Patent Application
20230167020
The present specification generally relates to glass-based articles with high stored strain energy and a reduced risk of delayed failure.
The mechanical strength of pristine glasses, such as optical fiber, is extremely high (GPa range) but the strength of everyday glass products such as windows and bottles is significantly lower (MPa range) primarily due to the presence of pre-existing surface flaws. It has been known that these glasses can be made mechanically stronger and more wear-resistant by forming a compressive stress layer on the surface of the glass. It has been long recognized that is desirable when improving the mechanical performance of glass to have a surface compressive stresses (CS) which prevents flaw/crack nucleation and/or growth. It is not only the magnitude of compression, but also the depth of the compressive stress (DOC) into the glass surface, that must be considered. It is desirable to achieve both a high surface compression and a deep depth of compression in the same glass article.
There are two popular approaches to produce a compressive surface stress on a glass surface, thermal tempering and ion-exchange. In order to thermally temper a glass, a glass product is heated to near the softening temperature and then quenched. As a result, the glass will possess a lower surface temperature than the interior temperature during cooling. This temperature difference is maintained until the surface of the glass cools to room temperature. As the center of the glass also cools, more slowly, to room temperature it will contract to a smaller specific volume while the high specific volume of the surface layer remains unchanged. This leads to a surface compressive layer that gives tempered glass its strength. This process is commonly used to strengthen automobile side and rear windows.
A second popular strengthening method, ion-exchange (IOX) or chemical tempering is limited in applicability to glasses containing mobile cations. In this method, glasses containing alkali ions, e.g. Na+, are treated in a molten salt containing larger alkali ions, e.g. K+, at a temperature below the glass transition temperature. Although alkali ions rest in specific positions within the rigid glass network, they possess the ability to jump between sites. As a result, when an alkali-containing glass is immersed in a molten salt containing another type of larger alkali ions, some larger ions from the molten salt will exchange with those in the outer layers of the glass. If this process is performed at a temperature below the glass transition temperature, such that stress relaxation is sluggish compared to the rate of ion-exchange, large ions will find themselves stuffed into rigid sites that are too small. Since the structure cannot relax to accommodate the newly acquired larger ions, a biaxial compressive stress is formed. This process, sometimes called ion-stuffing or chemical tempering, can produce a surface layer with a high compressive stress on the glass and is commonly employed to strengthen products such as aircraft windows and scratch resistant cover glasses on electronic devices.
High stored energy strengthened glass articles may fragment into many pieces, and can create dangerous shards and/or eject particles, upon failure. So-called parabolic stress profiles with a high surface compressive stress values and high central tension values are attractive due to the high degree of strengthening provided to the glass and the resistance to fracture. However, such high stored energy stress profiles can result in an inconvenient and potentially dangerous delayed fracture behavior.
Accordingly, a need exists for strengthened glass articles that provide the benefits of high stored energy stress profiles with a reduced propensity for delayed fracture.
According to aspect (1), a glass-based article is provided. The glass-based article comprises: a thickness t; a first clad layer having a first thickness tC1; a second clad layer having a first thickness tC2; a core layer having a first thickness to, wherein the core layer is disposed between and bonded to the first clad layer and the second clad layer; a first compressive stress region extending from a surface of the first clad layer to a first depth of compression DOC1, the first compressive stress region comprising a first maximum compressive stress CS1 greater than or equal to 500 MPa; a second compressive stress region extending from a surface of the second clad layer to a second depth of compression DOC2, the second compressive stress region comprising a second maximum compressive stress CS2 greater than or equal to 500 MPa; and a central tension region extending from DOC1 to DOC2, comprising a maximum central tension CT greater than or equal to 250 MPa, wherein a difference in flaw sizes that produce delayed fracture is less than or equal to 3 μm.
According to aspect (2), the glass-based article of aspect (1) is provided, wherein the first compressive stress region comprises a parabolic stress profile.
According to aspect (3), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein tC1 is greater than or equal to 100 μm.
