LAUSR

Ti-6Al-4V alloy sheet with two kinds of initial microstructure (base material (BM) and heat-treated material) was subjected to friction stir processing (FSP). These two kinds of friction stir processed (FSPed) materials show similar characteristics that the microstructure exhibited equiaxed ultrafine-grained (UFG) structure with high fraction of high angle grain boundaries (HAGBs) and random crystallographic orientations. Furthermore, slightly finer grains were observed in FSPed heat-treated material than that in FSPed BM. Superplastic tensile tests were conducted utilizing the FSPed heat-treated material in the strain rates range from 1×10-2 to 1×10-4 s-1 at 650°C, and the optimal superplasciticy with an elongation of 1220% was achieved at 1×10-3 s-1. The superplastic deformation mechanism appears to be grain boundary sliding.