Non-basal slip in Ni3(Ti, Nb) and Ni3(Ti, Al) single crystals with various long-period stacking ordered structures

Abstract

Variations in operative non-basal slip systems in Ni3Ti-based long-period stacking ordered (LPSO) phases with the stacking sequence of the closely packed planes and the temperature dependence of the critical resolved shear stress (CRSS) were investigated. It was confirmed that the {1¯100} prism slip is operative in most of the LPSO phases with hexagonal unit cells, while the {1¯011} pyramidal slip is operative in 9R LPSO phase with rhombohedral unit cell. The mechanism controlling the deformation by non-basal slip at low temperatures is considered to be governed by the energy of the antiphase boundary (APB) formed between the a/6〈112¯0〉 superpartial dislocations in accordance with the kink pair nucleation mechanism proposed by Mitchell et al. The dependence of variations in CRSS for non-basal slip on the Nb content was found to be much smaller than that for basal slip. The present results suggest that the mobility of dislocations on the non-basal plane hardly affected the behavior of yield stress anomalies (YSAs) caused by basal slip in Ni-based LPSO phases, although the Kear–Wilsdorf locking process, which is responsible for the YSA by basal slip, accompanies microscopic cross-slip from the basal slip plane onto the non-basal planes.