According to aspect (4), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein tC1 is greater than or equal to 0.2t.
According to aspect (5), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein tC1=tC2.
According to aspect (6), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein tC1+tC2+to=t.
According to aspect (7), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein DOC1 is greater than or equal to 0.2t.
According to aspect (8), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein the stress at a depth of DOC1-2 μm is greater than or equal to 40 MPa greater than the stress at a depth of DOC1+2 μm.
According to aspect (9), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein the stress at a depth of DOC1-2 μm is greater than or equal to 100 MPa greater than the stress at a depth of DOC1+2 μm.
According to aspect (10), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein a stress profile of the glass-based article has a slope discontinuity at DOC1.
According to aspect (11), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein t is less than or equal to 2 mm.
According to aspect (12), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein t is greater than or equal to 0.2 mm.
According to aspect (13), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein the first clad layer and the second clad layer comprise a lithium aluminosilicate.
According to aspect (14), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein the first clad layer and the second clad layer are formed from the same glass composition.
According to aspect (15), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein the first clad layer and the core layer have substantially matched alkali ion diffusivity and diffusivity network dilation.
According to aspect (16), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein the first clad layer has a first coefficient of thermal expansion CTE1 and the core layer has a core coefficient of thermal expansion CTEo, and CTE1<CTEo.
According to aspect (17), the glass-based article of any of aspect (1) to the preceding aspect is provided, wherein the first clad layer has a first diffusivity network dilation and the core layer has a core diffusivity network dilation, and the first diffusivity network dilation is greater than the core diffusivity network dilation.
According to aspect (18), a consumer electronic product is provided. The consumer electronic product comprises: a housing comprising a front surface, a back surface and side surfaces; electrical components at least partially within the housing, the electrical components comprising a controller, a memory, and a display, the display at or adjacent the front surface of the housing; and a cover substrate disposed over the display, wherein at least a portion of at least one of the housing and the cover substrate comprises the glass-based article of any of aspect (1) to the preceding aspect.
According to aspect (19), a method is provided. The method comprises: forming a step-type stress profile in a glass-based substrate to form a strengthened glass-based substrate; and ion exchanging the strengthened glass-based substrate to form a glass-based article, wherein the glass-based article comprises: a thickness t; a first clad layer having a first thickness tC1; a second clad layer having a first thickness tC2; a core layer having a first thickness to, wherein the core layer is disposed between and bonded to the first clad layer and the second clad layer; a first compressive stress region extending from a surface of the first clad layer to a first depth of compression DOC1, the first compressive stress region comprising a first maximum compressive stress CS1 greater than or equal to 500 MPa; a second compressive stress region extending from a surface of the second clad layer to a second depth of compression DOC2, the second compressive stress region comprising a second maximum compressive stress CS2 greater than or equal to 500 MPa; and a central tension region extending from DOC1 to DOC2, comprising a maximum central tension CT greater than or equal to 250 MPa, wherein a difference in flaw sizes that produce delayed fracture is less than or equal to 3 μm.
According to aspect (20), the method of aspect (19) is provided, wherein forming the step-type stress profile comprises thermal tempering.
According to aspect (21), the method of any of aspect (19) to the preceding aspect is provided, wherein the first compressive stress region comprises a parabolic stress profile.
According to aspect (22), the method of any of aspect (19) to the preceding aspect is provided, wherein tC1 is greater than or equal to 100 μm.
According to aspect (23), the method of any of aspect (19) to the preceding aspect is provided, wherein tC1 is greater than or equal to 0.2t.
According to aspect (24), the method of any of aspect (19) to the preceding aspect is provided, wherein tC1=tC2.
According to aspect (25), the method of any of aspect (19) to the preceding aspect is provided, wherein tC1+tC2+to=t.
According to aspect (26), the method of any of aspect (19) to the preceding aspect is provided, wherein DOC1 is greater than or equal to 0.2t.
According to aspect (27), the method of any of aspect (19) to the preceding aspect is provided, wherein the stress at a depth of DOC1-2 μm is greater than or equal to 40 MPa greater than the stress at a depth of DOC1+2 μm.
