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 strengthened glass having a thickness t, the strengthened glass comprising:
an inner region under a central tension CT; and
at least one compressive stress layer under a compressive stress CS, the compressive stress layer extending from a surface of the glass 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 being adjacent to the inner region,
wherein the strengthened glass that has had a surface sandblasted with abrasive material at a load of 15 psi for 5 seconds has a peak load at failure of at least about 10 kgf as determined by abraded ring-on-ring testing wherein a ratio of a diameter of a loading ring D1 to a diameter of a support ring D2 is about 0.5,
wherein the glass is lithium-free, and
wherein a CS at a surface of the glass is in a range from about 500 MPa up to about 1200 MPa and wherein the compressive layer has a compressive stress profile comprising:
a first portion b extending from the surface to a depth d b and having an average slope m b ;
a second portion c extending from a depth d c to the DOC and having an average slope m c , wherein slope m b is different from slope m c ; and
a transition region extending from d b to d c having a slope that transitions from slope m b to slope m c .
2. The strengthened glass of claim 1 , wherein 3 μm≦d b ≦15 μm, −40 MPa/μm≧m b ≧−200 MPa/μm, and −2 MPa/μm≧m c ≧−8 MPa/μm.
3. The strengthened glass of claim 2 , wherein −40 MPa/μm≧m b ≧−120 MPa/μm.
4. The strengthened glass of claim 1 , wherein the first portion b is 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 b 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.
5. The strengthened glass of claim 1 , wherein the second portion c is is linear such that
σ
″
(
x
)
<
2
σ
′
(
x
)
d
c
where σ″(x) is the second derivative of the stress profile in the second portion c 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.
6. The strengthened glass a of claim 1 , wherein the thickness t is in a range from about 0.15 mm up to about 2.0 mm.
7. The strengthened glass of claim 1 , wherein the strengthened glass comprises an alkali aluminosilicate glass.
8. The strengthened glass of claim 7 , 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.
9. An electronic device comprising the strengthened glass of claim 1 .
10. The strengthened glass of claim 1 , wherein 3 μm≦d b ≦15 μm and −40 MPa/μm≧m b ≧−200 MPa/μm.
11. The strengthened glass of claim 1 , wherein 3 μm≦d b ≦15 μm and −2 MPa/μm≧m c ≧−8 MPa/μm.