Patent Publication Number: US-RE49530-E

Title: Crack and scratch resistant glass and enclosures made therefrom

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     More than one reissue application has been filed for the reissue of U.S. Pat. No. 9,290,407. The reissue applications are the present application and U.S. patent application Ser. No. 15/862,353. This application is a continuation reissue application of U.S. patent application Ser. No. 15/862,353, filed Apr. 1, 2018, which is an application for reissue of U.S. Pat. No. 9,290,407, issued Mar. 22, 2016, filed as U.S. patent application Ser. No. 14/082,847 on Nov. 18, 2013, which is a continuation application of U.S. patent application Ser. No. 12/858,490, filed Aug. 18, 2010, now U.S. Pat. No. 8,586,492, which claims the benefit of U.S. Provisional Application No. 61/235,767, filed Aug. 21, 2009, each of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     The disclosure is related to glass enclosures, including windows, cover plates, and substrates for electronic devices. More particularly, the disclosure relates to crack- and scratch-resistant enclosures. 
     Glass is being designed into electronic devices, such as telephones, and entertainment devices, such as games, music players and the like, and information terminal (IT) devices, such as laptop computers. A predominant cause of breakage of cover glass in mobile devices is point contact or sharp impact. The solution for this problem has been to provide a bezel or similar protective structure to hold and protect the glass from such impacts. In particular, the bezel provides protection from impact on the edge of the glass. The edge of the cover glass is most vulnerable to fragmentation by direct impact. Incorporation of the bezel limits the use of glass to flat pieces in the device and prevents utilization of designs that exploit the crystal-like appearance of glass. 
     SUMMARY 
     A glass and a glass enclosure, including windows, cover plates, and substrates for mobile electronic devices comprising the glass are provided. The glass has a crack initiation threshold that is sufficient to withstand direct impact, a retained strength following abrasion that is greater than soda lime and alkali aluminosilicate glasses, and is more resistant to damage when scratched. The enclosure includes cover plates, windows, screens, touch panels, casings, and the like for electronic devices and information terminal devices. The glass can also be used in other applications, such as a vehicle windshield, where light weight, high strength, and durable glass is be desired. 
     Accordingly, one aspect of the disclosure is to provide an aluminoborosilicate glass comprising at least 50 mol % SiO 2  in some embodiments, at least 58 mol % SiO 2 , in other embodiments, and at least 60 mol % SiO 2  in still other embodiments, and at least one modifier selected from the group consisting of alkali metal oxides and alkaline earth metal oxides. The aluminoborosilicate glass is ion exchangeable, and exhibits the ratio 
     
       
         
           
             
               
                 
                   
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             1. 
           
         
       
     
     A second aspect of the disclosure is to provide an aluminoborosilicate glass. The aluminoborosilicate glass comprises: 50-72 mol % SiO 2 ; 9-17 mol % Al 2 O 3 ; 2-12 mol % B 2 O 3 ; 8-16 mol % Na 2 O; and 0-4 mol % K 2 O, wherein the ratio 
                       Al   2     ⁢       O   3     (     mol   ⁢         %     )       +       B   2     ⁢       O   3     (     mol   ⁢         %     )           Σ   ⁢   m   ⁢   o   ⁢   d   ⁢   i   ⁢   fiers   ⁢           (     mol   ⁢         %     )         &gt;   1     ,         
where the modifiers are selected from the group consisting of alkali metal oxides and alkaline earth metal oxides. The aluminoborosilicate glass is ion exchangeable.
 
