EVALUATION OF THE TRUE ACTIVATION ENTHALPY OF SUPERPLASTIC FLOW INCLUDING A THRESHOLD STRESS

A new method is suggested for the evaluation of the true activation en thalpy for alloys where the strain rate of the superplastic flow varie s with a power of an effective stress sigma(e) = sigma-sigma(O), where sigma and sigma(O) are the applied stress and a threshold stress, res pectively. Some earlier results concerning superplastic AlMgZnCu alloy s containing chromium and in which a strongly temperature-dependent th reshold stress can be revealed, are reanalysed. The results are in goo d agreement with the previous ones. It has been shown further that for the alloys investigated the true activation energy increases with inc reasing chromium content.