Abstract:Ti-47Al-8Cr-2Nb alloys with high Cr content were synthesized by non-consumable arc melting in argon atmosphere. Superplastic behavior and deformation mechanism of the as-cast alloy were investigated by optical microscope, scanning electron microscope (SEM), transmission electron microscopy (TEM) and elevated-temperature tensile testing at temperatures ranging 800~1 000 ℃. The results show that the as-cast alloy with high Cr content reveals excellent lower temperature superplasticity with the maximum elongation-to-failure of 630% at 850 ℃ and strain rate of 1×10−4 /s, and the strain rate sensitivity exponent m is 0.51. The activation energy calculated is 245 kJ/mol. The dominant deformation mechanism of Ti-Al-Cr-Nb alloy with high Cr content between 800 ℃ and 1 000 ℃ is the grain boundary sliding controlled by volume diffusion. The presence of β phase and its transformation to γ phase during deformation are beneficial to the grain boundary sliding.

Key words: titanium aluminum alloy; casting; superplasticity; microstructure