A model for the anomalous mechanical properties of nickel-base L12 ordered alloys — II. Cross-slip processes and mechanical properties

Abstract

A model based on the results of Part I, but taking into account more realistic cross-slip processes, is presented in this second part. It is based on a competition between two different cross-slip mechanisms onto the cube plane. Cross slip and glide over interatomic distances are shown to take place by a kink-pair (or double jog) mechanism, whereas cross slip and glide over larger distances are shown to take place by a cross-slip (or critical bow-out) mechanism. Assuming that the kink-pair mechanism is easier than the cross-slip mechanism, in agreement with microscopic observations, analytical expressions are obtained for the strain and temperature dependence of the yield-stress and strain-hardening coefficient, which are in fairly good agreement with experimental results. The role of the complex stacking fault energy, the orientation effects, and the tension-compression asymmetries, can be explained as in the PPV model. The stress-strain rate sensitivity and the reversibility of flow-stress upon a temperature decrease are also discussed.