Glass laminate having embedded stress peaks for crack arrest and method of making the same

Abstract

A laminated glass article includes a core layer including a core glass composition and a cladding layer directly adjacent to the core layer and including a cladding glass composition. The stress of the cladding layer increases from compressive stress to tensile stress with increasing distance from an outer surface of the cladding layer, transitions in a step change manner to compressive stress at an interface region between the core layer and the cladding layer, and increases from compressive stress to tensile stress with increasing distance from the interface region to a center of the core layer.

Description

[0001] This application is a divisional application of patent application number 202080069852.X, filed on July 31, 2020, entitled “GLASS LAMINATE WITH BURIED STRESS PEAK FOR CRACK ARREST AND METHOD OF MAKING THE SAME”.

[0002] Cross Reference to Related Applications

[0003] This application claims priority under 35 U.S.C. § 119 to U.S. Provisional Application Serial No. 62 / 883401, filed August 6, 2019, the contents of which are relied upon and incorporated herein by reference in their entirety.

[0004] BACKGROUND

[0005] TECHNICAL FIELD

[0006] The present specification generally relates to glass articles, and more particularly to laminated glass articles comprising a plurality of glass layers and methods of forming the same. BACKGROUND

[0007] Glass articles can be used in a wide variety of products, including, for example, automotive glazing, architectural panels, home appliances, and cover glasses (e.g., for touch screen devices such as smartphones, tablets, laptop computers, and monitors). During use, relatively large defects can be introduced into the surface of the glass article. For example, when a smartphone is dropped on a rough surface (e.g., asphalt), a local indention caused by contact with a sharp feature of the rough surface can create a defect as deep as about 300 pm in the surface of the cover glass.

[0008] Accordingly, there is a need for glass articles having improved resistance to breakage from deep flaws, improved mechanical reliability, and improved drop performance. SUMMARY

[0009] According to a first aspect disclosed herein, a laminated glass article comprises a core layer comprising a core glass composition and a clad layer directly adjacent to the core layer and comprising a clad glass composition. The stress of the clad layer increases from compressive stress to tensile stress with increasing distance from an outer surface of the clad layer, transitions as a step change to compressive stress at an interface region between the core layer and the clad layer, and increases from compressive stress to tensile stress with increasing distance from the interface region to a center of the core layer.

[0010] According to a second aspect, a laminated glass article comprises the laminated glass article according to the first aspect, wherein the core glass composition has an average core coefficient of thermal expansion (CTE 核心 ) and the cladding layer has an average cladding coefficient of thermal expansion (CTE 核心 ) that is greater than the CTE 包覆 .

[0011] According to a third aspect, a laminated glass article comprises the laminated glass article according to the first or second aspect, wherein the laminated glass article is ion exchange strengthened.

[0012] According to a fourth aspect, a laminated glass article comprises the laminated glass article according to any preceding aspect, wherein the core glass composition and the cladding glass composition comprise one or more alkali oxides.

[0013] According to a fifth aspect, a laminated glass article comprises the laminated glass article according to any preceding aspect, wherein the maximum tensile stress in the cladding layer is greater than or equal to the maximum tensile stress in the core layer.

[0014] According to a sixth aspect, a laminated glass article comprises the laminated glass article according to any preceding aspect, wherein the maximum compressive stress of the core layer is greater than the maximum compressive stress of the cladding layer.

[0015] According to a seventh aspect, a laminated glass article comprises the laminated glass article according to any preceding aspect, wherein the magnitude of stress at the outer surface is greater than or equal to about 300 MPa.

[0016] According to an eighth aspect, a laminated glass article comprises the laminated glass article according to any preceding aspect, wherein the maximum magnitude of stress of the laminated glass article is less than or equal to about 400 MPa.

[0017] According to a ninth aspect, a laminated glass article comprises a core layer comprising a core glass composition and a cladding layer directly adjacent to the core layer and comprising a cladding glass composition. The concentration of Li ions increases with increasing distance from an outer surface of the cladding layer to a centerline of the core layer; the concentration of K ions decreases with increasing distance from the outer surface of the cladding layer to an interface between the cladding layer and the core layer; and the concentration of Na ions increases with increasing distance from the outer surface of the cladding layer to a maximum concentration of Na ions in the cladding layer or at the interface between the cladding layer and the core layer, and transitions to a lower concentration of Na ions via a step change at the interface between the cladding layer and the core layer relative to the maximum concentration of Na ions.

[0018] According to a tenth aspect, a laminated glass article comprises the laminated glass article according to the ninth aspect, wherein the concentration of Na ions decreases as a function of distance from the interface between the cladding layer and the core layer to the centerline of the core layer.

[0019] According to an eleventh aspect, a laminated glass article comprises the laminated glass article according to the ninth aspect, wherein the concentration of Na ions increases and then decreases as a function of distance from the interface between the cladding layer and the core layer to the centerline of the core layer.

[0020] According to a twelfth aspect, a laminated glass article comprises the laminated glass article according to any one of the ninth through eleventh aspects, wherein the concentration of Li ions increases according to a non-linear relationship.

[0021] According to a thirteenth aspect, a laminated glass article comprises the laminated glass article according to any one of the ninth through twelfth aspects, wherein the concentration of K ions in the core layer is zero.

[0022] According to a fourteenth aspect, a laminated glass article comprises the laminated glass article according to the ninth aspect, wherein the concentration of Na ions increases according to a linear relationship from the outer surface of the cladding layer to a maximum concentration of Na ions.

[0023] According to a fifteenth aspect, a laminated glass article comprises the laminated glass article according to the ninth aspect, wherein the concentration of Na ions increases according to a non-linear relationship from the outer surface of the cladding layer to a maximum concentration of Na ions.

[0024] According to a sixteenth aspect, a method of making a laminated glass article comprises laminating at least one core layer and at least one cladding layer to form a laminated glass article, the at least one core layer comprising an ion-exchangeable core glass composition and the at least one cladding layer comprising an ion-exchangeable cladding glass composition; and contacting the laminated glass article with an ion exchange bath comprising at least one ion source for a period of time such that the maximum compressive stress in the at least one core layer is greater than the maximum compressive stress in the at least one cladding layer.

[0025] According to a seventeenth aspect, a method comprises the method according to the sixteenth aspect, wherein the at least one core layer has an average core coefficient of thermal expansion (CTE 核心 ) and the at least one cladding layer has an average cladding coefficient of thermal expansion (CTE 核心 ) that is greater than the CTE 包覆 ).

[0026] According to an eighteenth aspect, a method includes the method of the sixteenth or seventeenth aspect, wherein the ion exchange bath comprises at least a first ion source and a second ion source different from the first ion source.

[0027] According to a nineteenth aspect, a method includes the method of any of the sixteenth through eighteenth aspects, wherein a maximum tensile stress in the at least one cladding layer after contact with the ion exchange bath is greater than or equal to a maximum tensile stress in the at least one core layer.

[0028] According to a twentieth aspect, a method includes the method of any of the sixteenth through nineteenth aspects, wherein a stress magnitude at an outer surface of the glass article after contact with the ion exchange bath is greater than or equal to about 300 MPa.

