ON ACTIVATION ENERGY DURING INITIAL STAGE OF SUPERPLASTIC DEFORMATION

The current paper addresses the issue of extracting activation energy from flow stress data under fixed strain rate and strain levels. If the micro structure s in the superplastic materials after thermomechanical treatments need to evolve gradually during the initial stage of superplastic straining, the structure evolution rate might be different at different test temperatures. A higher activation energy would result in if one uses the flow stress data at ∈ < 0.5, where the structure has not yet reached its stable condition. The calculated activation energy might not reflect the true deformation mechanisms.