Characterization of low-temperature superplasticity in a thermomechanically processed TiAl based alloy

Superplasticity of a TiAl based alloy at low temperature ranging from 750 to 900 degreesC and at strain rates from 2 x 10(-5) to 2 x 10(-1) s(-1) is characterized in this work. In order to refine the grains, two-step forging techniques were applied for materials processing without subsequent annealing after forging. The tensile elongations between 150 and 533% were obtained. An extensive strain hardening on the true stress-strain curves is linked to the high dense mobile dislocations during deformation. The activation energy of 220 U mol (-1) was measured which is close to the activation energy of dislocation pipe diffusion. Evolution of the microstructures after superplastic deformation were also performed by optical microscope and transmission electron microscope to correlate the mechanical properties. Based on these studies, it is suggested that the predominant mechanism for low temperature superplasticity is grain boundary sliding at low strain and dislocation glide creep at high strain rates, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.