Metallographic evidence for superplastic flow

Abstract

K. N. Melton (Central Laboratories ZLM, Brown Boveri, Baden, Switzerland) and J. W. Edington (Alcan International Ltd, Banbury Laboratories, Banbury, Oxfordshire) wrote: During the last decade, there has been considerable controversy over the mechanisms of superplastic deformation. However, it is now generally accepted that grain boundary sliding plays an important role; for a review of the supporting data see Ref. 1. Experiments performed on several materials have also provided evidence for limited dislocation motion during superplastic deformation. These included (in wt-%) Zn–40Al, Al–33Cu, Al–5·8Mg, 0·37 wt-%Zr, 0·07 wt-%Cr, 0·16 wt-%Mn, Al–9·3Zn–1·03Mg–0·22Zr, Mg–1·5Mn–0·3Ce, Zn–0·4Al, Al–6Cu–0·4Zr. The studies cited were not the only ones that concluded dislocation motion was important, but they fulfilled two important requirements. First, the materials contained fine precipitates that acted as barriers to dislocation motion. Thus, loss of dislocations to grain boundaries was minimized during unloading and cooling the tensile specimen, which optimized conditions for detecting them by transmission electron microscopy (TEM). Second, changes in crystallographic texture were produced by superplastic deformation.