According to aspect (28), the method of any of aspect (19) to the preceding aspect is provided, wherein the stress at a depth of DOC1-2 μm is greater than or equal to 1001 MPa greater than the stress at a depth of DOC1+2 μm.
According to aspect (29), the method of any of aspect (19) to the preceding aspect is provided, wherein a stress profile of the glass-based article has a slope discontinuity at DOC1.
According to aspect (30), the method of any of aspect (19) to the preceding aspect is provided, wherein t is less than or equal to 2 mm.
According to aspect (31), the method of any of aspect (19) to the preceding aspect is provided, wherein t is greater than or equal to 0.2 mm.
According to aspect (32), the method of any of aspect (19) to the preceding aspect is provided, wherein the first clad layer and the second clad layer comprise a lithium aluminosilicate.
According to aspect (33), the method of any of aspect (19) to the preceding aspect is provided, wherein the first clad layer and the second clad layer are formed from the same glass composition.
According to aspect (34), the method of any of aspect (19) to the preceding aspect is provided, wherein the first clad layer and the core layer have substantially matched alkali ion diffusivity and diffusivity network dilation.
According to aspect (35), the method of any of aspect (19) to the preceding aspect is provided, wherein the first clad layer has a first coefficient of thermal expansion CTE1 and the core layer has a core coefficient of thermal expansion CTEo, and CTE1<CTEo.
According to aspect (36), the method of any of aspect (19) to the preceding aspect is provided, wherein the first clad layer has a first diffusivity network dilation and the core layer has a core diffusivity network dilation, and the first diffusivity network dilation is greater than the core diffusivity network dilation.
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 from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.
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 into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.
Reference will now be made in detail to strengthened glass-based articles according to various embodiments. The stress profiles of the strengthened glass-based articles have a high degree of stored energy and have a reduced flaw size range that may result in delayed fracture.
As used herein, a trailing 0 in a number is intended to represent a significant digit for that number. For example, the number “1.0” includes two significant digits, and the number “1.00” includes three significant digits.
As utilized herein, a “glass substrate” refers to a glass piece that has not been ion exchanged. Similarly, a “glass article” refers to a glass piece that has been ion exchanged and is formed by subjecting a glass substrate to an ion exchange process. A “glass-based substrate” and a “glass-based article” are defined accordingly and include glass substrates and glass articles as well as substrates and articles that are made wholly or partly of glass, such as glass substrates that include a surface coating or glass-ceramic substrates. While glass substrates and glass articles may generally be referred to herein for the sake of convenience, the descriptions of glass substrates and glass articles should be understood to apply equally to glass-based substrates and glass-based articles.
The glass-based articles described herein have stress profiles adapted to provide the benefits of a parabolic stress profile while exhibiting a reduced likelihood of a delayed fracture. As utilized herein, a delayed fracture refers to a fracture that occurs in time range greater than or equal to 10−2 minutes (6 seconds) to less than or equal to 104 minutes (about 17 hours) after the introduction of a flaw. Delayed fracture is produced by the sub-critical growth of flaws, and sub-critical flaw growth is generally produced by a specific flaw size range for a given stress profile. The stress profiles described herein reduce the flaw size range that is capable of producing delayed fracture.
The stress profiles of the glass-based articles described herein have a high rate of increase in the tensile stress beyond the depth of compression. The rapid increase in the tensile stress produces a rapid increase in the stress intensity factor of flaws at depths around the DOC, limiting the flaw depths that will be capable of sub-critical growth and delayed fracture.
To address the problem of delayed failures a stress profile that combines the features of a parabolic stress profile and a laminate stress profile is provided. A laminate stress profile as utilized herein refers to a step-type stress profile, with compression on the outer clad layers that is balanced by tension in the core layer. At the interface between the clad layers and the core layers defines the depth of compression and is a nearly step change in stress, from peak compression to peak tension. This step-change feature generates a rapid increase in stress intensity factor when cracks enter into the tension region. The rapid increase in the stress intensity factor reduces the flaw size range that is capable of producing delayed fracture when compared to a parabolic stress profile alone.
