Cracking resistance of technical glasses and glass ceramics

The crack resistance of various industrial glasses and glass-ceramics was investigated, looking at the systems Li2O-Al2O3-SiO2-TiO2 (S-418); MgO-Al2O3-SiO2-TiO2 (S-370); MgO-MnO-Al2O3-SiO2-TiO2 (S-380); and Li2O-K2O-Al2O3-SiO2 (S-023). The crack resistance was determined using Vickers indentation. It was shown that indentation of all the material mainly forms radial microcracks, and Niihara's equation was used to calculate KIC. Average values of KIC and sample coefficient of variation are given. Observed differences are related to the degree of crystallisation of the glass-ceramics. Glass-ceramic samples were hardened by ion exchange, and the effect on KIC and Vickers hardness, as well as their sample coefficients of variation, is shown. Calculated values of KIC indicated that hardening significantly increases the crack (damage) resistance of samples. This is also indicated by an increase in Vickers hardness of the glass-ceramics. 6 refs.