[0029] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art who practice the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0030] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated and constitute part of this specification. The drawings illustrate various embodiments described herein and, together with the description, serve to explain principles and operations of the claimed subject matter. BRIEF DESCRIPTION OF DRAWINGS

[0031] FIG. 1 is a cross-sectional view of a glass article according to one or more embodiments shown and described herein;

[0032] FIG. 2 is a cross-sectional view of an overflow distributor that can be used to form a glass article according to one or more embodiments shown and described herein;

[0033] FIG. 3 is a plot of ion concentration for an exemplary embodiment, where concentration is plotted on the y-axis and depth within the glass article is plotted on the x-axis;

[0034] FIG. 4 is a plot of stress distribution for an exemplary embodiment corresponding to FIG. 3 is a plot of stress distribution for an exemplary embodiment corresponding to

[0035] FIG. 5is a plot of ion concentration for another example embodiment, where concentration is plotted on the y-axis and depth within the glass article is plotted on the x-axis;

[0036] FIG. 6 is a plot of stress distribution for an example embodiment corresponding to FIG. 5 is a plot of stress distribution for an example embodiment corresponding to

[0037] FIG. 7 is a plot of ion concentration for another example embodiment, where concentration is plotted on the y-axis and depth within the glass article is plotted on the x-axis;

[0038] FIG. 8 is a plot of stress distribution for an example embodiment corresponding to FIG. 7 is a plot of stress distribution for an example embodiment corresponding to

[0039] FIG. 9 is a plot of stress distribution for an example embodiment, where stress is plotted on the y-axis and depth within the glass article is plotted on the x-axis;

[0040] FIG. 10 is a plot of stress distribution for an example embodiment, where stress is plotted on the y-axis and depth within the glass article is plotted on the x-axis;

[0041] FIG. 11 is a plot of stress distribution for an example embodiment, where stress is plotted on the y-axis and depth within the glass article is plotted on the x-axis.

[0042] FIG. 12 is a representation of a non-frangible sample after a frangibility test;

[0043] FIG. 13 is a representation of a frangible sample after a frangibility test;

[0044] FIG. 14 is a plot of stress distribution for another example embodiment, where stress is plotted on the y-axis and depth within the glass article is plotted on the x-axis;

[0045] FIG. 15 is a plot of stress distribution for an example embodiment, where stress is plotted on the y-axis and depth within the glass article is plotted on the x-axis;

[0046] FIG. 16 is a plot of residual strength distribution for an example embodiment, where residual strength is plotted on the y-axis and defect size is plotted on the x-axis;

[0047] FIG. 17 is a stress profile graph of an exemplary embodiment, where stress is plotted on the y-axis and depth within the glass article is plotted on the x-axis; and

[0048] FIG. 18 is a residual strength profile graph of an exemplary embodiment corresponding to the stress profile of FIG. 17 DETAILED DESCRIPTION

[0049] Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

[0050] Ranges can be expressed herein as from "about" one particular value, and / or to "about" another particular value. When such ranges are expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are associated with another embodiment.

[0051] Directional terms as used herein - for example up, down, right, left, front, back, top, bottom - are made only with reference to the figures as drawn and are not intended to mean absolute directions.

[0052] Unless specifically stated otherwise, any methods described herein are not intended to be construed as requiring their steps to be performed in any particular order, nor requiring any particular direction of devices. Accordingly, in an embodiment where there are more steps or elements than can be practically associated with in a claim, the use of "comprise" or "comprises" or "including" or "including" in the claims has not been used, unless explicitly stated otherwise. No language in the specification should be construed as implying any specific order, or requiring an order of steps or device elements other than that which has otherwise been specifically stated in the claims or specification and no language will be construed as implying a specific order of steps or device elements other than that which has otherwise been specifically stated in the claims or specification. This applies regardless of, and independently of the use of, any drawn logic flow, any actual human interactions with devices, any specific computer software employed, or any hardware utilized. This applies special to any possible non- explicitly stated basis for an order of steps or device elements, including: logical subject matter; common sense; and the number or type of embodiments described in the specification.

[0053] ​As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components unless the context clearly indicates otherwise. In addition, the use of the term “or” in the absence of “either,” “neither,” or some other similar language expressly specifying a choice of either the left, the right, or both, covers an inclusive or, for example, “x or y” means x or y or both, unless the context clearly indicates otherwise.

[0054] All disclosed ranges are to be understood to encompass and provide support for claims that refer to any and all sub-ranges that fall within each disclosed range, as well as any and all individual values within each disclosed range. For example, a stated range of 1 to 10 should be considered to include and provide support for claims that refer to any and all sub-ranges between and / or including the minimum value of 1 and the maximum value of 10; that is, all sub-ranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, etc.) or any value from 1 to 10 (e.g., 3, 5.8, 9.9994, etc.).

[0055] As used herein, the term “average coefficient of thermal expansion” or “average CTE” refers to the average linear coefficient of thermal expansion of a given material or layer between 0°C and 300°C. Unless otherwise specified, the term “coefficient of thermal expansion” or “CTE” as used herein refers to the average coefficient of thermal expansion.

[0056] Compressive stress (including surface compressive stress) is measured by refracted near-field (RNF) techniques. Surface stress measurements rely on accurate measurement of the stress-optical coefficient (SOC), which is related to the birefringence of the glass. SOC is then measured according to Procedure C (glass disk method) described in ASTM Standard C770-16, entitled “Standard Test Method for Measurement of Glass Stress-Optical Coefficient,” the contents of which are incorporated herein in their entirety. Depth of compression (DOC) can be measured using RNF techniques or scattered light polariscope (SCALP) techniques known in the art. Maximum central tension (CT) values are measured using scattered light polariscope (SCALP) techniques known in the art.

[0057] Concentration profiles of various constituent components (e.g., alkali constituent components) in the glass are measured by electron probe microanalysis (EPMA). For example, EPMA can be used to distinguish between compressive stress in the glass due to ion exchange of alkali ions into the glass and compressive stress due to lamination.

[0058] The phrases "depth of compression" and "DOC" refer to the location in the glass where the compressive stress transitions to tensile stress.

[0059] The term "formed from" can mean one or more of comprising, consisting essentially of, or consisting of. For example, a component formed from a particular material can comprise the particular material, consist essentially of the particular material, or consist of the particular material.

[0060] In various embodiments, the glass article comprises at least a first layer and a second layer. For example, the first layer comprises a core layer, and the second layer comprises one or more cladding layers 104, 106 adjacent to the core layer. The first layer and / or the second layer is a glass layer comprising a glass material, a ceramic material, a glass-ceramic material, or a combination thereof. In some embodiments, the first layer and / or second layer is a transparent glass layer.

[0061] The core layer has a core CTE, and the cladding layer has a cladding CTE. For example, the core layer is formed from a first glass composition having the core CTE, and the cladding layer is formed from a second glass composition having the cladding CTE. In some embodiments described herein, the core CTE is less than the cladding CTE (i.e., the cladding CTE is greater than the core CTE) prior to any ion exchange treatment, such that the core layer is in a compressive state and the cladding layer is in a tensile state. In some embodiments, after ion exchange treatment of the glass article, the stress profile of the glass article increases from compressive stress to tensile stress with increasing distance from the outer surface of the cladding layer, transitions in a step change manner to compressive stress at an interface region between the core layer and the cladding layer, and increases from compressive stress to tensile stress with increasing distance from the interface region to the center of the core layer. This "jump" tensile-compressive profile in the glass article and other non-conventional stress profiles can prevent deeper cracking, which is described in more detail below.

[0062] FIG. 1 is a cross-sectional view of one embodiment of a glass article 100. The glass article 100 is a laminated sheet comprising a plurality of glass layers. In embodiments, the laminated sheet can be substantially planar, as shown in FIG. 1 or the laminated sheet can be non-planar. The glass article 100 comprises a core layer 102 disposed between a first cladding layer 104 and a second cladding layer 106. In some embodiments, the first cladding layer 104 and the second cladding layer 106 are outer layers relative to the core layer 102, as shown in FIG. 1The outer surface 108 of the first cladding layer 104 serves as an outer surface of the glass article 100 and / or the outer surface 110 of the second cladding layer 106 serves as an outer surface of the glass article 100, for example. In other embodiments, the first cladding layer 104 and / or the second cladding layer 106 is an intermediate layer disposed between the core layer 102 and an outer layer (not shown).

