Microstructural and residual stress effects on toughening of stoichiometric BaO.2SiO2 glass-ceramics

Barium disilicate (BaO.2SiO2=BS2) glass is one of the few stoichiometric glasses that nucleates internally, homogeneously via thermal treatment. This system has been scarcely assessed in microstructure-property studies. Here we address fracture strength and toughness (KIC) variation as a function of crystallized volume fraction and crystal size, as well as the possible effect of residual stresses (RS) in BS2 glass-ceramics (GCs) by independently varying these two microstructural parameters. KIC increased with spherulite size and crystallized volume fraction. KIC variation with crystallized volume fraction was similar for GCs with different crystal sizes. Combination of the current findings on BaO.2SiO2 (crystals under tensile RS) with previous studies of Li2O.2SiO2 GCs (compressive RS) indicates that crystallization of a tougher phase - not type of residual stress in the crystals - is the crucial parameter controlling fracture toughness and strength. These findings are quite useful to design novel strong and tough GCs.