Damage resistant glass article
A strengthened glass sheet product along with a process and an apparatus for strengthening a glass sheet are provided. The process comprises cooling the glass sheet by non-contact thermal conduction for sufficiently long to fix a surface compression and central tension of the sheet. The process results in thermally strengthened glass sheets having improved breakage properties.
1. A thermally strengthened glass sheet:
the glass sheet having a thickness, expressed in millimeters, of t, a length, expressed in millimeters, of l, and a width, expressed in millimeters, of w, t being less than l and less than w;
the glass sheet having a first major surface and a second major surface separated by the thickness t;
the glass sheet comprising a glass having a softening temperature, expressed in units of ° C., of T soft and an annealing temperature, expressed in units of ° C., of T anneal , and a surface fictive temperature measured on the first major surface of the glass sheet represented by Tfs, when expressed in units of ° C.;
the glass sheet having a non-dimensional surface fictive temperature parameter θs given by (Tfs−T anneal )/(T soft −T anneal ),
wherein the parameter θs is in the range of from 0.50 to 0.9,
and wherein the first major surface has a roughness in the range of from 0.2 to 0.4 nm Ra over an area of 10 μm×10 μm.
2. The glass sheet according to claim 1 wherein the parameter θs is in the range of from 0.51 to 0.9.
3. The glass sheet according to claim 1 wherein the parameter θs is in the range of from 0.52 to 0.9.
4. The glass sheet according to claim 1 wherein the parameter θs is in the range of from 0.53 to 0.9.
5. The glass sheet according to claim 1 wherein the parameter θs is in the range of from 0.54 to 0.9.
6. The glass sheet according to claim 1 wherein the parameter θs is in the range of from 0.55 to 0.9.
7. The glass sheet according to claim 1 wherein the parameter θs is in the range of from 0.60 to 0.9.
8. The glass sheet according to claim 1 wherein the parameter θs is in the range of from 0.65 to 0.9.
9. The glass sheet according to claim 1 , l and w each being at least 10 mm.
10. The glass sheet according to claim 1 , l and w each being at least 40 mm.
11. The glass sheet according to claim 1 , wherein the ratio l/t and the ratio w/t each are equal to 10/1 or more.
12. The glass sheet according to claim 1 , wherein the ratio l/t and the ratio w/t each are equal to 20/1 or more.
13. The glass sheet according to claim 1 , wherein the ratio l/t and the ratio w/t each are equal to 100/1 or more.
14. The glass sheet according to claim 1 wherein the first major surface of the sheet is flat to 100 μm total indicator run-out (TIR) along any 50 mm or less profile of the first major surface.
15. The glass sheet according to claim 1 wherein the first major surface of the sheet is flat to 50 μm total indicator run-out (TIR) along any 50 mm or less profile of the first major surface.
16. The glass sheet according to claim 1 wherein the first major surface has a roughness in the range of from 0.2 to 0.3 nm Ra over an area of 10 μm×10 μm.
17. The glass sheet according to claim 1 wherein the first major surface has a coating.
18. The glass sheet according to claim 1 wherein t is 6 mm or less.
19. The glass sheet according to claim 1 wherein t is 3 mm or less.
20. The glass sheet according to claim 1 wherein t is less than 2 mm.
21. The glass sheet according to claim 1 wherein t is 1 mm or less.
22. The glass sheet according to claim 1 wherein t is 0.7 mm or less.
23. The glass sheet according to claim 1 wherein t is 0.5 mm or less.
24. The glass sheet according to claim 1 wherein t is 0.28 mm or less.
25. The glass sheet according to claim 1 wherein the sheet exhibits a 50% cracking threshold at 5 Newtons or greater after a 15 second Vickers Hardness Test.
26. The glass sheet according to claim 1 wherein the sheet exhibits a 50% cracking threshold at 10 Newtons or greater after a 15 second Vickers Hardness Test.
27. The glass sheet according to claim 1 wherein the glass has a low temperature linear CTE, expressed in 1/° C., of α S CTE , a high temperature linear CTE, expressed in 1/° C., of α L CTE , an elastic modulus, expressed in GPa, of E, and a strain temperature, expressed in units of ° C., of T strain ,;
the first major surface of the glass sheet having a thermally induced surface compressive stress of less than 800 MPa and greater than
P
1
(
h
)
*
t
(
P
2
(
h
)
+
t
)
·
E
·
[
T
strain
·
a
CTE
S
+
a
CTE
L
·
(
T
soft
-
T
strain
)
]
;
in units of MPa;
wherein P 1 is given by
910.2
-
259.2
·
exp
(
-
h
0.143
)
;
P 2 is given by
2.53
+
23.65
(
1
+
(
h
0.00738
)
1.58
)
;
and h is greater than or equal to 0.0625.
28. The glass sheet according to claim 27 wherein h is greater than or equal to 0.10.
29. The glass sheet according to claim 1 wherein the glass has a low temperature linear CTE, expressed in 1/° C., of α S CTE , a high temperature linear CTE, expressed in 1/° C., of α L CTE , an elastic modulus, expressed in GPa, of E, and a strain temperature, expressed in units of ° C., of T strain ,;
the glass sheet having a thermally induced central tension of less than 400 MPa and greater than
P
1
CT
(
h
CT
)
*
t
2
(
P
2
CT
(
h
CT
)
+
t
)
·
E
·
[
T
strain
·
a
CTE
S
+
a
CTE
L
·
(
T
soft
-
T
strain
)
]
;
in units of MPa;
wherein P 1CT is given by
910.2
-
259.2
·
exp
(
-
h
CT
0.143
)
;
P 2CT is given by
2.53
+
23.65
(
1
+
(
h
CT
0.00738
)
1.58
)
;
and h cT is greater than or equal to 0.0625.
30. The glass sheet according to claim 29 wherein h CT is greater than or equal to 0.10.
31. The glass sheet according to claim 1 , wherein the compressive stress of said first major surface is larger than 100 MPa.
32. The glass sheet according to claim 1 , wherein the compressive stress of said first major surface is larger than 150 MPa.
33. The glass sheet according to claim 1 , wherein the compressive stress of said first major surface is larger than 200 MPa.
34. The glass sheet according to claim 1 , wherein the central tension of the sheet is larger than 50 MPa.
35. The glass sheet according to claim 1 , wherein the central tension of the sheet is larger than 75 MPa.
36. The glass sheet according to claim 1 , wherein the central tension of the sheet is larger than 100 MPa.
37. The glass sheet according to claim 1 , wherein the surface fictive temperature measured on the first surface of the sheet is at least 75° C. above a glass transition temperature of the glass.
38. The glass sheet according to claim 1 , wherein the surface fictive temperature measured on the first surface of the sheet is at least 90° C. above a glass transition temperature of the glass.