The glass-based articles have a reduced flaw size range that may result in delayed fracture. The flaw size range that produces delayed fracture may be defined as the difference between the flaw size that will cause fracture at a time of 10−2 minutes and the flaw size that will cause fracture at a time of 104 minutes, referred to herein as the difference in flaw sizes. In embodiments, the difference in flaw sizes that produce delayed fracture is less than or equal to 3 μm, such as less than or equal to 2.5 μm, less than or equal to 2 μm, less than or equal to 1.5 μm, less than or equal to 1 μm, or less. The low difference in flaw sizes that produce delayed fracture of the glass-based articles described herein reduces the likelihood that a give flaw will fall within the range, reducing the chances for delayed fracture.
The parabolic stress profiles described herein are advantageous for providing fracture resistance against large flaws, such as those produced by high impact sharp contact events. In embodiments, the parabolic stress profile may be of the type described in U.S. Patent Application Publication No. 2016/0102014, which is incorporated herein by reference in its entirety. The glass-based articles may include a parabolic stress profile in the first compressive stress region, the second compressive stress region, the central tension region, or all regions.
The stress profile of the glass-based articles described herein is additive, including the features of the step-type stress profile and the parabolic stress profile. For example, the step-type profile is added to the parabolic stress profile, shifting the parabolic stress profile to higher stresses in the compressive stress region and increasing tension in the central tension region. The additive stress profile includes the discontinuity of the step-type profile at the depth of compression, and the depth of compression may be located at the clad-core transition.
As mentioned above, in embodiments, the glass-based articles described herein are strengthened, such as by ion exchange, making a glass-based article that is damage resistant for applications such as, but not limited to, display covers. With reference to
According to the convention normally used in the art, compression or compressive stress is expressed as a negative (<0) stress and tension or tensile stress is expressed as a positive (>0) stress. Throughout this description, however, CS is expressed as a positive or absolute value—i.e., as recited herein, CS=|CS|. The compressive stress (CS) has a maximum at or near the surface of the glass-based article, and the CS varies with distance d from the surface according to a function. Referring again to
The compressive stress of both major surfaces (110, 112 in
The glass-based articles disclosed herein may be incorporated into another article such as an article with a display (or display articles) (e.g., consumer electronics, including mobile phones, tablets, computers, navigation systems, and the like), architectural articles, transportation articles (e.g., automobiles, trains, aircraft, sea craft, etc.), appliance articles, or any article that requires some transparency, scratch-resistance, abrasion resistance or a combination thereof. An exemplary article incorporating any of the glass-based articles disclosed herein is shown in
In embodiments, the CS of the glass-based articles is from greater than or equal to 500 MPa to less than or equal to 2000 MPa, such as greater than or equal to 600 MPa to less than or equal to 1900 MPa, greater than or equal to 700 MPa to less than or equal to 1800 MPa, greater than or equal to 800 MPa to less than or equal to 1700 MPa, greater than or equal to 900 MPa to less than or equal to 1300 MPa, greater than or equal to 1000 MPa to less than or equal to 1200 MPa, greater than or equal to 500 MPa to less than or equal to 1100 MPa, and all ranges and sub-ranges between the foregoing values.
The measurement of a maximum CT value is an indicator of the total amount of stress stored in the strengthened articles. For this reason, the ability to achieve higher CT values correlates to the ability to achieve higher degrees of strengthening. In embodiments, the glass-based article may have a maximum CT greater than or equal to 250 MPa, or more.
