The superplastic properties and microstructures evolution of high Nb Ti_3Al based alloy

摘要

The superplasticity of high Nb Ti_3Al based alloy - Ti-23Al-17Nb (at.%) alloy sheet under the conditions of 940～1000℃ and 5.5×10~(-5)s~(-1)V～1.7×10~(-3)s~(-1) were studied. The results showed the elongation changes as a parabola with the deformation temperature increasing, and the maximum elongation obtained at 960℃ and 5.5×10~(-5)s~(-1) was 1447.5%. Work hardening stage increases much more than softening stage when strain rate was decreased because of the increasing of element Nb. Compared with primary microstructure, the lath-like α_2 grains gradually disappeared, the α_2 grains became more equiaxed, and the content and size of α_2 grains were decreasing with increasing of deformation temperature. The volume fraction ratio of α_2 and β phase at the optimum deformation condition was 50:50%. The cavities mechanism at the fracture tip was discussed; it can be defined that the cavities could be avoided when deformation temperature was higher than 940 ℃.