     A third aspect of the disclosure is to provide a glass enclosure for use in an electronic device. The glass enclosure comprises a strengthened glass that, when scratched with a Knoop diamond at a load of at least 5 N to form a scratch of width w, is free of chips having a size greater than three times the width w. 
     These and other aspects, advantages, and salient features will become apparent from the following detailed description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 a  is an schematic representation of a prior art glass cover plate held in place by a bezel; 
         FIG.  1 b  is a schematic representation of glass cover plate that is proud of the bezel; 
         FIG.  2 a  is a microscopic image of an ion exchanged alkali aluminosilicate glass of the prior art having a scratch formed with a Knoop diamond at a load of 10 N; 
         FIG.  2 b  is a microscopic image of a strengthened aluminoborosilicate glass having a scratch formed with a Knoop diamond at a load of 10 N; 
         FIG.  3 a  is a top view of a 1 kilogram force (kgf) Vickers indentation  305  in a soda lime silicate glass of the prior art that had not been ion exchanged; 
         FIG.  3 b  is a side or cross-sectional view of a 1 kgf Vickers indentation in a soda lime silicate glass of the prior art that had not been ion exchanged; 
         FIG.  4    is a side or cross-sectional view of a 1 kgf Vickers indentation of an ion-exchanged soda lime silicate glass of the prior art; 
         FIG.  5 a  is a top view of a 1 kgf Vickers indentation in an aluminoborosilicate glass that had not been ion exchanged; 
         FIG.  5 b  is a side or cross-sectional view of a 1 kgf Vickers indentation in an aluminoborosilicate glass that had not been ion exchanged; 
         FIG.  6    is top view of a 30 kgf Vickers indentation of a ion exchanged aluminoborosilicate glass; and 
         FIG.  7    is a plot of crack initiation thresholds measured of aluminoborosilicate glasses as a function of Al 2 O 3 +B 2 O 3 —Na 2 O. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that, unless otherwise specified, terms such as “top,” “bottom,” “outward,” “inward,” and the like are words of convenience and are not to be construed as limiting terms. In addition, whenever a group is described as comprising at least one of a group of elements and combinations thereof, it is understood that the group may comprise, consist essentially of, or consist of any number of those elements recited, either individually or in combination with each other. Similarly, whenever a group is described as consisting of at least one of a group of elements or combinations thereof, it is understood that the group may consist of any number of those elements recited, either individually or in combination with each other. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range as well as any sub-ranges therebetween. Unless otherwise specified, all compositions and relationships that include constituents of compositions described herein are expressed in mole percent (mol %). 
     Referring to the drawings in general, it will be understood that the illustrations are for the purpose of describing particular embodiments and are not intended to limit the disclosure or appended claims thereto. The drawings are not necessarily to scale, and certain features and views of the drawings may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
     As used herein, the terms “enclosure,” “cover plate,” and “window” are used interchangeably and refer to glass articles, including windows, cover plates, screens, panels, and substrates, that form the outer portion of a display screen, window, or structure for mobile electronic devices. 
     Glass is being designed into mobile electronic devices, such as telephones, and entertainment devices, including games, music players and the like; information terminal (IT) devices, such as laptop computers; and analogous stationary versions of such devices. 
     In some instances, such designs are limited to a flat piece of glass that is protected by a bezel; i.e., a rim that is used to hold and protect a glass window or cover plate in a given device. An example of a glass cover plate or window that is held in place by a bezel is schematically shown in  FIG.  1 a . Cover plate  110  rests in rim  122  of bezel  120 , which holds cover plate  110  in place on body  105  of device  100  and protects the edge  112  of cover plate  110  from sharp impacts. 
     In order to exploit the crystal-like appearance of glass windows, cover plates, and the like in such devices, designs are being extended to make the glass “proud” of the bezel. The term “proud of the bezel” means that the glass extends to the edge of the device and protrudes above and beyond any bezel or rim of the device.  FIG.  1 b  schematically shows an example of a glass cover plate  110  that is proud of the bezel  120  and is affixed to body  105  of device  100 . Glass cover plate  110  is mounted on the surface of bezel  120  such that edges  112  of glass cover plate  110  are exposed and otherwise not covered by bezel  120 . Edges  112  of cover plate  110  extend to the edges of  107  of body  105 . 
     The primary limitation to implementing a cover plate or window that is proud of the bezel in such designs is the inability of glass cover plate  110 —particularly edges  112 —to withstand direct impact, thus necessitating protection of edge  112  of glass cover plate  110  by bezel  120  ( FIG.  1 a ). Furthermore, a glass cover plate  110  that is proud of the bezel  120  ( FIG.  1 b ) will have a greater chance of being scratched during handling and use due to exposure of edge  112  of glass cover plate  110 . In order to implement the aforementioned new designs, a glass cover plate must therefore be better able to withstand direct impacts than those glasses that are presently used in such applications. Moreover, a glass must also be resistant to scratching and should have a high retained strength after being scratched or abraded. 
     The predominant cause of glass breakage in applications such as windshields or cover glass in electronic devices is point contact or sharp impact. To serve as a cover glass or other enclosure in such applications, the crack initiation load of the glass has to be sufficiently high so that it can withstand direct impact. The depth of the surface layers of the glass that are under compressive stress has to be sufficient to provide a high retained strength and increased resistance to damage incurred upon being scratched or abraded. 
     Accordingly, a glass or glass article that is more resistant to sharp impact and is be able to withstand direct or point impacts is provided. Such glass articles include a windshield or glass enclosure such as, but not limited to, a cover plate, window, casing, screen, touch panel, or the like, for electronic devices. The glass enclosure comprises a strengthened glass which does not exhibit lateral damage such as, but not limited to, chipping when scratched at a rate of 0.4 mm/s with a Knoop diamond that is oriented so that the angle between the leading and trailing edges of the tip of the Knoop diamond is 172°30′ at a load of 5 N and, in some embodiments, at a load of 10 N. As used herein, “chipping” refers to the removal or ejection of glass fragments from a surface of a glass when the surface is scratched with an object such as a stylus. As used herein, “chip” can refer to either a glass fragment removed during scratching of the glass surface or the region on the surface from which the chip is removed. In the latter sense, a chip is typically characterized as a depression in the vicinity of the scratch. When scratched, the glass article described herein does not exhibit chipping (i.e., chips are not generated, or the glass is free of chips) beyond a region extending laterally on either side of the scratch track (i.e., the scratch formed by the Knoop diamond) formed for a distance d that is greater than twice the width w of the scratch and, in another embodiment, three times the width w of the scratch. In other words, chipping generated by scratching is limited to a region bordering either side of the scratch track, wherein the width of the region is no greater than twice (in some embodiment, no greater than three times) the width w of the scratch. In one embodiment, the glass enclosure is proud of a bezel, extending above and protruding beyond the bezel, in those instances where a bezel is present. In one embodiment, the glass enclosure has a thickness in a range from about 0.1 mm up to about 2.0 mm. In another embodiment, the glass enclosure has a thickness in a range from about 0.1 mm up to about 2.3 mm and, in other embodiments, the glass enclosure has a thickness of up to about 5.0 mm. 
     The scratch resistance or response of a glass enclosure to scratching is illustrated in  FIG.  2 a . The glass shown in  FIG.  2 a  is an alkali aluminosilicate glass having the composition 66 mol % SiO 2 , 10.3 mol % Al 2 O 3 , 0.6 mol % B 2 O 3 , 14 mol % Na 2 O, 2.45 mol % K 2 O, and 0.21 mol % SnO 2 , wherein the ratio (Al 2 O 3 +B 2 O 3 )/Σ(modifiers), expressed in mol %, is 0.66. The glass was strengthened by ion exchange by immersion in a molten KNO 3  salt bath at 410° C. for 8 hrs.  FIG.  2 a  is a microscopic image of the glass having a scratch  210  of width w formed at a rate of 0.4 mm/s with a Knoop diamond at a load of 10 N. Numerous chips  220  are formed along scratch  210 , with some chips extending from scratch  210  for a distance d exceeding twice the width w (2w) of scratch  210 . In contrast to the behavior of the glass shown in  FIG.  2 a , the response of the glass enclosure and glasses described herein to scratching is illustrated in  FIG.  2 b .  FIG.  2 b  is a microscopic image of an aluminoborosilicate glass (64 mol % SiO 2 , 14.5 mol % Al 2 O 3 , 8 mol % B 2 O 3 , 11.5 mol % Na 2 O, 0.1 mol % SnO 2 ; wherein the ratio (Al 2 O 3 +B 2 O 3 )/Σ(modifiers), wherein Al 2 O 3 , B 2 O 3 , and Na 2 O modifier concentrations are expressed in mol %, is 1.96) that is representative of those aluminoborosilicate glasses described herein. The glass shown in  FIG.  2 b  was ion exchanged by immersion in a molten KNO 3  salt bath at 410° C. for 8 hrs. The glass shown in  FIG.  2 b  has a scratch  210  of width w formed with a Knoop diamond at a load of 10 N. The chips  220  formed in the aluminoborosilicate glass shown in  FIG.  2 b  are significantly smaller than those seen in  FIG.  2 a . In  FIG.  2 b , chip formation is limited to a zone extending from an edge  212  of scratch  210  to a distance d. The width d of the zone or region in which such chipping occurs is significantly less than 2w. In other words, most of the chips  220  seen in  FIG.  2 b  extend for a distance d, which is less than about width w from crack  210 . The glass retains at least 30% of its original load at failure and, in some embodiments, at least 50% of its original load at failure as a determined by ring on ring measurements after scratching with a 3 N Vickers load at a rate of 0.4 mm/s. 
     The glass enclosures described herein comprise a strengthened glass that deforms upon indentation under an indentation load of at least 500 gf primarily by densification rather than by shear faulting. The glass is free of subsurface faulting and radial and median cracks upon deformation and is consequently more resistant to damage than typical ion-exchangeable glasses. In addition, the glass is more resistant to crack initiation by shear faulting when strengthened by ion exchange. In one embodiment, the glass enclosure comprises an ion exchanged glass and has a Vickers median/radial crack initiation threshold of at least 10 kilogram force (kgf). In a second embodiment, the glass enclosure has a Vickers median/radial crack initiation threshold of at least about 20 kgf and, in a third embodiment, the glass enclosure has a Vickers median/radial crack initiation threshold of at least about 30 kgf. Unless otherwise specified, the Vickers median/radial crack threshold is determined by measuring the onset of median or radial cracks in 50% relative humidity at room temperature. 
     In another embodiment, the glass enclosures described herein are non-frangible. As used herein, the term “non-frangible” means that the glass enclosures and the glass comprising the glass enclosures do not exhibit forceful fragmentation upon fracture. Such forceful fragmentation is typically characterized by multiple crack branching with ejection or “tossing” of small glass pieces and/or particles from the glass enclosure in the absence of any external restraints, such as coatings, adhesive layers, or the like. More specifically frangible behavior is characterized by at least one of: breaking of the strengthened glass article (e.g., a plate or sheet) into multiple small pieces (e.g., ≤1 mm); the number of fragments formed per unit area of the glass article; multiple crack branching from an initial crack in the glass article; and violent ejection of at least one fragment a specified distance (e.g., about 5 cm, or about 2 inches) from its original location; and combinations of any of the foregoing breaking (size and density), cracking, and ejecting behaviors. The glass enclosure and the glass comprising the enclosure are deemed to be substantially non-frangible if they do not exhibit any of the foregoing criteria. 
     The strengthened glass comprising the glass enclosure can be strengthened by either thermal or chemical processes known in the art. The glass, in one embodiment, can be thermally tempered by heating the glass at a temperature that is between the strain point and the softening point of the glass, followed by cooling to room temperature. In another embodiment, the glass is chemically strengthened by ion exchange in which smaller metal ions in the glass are replaced or “exchanged” by larger metal ions of the same valence within a layer of the glass that extends from the outer surface of the glass to a depth below the surface (commonly referred to as the “depth of layer” or “DOL”). The replacement of smaller ions with larger ions creates a compressive stress within the layer. In one embodiment, the metal ions are monovalent alkali metal ions (e.g., Na + , K + , Rb+, and the like), and ion exchange is accomplished by immersing the glass in a bath comprising at least one molten salt (e.g., KNO 3 , K 2 SO 4 , KCl, or the like) of the larger metal ion that is to replace the smaller metal ion or ions (e.g., Na +  ions) in the glass. Alternatively, other monovalent cations such as Ag + , Tl + , Cu + , and the like can be exchanged for the alkali metal cations in the glass. The ion exchange process or processes that are used to strengthen the glass can include, but are not limited to, immersion in a single bath or multiple baths of like or different compositions with washing and/or annealing steps between immersions. 
     The depth of the compressive stress layer (depth of layer) present in ion-exchanged glasses prevents the propagation of flaws at or near the surface of the glass. Glasses such as soda lime silicate and alkali aluminosilicate glasses deform with a high shear band density. Such behavior is known to lead to crack nucleation and propagation in the non-ion exchanged versions of such glasses. An example of shear fault formation and crack initiation is shown in  FIGS.  3 a and  3 b .  FIGS.  3 a and  3 b  are top and side (i.e., cross-sectional) views, respectively, of a 1 kilogram force (kgf) Vickers indentation  305  in a soda lime silicate glass that has not been ion exchanged. Radial cracks  310  extend from the Vickers indentation  305  ( FIG.  3 a ) and shear deformation zone A. Lateral cracks  317 , median cracks  319 , and subsurface shear faults  315  are seen in the side view of the glass ( FIG.  3 b ). Shear faults  315  serve as initiation sites for lateral and median cracks  317 ,  319 . 
     The compressive stress created in the surface layers of ion exchanged glasses prevents or mitigates the propagation of nucleated cracks, but does not totally eliminate shear deformation.  FIG.  4    is a cross-sectional view of a 1 kgf Vickers indentation of an ion-exchanged soda lime silicate glass having a compressive stress of 400 MPa and a depth of layer of 13 μm. Although mitigated, deformation still occurs by the shearing mechanism and leads to crack initiation, as seen in the shear deformation zone A. The compressive layer prevents radial cracks  310  from extending far away from their nucleation sites in the shear deformation zone A. Under flexural loading, subsurface cracks  415  overcome the compressive stress created by ion exchange and propagate into the central tensile region of the glass, thereby causing failure. 
     To improve the mechanical properties of glass enclosures beyond those of currently available ion-exchanged glasses, a glass having higher damage resistance is needed. Accordingly, the glass enclosure described herein comprises an ion-exchanged glass that does not exhibit deformation by subsurface shear faulting, but instead exhibits indentation deformation by densification when submitted to an indentation load of at least 500 gf, which makes flaw/crack initiation more difficult. An example of deformation by densification is shown in  FIGS.  5 a and  5 b , which are top and side views, respectively, of a 1 kilogram force (kgf) Vickers indentation in an alkaline earth aluminoborosilicate (EAGLE XG™, manufactured by Corning, Inc.) glass that has not been strengthened by ion exchange. The top view ( FIG.  5 a ) shows no radial cracks extending from the Vickers indentation  505 . As seen in the cross-sectional view ( FIG.  5 b ), the glass deforms primarily by densification (region “B” in  FIG.  5 b ) with no shear faulting. A top view of a 30 kgf Vickers indentation of an aluminoborosilicate glass having the composition: 64 mol % SiO 2 , 14.5 mol % Al 2 O 3 , 8 mol % B 2 O 3 , 11.5 mol % Na 2 O, and 0.1 mol % SnO 2 ; wherein the ratio (Al 2 O 3 +B 2 O 3 )/Σ(modifiers), with Al 2 O 3 , B 2 O 3 , and Na 2 O modifier concentrations expressed in mol %, is 1.96, and strengthened by ion exchange by immersion in a molten KNO 3  salt bath at 410° C. for 8 hours is shown in  FIG.  6   . At maximum load, the indenter tip has a depth of about 48 μm. No radial cracks extend from Vickers indentation  605 . 
     The densification mechanism described hereinabove can be attributed to the absence or lack of non-bridging oxygens (NBOs) in the glass structure, high molar volume (at least 27 cm 3 /mol), and low Young&#39;s modulus (less than about 69 GPa) of the glass. In the aluminoborosilicate glasses described herein, a structure having substantially no non-bridging oxygens (NBO-free) is achieved through compositions in which the relationship 
                             Al   2     ⁢       O   3     (     mol   ⁢         %     )       +       B   2     ⁢       O   3     (     mol   ⁢         %     )           Σmodifiers   ⁢           (     mol   ⁢         %     )         &gt;   1     ,           (   1   )               
where Al 2 O 3  and B 2 O 3  are intermediate glass formers and alkali metal (e.g., Li 2 O, Na 2 O, K 2 O, Rb 2 O, Cs 2 O) and alkaline earth metal oxides (e.g., MgO, CaO, SrO, BaO) are modifiers, is satisfied. Such modifiers are intentionally or actively included in the glass composition, and do not represent impurities that are inadvertently present in the batched material used to form the glass. To obtain sufficient depth of layer and compressive stress by ion exchange, it is preferable that 0.9&lt;R 2 O/Al 2 O 3 &lt;1.3, wherein Al 2 O 3  and R 2 O modifier concentrations are expressed in mol %. Given a particular compressive stress and compressive depth of layer, any ion-exchangeable silicate glass composition that obeys equation (1) and contains alkali metals (e.g., Li + , Na + , K + ) should have a high resistance to both crack initiation and crack propagation following ion exchange. Prior to ion exchange, such aluminoborosilicate glasses have a Vickers median/radial crack initiation threshold of at least 500 gf and, in one embodiment, the glasses have Vickers median/radial crack initiation threshold of at least 1000 gf.
 
