Microstructural analysis on boundary sliding and its accommodation mode during superplastic deformation of Ti-6Al-4V alloy

Abstract

study was carried out to investigate the mechanisms of superplastic deformation in two phase Ti-6Al-4V alloy. Tensile tests were carried out using fine (3 mu m) and coarse (11 mu m) grained microstructures at 600 and 900 degrees C with a strain rate of 10(-3)s(-1), and the quenched microstructures were analyzed by transmission electron microscopy. In the coarse grain microstructure, the planar arrays of dislocations were developed well in the alpha-phase both at 600 and 900 degrees C. However, in the fine grain microstructure, dislocations were rarely observed in the alpha-phase at 600 degrees C, while a few dislocations were observed near the alpha/beta boundaries at 900 degrees C. The results indicate that most of deformation is imposed on the beta-phase in the fine grain microstructure, and on the alpha-phase as well as the beta-phase in the coarse-grain microstructure. It is also considered that accommodation processes for phase/grain boundary sliding in the alpha and beta phase are closely associated with the dislocation motion. (C) 1999 Elsevier Science S.A. All rights reserved.