Evidence of alpha ->omega phase transition in titanium after high pressure torsion

It is well known that a high pressure omega-phase is formed in Ti at high pressures in the range between 2 and 8 GPa. This martensitic-type transformation demonstrates very large hysteresis, and hence the w-phase can be retained in the material after release of pressure. Additionally, applied shear stresses are known to facilitate the alpha -> omega transformation. This paper describes an investigation on the omega-phase formation after high pressure torsion under a wide range of pressures and shear strains by means of X-ray diffraction and transmission electron microscopy. We show that the omega-phase forms in Ti upon high pressure torsion deformation after 300 s under a pressure of 3 GPa. This suggests that the transformation kinetics are notably increased as compared with the kinetics of pressure-induced transformation.