Abstract
The chemical strengthening of Li2O•2SiO2 transparent glass-ceramics was investigated. The fracture strength of glass and glass-ceramics increased first and then decreased, and the crack formation and peeling of ion exchanged layer were observed for both Li+↔Na+ and Li+↔K+ ion exchange. This suggests that the submicroscopic crack generates perpendicular to the surface when the ion exchanged layer peels off from the surface. The volume change by Li+↔Na+ and Li+↔K+ ion exchange is very large, over 10%, this large volume change causes the peeing and crack formation of ion exchanged layer despite in which the compressive stress arise. In the early stage of ion exchange, the compressive stress arisen affects effectively on the increase in strength. However, as increase in the thickness of ion exchanged layer, the volume change of ion exchanged layer can not be neglected, and crack and peeling may generate in that layer. Finally, the fracture strength decreases.