     In some embodiments, the glass enclosure comprises, consists essentially of, or consists of a strengthened glass that, when ion exchanged, is resistant to damage, such as crack initiation and propagation. The glass comprises at least 50 mol % SiO 2  in some embodiments, at least 58 mol % SiO 2  in some embodiments, at least 60 mol % SiO 2  in other embodiments, and includes at least one alkali metal modifier, wherein the ratio (Al 2 O 3 +B 2 O 3 )/Σ(modifiers)&gt;1, wherein Al 2 O 3 , B 2 O 3 , and modifier concentrations are expressed in mol %, and wherein the modifiers are selected from the group consisting of alkali metal oxides and alkaline earth metal oxides. In some embodiments, (Al 2 O 3 +B 2 O 3 )/Σ(modifiers)≥1.45. As the value of this ratio increases, the damage resistance of the glass increases. In addition, an increase in the ratio or a substitution of B 2 O 3  for Al 2 O 3  results in a decrease in Young&#39;s modulus. In one embodiment, the Young&#39;s modulus of the aluminoborosilicate glass is less than about 69 GPa. In one embodiment, the Young&#39;s modulus of the aluminoborosilicate glass is less than about 65 GPa. In another embodiment, the Young&#39;s modulus of the aluminoborosilicate glass is in a range from about 57 GPa up to about 69 GPa. In another embodiment, the strengthened glass of the glass enclosure has a compressive stress of at least about 400 MPa and a depth of layer of at least about 15 μm, in another embodiment, at least about 25 μm, and, in yet another embodiment, at least about 30 μm. 
     In one embodiment, the glass enclosure comprises, consists essentially of, or consists of an ion exchangeable aluminoborosilicate glass that has been strengthened, for example, by ion exchange. As used herein, “ion exchangeable” means that a glass is capable of exchanging cations located at or near the surface of the glass with cations of the same valence that are either larger or smaller in size. In a particular embodiment, the aluminoborosilicate glass comprises, consists essentially of, or consists of: 50-72 mol % SiO 2 ; 9-17 mol % Al 2 O 3 ; 2-12 mol % B 2 O 3 ; 8-16 mol % Na 2 O; and 0-4 mol % K 2 O, wherein (Al 2 O 3 +B 2 O 3 )/Σ(modifiers)&gt;1, and has a molar volume of at least 27 cm 3 /mol. In another embodiment, the aluminoborosilicate glass comprises, consists essentially of, or consists of: 60-72 mol % SiO 2 ; 9-16 mol % Al 2 O 3 ; 5-12 mol % B 2 O 3 ; 8-16 mol % Na 2 O; and 0-4 mol % K 2 O, wherein the ratio of concentrations of Al 2 O 3  and B 2 O 3  to the total concentrations of modifiers, (Al 2 O 3 +B 2 O 3 )/Σ(modifiers), is greater than 1, and has a molar volume of at least 27 cm 3 /mol. In the above embodiments, the modifiers are selected from alkali metal oxides (e.g., Li 2 O, Na 2 O, K 2 O, Rb 2 O, Cs 2 O) and alkaline earth metal oxides (e.g., MgO, CaO, SrO, BaO). In some embodiments, the glass further includes 0-5 mol % of at least one of P 2 O 5 , MgO, CaO, SrO, BaO, ZnO, and ZrO 2 . In other embodiments, the glass is batched with 0-2 mol % of at least one fining agent selected from a group that includes Na 2 SO 4 , NaCl, NaF, NaBr, K 2 SO 4 , KCl, KF, KBr, and SnO 2 . The aluminoborosilicate glass is, in some embodiments, substantially free of lithium, whereas in other embodiments, the aluminoborosilicate glass is substantially free of at least one of arsenic, antimony, and barium. In other embodiments, the aluminoborosilicate glass is down-drawable by processes known in the art, such as slot-drawing, fusion drawing, re-drawing, and the like, and has a liquidus viscosity of at least 130 kilopoise. 
     Various non-limiting compositions of the aluminoborosilicate glasses described herein are listed in Table 1. Table 1 also includes properties measured for these glass compositions. Crack initiation thresholds were measured by making multiple indentations (indents) in the glass using a Vickers diamond indenter loaded onto the surface. The load was increased until formation of median or radial cracks extending out from the corners of the indent impression was observed at the surface of the glass in greater than 50% of indents. Crack initiation thresholds for the samples listed in Table 1 are plotted in  FIG.  7    as a function of Al 2 O 3 +B 2 O 3 —Na 2 O in the glass samples. 
     Samples a, b, c, and d in Table 1 have compositions that are nominally free of non-bridging oxygens; i.e., Al 2 O 3 +B 2 O 3 ═Na 2 O, or Al 2 O 3 +B 2 O 3 —Na 2 O=0 (i.e. (Al 2 O 3 +B 2 O 3 )/Σ(modifiers)=1). Regardless of whether B 2 O 3  or Al 2 O 3  is used to consume the NBOs created by the presence of the Na 2 O modifier in these sample compositions, all of the above samples exhibited low (i.e., 100-300 gf) crack initiation thresholds. 
     In samples e and f, however, an excess of B 2 O 3  is created by increasing the Al 2 O 3  content while decreasing the concentration of alkali metal oxide modifiers. For samples e and f, (Al 2 O 3 +B 2 O 3 )/Σ(modifiers)&gt;1. In these samples, the crack initiation threshold increases dramatically, as shown in  FIG.  7   . Specifically, sample e exhibited a crack initiation threshold of 700 gf prior to strengthening by ion exchange, whereas sample f exhibited a crack initiated threshold of 1000 gf prior to strengthening. 
     Non-limiting examples of the aluminoborosilicate glasses described herein are listed Table 2, which lists various compositions and properties of glasses. Several compositions ( 34 ,  35 ,  36 ,  37 ,  38 , and  39 ), when ion exchanged, have crack initiation thresholds that are less than 10 kgf. These compositions are therefore outside the scope of the disclosure and appended claims and thus serve as comparative examples. Among the properties listed in Table 2 is the coefficient of thermal expansion (CTE), given in units of 1×10 −7 /° C. CTE is one consideration that is taken into account when designing devices that develop minimal thermal stresses upon temperature changes. Glasses having lower CTEs are desirable for down-draw processes (e.g., fusion-draw and slot-draw) to minimize sheet distortion during the drawing process. The liquidus temperature and corresponding liquidus viscosity (expressed in kP (kilopoise) or MP (megapoise)) indicate the suitability of glass compositions for hot forming the glass into sheets or other shapes. For down-draw processes, it is desirable that the aluminoborosilicate glasses glass described herein have a liquidus viscosity of at least 130 kP. The 200P temperature is the temperature at which the glass has a viscosity of 200 Poise, and is the process temperature typically used in manufacturing to remove gaseous inclusions (fining) and melt any remaining batch materials. The columns labeled 8 and 15 hr DOL and CS in Table 2 are the depth of the compressive layer and the surface compressive stress resulting from ion exchange in 100% KNO 3  at 410° C. in 8 and 15 hours, respectively. 
     To maintain desirable ion exchange properties for the glasses described herein, the total alkali metal oxide modifier concentration should equal that of Al 2 O 3  and any excess (Al 2 O 3 +B 2 O 3 ) that is needed should be made up with B 2 O 3  alone to increase the crack initiation load. For optimum ion exchange, the aluminoborosilicate glass should the total concentration of alkali metal oxide modifiers should equal that of alumina—i.e., (Li 2 O+Na 2 O+K 2 O+Rb 2 O+Cs 2 O)═Al 2 O 3 — to achieve the greatest compressive stress and depth of layer, with excess B 2 O 3  to improve damage resistance of the glass. However, excess B 2 O 3  content should be balanced against the rate of ion exchange. For deep (e.g., &gt;20 μm) ion exchange, the B 2 O 3  concentration should, in some embodiments, be less than that of Al 2 O 3 . To achieve the lowest level of melting defects such as undissolved batch or gaseous inclusions, it is best to that R 2 O/Al 2 O 3 &gt;1.0 and, preferably, between 1.05≥R 2 O/Al 2 O 3 ≥1.2. Since this condition would create NBOs, given by R 2 O—Al 2 O 3 , enough B 2 O 3  should, in some embodiments, be added to consume the excess modifiers (i.e., B 2 O 3 &gt;R 2 O—Al 2 O 3 ) to maintain damage resistance. More preferably, B 2 O 3 &gt;2(R 2 O—Al 2 O 3 ). 
     Divalent cations can be added to lower the 200 P temperature (i.e., the typical melting viscosity) of the aluminoborosilicate glass and eliminate defects such as undissolved and/or unmelted batch materials. Smaller divalent cations, such as Mg 2+ , Zn 2+ , or the like are preferable, as they have beneficial impact on the compressive stress developed during ion exchange of the glass. Larger divalent cations such as Ca 2+ , Sr 2+ , and Ba 2+  decrease the ion exchange rate and the compressive stress achieved by ion exchange. Likewise, the presence of smaller monovalent cations such as Li +  in the glass can have a positive effect on the crack initiation threshold, whereas larger ions such as K +  are not as desirable. In addition, whereas small amounts of K 2 O can increase the depth of layer of the compressive stress region, high concentrations of larger monovalent ions such as K +  decrease compressive stress and should therefore be limited to less than 4%. 
     The aluminoborosilicate glass described herein comprises at least 50 mol %, 58 mol % SiO 2  in some embodiments, and in other embodiments, at least 60 mol % SiO 2 . The SiO 2  concentration plays a role in controlling the stability and viscosity of the glass. High SiO 2  concentrations raise the viscosity of the glass, making melting of the glass difficult. The high viscosity of high SiO 2 -containing glasses frustrates mixing, dissolution of batch materials, and bubble rise during fining. High SiO 2  concentrations also require very high temperatures to maintain adequate flow and glass quality. Accordingly, the SiO 2  concentration in the glass should not exceed 72 mol %. 
     As the SiO 2  concentration in the glass decreases below 60 mol %, the liquidus temperature increases. The liquidus temperature of SiO 2 —Al 2 O 3 —Na 2 O compositions rapidly increases to temperatures exceeding 1500° C. at SiO 2  contents of less than 50 mol %. As the liquidus temperature increases, the liquidus viscosity (the viscosity of the molten glass at the liquidus temperature) of the glass decreases. While the presence of B 2 O 3  suppresses the liquidus temperature, the SiO 2  content should be maintained at greater than 50 mol % to prevent the glass from having excessively high liquidus temperature and low liquidus viscosity. In order to keep the liquidus viscosity from becoming too low or too high, the SiO 2  concentration of the gasses described herein should therefore be within the range between 50 mol % and 72 mol %, between 58 mol % in some embodiments, and between 60 mol % and 72 mol % in other embodiments. 
     The SiO 2  concentration also provides the glass with chemical durability with respect to mineral acids, with the exception of hydrofluoric acid (HF). Accordingly, the SiO2 concentration in the glasses described herein should be greater than 50 mol % in order to provide sufficient durability. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Compositions and properties of alkali aluminoborosilicate glasses. 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Mol % 
                 a 
                 b 
                 c 
                 d 
                 e 
                 f 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 SiO 2   
                 64 
                 64 
                 64 
                 64 
                 64 
                 64 
               
