Superplastic Deformation Behavior of Multi‐Pass Warm Rolled Ti–6Al–4V Titanium Alloy at Low Temperature and High Strain Rate

The superplastic deformation behavior of Ti–6Al–4V alloy is investigated by the tensile tests for multi‐pass warm rolled Ti–6Al–4V alloy at temperature of 700–870 °C and strain rate of 10⁻³–10⁻² s⁻¹. A maximum elongation of 1550% is obtained at temperature of 800 °C and strain rate of 10⁻³ s⁻¹. Even at the low temperature of 700 °C and the high strain rate of 10⁻² s⁻¹, the elongation is still 356%. The enhanced superplasticity at low temperature and high strain rate is due to the refined microstructure with fragmented and uniformly distributed fine β grains and to the high density dislocation around grain boundaries as well as dynamic recrystallization. The activation energy at temperature of 800 and 870 °C is 226.8 and 220.2 kJ mol⁻¹, but it increases to 377.5 kJ mol⁻¹ at temperature of 700 °C. The average activation energy is 274.8 kJ mol⁻¹ suggesting that the predominant deformation mechanism is grain boundary sliding. The coefficient of strain rate sensitivity increases with the temperature.