[0063] The core layer 102 includes a first major surface and a second major surface opposite the first major surface. In some embodiments, the first cladding layer 104 is fused to the first major surface of the core layer 102. Additionally or alternatively, the second cladding layer 106 is fused to the second major surface of the core layer 102. In such embodiments, the interface 112 between the first cladding layer 104 and the core layer 102 and / or the interface 114 between the second cladding layer 106 and the core layer 102 is free of any bonding material, such as an adhesive, coating, or any non-glass material added or configured to adhere the respective cladding layer 104, 106 to the core layer 102. Thus, the first cladding layer 104 and / or the second cladding layer 106 is directly fused to and / or directly adjacent to the core layer 102. In some embodiments, the glass article 100 includes one or more intermediate layers disposed between the core layer 102 and the first cladding layer and / or between the core layer 102 and the second cladding layer. For example, the intermediate layers can include intermediate glass layers and / or diffusion layers formed at the interface of the core layer 102 and the cladding layers. The diffusion layers can include a mixing region that includes the constituents of each layer adjacent to the diffusion layer (e.g., a mixing region between two directly adjacent glass layers). In some embodiments, the glass article 100 includes a glass-glass laminate, where the interface between directly adjacent glass layers is a glass-glass interface.

[0064] In some embodiments, the core layer 102 includes a first glass composition (also referred to herein as a core glass composition) and the first cladding layer 104 and / or the second cladding layer 106 includes a second glass composition (also referred to herein as a cladding glass composition) that is different from the first glass composition. The first glass composition and the second glass composition are different from one another prior to chemically strengthening the glass article 100 as described herein. For example, in embodiments where the core layer 102 and the first cladding layer 104 are fused to one another, the first glass composition and the second glass composition are different from one another prior to fusing the core layer 102 and the first cladding layer 104 to one another. FIG. 1 In the illustrated embodiment, the core layer 102 includes a first glass composition and the first cladding layer 104 and the second cladding layer 106 each include a second glass composition. In other embodiments, the first cladding layer includes a second glass composition and the second cladding layer includes a third glass composition that is different from the first glass composition and / or the second glass composition.

[0065] In various embodiments, the core layer 102 is formed from an ion-exchangeable core glass composition and the cladding layers 104, 106 are formed from an ion-exchangeable cladding glass composition. In embodiments, the core glass composition and the cladding glass composition have different coefficients of thermal expansion, as described above and below.

[0066] The glass article can be formed using a suitable method, such as a fusion draw method, a down-draw method, a slot draw method, an up-draw method, or a float method. In some embodiments, the glass article 100 is formed using a fusion draw method. FIG. 2 FIG. 1 is a cross-sectional view of an exemplary embodiment of a glass article 100 that can be formed using the overflow distributor 200.

[0067] The overflow distributor 200 can be configured in the manner described in U.S. Patent No. 4,214,886, which is incorporated herein by reference in its entirety. For example, the fusion draw apparatus includes a lower overflow distributor 220 and an upper overflow distributor 240 positioned above the lower overflow distributor 220. The lower overflow distributor 220 includes a trough 222. A first glass composition 224 is melted and fed into the trough 222 in a viscous state. As described further below, the first glass composition 224 forms the core layer 102 of the glass article 100. The upper overflow distributor 240 includes a trough 242. A second glass composition 244 is melted and fed into the trough 242 in a viscous state. As described further below, the second glass composition 244 forms the first cladding layer 104 and the second cladding layer 106 of the glass article 100.

[0068] The first glass composition 224 overflows the trough 222 and flows downward along opposing outer forming surfaces 226 and 228 of the lower overflow distributor 220. The outer forming surfaces 226 and 228 converge at a draw line 230. The separate streams of the first glass composition 224 that flow downward along the respective outer forming surfaces 226 and 228 of the lower overflow distributor 220 converge at the draw line 230, where they fuse together to form the core layer 102 of the glass article 100.

[0069] The second glass composition 244 overflows from the groove 242 and flows downward along the opposing outer forming surfaces 246 and 248 of the upper overflow distributor 240. The second glass composition 244 is deflected outward by the upper overflow distributor 240 such that it flows around the lower overflow distributor 220 and contacts the first glass composition 224 flowing through the outer forming surfaces 226 and 228 of the lower overflow distributor 220. The individual flow of the second glass composition 244 fuses with the corresponding individual flow of the first glass composition 224 flowing downward along the respective outer forming surfaces 226 and 228 of the lower overflow distributor 220. After the flow of the first glass composition 224 converges at the stretch line 230, the second glass composition 244 forms the first coating layer 104 and the second coating layer 106 of the glass article 100.

[0070] In some embodiments, the first glass composition 224 of the core layer 102 in an viscous state contacts the second glass composition 244 of the first covering layer 104 and the second covering layer 106 in an viscous state to form a laminated sheet. In some such embodiments, such as FIG. 2 As shown, the laminated sheet is part of a glass ribbon traveling along a stretch line 230 away from the overflow distributor 220. The glass ribbon can be pulled out of the overflow distributor 220 by a suitable means, including, for example, gravity and / or traction rollers. The glass ribbon cools as it leaves the overflow distributor 220. The glass ribbon is served to separate the laminated sheet from it. Thus, the laminated sheet is cut from the glass ribbon. Suitable techniques such as scribing, bending, thermal shock, and / or laser cutting can be used to process the glass ribbon. In some embodiments, the glass article 100 comprises, as shown in the figure below, a glass ribbon with a lamination diameter of 100. FIG. 1 The laminated sheet shown. In other embodiments, the laminated sheet may be further processed (e.g., by cutting or molding) to form a glass article.

[0071] Although glass products 100 FIG. 1 The text shows a three-layer glass article, but other embodiments are also possible. For example, the glass article may have two, four, or more layers. A two-layer glass article can be formed using two positioned overflow distributors such that the two layers join as they travel away from their respective stretch lines, or by using a single overflow distributor with separate grooves, such that the two glass compositions flow across opposing outer forming surfaces of the overflow distributor and converge at the stretch line of the overflow distributor. A four-layer glass article can be formed using additional overflow distributors and / or overflow distributors with separate grooves. Therefore, a glass article with a predetermined number of layers can be formed by modifying the overflow distributor accordingly.

[0072] Although glass products 100 FIG. 1The glass article can be in the form of a laminate sheet as shown, but other forms are also contemplated. For example, the glass article can be in the form of a laminate tube comprising a plurality of tubular layers (e.g., formed from one or more annular holes), and a portion of the cross-section of the laminate tube can have a similar shape as the laminate structure shown. FIG. 1 In other embodiments, the glass article can be a shaped glass article, for example, can be formed by shaping or molding the laminate sheet.

[0073] In some embodiments, the glass article 100 has a thickness of at least about 0.05 mm, at least about 0.1 mm, at least about 0.2 mm, or at least about 0.3 mm. Additionally or alternatively, the glass article 100 has a thickness of less than about 2 mm, less than about 1.5 mm, less than about 1 mm, less than about 0.7 mm, or less than about 0.5 mm. In some embodiments, the ratio of the thickness of the core layer 102 to the thickness of the glass article 100 is at least about 0.7, at least about 0.8, at least about 0.85, at least about 0.9, or at least about 0.95. Additionally or alternatively, the ratio of the thickness of the core layer 102 to the thickness of the glass article 100 is less than about 0.95, less than about 0.93, less than about 0.9, less than about 0.87, or less than about 0.85. In some embodiments, the thickness of each of the second layers (e.g., the first cladding layer 104 and the second cladding layer 106) is from about 0.01 mm to about 0.3 mm.