               
                 Al 2 O 3   
                 0 
                 6 
                 9 
                 15 
                 12 
                 13.5 
               
               
                 B 2 O 3   
                 18 
                 12 
                 9 
                 3 
                 9 
                 9 
               
               
                 Na 2 O 
                 18 
                 18 
                 18 
                 18 
                 15 
                 13.5 
               
               
                 SnO 2   
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
               
               
                 Al 2 O 3  + B 2 O 3  − Na 2 O 
                 0 
                 0 
                 0 
                 0 
                 6 
                 9 
               
               
                 Strain Point (° C.) 
                 537 
                 527 
                 524 
                 570 
                 532 
                 548 
               
               
                 Anneal Point (° C.) 
                 575 
                 565 
                 564 
                 619 
                 577 
                 605 
               
               
                 Softening Point (° C.) 
                 711 
                 713 
                 730 
                 856 
                 770 
                 878 
               
               
                 Coefficient of Thermal Expansion (×10 −7 / 
                 81.7 
                 81.8 
                 84.8 
                 88.2 
                 78 
                 74.1 
               
               
                 ° C.) 
                   
                   
                   
                   
                   
                   
               
               
                 Density (g/cm 3)   
                 2.493 
                 2.461 
                 2.454 
                 2.437 
                 2.394 
                 2.353 
               
               
                 Crack Initiation Load (gf) 
                 100 
                 200 
                 200 
                 300 
                 700 
                 1100 
               
               
                 Vickers Hardness at 200 gf 
                   
                 511 
                 519 
                 513 
                 489 
                 475 
               
               
                 Indentation Toughness (MPa m{circumflex over ( )}0.5) 
                   
                 0.64 
                 0.66 
                 0.69 
                 0.73 
                 0.77 
               
               
                 Brittleness (μm{circumflex over ( )}0.5) 
                   
                 7.8 
                 7.6 
                 7.3 
                 6.6 
                 6 
               
               
                 IX at 410° C. for 8 hrs in 100% KNO 3   
                   
                   
                   
                   
                   
                   
               
               
                 DOL (μm) 
                 10.7 
                 15.7 
                 20.4 
                 34.3 
                 25.6 
                 35.1 
               
               
                 CS (MPa) 
                 874 
                 795 
                 773 
                 985 
                 847 
                 871 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Table 2. Compositions, expressed in mol %, and properties of alkali aluminoborosilicate glasses. 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 Composition (mol %) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Sample 
                 SiO 2   
                 Al 2 O 3   
                 B 2 O 3   
                 Li 2 O 
                 Na 2 O 
                 K 2 O 
                 MgO 
                 CaO 
                 P 2 O 5   
                 SnO 2   
                 ZnO 
                 ZrO 2   
               
               
                   
               
               
                 1 
                 64.0 
                 13.5 
                 8.9 
                   
                 13.4 
                 0.0 
                 0.0 
                 0.0 
                   
                 0.10 
                   
                 0.00 
               
               
                 2 
                 65.7 
                 12.3 
                 9.0 
                   
                 11.5 
                 1.3 
                 0.0 
                 0.0 
                   
                 0.10 
                   
                 0.00 
               
               
                 3 
                 65.7 
                 12.3 
                 9.0 
                   
                 9.5 
                 3.3 
                 0.0 
                 0.0 
                   
                 0.10 
                   
                 0.00 
               
               
                 4 
                 65.7 
                 12.3 
                 9.0 
                   
                 12.8 
                 0.0 
                 0.0 
                 0.0 
                   
                 0.10 
                   
                 0.00 
               
               
                 5 
                 64.0 
                 13.0 
                 8.9 
                   
                 13.9 
                 0.00 
                 0.02 
                 0.05 
                   
                 0.10 
                   
                 0.00 
               
               
                 6 
                 64.0 
                 13.5 
                 8.9 
                   
                 13.4 
                 0.00 
                 0.02 
                 0.04 
                   
                 0.10 
                   
                 0.00 
               
               
                 7 
                 64.0 
                 14.0 
                 8.9 
                   
                 12.9 
                 0.00 
                 0.02 
                 0.04 
                   
                 0.10 
                   
                 0.00 
               
               
                 8 
                 64.0 
                 14.5 
                 7.9 
                   
                 13.4 
                 0.00 
                 0.02 
                 0.04 
                   
                 0.10 
                   
                 0.00 
               
               
                 9 
                 64.0 
                 12.5 
                 9.9 
                   
                 13.4 
                 0.00 
                 0.02 
                 0.04 
                   
                 0.10 
                   
                 0.00 
               
               
                 10 
                 64.0 
                 13.5 
                 8.9 
                   
                 11.4 
                 2.01 
                 0.02 
                 0.04 
                   
                 0.10 
                   
                 0.00 
               
               
                 11 
                 64.0 
                 14.5 
                 7.0 
                   
                 14.4 
                 0.00 
                 0.00 
                 0.05 
                   
                 0.10 
                   
                 0.00 
               
               
                 12 
                 64.0 
                 13.5 
                 7.9 
                   
                 13.4 
                 0.00 
                 1.00 
                 0.05 
                   
                 0.10 
                   
                 0.00 
               
               
                 13 
                 63.3 
                 12.3 
                 9.8 
                   
                 12.3 
                 0.99 
                 0.00 
                 0.02 
                   
                 0.15 
                   
                 0.02 
               
               
                 14 
                 64.0 
                 13.5 
                 8.5 
                   
                 14.0 
                 0.00 
                   
                   
                   
                 0.10 
                   
                   
               
               
                 15 
                 64.0 
                 12.5 
                 10.0 
                   
                 13.0 
                 0.50 
                   
                   
                   
                 0.10 
                   
                   
               
               
                 16 
                 64.0 
                 13.5 
                 9.0 
                   
                 12.5 
                 1.00 
                   
                   
                   
                 0.10 
                   
                   
               
               
                 17 
                 64.0 
                 13.5 
                 9.0 
                   
                 13.5 
                 0.00 
                   
                   
                   
                 0.10 
                   
                   
               
               
                 18 
                 65.7 
                 11.8 
                 9.5 
                   
                 11.5 
                 1.3 
                 0.0 
                 0.0 
                   
                 0.05 
                   
                 0.00 
               
               
                 19 
                 64.0 
                 12.5 
                 10.9 
                   
                 12.4 
                 0.00 
                 0.00 
                 0.04 
                   
                 0.10 
                   
                 0.00 
               
               
                 20 
                 64.0 
                 13.5 
                 8.0 
                   
                 14.5 
                 0.00 
                   
                   
                   
