Strengthened glass with deep depth of compression
Chemically strengthened glass articles having at least one deep compressive layer extending from a surface of the article to a depth of at least about 45 μm within the article are provided. In one embodiment, the compressive stress profile includes a single linear segment extending from the surface to the depth of compression DOC. Alternatively, the compressive stress profile includes two linear portions: the first portion extending from the surface to a relatively shallow depth and having a steep slope; and a second portion extending from the shallow depth to the depth of compression. The strengthened glass has a 60% survival rate when dropped from a height of 80 cm in an inverted ball drop test and an equibiaxial flexural strength of at least 10 kgf as determined by abraded ring-on-ring testing. Methods of achieving such stress profiles are also described.
1. A glass article having a thickness t, the glass article comprising:
a compressive layer having a compressive stress CS in a range from about 500 MPa up to about 1200 MPa at a surface of the glass article, wherein:
a. the compressive layer extends from the surface to a depth of compression DOC, wherein DOC≧0.1·t when t<0.5 mm and DOC≧50 μm when t≧0.5 mm, and wherein the compressive layer has a compressive stress profile; and
b. the compressive stress profile comprises:
i. a first portion b extending from the surface to a depth d b and having an average slope m b , wherein 3 μm≦d b ≦15 μm and −40 MPa/μm≧m b ≧−200 MPa/μm;
ii. a second portion c extending from a depth d c to the DOC and having an average slope m c , wherein −2 MPa/μm≧m c ≧−8 MPa/μm; and
iii. a transition region extending from d b to d c having a slope that transitions from slope m b to slope m c , wherein d c −d b is 8 μm or less.
2. The glass article of claim 1 , wherein d c −d b is 7 nm or less.
3. The glass article of claim 1 , wherein d c −d b is 5 μm or less.
4. The glass article of claim 1 , wherein 3 μm≦d b ≦12 μm.
5. The glass article of claim 4 , wherein d c −d b is 7 μm or less.
6. The glass article of claim 4 , wherein d c −d b is 5 μm or less.
7. The glass article of claim 1 , wherein −40 MPa/μm≧m b ≧−120 MPa/μm.
8. The glass article of claim 1 , wherein thickness t is in a range from about 0.15 mm up to about 2.0 mm.
9. The glass article of claim 1 , wherein the glass article comprises an alkali aluminosilicate glass.
10. The glass article of claim 1 , wherein the glass article has at least about a 60% survival rate when subjected to an inverted ball drop test with a 4.2 g stainless steel ball having a diameter of 10 mm from a height of about 80 cm onto a 30 grit sandpaper positioned above the surface of the glass so there is a 100 μm air gap between the sandpaper and the surface of the glass, wherein the survival rate is based on testing at least 5 samples.
11. The glass article of claim 1 , wherein the glass article has an equibiaxial flexural strength in a range from about 10 kgf up to about 50 kgf as determined by abraded ring-on-ring testing.
12. The glass article of claim 1 , wherein DOC≧0.11·t when t<0.5 mm and 55 μm≦DOC≦100 μm when t≧0.5 mm.
13. The glass article of claim 9 , wherein the alkali aluminosilicate glass comprises at least about 4 mol % P 2 O 5 and from 0 mol % to about 4 mol % B 2 O 3 , wherein 1.3<[(P 2 O 5 +R 2 O)/M 2 O 3 ]≦2.3, where M 2 O 3 =Al 2 O 3 +B 2 O 3 , and R 2 O is the sum of monovalent cation oxides present in the alkali aluminosilicate glass.
14. The glass article of claim 1 , wherein the glass is lithium-free.
15. An electronic device comprising the glass article of claim 1 .
16. The electronic device of claim 15 , wherein the glass article is a cover plate, window, or display.