Analysis of thermally activated formation and breakdown of Kear-Wilsdorf barriers in Ni₃Ge single crystals of various orientations

Abstract

The orientation dependence of the yield stress in Ni₃Ge single crystals has been examined both theoretically and experimentally. The positive temperature dependence of the yield stress in the low temperature region is attributed to formation of Kear-Wilsdorf barriers. The forces driving the formation and breakdown of barriers are calculated within the framework of the Hirsch scheme. A distinctive feature of the model proposed is that the barrier is considered on the screw component of the a/2[${a \mathord{\left/ {\vphantom {a 2}} \right. \kern-\nulldelimiterspace} 2}\left[ {\bar 101} \right]\left( {111} \right)$01](111) superdislocation in the primary octahedral plane. The major role in barrier formation belongs to anisotropy of elastic moduli, energy of antiphase boundaries in the octahedral plane, shear stresses in the cubic and octahedral planes, and friction-induced stress in the cubic plane. A comparison of predicted values of the driving force of barrier formation and breakdown with experimental values reveals their good agreement. An analysis of the orientation dependence of the driving force of barrier formation in the temperature range T = 77–293 K shows that the dependence Δ$\tau$(T) has an extremum for crystals deformed along the [${a \mathord{\left/ {\vphantom {a 2}} \right. \kern-\nulldelimiterspace} 2}\left[ {\bar 101} \right]\left( {111} \right)$39] crystallographic direction, which is confirmed experimentally.