                 0.10 
                   
                   
               
               
                 21 
                 64.0 
                 13.5 
                 8.9 
                   
                 13.4 
                 0.0 
                 0.0 
                 0.0 
                   
                 0.10 
                   
                 0.00 
               
               
                 22 
                 63.9 
                 13.0 
                 5.0 
                   
                 11.0 
                 3.0 
                 4.0 
                 0.0 
                   
                 0.10 
                   
                 0.00 
               
               
                 23 
                 65.7 
                 11.8 
                 10.0 
                   
                 11.0 
                 1.30 
                 0.02 
                 0.04 
                   
                 0.05 
                   
                 0.00 
               
               
                 24 
                 65.7 
                 11.3 
                 10.0 
                   
                 11.5 
                 1.3 
                 0.0 
                 0.0 
                   
                 0.05 
                   
                 0.00 
               
               
                 25 
                 65.7 
                 10.7 
                 10.6 
                   
                 11.5 
                 1.30 
                 0.02 
                 0.05 
                   
                 0.05 
                   
                 0.00 
               
               
                 26 
                 64.0 
                 13.5 
                 6.0 
                   
                 13.4 
                 0.00 
                 3.02 
                 0.06 
                   
                 0.10 
                   
                 0.00 
               
               
                 27 
                 64.0 
                 13.5 
                 7.0 
                   
                 15.5 
                 0.00 
                   
                   
                   
                 0.10 
                   
                   
               
               
                 28 
                 65.7 
                 12.3 
                 10.0 
                   
                 10.5 
                 1.30 
                 0.02 
                 0.04 
                   
                 0.05 
                   
                 0.00 
               
               
                 29 
                 64.0 
                 12.0 
                 11.9 
                   
                 11.9 
                 0.00 
                 0.00 
                 0.04 
                   
                 0.10 
                   
                 0.00 
               
               
                 30 
                 64.0 
                 14.0 
                 6.0 
                   
                 11.4 
                 2.50 
                 2.02 
                 0.05 
                   
                 0.10 
                   
                 0.00 
               
               
                 31 
                 64.0 
                 13.5 
                 7.0 
                   
                 13.4 
                 0.00 
                 2.01 
                 0.06 
                   
                 0.10 
                   
                 0.00 
               
               
                 32 
                 64.0 
                 12.0 
                 8.9 
                   
                 14.9 
                 0.0 
                 0.0 
                 0.0 
                   
                 0.10 
                   
                 0.00 
               
               
                 33 
                 62.0 
                 14.0 
                 6.0 
                   
                 12.9 
                 3.01 
                 2.01 
                 0.05 
                   
                 0.10 
                   
                 0.00 
               
               
                 34 
                 64.1 
                 13.2 
                 5.6 
                   
                 12.2 
                 2.83 
                 1.89 
                 0.05 
                   
                 0.09 
                   
                 0.00 
               
               
                 35 
                 64.0 
                 12.5 
                 6.0 
                   
                 12.9 
                 2.50 
                 2.02 
                 0.05 
                   
                 0.10 
                   
                 0.00 
               
               
                 36 
                 63.1 
                 13.6 
                 5.8 
                   
                 12.6 
                 2.92 
                 1.95 
                 0.05 
                   
                 0.10 
                   
                 0.00 
               
               
                 37 
                 64.0 
                 12.5 
                 5.5 
                   
                 14.9 
                 3.0 
                 0.0 
                 0.0 
                   
                 0.10 
                   
                 0.00 
               
               
                 38 
                 64.0 
                 13.0 
                 6.0 
                   
                 12.4 
                 2.50 
                 2.01 
                 0.05 
                   
                 0.10 
                   
                 0.00 
               
               
                 39 
                 65.7 
                 10.3 
                 11.0 
                   
                 11.5 
                 1.30 
                 0.02 
                 0.05 
                   
                 0.05 
                   
                 0.00 
               
               
                 40 
                 61.8 
                 12.9 
                 10.3 
                 0.0 
                 13.9 
                 1.03 
                 0.00 
                 0.0 
                 0.0 
                 0.12 
                 0.00 
                 0.0 
               
               
                 41 
                 62.6 
                 12.6 
                 10.1 
                 0.0 
                 13.6 
                 1.01 
                 0.00 
                 0.0 
                 0.0 
                 0.12 
                 0.00 
                 0.0 
               
               
                 42 
                 63.3 
                 12.4 
                 9.9 
                 0.0 
                 13.4 
                 0.99 
                 0.00 
                 0.0 
                 0.0 
                 0.12 
                 0.00 
                 0.0 
               
               
                 43 
                 64.0 
                 12.1 
                 9.7 
                 0.0 
                 13.1 
                 0.97 
                 0.00 
                 0.0 
                 0.0 
                 0.12 
                 0.00 
                 0.0 
               
               
                 44 
                 63.3 
                 11.4 
                 9.9 
                 0.0 
                 13.4 
                 0.99 
                 0.00 
                 0.0 
                 1.0 
                 0.12 
                 0.00 
                 0.0 
               
               
                 45 
                 63.3 
                 10.4 
                 9.9 
                 0.0 
                 13.4 
                 0.99 
                 0.00 
                 0.0 
                 2.0 
                 0.12 
                 0.00 
                 0.0 
               
               
                 46 
                 62.7 
                 12.2 
                 9.8 
                 0 
                 12.2 
                 0.98 
                 1.96 
                 0.00 
                 0 
                 0.12 
                 0.00 
                 0 
               
               
                 47 
                 61.5 
                 12.0 
                 9.6 
                 0 
                 12.0 
                 0.96 
                 3.84 
                 0.00 
                 0 
                 0.12 
                 0.00 
                 0 
               
               
                 48 
                 62.7 
                 12.2 
                 9.8 
                 0 
                 12.2 
                 0.98 
                 0.00 
                 0.00 
                 0 
                 0.12 
                 2.0 
                 0 
               
               
                 49 
                 61.5 
                 12.0 
                 9.6 
                 0 
                 12.0 
                 0.96 
                 0.00 
                 0.00 
                 0 
                 0.12 
                 3.8 
                 0 
               
               
                 50 
                 62.7 
                 12.2 
                 9.8 
                 0 
                 12.2 
                 0.98 
                 0.98 
                 0.00 
                 0 
                 0.12 
                 0.98 
                 0 
               
               
                 51 
                 63.9 
                 12.5 
                 10.0 
                 0 
                 12.5 
                 1.00 
                 0.00 
                 0.00 
                 0 
                 0.12 
                 0.00 
                 0 
               
               
                 52 
                 64.1 
                 16.9 
                 2.1 
                   
                 15.6 
                 1.01 
                 0.02 
                 0.12 
                   
                 0.10 
                   
                   
               
               
                 53 
                 64.0 
                 16.4 
                 2.1 
                   
                 16.3 
                 1.01 
                 0.02 
                 0.13 
                   
                 0.10 
                   
                   
               
               
                 54 
                 59.9 
                 16.5 
                 6.6 
                   
                 16.2 
                 0.5 
                 0.0 
                 0.1 
                   
                 0.1 
                   
                 0.0 
               
               
                 55 
                 50.5 
                 20.2 
                 9.8 
                   
                 19.4 
                   
                   
                   
                   
                 0.1 
                   
                   
               
               
                 56 
                 52.3 
                 19.4 
                 9.3 
                   
                 18.9 
                   
                   
                   
                   
                 0.1 
                   
                   
               
               
                 57 
                 55.2 
                 20.3 
                 9.7 
                   
                 14.6 
                   
                   
                   
                   
                 0.1 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 (R 2 O + 
                   
                 (Al 2 O 3  + 
                   
                 Molar 
               
               
                   
                   
                 RO)/(Al 2 O 3  + 
                   
                 B 2 O 3 )/(R 2 O + 
                 Density 
                 Volume 
               
               
                 Sample 
                 Total 
                 B 2 O 3 ) 
                 R 2 O/Al 2 O 3   
                 RO) 
                 g/cm 3   
                 cm 3 /mol 
               
               
                   
               
               
                 1 
                 100.0 
                 0.602 
                 0.997 
                 1.661 
                 2.353 
                 28.44 
               
               
                 2 
                 100.0 
                 0.606 
                 1.046 
                 1.651 
                 2.347 
                 28.47 
               
               
                 3 
                 100.0 
                 0.606 
                 1.046 
                 1.651 
                 2.345 
                 28.77 
               
               
                 4 
                 100.0 
                 0.605 
                 1.045 
                 1.652 
                 2.346 
                 28.31 
               
               
                 5 
                 100.0 
                 0.639 
                 1.074 
                 1.564 
                 2.363 
                 28.23 
               
               
                 6 
                 100.0 
                 0.602 
                 0.997 
                 1.661 
                 2.355 
                 28.41 
               
               
                 7 
                 100.0 
                 0.567 
                 0.926 
                 1.764 
                 2.335 
                 28.74 
               
               
                 8 
                 100.0 
                 0.602 
                 0.929 
                 1.661 
                 2.363 
                 28.45 
               
               
                 9 
                 100.0 
                 0.602 
                 1.076 
                 1.662 
                 2.354 
                 28.29 
               
               
                 10 
                 100.0 
                 0.602 
                 0.998 
                 1.660 
                 2.356 
                 28.67 
               
               
                 11 
                 100.0 
                 0.676 
                 0.997 
                 1.480 
                 2.376 
                 28.27 
               
               
                 12 
                 100.0 
                 0.676 
                 0.997 
                 1.479 
                 2.369 
                 28.12 
               
               
                 13 
                 99.00 
                 0.601 
                 1.077 
                 1.665 
                 2.346 
                 28.41 
               
