An evaluation of the hexagonal close-packed to face-centered cubic phase transformation in a Ti-6Al-4V alloy during high-pressure torsion

A Ti-6Al-4V alloy was used to examine the effect of martensitic (αʹ) or lamellar (α + β) microstructures on grain refinement and the hcp to fcc phase transformation during HPT processing. There was significant grain refinement with grain sizes of ~ 30 and ~ 40 nm in the αʹ and α + β microstructures, respectively, and with the occurrence of an allotropic hcp to fcc phase transformation in the αʹ sample after HPT. A high volume fraction of boundaries, together with a substructure containing initial defects of the martensitic sample, promotes the formation of the fcc phase during the HPT processing.