[0074] In some embodiments, the first glass composition and / or the second glass composition has a liquidus viscosity suitable for forming the glass article 100 using the fusion draw method described herein. For example, the first glass composition of the core layer 102 can have a liquidus viscosity of at least about 100 kP, at least about 200 kP, or at least about 300 kP. Additionally or alternatively, the first glass composition comprises a liquidus viscosity of less than about 3000 kP, less than about 2500 kP, less than about 1000 kP, or less than about 800 kP. The second glass composition of the first cladding layer 104 and / or the second cladding layer 106 can have a liquidus viscosity of at least about 50 kP, at least about 100 kP, or at least about 200 kP. Additionally or alternatively, the second glass composition comprises a liquidus viscosity of less than about 3000 kP, less than about 2500 kP, less than about 1000 kP, or less than about 800 kP. The first glass composition can facilitate carrying the second glass composition over the overflow distributor to form the second layers. Thus, the liquidus viscosity of the second glass composition can be lower than the liquidus viscosity typically considered suitable for forming a single layer sheet using the fusion draw method.

[0075] In various embodiments described herein, the glass article 100 is strengthened by a combination of mechanical strengthening and chemical strengthening. For example, the glass article 100 can have a CTE mismatch as described herein and can be chemically strengthened, e.g., by an ion exchange treatment, to further increase the compressive stress near the second outer surface of the second layer and / or to form a compressive spike within the second layer.

[0076] In various embodiments, the glass article 100 is mechanically strengthened. For example, the second glass composition forming the first cladding layer 104 and / or the second cladding layer 106 can have a different CTE than the first glass composition forming the core layer 102. In particular, in some embodiments, the first cladding layer 104 and the second cladding layer 106 can be formed from a glass composition having a higher CTE than the glass composition of the core layer 102. Upon cooling the glass article 100, the CTE mismatch (i.e., the difference between the CTE of the first cladding layer 104 and the second cladding layer 106 and the CTE of the core layer 102) results in the formation of compressive stress in the core layer 102 and tensile stress in the cladding layers 104, 106. In various embodiments, each of the first cladding layer 104 and the second cladding layer 106 can independently have a higher CTE, a lower CTE, or a substantially the same CTE as the core layer 102. Surface compressive stress tends to suppress the development of pre-existing surface defects into cracks.

[0077] In embodiments, the CTE of the core layer 102 differs from the CTE of the first cladding layer 104 and / or the second cladding layer 106 by at least about 5 x 10 -7 ° C -1 , at least about 15 x 10 -7 ° C -1 , at least about 25 x 10 -7 ° C -1 , or at least about 30 x 10 -7 ° C -1 . Additionally or alternatively, the CTE of the core layer 102 differs from the CTE of the first cladding layer 104 and / or the second cladding layer 106 by less than about 100 x 10 -7 ° C -1 , less than about 75 x 10 -7 ° C -1 , less than about 50 x 10 -7 ° C -1 , less than about 40 x 10 -7 ° C -1 , less than about 30 x 10 -7 ° C -1 , less than about 20 x 10 -7 ° C -1 , or less than about 10 x 10 -7 ° C -1For example, in some embodiments, the CTE of the core layer 102 differs from the CTE of the first cladding layer 104 and / or the second cladding layer 106 by about 5 x 10 -7 °C -1 to about 30 x 10 -7 °C -1 , or about 5 x 10 -7 °C -1 to about 20 x 10 -7 °C -1 . In some embodiments, the CTE of the second glass composition of the first and / or second cladding layer is less than about 66 x 10 -7 °C -1 , less than about 55 x 10 -7 °C -1 , less than about 50 x 10 -7 °C -1 , less than about 40 x 10 -7 °C -1 , or less than about 35 x 10 -7 °C -1 . Additionally or alternatively, the CTE of the second glass composition of the first and / or second cladding layer is at least about 10 x 10 -7 °C -1 , at least about 15 x 10 -7 °C -1 , at least about 25 x 10 -7 °C -1 , or at least about 30 x 10 -7 °C -1 . The first glass composition of the core layer 102 can have a CTE of at least about 40 x 10 -7 °C -1 , at least about 50 x 10 -7 °C -1 , at least about 55 x 10 -7 °C -1 , at least about 65 x 10 -7 °C -1 , at least about 70 x 10 -7 °C -1 , at least about 80 x 10 -7 °C -1 , or at least about 90 x 10 -7 °C -1 . Additionally or alternatively, the CTE of the first glass composition of the core layer can be less than about 120 x 10 -7 °C -1 , less than about 110 x 10 -7 °C -1 , less than about 100 x 10 -7 °C -1 , less than about 90 x 10 -7°C -1 less than about 75 x 10 -7 °C -1 or less than about 70 x 10 -7 °C -1 .

[0078] In various embodiments described herein, the glass article 100 is chemically strengthened. For example, the glass article 100 is treated via ion exchange to increase the compressive stress in the region of the glass article at the outer surface of the glass article (e.g., the exterior of the cladding layer). In some embodiments, the ion exchange treatment includes applying an ion exchange medium to one or more surfaces of the glass article 100. The ion exchange medium can be a solution, a paste, a gel, or another suitable medium that includes larger ions to exchange with smaller ions in the glass (e.g., the glass of the second layer). The terms "larger ion" and "smaller ion" are relative terms, referring to a larger ion being relatively larger compared to a smaller ion, and a smaller ion being relatively smaller compared to a larger ion. Thus, the larger ion has an ionic radius that is larger than the ionic radius of the smaller ion, and the smaller ion has an ionic radius that is smaller than the ionic radius of the larger ion. In some embodiments, the cladding layer of the glass article 100 includes an alkali aluminosilicate glass. Thus, the smaller ions in the cladding layer of the glass article and the larger ions in the ion exchange medium can be monovalent alkali metal cations (e.g., Li + , Na + , and / or K + ). Alternatively, the monovalent cations in the glass article 100 can be replaced with monovalent cations other than alkali metal cations (e.g., Ag + , etc.). In some embodiments, the cladding layer of the glass article 100 includes an alkaline earth aluminosilicate glass. Thus, the smaller ions in the cladding layer of the glass article and the larger ions in the ion exchange medium can be divalent alkaline earth cations (e.g., Be 2+ , Mg 2+ , Ca 2+ , and / or Sr 2+ ). In some embodiments, the ion exchange medium includes a molten salt solution, and the ion exchange treatment includes immersing the laminated glass article in a molten salt bath including larger ions (e.g., K + , Na + , Sr 2+ , and / or Ca 2+ ) that are to exchange with smaller ions (e.g., Na + , Li + , Ca 2+ , and / or Mg 2+) exchange. In some embodiments, the molten salt bath comprises a salt of a larger ion (e.g., nitrate, sulfate, and / or chloride). For example, the molten salt bath can comprise molten KNO3, molten NaNO3, or a combination thereof. Additionally or alternatively, the temperature of the molten salt bath can be from about 380 °C to about 450 °C, and the immersion time is from about 2 hours to about 16 hours.

[0079] By substituting the smaller ions in the glass with larger ions at the surface of the glass article 100, the compressive stress of the cladding layer is increased at the outer surface of the glass article. For example, during the ion exchange process, larger ions from the ion exchange medium diffuse into the outer portion of the cladding layer of the glass article 100, while smaller ions from the glass diffuse out of the outer portion of the cladding layer of the glass article. Thus, the outer portion of the cladding layer comprises an exchanged region of the glass article. The increase in the concentration of larger ions in the ion exchanged region results in crowding of the glass and increases the compressive stress of the glass article 100 in the ion exchanged region. In some embodiments, the glass article 100 is subjected to the ion exchange process to increase the surface compressive stress (e.g., the initial surface compressive stress resulting from the CTE mismatch) on the outer surface of the glass article to a final compressive stress value. For example, the final compressive stress value is at least about 200 MPa, at least about 300 MPa, at least about 400 MPa, at least about 500 MPa, at least about 600 MPa, at least about 700 MPa, at least about 800 MPa, at least about 900 MPa, or at least about 1,000 MPa. Additionally or alternatively, the final compressive stress value is less than about 1300 MPa, less than about 1200 MPa, less than about 1000 MPa, less than about 900 MPa, less than about 800 MPa, or less than about 600 MPa.

