Microstructure, residual stresses, and mechanical performance of surface crystallized translucent glass-ceramics

Mechanical properties of glasses can be significantly increased by inducing surface crystallization of a low coefficient of thermal expansion phase. In this work, we produced surface crystallized lithia-alumina-silica glassceramics with different crystallized layer thicknesses and analysed the resulting residual stresses and their effect on mechanical properties. The residual stress magnitude was estimated by analytical and experimental methods, as well as numerical modeling. The surface compressive stress reached 390 MPa and 490 MPa, as given by the analytical and experimental determination, respectively. These stresses prevented radial cracking in microhardness and scratch tests. The best glass-ceramic achieved a Vickers hardness of 7.5 GPa and fracture strength of 680 +/- 50 MPa in a ball-on-three-ball test. These glass-ceramics are translucent, providing 50-60% transmittance over the visible wavelength spectrum (1.3 mm-thick-sample). This study unveiled the causes of improved mechanical properties and validates the concept that surface crystallization is a valuable technique for developing high strength glass-ceramics.