Plastic asymmetry and anomaly of iron aluminides - An internal variable approach

Abstract

Tension-compression asymmetry in the high temperature flow and anomalous yield behavior of Fe-28 at.%Al-5 at.%Cr alloy has been investigated. Flow curves were obtained from a series of tensile and compressive load relaxation tests. Constitutive relations at each deformation conditions were formulated using the recently proposed internal variable theory based on dislocation dynamics. In this study, high temperature flow stress of selected material was described as the sum of the internal and frictional stress. The anomaly and peak temperature of yield strength seem to be controlled by the anomaly of internal stress and the relative portion of internal and frictional stress in total flow stress, respectively. Asymmetric flow stress was observed in analogy with yield strength. In terms of constitutive parameters, critical stress for frictional flow (Eo) exhibited considerably higher value in compression, which physically postulates increased critical resolved shear stress (CRSS). Considering the crystallography and microstructure, it is presumably due to the 'extrinsic' effect of non-deviatoric stress tensor, as proposed in other studies.