α Grain size and β volume fraction aspects of the superplasticity of Ti-6Al-4V

Abstract

The elevated temperature deformation behaviour of Ti-6Al-4V has been investigated in the temperature range between 775 and 925 °C and for true strain rates 2 × 10⁻⁵ to 0.005 s⁻¹. Region III was characterized by m = 0.13 and Q = 602 kJ mol⁻¹. Region II is subdivided into a low temperature region IIa and a high temperature region IIb. Region IIa is characterized by m = 0.77, Q = 216 kJ mol⁻¹ and relatively low ductility while region IIb is characterized by n = 1.3, and identical value of Q and high ductility. Low and high β-phase proportions are responsible for regions IIa and IIb respectively. An apparent region I was accounted for by concurrent grain growth utilizing a grain size sensitivity parameter which is dependent on the β-phase volume fraction. The strain rate-temperature regimes of regions IIa, IIb and III are illustrated in a “region” map.