Glass laminates having determined stress profiles and methods of making the same
A laminated glass article comprises a core layer comprising a core glass composition having an average core coefficient of thermal expansion (CTE core ) and a clad layer directly adjacent to the core layer and comprising a clad glass composition having an average clad coefficient of thermal expansion (CTE clad ) that is less than the CTE core such that the clad layer is in compression and the core layer is in tension. A compressive stress of the clad layer increases with increasing distance from the outer surface of the clad layer, transitions to a minimum tensile stress as a step-change at an interface region between the core layer and the clad layer, and a magnitude of the tensile stress increases continuously to a maximum tensile stress in the core layer. Other stress profiles, and methods of preparing laminated glass articles are also disclosed.
1. A laminated glass article comprising:
a core layer comprising a core glass composition having an average core coefficient of thermal expansion (CTE core ); and
a clad layer directly adjacent to the core layer and comprising a clad glass composition having an average clad coefficient of thermal expansion (CTE clad ) that is less than the CTE core such that the clad layer is in compression and the core layer is in tension;
wherein a compressive stress of the clad layer increases with increasing distance from the outer surface of the clad layer, transitions to a minimum tensile stress as a step-change at an interface region between the core layer and the clad layer, and a magnitude of tensile stress increases continuously from the step-change to a maximum tensile stress in the core layer.
2. The laminated glass article according to claim 1 , wherein a surface compressive stress of the clad layer is at least 200 MPa.
3. The laminated glass article according to claim 1 , wherein a surface compressive stress of the clad layer is at least 250 MPa.
4. The laminated glass article according to claim 1 , wherein the laminated glass article comprises a depth of compression of up to 50 μm.
5. A method of preparing a glass article comprising:
laminating at least one core layer and at least one clad layer to form a laminated glass article, the at least one core layer comprising a core glass composition having an average core coefficient of thermal expansion (CTE core ) and the at least one clad layer comprising a clad glass composition having an average clad coefficient of thermal expansion (CTE clad ) that is less than the CTE core such that the at least one clad layer is in compression and the at least one core layer is in tension;
heating the laminated glass article to a first temperature that is from 50° C. to 200° C. greater than a glass transition temperature T g of the laminated glass article;
equilibrating the laminated glass article at the first temperature for a predetermined period of time; and
quenching the laminated glass article to a second temperature below a strain point of the laminated glass article, wherein after quenching, a compressive stress of the clad layer increases with increasing distance from the outer surface of the clad layer, transitions to a minimum tensile stress as a step-change at an interface region between the core layer and the clad layer, and a magnitude of tensile stress increases continuously from the step-change to a maximum tensile stress in the core layer.
6. The method according to claim 5 , wherein the first temperature is greater than or equal to 750° C. and less than or equal to 900° C.
7. The method according to claim 5 , wherein the second temperature is 25° C.±10° C.
8. The method according to claim 5 , wherein one or more of (i) the core glass composition is an ion-exchangeable core glass composition and (ii) the clad glass composition is an ion-exchangeable clad glass composition.
9. The method according to claim 5 , wherein after quenching, a surface compressive stress of the clad layer is at least 200 MPa.