Superplastic Property of the Ti–6Al–4V Alloy with Ultrafine‐Grained Heterogeneous Microstructure

Abstract

Ti–6Al–4V alloy having a heterogeneous microstructure composed of ultrafine‐equiaxed‐ α ‐grains and fine‐lamellar‐ α ‐grains is investigated for microstructural changes during superplastic deformation at temperature of 700 °C. The Ti–6Al–4V alloy having an optimum fraction of fine‐lamellar‐ α ‐grains exhibits an excellent superplastic property and the highest elongation of 583% (tested at 700 °C 10 −3 s −1 ). This is mainly due to the optimized activation of grain‐boundary‐sliding and additional accommodation mechanism associated with frequent occurrences of dynamic recrystallization and β precipitation at boundaries during deformation of the heterogeneous starting microstructure. The present result suggests the possibility that optimizing the starting microstructure so as to have an optimum heterogeneous‐microstructure serves as an additional stress accommodation mechanism and leads to a large superplastic elongation.