[0080] In various embodiments herein, the core layer 102 is ion exchange strengthened by the cladding layers 104, 106. The core layer 102 and the cladding layers 104, 106 have different compositional properties to achieve these properties. After being strengthened by ion exchange, the compositional properties of each glass composition result in a unique alkali ion diffusion profile across the thickness of the laminated glass article.

[0081] Prior to ion exchange strengthening, the concentrations of various components of the glass network in cladding layers 104 and 106 (e.g., glass forming agents such as SiO2 and B2O3, intermediates such as Al2O3, and modifiers such as CaO and Na2O) are typically uniformly distributed from the outer surface of the laminated glass article to their respective interface regions. For example, cladding layers 104 and 106 contain at least one glass forming agent, and the concentration of the glass forming agent is substantially constant from the outer surface of the glass article to the interface between the cladding layer and the core layer 102. Furthermore, cladding layers 104 and 106 contain at least one modifier, such as Na2O and / or another alkali metal oxide, and the concentration of the modifier is substantially constant from the outer surface of the glass article to the interface between the cladding layer and the core layer 102.

[0082] Similarly, the concentrations of various components of the glass network in the core layer 102 (e.g., glass forming agents such as SiO2 and B2O3, intermediates such as Al2O3, and modifiers such as CaO and Na2O) are generally uniformly distributed from their respective interfaces to the centerline of the core layer 102. As used herein, the term "centerline" refers to the midpoint of the thickness of the core layer 102. For example, the core layer 102 contains at least one glass forming agent, and the concentration of the glass forming agent is substantially constant from the core side of the interface to the centerline of the core layer 102. Furthermore, the core layer 102 contains at least one modifier, such as Na2O and / or another alkali metal oxide, and the concentration of the glass modifier is substantially constant from the core side of the interface to the centerline of the core layer 102.

[0083] However, as FIG. 3 As shown, after ion exchange, the concentration of alkali metal oxides (e.g., K₂O) in both the core layer 102 and the cladding layers 104 and 106 varies with depth from the surfaces 108 and 110 of the glass article 100. Specifically, the concentration of K₂O₃O₂ decreases from the surfaces 108 and 110 of the glass article 100 through the cladding layers 104 and 106 to the cladding side of the interfaces 112 and 114. That is, the concentration of K₂O₃O₂ in the cladding layers 104 and 106 has a negative slope as a function of distance from the surfaces 108 and 110. Similarly, the concentration of K₂O₃O₂ decreases from the core side of the interface along the direction of the centerline CL of the core layer 102.

[0084] Furthermore, the concentration of Na2O 304 increases from the surfaces 108 and 110 of the glass article 100 through the coating layers 104 and 106 to the coating side of the interfaces 112 and 114. That is, the concentration of Na2O 304 in the coating layers 104 and 106 has a positive slope as a function of distance from the surfaces 108 and 110. Then, the Na2O concentration 304 changes in a step-like manner at the interface between the coating layers 104 and 106 and the core layer 102, and then continuously decreases within the core layer 102.

[0085] Further, in FIG. 3 , the Li2O concentration 306 increases from a surface concentration of zero to a maximum Li2O concentration 306 at the centerline CL as the distance from the surface of the cladding layer 104, 106 into the core layer 102 increases.

[0086] While the concentration of alkali metal oxide in the cladding layer 104, 106 changes due to ion exchange strengthening, it is understood that the concentration of other components of the glass network (i.e., glass formers, intermediates, and alkaline earth oxides (CaO, MgO, etc.) and other non- mobile modifiers) remain substantially the same (i.e., substantially uniform over the thickness of the cladding layer 104, 106 and substantially uniform over the thickness of the core layer 102).

[0087] The ion exchange process also results in a unique stress profile curve, an example of which is shown in FIG. 4 . As shown in FIG. 4 , the glass cladding layer has a stress profile curve due to ion exchange. The stress of the region from the surface of the glass to the core-clad interface at 100 pm contains both compressive stress and tensile stress due to ion exchange strengthening. The core layer 102 (i.e., the portion of the laminate at depths greater than 100 pm) also contains a region of compressive stress and a region under tensile stress due to ion exchange strengthening of the cladding layer into the core layer 102. In FIG. 4 , the stress profile curve 402 corresponds to a profile of a chemically strengthened glass using the dual ion exchange process chemistry described herein.

[0088] More specifically, in FIG. 4 , the stress of the cladding layer increases from compressive stress to tensile stress as the distance from the outer surface of the cladding layer increases and then transitions in a step change manner to compressive stress at the interface region between the core layer 102 and the cladding layer. The stress of the core layer 102 increases from compressive stress to tensile stress as the distance from the interface region to the center of the core layer 102 increases.

[0089] The alkali metal concentration profile of FIG. 3 and the stress profile of FIG. 4 are obtained using a lithium-containing cladding layer 104, 106 and a sodium-containing core layer 102. FIG. 5-8 Each shows the alkali metal concentration profile ( FIG. 5 and FIG. 7 ) or the stress profile ( FIG. 6 and FIG. 8 ) of a glass laminate containing a lithium-containing core layer 102 and a sodium-containing cladding layer 104, 106. The FIG. 5 and FIG. 6the distribution profile in FIG. 6A, while using a cladding layer thickness of 25 pm FIG. 7 and FIG. 8 the distribution profile in FIG. 6A.

[0090] As with the previous examples, as shown in FIG. 5 and FIG. 7 the concentration of alkali metal oxide (e.g., K20) varies with depth from the surface 108, 110 of the glass article 100 in the core layer 102 and the cladding layers 104, 106 after ion exchange. Specifically, the concentration of K20 502, 702 decreases from the surface 108, 110 of the glass article 100 through the cladding layers 104, 106 to the cladding side of the interface 112, 114. That is, the concentration of K20 502, 702 in the cladding layers 104, 106 has a negative slope as a function of distance from the surface 108, 110. Similarly, the concentration of K20 502, 702 decreases from the core side of the interface in the direction of the centerline CL of the core layer 102.

[0091] Additionally, in FIG. 5 and FIG. 7 the Li20 concentration 504, 704 increases from a surface concentration of 0 to a maximum Li20 concentration 504, 704 at the centerline CL as the distance from the surface of the cladding layer 104, 106 to the centerline in the core layer 102 increases.

[0092] However, in FIG. 5 and FIG. 7 the concentration of Na20 506, 706 increases from the surface 108, 110 of the glass article 100 through the cladding layers 104, 106 to the cladding side of the interface 112, 114. That is, the concentration of Na20 506, 706 in the cladding layers 104, 106 has a positive slope as a function of distance from the surface 108, 110. The Na20 concentration 506, 706 then changes in a step change manner at the interface between the cladding layers 104, 106 and the core layer 102, where it initially increases and then decreases within the core layer 102.

[0093] While the concentration of alkali metal oxide in the cladding layers 104, 106 changes due to ion exchange strengthening, it should be understood that the concentration of other components of the glass network (i.e., glass formers, intermediates, and alkaline earth metal oxides (CaO, MagO, etc.) non-mobility modifiers) remain substantially the same (i.e., substantially uniform over the thickness of the cladding layers 104, 106 and substantially uniform over the thickness of the core layer 102).

[0094] In the stress distribution profiles shown in FIG. 6 and FIG. 8 the cladding layers 104, 106 have a distribution profile due to ion exchange. InFIG. 6 In the illustrated example, the stress profile curve 602 corresponds to a chemically strengthened glass using a double ion exchange process as described herein. FIG. 6

[0095] More specifically, in the illustrated example, the stress of the core layer 102 increases from a compressive stress to a tensile stress as the distance from the outer surface of the core layer 102 increases. The stress of the core layer 102 then transitions in a step change manner to a compressive stress at the interface region between the core layer 102 and the cladding layer. The stress of the core layer 102 increases from a compressive stress to a tensile stress as the distance from the interface region to the center of the core layer 102 increases. FIG. 6 In the illustrated example, the stress profile curve 802 corresponds to a chemically strengthened glass using a double ion exchange process as described herein.

