Subcritical Crack Growth and Creep Deformation at Elevated Temperatures in Silicon Nitrides and Glass Ceramics

Abstract

Subcritical crack growth (SCG) and creep deformation at elevated temperatures were investigated in three types of silicon nitrides and glass ceramics under quasi-static and cyclic loading conditions. The SCG behavior was observed at lower temperature in the silicon nitrides which has lower flexural strength at elevated temperatures. The critical stress intensity factor for SCG in glass ceramics showed similar temperature dependence to the structural ceramics having grain boundary glass phase. The results revealed that the high temperature SCG behavior, caused by the softening of the grain boundary glass phase, was timedependent under cyclic loading condition, which suggested the creep crack growth mechanism. The observation of the creep deformation under cyclic loading condition indicated that unidirectional creep deformation was much more remarkable than cyclic creep deformation where the direction of the creep deformation is reversed due to load reversals.