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-4 V alloy with Widmanstatten preform microstructure over wide temperature (75 0-1100 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 lam ellar structure occurs while at higher temperatures (980-1100 degrees C) th e 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 possib le 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 boundar ies 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 w ide regime of flow instabilities. On the basis of these results, a temperat ure-strain rate window for hot working this material without microstructura l defects is identified. Published by Elsevier Science S.A.