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 (alpha) or lamellar (alpha + beta) microstructures on grain refinement and the hcp to fcc phase transformation during HPT processing. There was significant grain refinement with grain sizes of similar to 30 and similar to 40 nm in the alpha' and alpha + beta microstructures, respectively, and with the occurrence of an allotropic hcp to fcc phase transformation in the alpha' 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.