An analysis of the role of grain size on superplasticity of γ titanium aluminides

Research paper by R. S. Mishra, A. K. Mukherjee

Indexed on: 01 Jan '00Published on: 01 Jan '00Published in: Journal of Materials Science


The superplastic data for several microcrystalline and submicrocrystalline TiAl alloys has been analyzed to establish the rate controlling mechanism. The results show that the lattice diffusion controlled slip-accommodated grain boundary sliding mechanism is operative for the entire grain size range, 150 nm–20 μm. The detail of the nature of α2 phase, i.e. ordered or disordered, does not influence the kinetics of superplastic flow. The optimum superplastic temperature decreases with the decrease in grain size. The optimum superplastic flow stress shows an intrinsic inverse dependence on the grain size. This grain size dependence of the optimum superplastic flow stress can be explained as the stress required to nucleate dislocations from grain boundary edge during slip accommodation of grain boundary sliding. Superplasticity in nanocrystalline TiAl remains an intriguing possibility because it has the potential for increasing the optimal superplastic strain rate or alternatively, decreasing the superplastic forming temperatures.