Plastic deformation behaviour in Ni 3Ti single crystals with D0 24 structure

Abstract

The plastic deformation behaviour of Ni 3Ti single crystals with the D0 24 structure was investigated in compression tests. Two slip planes of the type {1 1 ̄ 00} and (0001) were selected depending on crystal orientation. Temperature dependences of the critical resolved shear stress (CRSS), strain rate sensitivity of flow stress, activation volume and dislocation structure were examined. Anomalous strengthening slightly appeared for the {1 1 ̄ 00}<11 2 ̄ 0> prism slip system in a narrow temperature range between 300 and 500 °C. Accompanying the yield stress anomaly (YSA) were small jogs formed on 1/3<11 2 ̄ 0> screw dislocations, acting as pinning points for motion of the dislocations and resulting in a zigzag shape of dislocation lines inclined to the Burgers vector by ±15~20°. In contrast, a remarkable YSA was found for the (0001) basal slip system over a wide temperature range between −196 and 800 °C. At low temperatures at and below 300 °C, 1/3<2 1 ̄ 1 ̄ 0> superlattice dislocations were dissociated into two 1/3<10 1 ̄ 0> super-Shockley partials bounded by an SISF after unloading. Above 300 °C, the dissociation mode of 1/3<2 1 ̄ 1 ̄ 0> superlattice dislocations changed to APB-type splitting accompanied by a large increase in CRSS. The strong YSA was caused by the Kear-Wilsdorf locking of 1/3<2 1 ̄ 1 ̄ 0> screw dislocations from the (0001) slip plane onto the {01 1 ̄ 0} planes.