b. Approximately the depth d c to the compression depth DOC, and has a gradient m c a second substantially linear portion c having a c ≥-3.0MPa / μm; A glass article having

[0163] Embodiment 22 22. The glass article of claim 21, wherein the compression depth DOC is in the range of about 95 μm to about 250 μm.

[0164] Embodiment 23 23. The glass article of claim 22, wherein the compression depth DOC is in the range of about 100 μm to about 190 μm.

[0165] Embodiment 24 22. The glass article of claim 21, wherein 0.12 t≦DOC≦0.22 t

[0166] Embodiment 25 22. The glass article of claim 21, wherein the thickness t is in the range of about 0.15 mm to about 2.0 mm.

[0167] Embodiment 26 The gradient m c 22. The glass article of claim 21, wherein the modulus of elasticity is in the range of about -0.7 MPa / μm to -2.7 MPa / μm.

[0168] Embodiment 27 The gradient m c 27. The glass article of claim 26, wherein the modulus of elasticity is in the range of about -1.5 MPa / μm to -2.7 MPa / μm.

[0169] Embodiment 28 22. The glass article of claim 21, wherein the glass article is made from an alkali aluminosilicate glass.

[0170] Embodiment 29 29. The glass article of claim 28, wherein the alkali aluminosilicate glass comprises up to about 10 mol% LiO.

[0171] Embodiment 30 29. The glass article of claim 28, wherein the alkali aluminosilicate glass comprises at least about 4 mol% P2O5 and 0 mol% to about 4 mol% B2O3, where 1.3<[(P2O5+R2O) / M2O3]≦2.3, M2O3=Al2O3+B2O3, and R2O is the sum of monovalent cation oxides present in the alkali aluminosilicate glass.

[0172] Embodiment 31 29. The glass article of claim 28, wherein the glass is lithium-free.

[0173] Embodiment 32 The glass is comprised of about 40 mol % to about 70 mol % SiO, about 11 mol % to about 25 mol % AlO, about 4 mol % to about 15 mol % PO, about 13 mol % to about 25 mol % NaO, about 13 mol % to about 30 mol % R x 0, from about 11 mol% to about 30 mol% M2O3, from 0 mol% to about 1 mol% K2O, from 0 mol% to about 4 mol% B2O3, and up to 3 mol% of one or more of TiO2, MnO, Nb2O5, MoO3, Ta2O5, WO3, ZrO2, Y2O3, La2O3, HfO2, CdO, SnO2, Fe2O3, CeO2, As2O3, Sb2O3, Cl, and Br, wherein 1.3<[(P2O5+R2O) / M2O3]≦2.3, wherein R x 29. The glass article of claim 28, wherein O is the sum of alkali metal oxides, alkaline earth metal oxides, and transition metal monoxides present in the glass, MO = AlO + BO, and RO is the sum of monovalent cation oxides present in the glass. [Explanation of symbols]

[0174] 100 Glass items 110 First Surface 112 Second Surface 120 First Compression Region 130 Central area 200 equipment 212 Base 214 Abrasive paper, sheets with abrasive material 215 Sample holder 216 void 218, 220 Glass samples 230 steel ball 250 Ball Drop Test Assembly 400 Ring-on-ring configuration when polishing 410 Glass Sample 420 Support Ring 430 Load Ring

Claims

1. In a glass article, a thickness t in the range of 0.4 mm to 1.5 mm and a compressive stress CS in the range of 400 MPa to 1200 MPa at the surface of the glass article. s the compressed region extending from the surface to a compression depth DOC and having a compressive stress profile having: a. extending from the surface to a first depth below the surface in a range of 3 μm to 15 μm, with a slope m b a first portion b having a viscosity of −40 MPa / μm≧m b ≧−200 MPa / μm; and b. extending from a second depth in the range of 3 μm to 15 μm to said compression depth DOC, with a gradient m c A second portion c having a viscosity of −0.4 MPa / μm≧m c ≧-3.0MPa / μm; A glass article having

2. 2. The glass article of claim 1, wherein the compression depth DOC is in the range of 95 μm to 250 μm.

3. 3. The glass article of claim 1, wherein the compression depth DOC is in the range of 100 μm to 190 μm and the thickness t is in the range of 0.5 mm to 1.0 mm.

4. 4. The glass article according to claim 1, wherein 0.12·t≦DOC≦0.22·t.

5. The gradient m ｃ The glass article according to any one of claims 1 to 4, wherein the elastic modulus of elasticity is in the range of -0.7 MPa / μm to -2.7 MPa / μm.

6. The gradient m ｃ The glass article according to claim 5, wherein the elastic modulus of elasticity is in the range of -1.5 MPa / μm to -2.7 MPa / μm.

7. 7. The glass article of any of claims 1 to 6, wherein the glass article comprises an alkali aluminosilicate glass.

8. The alkali aluminosilicate glass contains up to 10 mol % Li 2 The glass article of claim 7, comprising O.

9. The alkali aluminosilicate glass contains at least 4 mol % P 2 O 5 and 0 mol % to 4 mol % B 2 O 3 1.3<[(P 2 O 5 +R 2 O) / M 2 O 3 ]≦2.3, M 2 O 3 = Al 2 O 3 +B 2 O 3 , R 2 9. The glass article of claim 7 or 8, wherein O is the sum of monovalent cation oxides present in the alkali aluminosilicate glass.

10. 8. The glass article of claim 7, wherein the glass is lithium-free.

11. The glass is 40 mol % to 70 mol % SiO 2 ; 4 mol % to 15 mol % P ２ O ５ ; 13 mol % to 30 mol % of R ｘ O, here R ｘ O is the sum of alkali metal oxides, alkaline earth metal oxides, and transition metal monoxides present in the glass, and R ｘ O is 13 mol % to 25 mol % Na ２ O and 0 to 1 mol % K ２ Contains O; 3 mol% or less of TiO 2 , MnO, Nb 2 O 5 , MoO 3 , Ta 2 O 5 , W.O. 3 , ZrO 2 , Y 2 O 3 , La 2 O 3 , HfO 2 , CdO, SnO 2 , Fe 2 O 3 , CeO 2 , As 2 O 3 , Sb 2 O 3 one or more of: Cl, and Br; and 1.3 < [(P 2 O 5 +R 2 O) / M 2 O 3 ]≦2.3, where M 2 O 3 = Al 2 O 3 +B 2 O 3 , R 2 8. The glass article of claim 7, wherein O consists essentially of the sum of monovalent cation oxides present in the alkali aluminosilicate glass.

12. An electronic device comprising the glass article according to claim 1.

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