A mechanistic model for boundary sliding controlled optimal superplastic flow: III numerical verification

It was suggested in Part I [1] that an accurate description of optimal superplastic flow behaviour in metals and alloys could be obtained based on a model that considers grain/interphase boundary sliding (GBS) to be controlling the rate of flow. With the help of a simplifying assumption, iso-structural optimal superplastic flow could be explained using three empirical constants and a true activation energy for the rate controlling deformation process. In Part II [2], experimental studies on an aluminium-lithium alloy and two titanium alloys were presented, and the model presented in Reference [1] was validated. In this investigation, steady state data in the form of log stress - log strain rate plots were collected from literature for several superplastic systems and analysed in terms of the mechanistic model. The activation energy for optimal superplastic deformation as well as the deformation parameters were determined for each of the systems. It is shown that the model is capable of estimating the optimal superplastic strain rate accurately. Further, the activation energy determined at a constant stress or a constant strain rate is demonstrated to be apparent and distinct from the true activation energy of the rate controlling process. The model also is capable of predicting the apparent activation energy at a constant stress or a constant strain rate accurately. © 1997 Technomic Publishing Co., Inc.