[0096] However, in the illustrated example, the stress profile curve 802 indicates that the stress in the region from the glass surface to the core-cladding interface at 25 μιη contains only compressive stress due to ion exchange strengthening. The core layer 102 (i.e., the portion of the laminate at depths greater than 25 μιη) contains regions of compressive stress and regions under tensile stress due to ion exchange strengthening of the core layer 102 through the cladding layers 104, 106. FIG. 8 More specifically, in the illustrated example, the stress of the core layer 102 increases from an initial compressive stress to a minimum compressive stress as the distance from the outer surface of the core layer 102 increases. The stress of the core layer 102 then transitions in a step change manner to a maximum compressive stress at the interface region between the core layer 102 and the cladding layer. The stress of the core layer 102 increases from a compressive stress to a tensile stress as the distance from the interface region to the center of the core layer 102 increases.

[0097] FIG. 8

[0098] Notably, the reduction in the cladding layer thickness eliminates the tensile stress in the cladding layer, reduces the central tension in the glass article, and maintains a depth of compression (DOC) of about 100 μιη or about 21% of the total thickness of the glass laminate. In other words, a high level of compression can be generated without significant tension within the core layer 102.

[0099] ​​​The residual strength of a glass article can be determined based on the stress profile of the glass article. For example, the residual strength is determined by forming a flaw extending from the surface of the glass article to a specified depth, and then determining the strength of the glass article after the flaw is formed. The strength is the flexural strength of the glass article determined using, for example, a ring-on-ring test method (e.g., as described in ASTM C1499-09), a ball-on-ring test method, a three-point bend test method, a four-point bend test method, or another suitable method or technique. Such residual strength determinations can be made using a fracture mechanics simulation based on the stress profile of the glass article.

[0100] In addition, in contrast to the residual strength profile 602 and / or the residual strength profile 402, the improved resistance to fracture for large flaws can be achieved by the strength profile 802 while reducing the maximum tensile stress of the tensile region. For example, maintaining the compressive stress relatively constant through the compressive region (e.g., above the middle portion) can help maintain the area below the compressive portion of the stress profile that is relatively low (which is proportional to the maximum tensile stress in the tensile region), while also providing protection against fracture from relatively deep flaws. Thus, the maximum tensile stress can be maintained below the frangibility limit.

[0101] In various embodiments, the ion exchange parameters and glass compositions selected for each of the cladding layers 104, 106 and the core layer 102 can be selected to achieve a particular stress profile. In various embodiments, the stress profile can be selected to achieve a desired residual strength profile. FIG. 9 Various example stress profiles are depicted in FIG. 8.

[0102] For example, the stress profile 902 can be obtained in the case where the stress gradient in the deeper portion of the cladding layer is discontinuous. Instead, the stress in the cladding layer changes monotonically from the surface to the cladding-core interface, where it jumps to compression within the core layer 102. Alternatively, the stress can have a gradient across the cladding-core interface, taking into account the presence of an interdiffusion layer between the cladding layer and the core layer 102, the composition in the interdiffusion layer gradually changing from the cladding glass composition to the core glass composition. In one particular embodiment, the stress profile 902 can be achieved by using a core glass composition having a much higher alkali content than the cladding glass composition.

[0103] For example, in one particular embodiment, the cladding glass composition comprises 6 mol% Na20 and 1 mol% K20 as alkalis, and the core glass composition comprises 18 mol% Na20 and 3 mol% K20. After ion exchange (as a first step) in a bath having 50% NaNCb and 50% KNCb for a first exchange time (such as, but not limited to, greater than or equal to 1 hour to less than or equal to 100 hours), K ions substantially penetrate into the core glass B. Then, in a second step, the sample is ion exchanged in a bath having 100% KNCb for a second exchange time that is less than the first exchange time sufficient to produce a gradient distribution profile of K ions within the cladding layer. The second exchange time can be, for example, but not limited to, about 10 minutes to less than or equal to 5 hours, as long as the second exchange time is less than the first exchange time.

[0104] As another example, the stress profile 904 can be obtained after a first long ion exchange step (e.g., after an ion exchange time of, for example, but not limited to, greater than or equal to 1 hour to less than or equal to 100 hours), but the second step is an ion exchange step with a non-penetrating boundary condition, where only the ions already present in the glass diffuse between the core and cladding layers, without additional ions from an external source (e.g., a molten salt bath) diffusing into the glass article. The second ion exchange step can be, for example, but not limited to, by heating the glass article to a temperature sufficient to perform ion exchange (e.g., about 350 °C to about 550 °C). This increases the ion exchange between the core and cladding layers (one or more) and results in an increase in the compressive stress at the interface between the core and cladding layers. However, due to the balance of forces, the compressive stress at or near the surface of the cladding layer decreases. As a result, the stress profile 904 in the cladding layer is substantially linear. In this embodiment, the second derivative of the stress profile can be ignored for the purpose of differentiating mechanical properties.

[0105] In yet another example, the stress profile 906 can be obtained by using a cladding glass composition having a much higher alkali metal diffusivity than the core glass composition, thus substantially eliminating the stress gradient in the cladding layer(s). In this embodiment, the stress gradient in the cladding layer(s) is sufficiently reduced that it is irrelevant for the purpose of differentiating mechanical properties. The glass laminate is subjected to a first long ion exchange (e.g., an ion exchange time of, for example, but not limited to, greater than or equal to 1 hour to less than or equal to 100 hours) such that the stress profile penetrates all the way to the core layer 102, followed by a heat treatment to produce a flat region near the surface of the cladding layer.

[0106] The stress profile 908 can be obtained by combining long ion exchange and using a cladding glass composition with a much higher diffusivity than the core glass composition, but lower than the cladding glass composition used to obtain the stress profile 906, as a first step, so that the stress profile penetrates all the way through the core layer 102, followed by a heat treatment to create a flat region of the stress profile near the surface of the cladding layer.

[0107] In various embodiments, enabling ion exchange along the cladding-core interface can also result in various stress profiles. For example, as shown in FIG. 11, a glass laminate having a potassium-rich cladding glass composition and a sodium-rich core glass composition was ion exchanged for various amounts of time. In particular, the stress profile 1102 was obtained after an ion exchange step of a first duration Di (hours), the stress profile 1104 was obtained after an ion exchange step of about 4xDi, the stress profile 1106 was obtained after an ion exchange step of about 15xDi, and the stress profile 1108 was obtained after an ion exchange step of about 25xDi. Although the stresses from the CTE mismatch between the cladding layer and the core layer 102 are not included in the stress profiles shown in FIG. 11, the CTE stresses would shift the stresses within the cladding layer in the -Y direction, while the CTE stresses would shift the stresses within the core layer 102 in the +Y direction. Thus, by this particular combination of alkali metals in the core and cladding glass compositions, a thicker cladding layer can be employed without introducing tensile stresses into the cladding layer. FIG. 10 FIG. 10 In various embodiments, the amount of time the sample is subjected to the ion exchange process can change the resulting stress profile. In FIG. 10 for example, a glass laminate having a sodium-rich cladding glass composition and a potassium-rich core glass composition was ion exchanged for various amounts of time. In particular, the stress profile 1002 was obtained after an ion exchange step of a first duration Di (hours), the stress profile 1004 was obtained after an ion exchange step of about 4xDi, the stress profile 1006 was obtained after an ion exchange step of about 15xDi, and the stress profile 1008 was obtained after an ion exchange step of about 25xDi. Although the stresses from the CTE mismatch between the cladding layer and the core layer 102 are not included in the stress profiles shown in FIG. 10, the CTE stresses would shift the stresses within the cladding layer in the -Y direction, while the CTE stresses would shift the stresses within the core layer 102 in the +Y direction. Thus, by this particular combination of alkali metals in the core and cladding glass compositions, a thicker cladding layer can be employed without introducing tensile stresses into the cladding layer.