The glass-based article 300 is shown having a thickness (t), which is the thickness of the final article upon lamination of the layers and any thermal and/or chemical treatment. The core layer 310 has a thickness to, the first clad layer 320 has a thickness tC1, and the second clad layer 340 has a thickness tC2. The nominal thickness of the glass-based article 300 is the sum of tc1, tc2, and to. In one or more embodiments, the glass-based article of any embodiment disclosed herein has a thickness in a range of greater than or equal to 0.2 mm to less than or equal to 2 mm, such as greater than or equal to 0.3 mm to less than or equal to 1 mm, greater than or equal to 0.4 mm to less than or equal to 0.9 mm, greater than or equal to 0.5 mm to less than or equal to 0.8 mm, greater than or equal to 0.6 mm to less than or equal to 0.7 mm, and any and all sub-ranges formed between any of the foregoing endpoints.
In embodiment, the first clad layer 320 has a thickness tC1 that is at greater than or equal to 0.2t, such as greater than or equal to 0.21t, greater than or equal to 0.22t, greater than or equal to 0.23t, greater than or equal to 0.24t, greater than or equal to 0.25t, or any values or sub-ranges therebetween. The first clad layer 320 may have a thickness tC1 greater than or equal to 100 microns, such as greater than or equal to 200 microns, greater than or equal to 300 microns, greater than or equal to 400 microns, or any values or sub-ranges therebetween. Generally, the first clad layer is a different thickness than the core layer (tC1≠to); in a specific embodiment, the first clad layer is thicker than the sheet forming the core substrate (tC1>to). The second clad layer may be approximately the same thickness as the first clad layer, or the same as the first clad layer (tC1=tC2), in which case a symmetrical article is formed. As a result, the thickness of the second clad layer may be any of the thicknesses described herein for the first clay layer.
The first clad layer 320 may comprise a first glass composition and the core layer 310 may comprise a second glass composition, wherein the first glass composition is different from the second glass composition. In embodiments, the first glass composition has a first alkali ion diffusivity and the second glass composition has a second alkali ion diffusivity, and the first ion diffusivity and second ion diffusivity are different. In embodiments, the first glass composition has a first alkali ion diffusivity and the second glass composition has a second alkali ion diffusivity, and the first ion diffusivity and second ion diffusivity are substantially matched or the same. For example, the first clad layer and the core layer may have a substantially matched alkali ion diffusivity. Such matched alkali ion diffusivity aids in the achievement of the desired parabolic stress profile by ion exchange.
In embodiments, the first glass composition has a first diffusivity network dilation and the second glass composition has a second diffusivity network dilation, and the first diffusivity network dilation and second diffusivity network dilation are substantially matched or the same. For example, the first clad layer and the core layer may have a substantially matched diffusivity network dilation. Such matched diffusivity network dilation aids in the achievement of the desired parabolic stress profile by ion exchange. In embodiments, the first clad layer has a first diffusivity network dilation and the core layer has a core diffusivity network dilation, and the first diffusivity network dilation may be greater than the core diffusivity network dilation. The mismatched diffusivity network dilation properties may allow the formation of a step-type stress profile.
In embodiments, the first glass composition has a first coefficient of thermal expansion (CTE1) and the second glass composition has a second coefficient of thermal expansion (CTEo), and CTE1 and CTEo are different. In embodiments, CTE1 is lower than the CTEo to impart a compressive stress in the first clad layer and the second clad layer. Stated differently, the first clad layer has a first coefficient of thermal expansion (CTE1) and the core layer has a core coefficient of thermal expansion (CTEo), and in embodiments CTE1<CTEo.
In embodiments, the sheet that forms the second clad layer may comprise the same chemical composition as the first clad layer, in which case a symmetrical article is formed. In embodiments, the sheet that forms the second clad layer may comprise a third chemical composition that is different from the first and second chemical compositions, in which case an asymmetrical article is formed. Thus, the sheet that forms the second clad layer may have approximately the same or the same CTE as the sheet that forms the first clad layer; or the sheet that forms the second clad layer may have a different CTE than the sheet that forms the first clad layer. In embodiments, one or more additional clad layers are bonded to a surface of the first clad layer, the second clad layer, or both.
The first clad layer and the second clad layer may be formed from the same glass composition. In embodiments, the first and/or second clad layer include an alkali aluminosilicate glass. In a preferred embodiment, the first and second clad layers include a lithium aluminosilicate glass.
