A model for the anomalous mechanical properties of nickel-base L12 ordered alloys—I. Dislocations dynamics

Abstract

A new model has been set up with the aim of explaining the mechanical properties of L12 nickel base alloys, in particular their anomalous increase of yield-stress with increasing temperature. In agreement with recent microscopic observations, dislocations movements are assumed to be controlled by a series of double cross-slip mechanisms between octahedral and cube planes, leading to formations and destructions of incomplete Kear-Wilsdorf locks. In this first part, the model is two-dimensional, and the splitting of superpartials into Shockley partials is not taken into account. The forces acting on leading and trailing superpartials of incomplete Kear-Wilsdorf locks have been computed, with the aim of studying the kinetics of their evolution under an applied stress. Fairly good values of the flow-stress have been obtained at low and high temperature in Ni3Ga, assuming that the ratio of the antiphase boundary (APB) energies in cube and octahedral planes is 0.9, and assuming that the distance of cross-slip onto the cube plane increases with increasing temperature.