Brittle–Ductile Transition and Dislocation Mobility in Sapphire

Abstract

The brittle‐to‐ductile transition (BDT) of Precracked sapphire in four‐point bending was studied as a function of orientation and strain rate from room temperature to 1500°C. Plastic deformatiom of sapphire occurs via basal and prismatic slip during loading at high temperature (above 1030–1100°C, depending on orientation). The BDT temperature, Tc, varies with strain rate and crystallographic orientation of the fracture plane. The activation, derived from the strain rate variation of Tc, is approximately energy of the process controllingh the BDT in sapphire, derived from the strain rate variation of Tc is sapproximately 3.2 eV, close to that for dislocation glide. In one specimen orientation, “warm‐prestressing” increases the room‐temperature fracture stress.