               
                 14 
                 100.1 
                 0.636 
                 1.037 
                 1.571 
                   
                   
               
               
                 15 
                 100.1 
                 0.600 
                 1.080 
                 1.667 
                   
                   
               
               
                 16 
                 100.1 
                 0.600 
                 1.000 
                 1.667 
                   
                   
               
               
                 17 
                 100.1 
                 0.600 
                 1.000 
                 1.667 
                   
                   
               
               
                 18 
                 100.0 
                 0.606 
                 1.090 
                 1.652 
                 2.346 
                 28.4 
               
               
                 19 
                 100.0 
                 0.533 
                 0.996 
                 1.877 
                 2.353 
                 28.34 
               
               
                 20 
                 100.1 
                 0.674 
                 1.074 
                 1.483 
                   
                   
               
               
                 21 
                 100.0 
                 0.602 
                 0.997 
                 1.661 
                 2.354 
                 28.43 
               
               
                 22 
                 100.0 
                 1.002 
                 1.076 
                 0.998 
                 2.407 
                 27.62 
               
               
                 23 
                 100.0 
                 0.569 
                 1.048 
                 1.759 
                 2.336 
                 28.54 
               
               
                 24 
                 100.0 
                 0.606 
                 1.138 
                 1.651 
                 2.347 
                 28.32 
               
               
                 25 
                 100.0 
                 0.606 
                 1.203 
                 1.651 
                 2.349 
                 28.21 
               
               
                 26 
                 100.0 
                 0.850 
                 0.997 
                 1.176 
                 2.395 
                 27.56 
               
               
                 27 
                 100.1 
                 0.756 
                 1.148 
                 1.323 
                   
                   
               
               
                 28 
                 100.0 
                 0.533 
                 0.964 
                 1.875 
                 2.331 
                 28.68 
               
               
                 29 
                 100.0 
                 0.502 
                 0.997 
                 1.994 
                 2.326 
                 28.62 
               
               
                 30 
                 100.0 
                 0.804 
                 0.998 
                 1.244 
                 2.392 
                 28.11 
               
               
                 31 
                 100.0 
                 0.758 
                 0.996 
                 1.319 
                 2.385 
                 27.81 
               
               
                 32 
                 100.0 
                 0.717 
                 1.246 
                 1.395 
                 2.394 
                 27.7 
               
               
                 33 
                 100.0 
                 0.903 
                 1.141 
                 1.108 
                 2.418 
                 27.89 
               
               
                 34 
                 100.0 
                 0.903 
                 1.141 
                 1.108 
                 2.409 
                 27.82 
               
               
                 35 
                 100.0 
                 0.949 
                 1.237 
                 1.053 
                 2.414 
                 27.61 
               
               
                 36 
                 100.0 
                 0.903 
                 1.141 
                 1.108 
                 2.411 
                 27.88 
               
               
                 37 
                 100.0 
                 1.002 
                 1.438 
                 0.998 
                 2.444 
                 27.5 
               
               
                 38 
                 100.0 
                 0.897 
                 1.151 
                 1.115 
                 2.406 
                 27.78 
               
               
                 39 
                 100.0 
                 0.606 
                 1.249 
                 1.651 
                 2.431 
                 27.21 
               
               
                 40 
                 100.0 
                 0.644 
                 1.160 
                 1.552 
                 2.358 
                   
               
               
                 41 
                 100.0 
                 0.644 
                 1.160 
                 1.552 
                 2.355 
                 28.48 
               
               
                 42 
                 100.0 
                 0.644 
                 1.160 
                 1.552 
                 2.352 
                 28.46 
               
               
                 43 
                 100.0 
                 0.644 
                 1.160 
                 1.552 
                 2.350 
                 28.42 
               
               
                 44 
                 100.0 
                 0.644 
                 1.261 
                 1.552 
                 2.356 
                   
               
               
                 45 
                 100.0 
                 0.644 
                 1.381 
                 1.552 
                 2.358 
                   
               
               
                 46 
                 100.0 
                 0.689 
                 1.080 
                 1.452 
                 2.369 
                 28.03 
               
               
                 47 
                 100.0 
                 0.778 
                 1.080 
                 1.286 
                 2.386 
                 27.62 
               
               
                 48 
                 100.0 
                 0.600 
                 1.080 
                 1.667 
                 2.395 
                 28.06 
               
               
                 49 
                 100.0 
                 0.600 
                 1.080 
                 1.667 
                 2.432 
                 27.75 
               
               
                 50 
                 100.0 
                 0.644 
                 1.080 
                 1.552 
                 2.383 
                 28.04 
               
               
                 51 
                 100.0 
                 0.600 
                 1.080 
                 1.667 
                 2.354 
                 28.04 
               
               
                 52 
                 100.0 
                 0.877 
                 0.979 
                 1.141 
                 2.425 
                 28.07 
               
               
                 53 
                 100.0 
                 0.940 
                 1.052 
                 1.064 
                 2.433 
                 27.89 
               
               
                 54 
                 100.0 
                 0.727 
                 1.013 
                 1.375 
                 2.399 
                 28.32 
               
               
                 55 
                 100.0 
                 0.647 
                 0.960 
                 1.546 
                 2.412 
                 28.97 
               
               
                 56 
                 100.0 
                 0.659 
                 0.974 
                 1.519 
                 2.413 
                 28.73 
               
               
                 57 
                 99.9 
                 0.487 
                 0.719 
                 2.055 
                 2.399 
                 29.09 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                 Liquidus 
                 200 
                 Elastic 
                 Shear 
               
               
                   
                 Strain 
                 Anneal 
                 Softening 
                 CTE × 
                 Liquidus 
                 Viscosity 
                 poise T 
                 modulus 
                 modulus 
               
               
                 Sample 
                 pt. (° C.) 
                 pt. (° C.) 
                 pt. (° C.) 
                 10 7  K −1   
                 T (° C.) 
                 (Mpoise) 
                 (° C.) 
                 (GPa) 
                 (GPa) 
               
               
                   
               
               
                 1 
                 548 
                 605 
                 878 
                 74.1 
                   
                   
                   
                 62.3 
                 25.6 
               
               
                 2 
                 543 
                 603 
                   
                   
                   
                   
                 1694 
                   
                   
               
               
                 3 
                 524 
                 580 
                   
                   
                   
                   
                   
                   
                   
               
               
                 4 
                 538 
                 593 
                   
                   
                   
                   
                 1690 
                   
                   
               
               
                 5 
                 539 
                 590 
                 824 
                 76.0 
                 &lt;750 
                 &gt;1786 
                 1680 
                 63.4 
                 26.1 
               
               
                 6 
                 548 
                 605 
                 864 
                 72.8 
                 &lt;750 
                 &gt;9706 
                 1684 
                 62.2 
                 25.6 
               
               
                 7 
                 559 
                 618 
                 885 
                 69.9 
                 &lt;750 
                   
                   
                 62.7 
                 25.7 
               
               
                 8 
                 566 
                 625 
                 893 
                 72.1 
                   
                   
                   
                 63.3 
                 26.1 
               
               
                 9 
                 528 
                 577 
                 804 
                 74.0 
                 &lt;730 
                 &gt;474 
                 1650 
                 62.9 
                 25.7 
               
               
                 10 
                 534 
                 590 
                 864 
                 78.4 
                 &lt;745 
                   
                   
                 62.3 
                 25.8 
               
               
                 11 
                 563 
                 620 
                 900 
                 80.0 
                 &lt;715 
                 &gt;132346 
                 1732 
                 64.0 
                 26.3 
               
               
                 12 
                 546 
                 599 
                 864 
                 74.8 
                 &lt;715 
                 &gt;11212 
                 1655 
                 64.4 
                 26.4 
               
               
                 13 
                 542 
                 597 
                   
                 75.4 
                   
                   
                 1669 
                 61.6 
                 25.4 
               
               
                 14 
                 547 
                 600 
                   
                 75.7 
                 &lt;720 
                   
                   
                   
                   
               
               
                 15 
                 523 
                 574 
                   
                   
                 &lt;745 
                   
                   
                   
                   
               
               
                 16 
                 539 
                 595 
                   
                   
                 &lt;720 
                   
                   
                   
                   
               
               
                 17 
                 569 
                 628 
                   
                   
                 &lt;720 
                   
                   
                   
                   
               
               
                 18 
                 518 
                 570 
                 820 
                 72.8 
                   
                   
                 1692 
                 63.2 
                 26.1 
               
               
                 19 
                 522 
                 578 
                 874 
                 70.3 
                 &lt;705 
                   
                   
                 60.6 
                 24.8 
               
               
                 20 
                 545 
                 596 
                   
                 78.2 
                 &lt;700 
                   
                   
                   
                   
               
               
                 21 
                 546 
                 604 
                 871 
                 72.0 
                 &lt;700 
                 &gt;100 
                 1665 
                 62.6 
                 25.7 
               
               
                 22 
                 556 
                 608 
                 864 
                 81.8 
                 1115 
                   
                   
                   
                   
               
               
                 23 
                 521 
                 575 
                 831 
                 73.8 
                   
                   
                   
                 62.4 
                 25.5 
               
               
                 24 
                 517 
                 568 
                 798 
                 75.2 
                   
                   
                 1702 
                 64.1 
                 26.3 
               
               
                 25 
                 513 
                 561 
                 777 
                 73.2 
                   
                   
                 1663 
                 64.6 
                 26.6 
               
               
                 26 
                 564 
                 616 
                 872 
                 73.0 
                 1050 
                   
                   
                 67.6 
                 27.8 
               
               
                 27 
                 547 
                 594 
                   
                   
                 &lt;745 
                   
                   
                   
                   
               
               
                 28 
                 528 
                 587 
                 883 
                 68.9 
                   
