Effect of dislocation activities on crack extension in ionic crystals

Abstract

The effect of dislocation activities on crack extension has been investigated using NaCl, KCl and NaClBr mixed crystals. In NaCl and KCl crystals {110}<1 1 0 > slip systems operate actively around a crack tip at room temperature, while the threshold stress intensity K IC for crack extension is very small, less than 0.1 MPa m 1 2 . When test temperature are lowered to 77 K, the dislocation activities are reduced and the K IC values are also increased at room temperature when the crystals are hardened by the partial substitution of Br for Cl in order to reduce dislocation activities. When temperatures are raised above 400 K, {001}<1 1 0 > slip operation in addition to the abundant operation of {110}<1 1 0 > slips place around a crack tip and the K IC values are markedly increased. Such peculiar effects of dislocation activities on K IC values are discussed in connection with the activities of shielding and antishielding dislocations estimated from computer simulations as well as experimental observations.