Formability and microstructure of Ti22Al24.5Nb0.5Mo rolled sheet within hot gas bulging tests at constant equivalent strain rate

Abstract

The hot formability of Ti22Al24.5Nb0.5Mo rolled sheet was studied by hot constant strain rate uniaxial tensile tests, hot gas bulging tests with nearly constant equivalent strain rate and theoretical analysis. The microstructures of the specimens with three strain states, prepared by hot tensile and hot gas bulging tests, were observed in details. The forming limit curve (FLC) of the rolled sheet at 970°C with the equivalent strain rate 0.001s−1 was measured by gas bulging tests. Based on Mises, Hill48, Logan–Hosford yield functions, the theoretical FLCs of the rolled sheet were predicted by introducing the modified swift equation into the Marciniak-Kuczynski (M-K) model. The results show that the predicted FLC by Logan–Hosford function fits the experimental data better than Mises and Hill48 yield functions. Compared to the tension-compression deformation, the tension-tension deformation is more beneficial for the B2/β grains refinement, the existence of texture B2/β 111〈0−11〉 and the precipitation of α2 and O phase. The main deformation mechanisms of the specimen in hot tensile test are the grain boundaries sliding and dynamic recovery, while the main deformation mechanism of the specimen in tension–tension bulging test is dynamic recrystallization.