A MODEL FOR THE ANOMALOUS MECHANICAL-PROPERTIES OF NICKEL-BASE L1(2) ORDERED ALLOYS .1. DISLOCATIONS DYNAMICS

A new model has been set up with the aim of explaining the mechanical properties of L1(2) nickel base alloys, in particular their anomalous increase of yield-stress with increasing temperature. In agreement wit h recent microscopic observations, dislocations movements are assumed to be controlled by a series of double cross-slip mechanisms between o ctahedral and cube planes, leading to formations and destructions of i ncomplete Kear-Wilsdorf locks. In this first part, the model is two-di mensional, and the splitting of superpartials into Shockley partials i s not taken into account. The forces acting on leading and trailing su perpartials 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 lo w and high temperature in Ni-3 Ga, assuming that the ratio of the anti phase boundary (APB) energies in cube and octahedral planes is 0.9, an d assuming that the distance of cross-slip onto the cube plane increas es with increasing temperature. Copyright (C) 1996 Acta Metallurgica I nc.