Superplastic deformation behaviors of powder-metallurgical Ti-6Al-4V

Powder-metallurgical (PM) Ti-6Al-4V with an average grain size of 22.3 mu m was prepared via cold isostatic pressing and vacuum sintering. The superplastic deformation behaviors of PM Ti-6Al-4V in the temperature range of 800-1000 degrees C and strain rate range of 0.01-0.001 s-1 were investigated in terms of microstructural evolution, kinetics, and superplasticity mechanisms. The dominant microstructural evolution mechanisms of PM Ti-6Al-4V samples at 950 and 1000 degrees C were continuous dynamic recrystallization (CDRX) and CDRX with a dynamic recovery of R, respectively. The increase in R-coordinated deformation restrained cavitation and promoted superplasticity. The dominant superplastic deformation mechanism of PM Ti-6Al-4V was Rachinger sliding. The dislocation creep in R, with the stress-induced phase transformation of alpha - R, accommodated the Rachinger sliding at 1000 degrees C. The intersection of the flow stress is considered to be the transition point of dynamic recrystallization - superplasticity.