Strength anomaly and dislocation structure at 4.2 k in ni₃(si, ti) single crystals

Abstract

The critical resolved shear stress (CRSS) at 4.2 K for the (111)[01] slip system activation in Ni₃(Si, Ti) single crystals with the Ll₂ structure was measured by compression testing and the corresponding dislocation structures were investigated by means of TEM strong-and weak-beam methods. The CRSS showed strong orientation anisotropy and correspondingly a positive temperature dependence at this temperature. [01] screw superdislocations were dominant and sessile in all the observed crystal orientations. The superpartial dislocations combined with the APB tended to dissociate more widely onto the (010) cross-slip plane as the crystal orientation changed from [001] through [011] to [11]. It is suggested that the Kear-Wilsdorf locking is the most likely mechanism by means of which the strength anomaly observed at this temperature can be explained.