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

A 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 μm) and coarse (11 μm) grained microstructures at 600 and 900°C with a strain rate of 10−3s−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 α-phase both at 600 and 900°C. However, in the fine grain microstructure, dislocations were rarely observed in the α-phase at 600°C, while a few dislocations were observed near the α/β boundaries at 900°C. The results indicate that most of deformation is imposed on the β-phase in the fine grain microstructure, and on the α-phase as well as the β-phase in the coarse-grain microstructure. It is also considered that accommodation processes for phase/grain boundary sliding in the α and β phase are closely associated with the dislocation motion.