Superplastic deformation behaviour and microstructure evolution of near-α Ti-Al-Mn alloy

Superplastic deformation behaviour of conventional sheets of a near-α titanium alloy (Ti-2.5Al-1.8Mn) was studied by a step-by-step decrease of the strain rate and constant strain rate tests in a temperature range of 790-915 °C. The research found that superplastic deformation is possible in a temperature range of 815-890 °С and a constant strain rate range of 2 × 10−4 to 1 × 10−3 s−1 with elongation above 300% and m-index above 0.4. Also, the research identified the optimum superplastic temperature range of 815-850 °C and constant strain rate of 4 × 10−4 s−1 which provide a maximum elongation of 600-650%. Strain hardening is accelerated by dynamic grain growth at high temperatures of 865 and 890 °С. High dislocation activity is observed at superplastic flow in α-phase. Constitutive modelling of superplastic deformation behaviour is performed, and possible deformation mechanisms are discussed. It is suggested that grain boundary sliding between the α-grains is accommodated by a dislocation slip/creep mechanism.