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 h 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 and wherein the first portion b is linear such that
σ
″
(
x
)
<
2
σ
′
(
x
)
d
b
where σ″(x) is the second derivative of the stress profile in the first portion h with respect to depth x and σ′(x) is the first derivative of the stress profile in the first portion b with respect to depth x;
ii. a second portion c extending from d b to the DOC and having an average slope m c , wherein −2 MPa/μm≧m c ≧−8 MPa/μm and wherein the second portion c is linear such that
σ
″
(
x
)
<
2
σ
′
(
x
)
D
O
C
where σ″(x) is the second derivative of the stress profile in the second portion e with respect to depth x and σ′(x) is the first derivative of the stress profile in the second portion c with respect to depth x.
2. The glass article of claim 1 , wherein −40 MPa/μm≧m b ≧−120 MPa/μm.
3. The glass article of claim 1 , wherein thickness t is in a range from about 0.15 mm up to about 2.0 mm.
4. The glass article of claim 1 , wherein the glass article comprises an alkali aluminosilicate glass.
5. The glass article of claim 4 , wherein the alkali aluminosilicate glass further comprises up to about 10 mol % Li 2 O.
6. 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 disposed on the surface of the glass, wherein the survival rate is based on testing at least 5 samples.
7. 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.
8. 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.
9. The glass article of claim 4 , wherein the alkali aluminosilicate glass is lithium-free.
10. The glass article of claim 1 , wherein thickness t is in a range from about 0.15 mm up to about 1.0 mm.
11. The glass article of claim 1 , wherein the DOC≦0.2t.
12. The glass article of claim 1 , wherein the second portion e is linear such that
σ
″
(
x
)
<
σ
′
(
x
)
D
O
C
.
13. The glass article of claim 12 , wherein the first portion b is linear such that
σ
″
(
x
)
<
σ
′
(
x
)
d
b
.
14. An electronic device comprising the glass article of claim 1 .
15. The electronic device of claim 14 , wherein the glass article is a cover plate, window, or display.