Phase evolution and mechanical behavior of super α{sub}2 Ti{sub}3Al base alloys during superplastic deformation at lower temperatures of 700-900°C

摘要

The Ti{sub}3Al based alloys exhibited admirable superplasticity of elongation greater than 1000% at temperatures between 950-1000°C. In this study, the phase evolution and mechanical behavior of a super α{sub}2 alloy at lower temperatures of 700-900°C are examined. The initial grain size was around 2.2 μm. Although the superα{sub}2 alloy exhibited superior superplastic elongations of 1500% at 960°C, the elongation dropped appreciably to 600% at 900°C, 330% at 850°C and 140% at 750°C. The β→α{sub}2{sup}' 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 900°C. With the fine acicular α{sub}2{sup}' plates inside theβ grains, the accommodation process across the BCC β grains was impeded, leading to premature failure and lower tensile elongations (even with the refined grain size).