[0108] Other stress profiles can be obtained by reversing the alkali metal content of the cladding layer and the core layer 102. For example, as shown in FIG. 11, a glass laminate having a potassium-rich cladding glass composition and a sodium-rich core glass composition was ion exchanged for various amounts of time. In particular, the stress profile 1102 was obtained after an ion exchange step of a first duration Di (hours), the stress profile 1104 was obtained after an ion exchange step of about 4xDi, the stress profile 1106 was obtained after an ion exchange step of about 15xDi, and the stress profile 1108 was obtained after an ion exchange step of about 25xDi. Although the stresses from the CTE mismatch between the cladding layer and the core layer 102 are not included in the stress profiles shown in FIG. 11, the CTE stresses would shift the stresses within the cladding layer in the -Y direction, while the CTE stresses would shift the stresses within the core layer 102 in the +Y direction. Thus, by this particular combination of alkali metals in the core and cladding glass compositions, a thicker cladding layer can be employed without introducing tensile stresses into the cladding layer. FIG. 11 FIG. 11 ​​In the illustrated stress profile, however, the CTE stress will shift the stress in the clad layer in the +Y direction, while the CTE stress will shift the stress in the core layer 102 in the -Y direction. Thus, with this particular combination of alkali metals in the core and clad glass compositions, a thicker clad layer can be employed to reduce the central tension in the glass laminate. In addition, the combination of the glass compositions with the CTE mismatch can result in compressive stress in the core layer 102.

[0109] The various embodiments described herein can also be used to reduce the spallation of a glass laminate. In some embodiments, the glass articles disclosed herein are not spallable after ion exchange. Spallation behavior refers to a particular fracture behavior when a glass article is subjected to an impact or insult. As used herein, a glass is considered to be not spallable when the glass exhibits at least one of the following as a result of a spallation test: (1) four or fewer fragments having a maximum dimension of at least 1 mm, and / or (2) a number of bifurcations less than or equal to the number of crack branches. Fragments, bifurcations, and crack branches are counted based on an arbitrary 2 inch by 2 square inch centered on the point of impact. Thus, a glass is considered to be not spallable if it satisfies one or both of tests (1) and (2) for any 2 inch by 2 square inch square centered on the point of impact resulting from an impact to cause a fracture according to the procedure described below. In the spallation test, an impact probe is brought into contact with the glass, with the depth of the impact probe into the glass increasing in successive contact iterations. The stepwise increase in the depth of the impact probe allows the defect created by the impact probe to reach the tension region, while preventing the application of excessive external forces that would hinder the accurate determination of the spallation behavior of the glass. In one embodiment, the depth of the impact probe into the glass can be increased by about 5 μιη in each iteration, with the impact probe removed from contact with the glass between each iteration. The test area is an arbitrary 2 inch by 2 square inch centered on the point of impact. FIG. 12 The results of the spallation test are shown. As shown, the test area is a square centered on the point of impact 1230, with the length of the side of square a being 2 inches. FIG. 12 The illustrated spallation sample includes three fragments 1242, and two crack branches 1240 and a single bifurcation 1250. Thus, FIG. 12 The illustrated spallation sample includes three fragments 1242, and two crack branches 1240 and a single bifurcation 1250. Thus, FIG. 12The illustrated unbreakable sample contains less than 4 fragments with a maximum dimension of at least 1 mm and the number of bifurcations is less than or equal to the number of crack branches. As used herein, a crack branch originates at the point of impact and a fragment is considered to be within the test area if any portion of the fragment extends into the test area. While coatings, adhesive layers, and the like can be used in conjunction with the strengthened glass articles described herein, such external constraints are not used to determine the unbreakability or unbreakable behavior of the glass article. In some embodiments, a film that does not affect the fracture behavior of the glass article can be applied to the glass article prior to the unbreakability test to prevent fragments from ejecting from the glass article while improving the safety of the person performing the test.

[0110] FIG. 13 An unbreakable sample is described. The unbreakable sample contains 5 fragments 1242 with a maximum dimension of at least 1 mm. FIG. 13 The illustrated sample contains 2 crack branches 1240 and 3 bifurcations 1250, which create more bifurcations than crack branches. Thus, FIG. 13 The sample described in FIG. 10 does not exhibit four or fewer fragments or the number of bifurcations is less than or equal to the number of crack branches.

[0111] In the unbreakability tests described herein, an impact is delivered to the surface of a strengthened glass article with a force that is just enough to release the internal stored energy present within the strengthened glass article. That is, the point impact force is sufficient to create at least one new crack at the surface of the strengthened glass sheet and cause the crack to extend through the compressive stress (CS) region (i.e., the compressive depth) into the region under central tension (CT).

[0112] Accordingly, the chemically strengthened glasses described herein are "unbreakable," i.e., they do not exhibit unbreakable behavior as described above when subjected to an impact by a sharp object.

[0113] The unbreakability of the chemically strengthened glasses described herein can be reduced by burying the compressive stress spike within the core layer 102. For example, as illustrated in FIG. 13, a glass article having a thin core layer 102 with a low potassium concentration and thick cladding layers 104, 106 containing potassium ions can have a stress profile curve 1302. When the glass article is subjected to an ion exchange treatment, the potassium ions from the cladding layers are exchanged into the core layer 102, which increases the compression within the core layer 102. Without being bound by theory, it is believed that the thinner the core layer 102 and the stronger the CTE mismatch, the higher the compressive stress barrier that can be formed in the glass. This compression reduces unbreakability by dividing the tensile region and stops cracks. FIG. 14 As described above, in various embodiments, the glass article is mechanically strengthened by the CTE mismatch between the core layer 102 and the cladding layers 104, 106.

[0114] FIG. 15 ​Various stress profile curves and CTE differences illustrating the dual ion exchange process described herein.

[0115] In FIG. 15 , stress profiles 1502 and 1506 correspond to glass articles that have undergone a dual ion exchange process as described herein but are not laminated. Stress profiles 1504 and 1508 correspond to laminated glass articles that have undergone the same dual ion exchange process that produced stress profiles 1502 and 1506, respectively. The glass article corresponding to stress profile 1508 has a lower laminated CTE difference, a lower peak compressive stress, and a deeper depth of ion exchange and compressive depth of the step profile than the glass article corresponding to stress profile 1504. As FIG. 15 shown, the stress profiles 1504 and 1508 of the mechanically and chemically strengthened glass articles provide good protection against both short and deep cracks, and the addition of the laminate (and in particular the constant stress profile region) is able to produce a higher stress at the compressive depth rather than an error function decay that would produce a low stress region prior to the compressive depth. Additionally, the dual ion exchange results in a stress profile with a non-constant stress as a function of depth.

[0116] FIG. 16 Residual strength based on a fracture mechanics calculation is shown as a function of flaw size for glass articles corresponding to the stress profiles in FIG. 15 . In particular, residual strength profile 1602 corresponds to stress profile 1502, residual strength profile 1604 corresponds to stress profile 1504, residual strength profile 1606 corresponds to stress profile 1506, and residual strength profile 1608 corresponds to stress profile 1508. In FIG. 16 , it can be seen that the mechanically and chemically strengthened glass articles corresponding to strength profiles 1604 and 1608 exhibit a greater residual strength for flaw sizes up to about 90 μιη. Additionally, it can be seen that the glass article corresponding to strength profile 1608 has a reduced strength for small flaws but a greater strength for deeper flaws than the glass article corresponding to strength profile 1604. Thus, for a given critical flaw size range, the dual ion exchange profile and the laminate stress can be combined to provide a desired residual strength.

