Hot deformation and microstructural damage mechanisms in extra-low interstitial (ELI) grade Ti-6Al-4V

The hot deformation behavior of extra-low interstitial (ELI) grade Ti-6Al-4V alloy with Widmanstatten preform microstructure over wide temperature (750-1100 degrees C) and strain rate ranges (0.001-100 s(-1)) has been studied with the help of processing maps. In the lower temperature and strain rate regime (850-950 degrees C and 0.001-0.1 s(-1)), globularization of the lamellar structure occurs while at higher temperatures (980-1100 degrees C) the beta phase exhibits large-grained superplasticity. The tensile ductility reaches peak values under conditions corresponding to these two processes. A dip in ductility occurs at the beta transus and is attributed to a possible nucleation of voids within prior beta grains. At lower temperatures and strain rates below about 0.1 s(-1),cracking at the prior beta grain boundaries occurs under mixed mode conditions. At strain rates higher than 1 s(-1) and temperatures lower than about 950 degrees C, the material exhibits a wide regime of flow instabilities. On the basis of these results, a temperature-strain rate window for hot working this material without microstructural defects is identified. Published by Elsevier Science S.A.