Microstructural evolution during superplastic bulge forming of Ti–6Al–4V alloy

An analytical model reflecting the microstructural evolution was made on the basis of Dutta and Mukherjeeʹs work, and applied to the superplastic bulge forming of Ti–6Al–4V alloy. Bulge forming of fine grain (2.5 μm) Ti–6Al–4V alloy sheets was conducted at 900°C, at three strain rates of 2.5×10−4, 5×10−4 and 1×10−3 s−1. It was found that the grain growth rate of biaxially bulge formed samples was quite different from that of uniaxially deformed specimens and that the grain growth rate was independent of the strain rate imposed at a fixed temperature. After incorporating the grain growth rate of biaxially deformed material into the analytical model, the bulge forming process was successfully controlled at different strain rates. Prediction of the thickness distribution by the modified model was in agreement with the experimental results.