Mechanism of trace oxygen promoting ductility in as-cast Ti-6Al-4V alloys

In this paper, the effect of oxygen content in the range of 0.15–0.44 wt% on the tensile properties at room temperature of cast Ti-6Al-4V alloy was studied, and the effect mechanism of oxygen on the tensile deformation behavior was discussed. The results show that with the increase in oxygen content, the strength of the alloy improves, while the elongation increases first and then decreases. Oxygen dissolving in α phase leads to obvious change of lattice constant c/a ratio. The activation of prismatic slips in α phase facilitates the migration of oxygen atoms from octahedral site to hexahedral site to reduce stacking fault energy. The improvement of strength and the decreasement of elongation are attributed to the solid solution strengthening mechanism, while the abnormal highest elongation of the alloy with 0.22 wt% oxygen is due to the oxygen atoms moving into the hexahedral site.