A model for a mechanical equation of state under continuously changing conditions of hot deformation

Abstract

A simple model, which takes into account the combined effects of dislocation climb and glide has been developed. In the extreme case when climb is slower than glide, the model predicts the direct transients observed in pure metals and class II alloys and in the other extreme case, when glide is slower than climb, the inverse transients observed in class I alloys. In the intermediate situation, when the velocity of climb is of the same order of magnitude as the velocity of glide, the model gives very small transients in flow stress even with large changes in strain rate. Under such conditions, the observed occurrence of a mechanical equation of state in two alloys: a ferritic stainless steel and an aluminium 1% magnesium alloy, under continuously changing strain rate conditions can be explained. The model also explains that a practical mechanical equation of state can be followed without the simultaneous existence of a microstructural equation of state, because it predicts that a change in flow stress can occur even without an appreciable change in the microstructure.