                   
                   
                 61.8 
                 25.3 
               
               
                 29 
                 509 
                 563 
                 826 
                 69.9 
                 &lt;745 
                 &gt;663 
                 1648 
                 59.6 
                 24.4 
               
               
                 30 
                 557 
                 613 
                 882 
                 79.5 
                 975 
                 4.72 
                 1689 
                 67.4 
                 27.6 
               
               
                 31 
                 550 
                 603 
                 862 
                 75.4 
                 945 
                   
                   
                 66.2 
                 27.2 
               
               
                 32 
                 532 
                 577 
                 770 
                 78.0 
                 865 
                   
                   
                 67.4 
                 27.8 
               
               
                 33 
                 538 
                 587 
                 830 
                 87.7 
                 &lt;710 
                   
                 1614 
                 68.8 
                 28.3 
               
               
                 34 
                 540 
                 591 
                 839 
                 82.1 
                 &lt;730 
                 &gt;885 
                 1671 
                 69.0 
                 28.4 
               
               
                 35 
                 533 
                 581 
                 803 
                 84.9 
                 &lt;710 
                 &gt;518 
                 1634 
                 69.0 
                 28.5 
               
               
                 36 
                 538 
                 588 
                 830 
                 85.7 
                 &lt;720 
                 &gt;1212 
                 1663 
                 68.4 
                 28.1 
               
               
                 37 
                 522 
                 564 
                 754 
                 91.2 
                 &lt;710 
                   
                   
                 72.1 
                 29.7 
               
               
                 38 
                 537 
                 586 
                 827 
                 82.1 
                 &lt;720 
                 &gt;1698 
                 1653 
                 68.1 
                 28.2 
               
               
                 39 
                 521 
                 561 
                 739 
                 83.7 
                 820 
                 1.26 
                 1480 
                 72.5 
                 29.9 
               
               
                 40 
                 517 
                 567 
                 805 
                 79.4 
                 &lt;720 
                   
                   
                 62.7 
                   
               
               
                 41 
                 518 
                 569 
                 811 
                 75.4 
                 &lt;710 
                 1662 
                 1668 
                 62.7 
                   
               
               
                 42 
                 520 
                 572 
                 831 
                 74.0 
                 &lt;745 
                   
                   
                 62.6 
                   
               
               
                 43 
                 519 
                 571 
                 824 
                 76.4 
                 &lt;700 
                 2053 
                 1679 
                 62.2 
                   
               
               
                 44 
                 508 
                 556 
                 785 
                 76.0 
                 &lt;710 
                   
                   
                 63.6 
                   
               
               
                 45 
                 500 
                 547 
                 785 
                 75.7 
                 &lt;745 
                   
                   
                 63.5 
                   
               
               
                 46 
                 524 
                 573 
                 809 
                 74.5 
                 &lt;750 
                   
                   
                   
                   
               
               
                 47 
                 526 
                 573 
                 791 
                 74.8 
                   
                   
                   
                   
                   
               
               
                 48 
                 507 
                 557 
                 796 
                 74.7 
                 &lt;700 
                   
                   
                   
                   
               
               
                 49 
                 507 
                 554 
                 781 
                 74.0 
                 955 
                   
                   
                   
                   
               
               
                 50 
                 513 
                 562 
                 795 
                 75.4 
                 &lt;730 
                   
                   
                   
                   
               
               
                 51 
                 489 
                 539 
                 791 
                   
                 &lt;710 
                   
                   
                   
                   
               
               
                 52 
                 666 
                 726 
                 1016 
                 88.8 
                 &lt;930 
                 &gt;500 
                 1743 
                   
                   
               
               
                 53 
                 620 
                 679 
                 969 
                 89.3 
                 1010 
                 8.2 
                 1727 
                   
                   
               
               
                 54 
                 588 
                 643 
                 905 
                 87.4 
                 1050 
                 0.86 
                 1628 
                   
                   
               
               
                 55 
                 559.0 
                 609.0 
                 849.5 
                 74.4 
                   
                   
                   
                   
                   
               
               
                 56 
                 559.0 
                 610.0 
                 841.0 
                 92.4 
                   
                   
                   
                   
                   
               
               
                 57 
                 577.0 
                 631.0 
                 877.7 
                 68.9 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Pre-IX Crack 
                 CS 1   
                 DOL 1   
                 CS 2   
                 DOL 2 , 
                   
               
               
                   
                 Poisson 
                 initiation 
                 IX 8 hrs 
                 IX 8 hrs 
                 IX 15 hrs 
                 IX 15 hrs 
                 Damage 
               
               
                 Sample 
                 ratio 
                 load (gf) 
                 (MPa) 
                 (μm) 
                 (MPa) 
                 (μm) 
                 Threshold (gf) 3   
               
               
                   
               
               
                 1 
                 0.219 
                 1100  
                 871 
                 35.1 
                   
                   
                 &gt;30000 
               
               
                 2 
                   
                 600 
                   
                   
                   
                   
                 &gt;30000 
               
               
                 3 
                   
                 600 
                   
                   
                   
                   
                 29000 
               
               
                 4 
                   
                 800 
                   
                   
                   
                   
                 &gt;30000 
               
               
                 5 
                 0.213 
                 500-1000 
                 803 
                 38.8 
                 762 
                 51.5 
                   
               
               
                 6 
                 0.215 
                 500-1000 
                 816 
                 38.8 
                 782 
                 51.8 
                   
               
               
                 7 
                 0.219 
                 500-1000 
                 803 
                 36.1 
                 761 
                 50.5 
                   
               
               
                 8 
                 0.213 
                 500-1000 
                 868 
                 40.3 
                 840 
                 53.6 
                   
               
               
                 9 
                 0.223 
                   
                 752 
                 34.8 
                 707 
                 47.2 
                   
               
               
                 10 
                 0.209 
                   
                 722 
                 47.8 
                 687 
                 65.1 
                   
               
               
                 11 
                 0.216 
                   
                 924 
                 46 
                 877 
                 60.9 
                   
               
               
                 12 
                 0.219 
                   
                 839 
                 36.2 
                 790 
                 48.8 
                   
               
               
                 13 
                 0.214 
                   
                 775 
                 43.5 
                 732 
                 60.8 
                   
               
               
                 14 
                   
                   
                 850 
                 38.5 
                 792 
                 50.7 
                   
               
               
                 15 
                   
                   
                 738 
                 33.7 
                 686 
                 47.2 
                   
               
               
                 16 
                   
                   
                 763 
                 40.7 
                 716 
                 55.5 
                   
               
               
                 17 
                   
                   
                 808 
                 40.5 
                 757 
                 55.4 
                   
               
               
                 18 
                 0.212 
                   
                   
                   
                   
                   
                 25000 
               
               
                 19 
                 0.224 
                   
                 691 
                 33.7 
                 641 
                 46.6 
                   
               
               
                 20 
                   
                   
                 868 
                 37.1 
                 810 
                 52.1 
                   
               
               
                 21 
                 0.217 
                   
                 824 
                 35.8 
                   
                   
                   
               
               
                 22 
                   
                   
                 771 
                 50.6 
                 747 
                 66 
                   
               
               
                 23 
                 0.222 
                   
                   
                   
                   
                   
                 21000 
               
               
                 24 
                 0.218 
                   
                   
                   
                   
                   
                 20000 
               
               
                 25 
                 0.216 
                   
                   
                   
                   
                   
                 20000 
               
               
                 26 
                 0.217 
                   
                 887 
                 34.8 
                 864 
                 46.7 
                   
               
               
                 27 
                   
                   
                 887 
                 34.7 
                 835 
                 48 
                   
               
               
                 28 
                 0.221 
                   
                   
                   
                   
                   
                 18000 
               
               
                 29 
                 0.219 
                   
                 623 
                 31.3 
                 557 
                 43 
                   
               
               
                 30 
                 0.219 
                 500-1000 
                 791 
                 54.1 
                 772 
                 67.5 
                   
               
               
                 31 
                 0.217 
                   
                 870 
                 35.2 
                 833 
                 46.9 
                   
               
               
                 32 
                 0.21 
                 600 
                 847 
                 25.6 
                   
                   
                   
               
               
                 33 
                 0.216 
                 500-1000 
                 814 
                 50.8 
                 773 
                 67 
                   
               
               
                 34 
                 0.217 
                 300-500  
                 825 
                 46.3 
                 792 
                 63.6 
                   
               
               
                 35 
                 0.21 
                 300-500  
                 794 
                 45.5 
                 750 
                 60.6 
                   
               
               
                 36 
                 0.217 
                 300-500  
                 801 
                 51.2 
                 779 
                 66.2 
                   
               
               
                 37 
                 0.215 
                 200-300  
                 747 
                 43.9 
                 698 
                 56.5 
                   
               
               
                 38 
                 0.208 
                 200-300  
                 803 
                 46.4 
                 761 
                 63.3 
                   
               
               
                 39 
                 0.213 
                   
                   
                   
                   
                   
                 5000 
               
               
                 40 
                   
                   
                 694 
                 38.1 
                 668 
                 54.2 
                   
               
               
                 41 
                   
                   
                 707 
                 40.1 
                 654 
                 50.6 
                   
               
               
                 42 
                   
                   
                 690 
                 39.9 
                 643 
                 52.6 
                   
               
               
                 43 
                   
                   
                 689 
                 38.6 
                 627 
                 55 
                   
               
               
                 44 
                   
                   
                 611 
                 37.5 
                 555 
                 51.2 
                   
               
               
                 45 
                   
                   
                 533 
                 37.4 
                 502 
                 50.4 
                   
               
               
                 46 
                   
                   
                 806 
                 40.1 
                 705 
                 71.7 
                   
               
               
                 47 
                   
                   
                 753 
                 27 
                 716 
                 36.3 
                   
               
               