As noted above, DOC is measured using a scattered light polariscope (SCALP) technique known in the art. The DOC of the first clad layer DOC1 is located at the transition between the first clad layer and the core layer. The DOC of the second clad layer DOC2 is located at the transition between the second clad layer and the core layer. In embodiments, DOC1 is the same as DOC2, when measured from the closest major surfaces, respectively. Additionally, DOC1 may be the same as the thicknesses of the first clad layer described herein, and DOC2 may be the same as the thicknesses of the second clad layer described herein.
The DOC may be described as a portion of the thickness (t) of the glass-based article. High DOC values provide improved resistance to fracture, especially for situations where deep flaws may be introduced. In embodiments, DOC1 is greater than or equal to 0.2t, such as greater than or equal to 0.21t, greater than or equal to 0.22, greater than or equal to 0.23t, greater than or equal to 0.24t, greater than or equal to 0.25t, or more. In embodiments, DOC2 is greater than or equal to 0.2t, such as greater than or equal to 0.21t, greater than or equal to 0.22, greater than or equal to 0.23t, greater than or equal to 0.24t, greater than or equal to 0.25t, or more.
As described above, the stress profiles described herein may have a discontinuity at DOC1. Similarly, the stress profiles described herein may have a discontinuity at DOC2. A discontinuity may be indicated by a large and substantially instantaneous change in the stress value at the DOC. The change in stress at the DOC may be substantially equivalent to or equivalent to the difference between the stress difference between the compressive stress region and the central tension region attributable to the step-type stress profile. The difference between the stress at a depth of DOC1-2 μm and the stress at a depth of DOC1+2 μm may be greater than or equal to 40 MPa, such as greater than or equal to 50 MPa, greater than or equal to 60 MPa, greater than or equal to 70 MPa, greater than or equal to 80 MPa, greater than or equal to 90 MPa, greater than or equal to 100 MPa, greater than or equal to 110 MPa, greater than or equal to 120 MPa, greater than or equal to 130 MPa, greater than or equal to 140 MPa, greater than or equal to 150 MPa, or more.
The time to fracture of the glass-based articles may be modeled to determine the likelihood of delayed failure and the associated flaw size range. The model simulates a plane strain geometry with a crack of variable length. The stress profiles are explicitly applied to the models. After application of the stress profile, the stress intensity factor for the flaw was calculated. An exponential function was fit to experimental data for the non-strengthened glass article and the predicted fatigue life as a function of crack length was calculated according to the equation:
where T is the time to failure, KIC is the fracture toughness, KI is the stress intensity factor for the initial flaw, a is the flaw length, m and n are parameters from the fit of the experimental data, and K is the stress intensity factor.
As utilized herein, the fracture toughness refers to the KIC value as measured by the chevron notched short bar method unless otherwise noted. The chevron notched short bar (CNSB) method utilized to measure the KIC value is disclosed in Reddy, K. P. R. et al, “Fracture Toughness Measurement of Glass and Ceramic Materials Using Chevron-Notched Specimens,” J. Am. Ceram. Soc., 71 [6], C-310-C-313 (1988) except that Y*m is calculated using equation 5 of Bubsey, R. T. et al., “Closed-Form Expressions for Crack-Mouth Displacement and Stress Intensity Factors for Chevron-Notched Short Bar and Short Rod Specimens Based on Experimental Compliance Measurements,” NASA Technical Memorandum 83796, pp. 1-30 (October 1992). Additionally, the KIC values are measured on non-strengthened glass samples, such as measuring the KIC value prior to ion exchanging a glass-based substrate to form a glass-based article.
The glass-based articles described herein may be formed by any appropriate method. In embodiments, a step-type stress profile is formed in a glass-based substrate to form a strengthened glass-based substrate. The formation of the step-type stress profile may include thermal tempering. The strengthened glass-based substrate may then be ion exchanged to form a glass-based article, and the glass-based article may include a parabolic stress profile.
