Phase evolution and mechanical behaviour of super α2 Ti3Al base alloys during superplastic deformation at lower temperatures of 700-900°C

The Tbi(3)Al based alloys exhibited admirable superplasticity of elongation greater than 1000% at temperatures between 950-1000degreesC. In this study, the phase evolution and mechanical behavior of a super alpha(2) alloy at lower temperatures of 700-900degreesC are examined. The initial grain size was around 2.2 mum. Although the super alpha(2) alloy exhibited superior superplastic elongations of 1500% at 960degreesC, the elongation dropped appreciably to 600% at 900degreesC, 330% at 850degreesC and 140% at 750degreesC. The beta-->alpha(2)' transformation occurred in accordance with the equilibrium phase diagram during static annealing; while the transformation seemed to be enhanced during dynamic straining at temperature lower than 900degreesC. With the fine acicular alpha(2)' plates inside the beta grains, the accommodation process across the BCC beta grains was impeded, leading to premature failure and lower tensile elongations (even with the refined grain size).