                 48 
                   
                   
                 712 
                 29.3 
                 670 
                 37.2 
                   
               
               
                 49 
                   
                   
                 720 
                 25 
                 688 
                 34.8 
                   
               
               
                 50 
                   
                   
                 716 
                 30.4 
                 680 
                 39.5 
                   
               
               
                 51 
                   
                   
                 574 
                 32.5 
                 540 
                 43.1 
                   
               
               
                 52 
                   
                   
                   
                   
                   
                   
                   
               
               
                 53 
                   
                   
                   
                   
                   
                   
                   
               
               
                 54 
                   
                   
                 1029 
                 51.2 
                   
                   
                   
               
               
                 55 
                   
                   
                 901 
                 38.3 
                 858 
                 57.5 
                 10000-15000 
               
               
                 56 
                   
                   
                 967 
                 37.8 
                 964 
                 50.7 
                 10000-15000 
               
               
                 57 
                   
                   
                 832 
                 18.3 
                 790 
                 29 
                 10000-15000 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Sample 
                 Damage Threshold (gf) 4   
                 Damage Threshold (gf) 5   
                 Damage Threshold (gf) 
               
               
                   
               
               
                   
                 1 
                   
                   
                 30 
               
               
                   
                 2 
                   
                   
                 30 
               
               
                   
                 3 
                   
                   
                 29 
               
               
                   
                 4 
                   
                   
                 30 
               
               
                   
                 5 
                 &gt;30000 
                   
                 30 
               
               
                   
                 6 
                 &gt;30000 
                   
                 30 
               
               
                   
                 7 
                 &gt;30000 
                   
                 30 
               
               
                   
                 8 
                 &gt;30000 
                   
                 30 
               
               
                   
                 9 
                 &gt;30000 
                   
                 30 
               
               
                   
                 10 
                 &gt;30000 
                   
                 30 
               
               
                   
                 11 
                 &gt;30000 
                   
                 30 
               
               
                   
                 12 
                 &gt;30000 
                   
                 30 
               
               
                   
                 13 
                 &gt;30000 
                   
                 30 
               
               
                   
                 14 
                 &gt;30000 
                   
                 30 
               
               
                   
                 15 
                 &gt;30000 
                   
                 30 
               
               
                   
                 16 
                 &gt;30000 
                   
                 30 
               
               
                   
                 17 
                 &gt;30000 
                   
                 30 
               
               
                   
                 18 
                   
                   
                 25 
               
               
                   
                 19 
                 25000 
                   
                 25 
               
               
                   
                 20 
                 25000 
                   
                 25 
               
               
                   
                 21 
                   
                 23000 
                 23 
               
               
                   
                 22 
                 20000-25000 
                   
                 22 
               
               
                   
                 23 
                   
                   
                 21 
               
               
                   
                 24 
                   
                   
                 20 
               
               
                   
                 25 
                   
                   
                 20 
               
               
                   
                 26 
                 20000 
                   
                 20 
               
               
                   
                 27 
                 &lt;25000 
                   
                 20 
               
               
                   
                 28 
                   
                   
                 18 
               
               
                   
                 29 
                 18000 
                   
                 18 
               
               
                   
                 30 
                 15000 
                   
                 15 
               
               
                   
                 31 
                 13000 
                   
                 13 
               
               
                   
                 32 
                   
                 11000 
                 11 
               
               
                   
                 33 
                 10000 
                   
                 10 
               
               
                   
                 34 
                 9000 
                   
                 9 
               
               
                   
                 35 
                 8000 
                   
                 8 
               
               
                   
                 36 
                 8000 
                   
                 8 
               
               
                   
                 37 
                 6000 
                   
                 6 
               
               
                   
                 38 
                 6000 
                   
                 6 
               
               
                   
                 39 
                   
                   
                 5 
               
               
                   
                 40 
                 19000 
                   
                 19 
               
               
                   
                 41 
                 22000 
                   
                 22 
               
               
                   
                 42 
                 &gt;30000 
                   
                 30 
               
               
                   
                 43 
                   
                   
                   
               
               
                   
                 44 
                 20000-25000 
                   
                 22.5 
               
               
                   
                 45 
                   
                   
                   
               
               
                   
                 46 
                 15000-20000 
                   
                 17.5 
               
               
                   
                 47 
                 &gt;30000 
                   
                 &gt;30 
               
               
                   
                 48 
                 &gt;30000 
                   
                 &gt;30 
               
               
                   
                 49 
                 &gt;30000 
                   
                 &gt;30 
               
               
                   
                 50 
                 &gt;30000 
                   
                 &gt;30 
               
               
                   
                 51 
                 20000-25000 
                   
                 22.5 
               
               
                   
                 52 
                   
                   
                 13.5 
               
               
                   
                 53 
                   
                   
                 11.5 
               
               
                   
                 54 
                 10000-15000 
                   
                 12.5 
               
               
                   
                 55 
                 10000-15000 
                   
                 12.5 
               
               
                   
                 56 
                 &lt;10000 
                   
                 12.5 
               
               
                   
                 57 
                 10000-15000 
                   
                 12.5 
               
               
                   
               
               
                   1 Compressive stress (CS) and depth of layer (DOL) after ion exchange (IX) in 100% KNO 3  at 410° C. for 8 hrs. 
               
               
                   3 Compressive stress (CS) and depth of layer (DOL) after ion exchange (IX) in 100% KNO 3  at 410° C. for 15 hrs. 
               
               
                   3 After ion exchange (IX) in 100% KNO 3  at 410° C. for 8 hrs. 
               
               
                   4 After ion exchange (IX) in 100% KNO 3  at 410° C. for 15 hrs. 
               
               
                   5 After ion exchange (IX) in 100% KNO 3  at 370° C. for 64 hrs. 
               
            
           
         
       
     
     Example 
     The following example illustrates features and advantages of the glasses described herein, and is in no way intended to limit the disclosure or appended claims thereto. 
     The purpose of this example was to verify that pre-ion exchange crack resistance improves post-ion exchange crack resistance in a glass. Samples of crack resistant aluminoborosilicate glass having composition e in Table 1 (64 mol % SiO 2 , 13.5 mol % Al 2 O 3 , 9 mol % B 2 O 3 , 13.5 mol % Na 2 O, 0.1 mol % SnO 2 ) and a pre-ion exchange crack initiation threshold of 1100 gram force (gf), were ion exchanged by immersion in a molten KNO 3  salt bath at 410° C. for 8 hrs to achieve depths of layer DOL and compressive stresses CS. One sample had a DOL of 55.8 μm and a CS of 838 MPa, and another sample had a DOL of 35.1 μm and a CS of 871 MPa. 
     For purposes of comparison, samples of Corning GORILLA™ Glass (an alkali aluminosilicate glass having the composition: 66.4 mol % SiO 2 ; 10.3 mol % Al 2 O 3 ; 0.60 mol % B 2 O 3 ; 4.0 mol % Na 2 O; 2.10 mol % K 2 O; 5.76 mol % MgO; 0.58 mol % CaO; 0.01 mol % ZrO 2 ; 0.21 mol % SnO 2 ; and 0.007 mol % Fe 2 O 3 ) with a pre-ion exchange crack initiation threshold of 300 gf were then ion exchanged to closely match the compressive stress and depths of layer of the samples having composition f, listed in Table 1. One sample had a DOL of 54 μm and a CS of 751 MPa, and another sample had a DOL of 35 μm and a CS of 790 MPa. Compressive stresses and depths of layer of the ion exchanged samples of composition f and GORILLA Glass are listed in Table 3. 
     Following ion exchange, Vickers crack initiation loads were measured for each of composition f in Table 1 and the GORILLA Glass samples. Post-ion exchange crack initiation loads were measured using a Vickers diamond indenter as previously described herein and are listed in Table 3. The results of the crack initiation testing listed in Table 3 demonstrate that greater pre-ion exchange crack resistance improves post-ion exchange crack resistance. The GORILLA Glass 55 samples required loads of 5,000-7,000 gf to initiate median/radial crack systems, whereas the composition f samples required loads of greater than 30,000 gf, or 4-6 times the load needed to initiate such cracks in GORILLA Glass samples, to initiate median/radial crack systems. The GORILLA Glass samples fractured into several pieces when the indentation load exceeded the measured crack initiation loads, and in all cases fracture was observed by the point at which the load exceeded 10,000 gf. In contrast, the composition f samples did not fracture at any of the indentation loads (3,000 up to 30,000 gf) studied. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Crack initiation loads of ion-exchanged glasses having 
               
               
                 composition f (listed in Table 1) and Gorilla ® Glasses. 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Pre-Ion-Exchange 
                   
                   
                 Post-Ion- 
               
               
                   
                 Crack 
                   
                   
                 Exchange Crack 
               
               
                   
                 Initiation Load 
                 DOL 
                 Compressive 
                 Initiation Load 
               
               
                 Glass 
                 (gf) 
                 (microns) 
                 Stress (MPa) 
                 (gf) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Comp. f 
                 1100 
                 55.8 
                 838 
                 30000+ 
               
               
                 Gorilla 
                 300 
                 54 
                 751 
                 7000 
               
               
                 Glass 
                   
                   
                   
                   
               
               
                 Comp. f 
                 1100 
                 35.1 
                 871 
                 30000+ 
               
               
                 Gorilla 
                 300 
                 35 
                 790 
                 5000 
               
               
                 Glass 
               
               
                   
               
            
           
         
       
     
     While typical embodiments have been set forth for the purpose of illustration, the foregoing description should not be deemed to be a limitation on the scope of the disclosure or appended claims. Accordingly, various modifications, adaptations, and alternatives may occur to one skilled in the art without departing from the spirit and scope of the present disclosure or appended claims.