Plastic deformation behaviour in Ni3Ti single crystals with D024 structure

The plastic deformation behaviour of Ni3Ti single crystals with the D0(24) structure was investigated in compression tests. Two slip planes of the type {1(1) over bar 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) over bar 00}<1(1) over bar 20 > prism slip system in a narrow temperature range between 300 and 500 degreesC. Accompanying the yield stress anomaly (YSA) were small jogs formed on 1/3<11(2) over bar 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 +/-1similar to20degrees. In contrast, a remarkable YSA was found for the (0001) basal slip system over a wide temperature range between -196 and 800 degreesC. At low temperatures at and below 300 degreesC, 1/3<2 (1) over bar(1) over bar0> superlattice dislocations were dissociated into two 1/3<10(1) over bar 0 > super-Shockley partials bounded by an SISF after unloading. Above 300 degreesC, the dissociation mode of 1/3 <2 (1) over bar(1) over bar0> 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) over bar(1) over bar0> screw dislocations from the (0001) slip plane onto the {01(1) over bar 0} planes. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.