The glass-based substrates utilized to form the glass-based article are laminates. The laminates may be produced by fusion bonding the clad and core layers. Fusion bonding may be achieved according to the process described in U.S. Pat. No. 9,522,836 or in a temperature-controlled oven. With fusion bonding, the sheets are put into contact in a fusion draw or oven at temperature above the softening point of the materials. The glass-based materials effectively fuse after controlled cooling to form a uniform laminate with induced stress based on the different mechanical properties of the sheets. The fusion bonding process may directly impart a step-type stress profile to the glass-based substrate without the need for additional thermal treatments. For fusion bonding, a laminate fusion draw apparatus may be used to form a laminated glass article, where the apparatus includes an upper isopipe which is positioned over a lower isopipe. The upper isopipe includes a trough into which a molten cladding material composition is fed from a melter. Similarly, the lower isopipe includes a trough into which a molten glass-based core composition is fed from a glass melter.
The parabolic stress profile may be formed in the glass by exposing the glass to an ion exchange medium. In embodiments, the ion exchange medium may be molten salt bath, such as a bath containing a molten nitrate salt. In embodiments, the ion exchange medium may be a molten salt bath including KNO3, NaNO3, or combinations thereof. In embodiments, other sodium and potassium salts may be used in the ion exchange medium, such as, for example sodium or potassium nitrites, phosphates, or sulfates. In embodiments, the ion exchange medium may include lithium salts, such as LiNO3. The ion exchange medium may additionally include additives commonly included when ion exchanging glass, such as silicic acid. The ion exchange process is applied to a glass-based substrate to form a glass-based article of the type described herein.
The ion exchange process may include a second ion exchange treatment. In embodiments, the second ion exchange treatment may include ion exchanging the glass-based article in a second molten salt bath. The second ion exchange treatment may utilize any of the ion exchange mediums described herein. In embodiments, the second ion exchange treatment utilizes a second molten salt bath that includes KNO3.
After an ion exchange process is performed, it should be understood that a composition at the surface of an ion exchanged glass-based article is be different than the composition of the as-formed glass substrate (i.e., the glass substrate before it undergoes an ion exchange process). This results from one type of alkali metal ion in the as-formed glass substrate, such as, for example Li+ or Na+, being replaced with larger alkali metal ions, such as, for example Na+ or K+, respectively. However, the glass composition at or near the center of the depth of the glass-based article will, in embodiments, still have the composition and microstructure of the as-formed non-ion exchanged glass substrate utilized to form the glass-based article. As utilized herein, the center of the glass-based article refers to any location in the glass-based article that is a distance of at least 0.5t from every surface thereof, where t is the thickness of the glass-based article.
Embodiments will be further clarified by the following examples. It should be understood that these examples are not limiting to the embodiments described above.
Crack velocity as a function of applied stress intensity factor was measured for a variety of glasses, including a soda lime glass (SLG) and various alkali aluminosilicate glasses.
Based on the measurements in
Stress profiles of the type described herein were modeled and compared to a 0.4 mm thick article with a parabolic stress profile and a surface compressive stress of 500 MPa. A first exemplary stress profile for a 0.4 mm thick article had a surface compressive stress of 500 MPa, with 440 MPa attributable to a parabolic profile and 60 MPa attributable to a step-type stress profile produced by the laminate. A second exemplary stress profile for a 0.4 mm thick article had a surface compressive stress of 500 MPa, with 400 MPa attributable to a parabolic profile and 100 MPa attributable to a step-type stress profile produced by the laminate. The exemplary stress profiles were modeled on a three-layer laminate where the first and second clad layers had a thickness of 100 μm. As shown in
Based on the above modeled results and an exponential relationship between crack velocity as a function of crack stress intensity factor, the fatigue life as a function of flaw length has been predicted. As shown in
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 modification and variations come within the scope of the appended claims and their equivalents.
This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 63/284,297 filed on Nov. 30, 2021 the content of which is relied upon and incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63284297 | Nov 2021 | US |
