A critical analysis of existing models for plastic flow in Ni3Al: Comparisons with transient deformation experiments

Abstract

A review of the intermediate temperature creep properties of Ni3Al indicates that octahedral glide, the mechanism associated with the anomalous temperature dependence of yielding in this alloy, is exhausted during primary creep. Comparisons of this primary creep transient with the various models proposed to explain the anomalous yielding behavior suggest that additional transient experiments are needed to fully characterize octahedral glide in this alloy. Cottrell–Stokes type temperature change experiments, stress relaxation experiments, and deformation exhaustion/temperature drop tests have been conducted in an attempt to better characterize octahedral glide in Ni3Al. The results of these transient experiments indicate that octahedral glide is only partially a thermally reversible process and that the formation of dislocation substructure, KW locks, plays an important role in determining the flow strength of this alloy. These experiments also suggest that flow in Ni3Al should not be viewed as a viscous drag process, but can best be described as a “pure-metal-like” process involving the rapid motion of a small number of highly mobile dislocations. The stochastic nature of dislocation motion and the importance of substructure formation are emphasized and a description of octahedral glide that is consistent with the transient deformation experiments is proposed.