[0117] Various other stress profiles that can be obtained in various embodiments described herein are shown in FIG. 17 . In particular, as described herein, FIG. 17The stress distribution curves in FIG. 17 illustrate two general strategies for utilizing step profiles obtained from glass articles having CTE mismatches. First, the stress distribution curve 1704 shows that a high compressive stress but low thickness cladding layer 104, 106 can be used to compensate for low compressive intensity in a parabolic stress distribution curve (e.g., stress distribution curves 1702, 1708, or 1710). Due to the high fictive temperature of the glass, this strategy can result in good scratch performance due to high compressive stress and high free volume. In particular, high free volume (e.g., low density) can result in improved scratch resistance and / or dent fracture resistance performance. Second, as can be seen by comparing stress distribution curves 1704, 1706, and 1712 with stress distribution curves 1702, 1708, and 1710, high compressive depth and low slope can result in improved drop performance as the compressive stress transitions to tensile stress. By mechanically strengthening the glass article, the compressive depth can be increased by adding a low compressive stress step profile that extends to or beyond the compressive depth of the combined distribution curve, thereby taking advantage of both features. The compressive stress can effectively "hide" the region that does not affect drop performance.

[0118] FIG. 18 The residual strength of glass articles corresponding to the stress distribution curves of FIG. 17 FIG. 17 shows that both strategies are effective in utilizing step profiles. In addition, as shown in FIG. 18 FIG. 17, the thickness of the cladding layer can be adjusted to provide improved residual strength for any defect range of interest. FIG. 18 The residual strength distribution curves in FIG. 17 further illustrate that a buried central tension increases the residual strength, while high compressive stress increases the strength for shallow defects.

[0119] The various embodiments described herein enable improved glass performance, such as scratch resistance and crack resistance, through mechanical and chemical strengthening. In addition, the various glass compositions are selected to obtain a particular CTE mismatch between the core layer and the cladding layer and ion exchange through the core layer of the cladding layer can result in a glass article having a range of compressive-tensile zones along the thickness of the glass article, which can reduce fragility and arrest cracks.

[0120] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modifications and variations come within the scope of the appended claims and their equivalents.

[0121] This application is also related to the following items.

[0122] 1. A laminated glass article comprising:

[0123] a core layer comprising a core glass composition; and

[0124] a cladding layer directly adjacent to the core layer and comprising a cladding glass composition;

[0125] wherein the stress of the cladding layer increases from compressive stress to tensile stress with increasing distance from an outer surface of the cladding layer, transitions in a step change manner to compressive stress at an interface region between the core layer and the cladding layer, and increases from compressive stress to tensile stress with increasing distance from the interface region to a center of the core layer.

[0126] 2. The laminated glass article of item 1, wherein the core glass composition has an average core coefficient of thermal expansion (CTE 核心 ) and the cladding layer has an average cladding coefficient of thermal expansion (CTE 核心 ) that is greater than CTE 包覆 .

[0127] 3. The laminated glass article of item 1, wherein the laminated glass article is ion exchange strengthened.

[0128] 4. The laminated glass article of item 3, wherein the core glass composition and the cladding glass composition comprise one or more alkali metal oxides.

[0129] 5. The laminated glass article of item 3, wherein the maximum tensile stress in the cladding layer is greater than or equal to the maximum tensile stress in the core layer.

[0130] 6. The laminated glass article of item 3, wherein the maximum compressive stress of the core layer is greater than the maximum compressive stress of the cladding layer.

[0131] 7. The laminated glass article of item 1, wherein the magnitude of the stress at the outer surface is greater than or equal to about 300 MPa.

[0132] 8. The laminated glass article of item 1, wherein the maximum magnitude of the stress of the laminated glass article is less than or equal to about 400 MPa.

[0133] 9. A laminated glass article comprising:

[0134] a core layer comprising a core glass composition; and

[0135] a cladding layer directly adjacent to the core layer and comprising a cladding glass composition;

[0136] wherein:

[0137] the concentration of Li ions increases with increasing distance from an outer surface of the cladding layer to a centerline of the core layer;

[0138] the concentration of K ions decreases with increasing distance from an outer surface of the cladding layer to an interface between the cladding layer and the core layer; and

[0139] the concentration of Na ions increases with increasing distance from an outer surface of the cladding layer to a maximum concentration of Na ions in the cladding layer or at an interface between the cladding layer and the core layer, and transitions to a lower concentration of Na ions via a step change at the interface between the cladding layer and the core layer relative to the maximum concentration of Na ions.

[0140] 10. The laminated glass article of item 9, wherein the concentration of sodium ions decreases with increasing distance from an interface between the cladding layer and the core layer to a centerline of the core layer.

[0141] 11. The laminated glass article of item 9, wherein the concentration of sodium ions increases and then decreases with increasing distance from an interface between the cladding layer and the core layer to a centerline of the core layer.

[0142] 12. The laminated glass article of item 9, wherein the concentration of Li ions increases according to a non-linear relationship.

[0143] 13. The laminated glass article of item 9, wherein the concentration of K ions in the core layer is zero.

[0144] 14. The laminated glass article of item 9, wherein the concentration of Na ions increases from an outer surface of the cladding layer to a maximum concentration of Na ions according to a linear relationship.

[0145] 15. The laminated glass article of item 9, wherein the concentration of Na ions increases from an outer surface of the cladding layer to a maximum concentration of Na ions according to a non-linear relationship.

[0146] 16. A method of making a laminated glass article, comprising:

[0147] laminating at least one core layer and at least one cladding layer to form a laminated glass article, the at least one core layer comprising an ion-exchangeable core glass composition and the at least one cladding layer comprising an ion-exchangeable cladding glass composition; and

[0148] contacting the laminated glass article with an ion exchange bath comprising at least one ion source for a period of time such that a maximum compressive stress in the at least one core layer is greater than a maximum compressive stress in the at least one cladding layer.

[0149] 17. The method of item 16, wherein the at least one core layer has an average core coefficient of thermal expansion (CTE 核心 ) and the at least one cladding layer has an average cladding coefficient of thermal expansion (CTE 核心 ) that is greater than the CTE 包覆 ).

[0150] 18. The method of item 16, wherein the ion exchange bath comprises at least a first ion source and a second ion source different from the first ion source.

[0151] 19. The method of item 16, wherein after contact with the ion exchange bath, a maximum tensile stress in the at least one cladding layer is greater than or equal to a maximum tensile stress in the at least one core layer.

[0152] 20. The method of item 16, wherein after contact with the ion exchange bath, a stress magnitude on an outer surface of the glass article is greater than or equal to about 300 MPa.

Claims

1. A laminated glass article comprising: The core layer comprises a core glass composition; and A cladding layer, which is directly adjacent to the core layer and comprises a cladding glass composition; in: The concentration of Li ions increases with the increase of the distance from the outer surface of the coating layer to the center line of the core layer; The concentration of K ions decreases with increasing distance from the outer surface of the coating layer to the interface between the coating layer and the core layer; and The concentration of Na ions increases with increasing distance from the outer surface of the coating layer to a maximum Na ion concentration in the coating layer or at the interface between the coating layer and the core layer, and then transitions to a lower Na ion concentration relative to the maximum Na ion concentration via a step change at the interface between the coating layer and the core layer.

2. The laminated glass article according to claim 1, wherein the sodium ion concentration decreases as the distance from the interface between the cladding layer and the core layer to the centerline of the core layer increases.

3. The laminated glass article according to claim 1, wherein the sodium ion concentration first increases and then decreases as the distance from the interface between the cladding layer and the core layer to the centerline of the core layer increases.

4. The laminated glass article according to claim 1, wherein the concentration of Li ions increases according to a nonlinear relationship.

5. The laminated glass article according to claim 1, wherein the concentration of K ions in the core layer is zero.

6. The laminated glass article according to claim 1, wherein the concentration of Na ions increases linearly from the outer surface of the coating layer to the maximum concentration of Na ions.

7. The laminated glass article according to claim 1, wherein the concentration of Na ions increases from the outer surface of the coating layer to the maximum concentration of Na ions according to a nonlinear relationship.

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