Modelling of cavity growth during the superplastic flow of a fine-grained Ti–6Al–4V titanium alloy processed by direct rolling

Ti–6Al–4V fine-grained plates were manufactured using a rolling method and then subjected to superplastic tensile tests at varying temperatures and strain rates on an AG 250KNE electronic tensile testing machine. The superplastic behaviours of the plates were also tested. A cavity-growth model was established and the changing laws of energy during cavity growth and microstructure evolution of superplastic deformation were predicted. The Ti–6Al–4V alloy possessed the maximum elongation rate of 886% at 840°C and a strain rate of 5 × 10−4 s−1. The strain-rate sensitivity index m for this alloy was 0.54. The mechanism of superplastic deformation was established to be strain-induced grain-boundary slip, and the mechanism of cavity growth to be plasticity-controlled cavity coalescence and growth.