A mechanistic model for boundary sliding controlled optimal superplastic flow .2. Experimental verification

In Part I, it was suggested that with a simplifying assumption, optimal isostructural superplasticity can be explained with the aid of three constants and a true activation energy for the rate controlling deformation process, i.e., grain/interphase boundary sliding. In this investigation, two aluminium A18090 alloys of different grain sizes and two titanium alloys, Ti-6A1-4V and a Ti-Al-Mn alloy, designated as OT4-1, were studied. Tensile tests were carried out over a wide range of temperatures and strain rates. From the load-elongation responses, superplasticity data in the form of isostructural log (stress)-log (strain rate) plots at different temperatures were generated. These data were analysed in terms of the mechanistic model presented in Part I. The activation energy for superplastic deformation as well as the deformation parameters were determined for each of the alloy systems investigated. It is shown that the model is capable of predicting the superplastic flow behaviour of these materials very accurately.