Effect of pre-annealing on the formation of the -phase in the Ti-2 wt%V alloy after high-pressure torsion

Although vanadium is used in many alloys as an alloying element, the binary Ti-V system has been studied very poorly. In particular, the effect of heat treatment in combination with high-pressure torsion (HPT) has not been studied at all for this system. The Ti-2 wt%V alloy was pre-annealed at three temperatures in two different regions of the Ti-V phase diagram, namely at 400 degrees C (alpha phase), 700 degrees C (alpha phase) and 1000 degrees C (beta phase). The as-cast state was also investigated. After annealing and quenching, all four samples contained only the alpha/alpha ' phase. After the HPT, the omega-phase appeared in the material. Its portion increased from 70 to 76% with an increase in the pre-annealing temperature, but the as-cast sample had after HPT the largest proportion of omega Ti phase of 86%. The values of nanohardness (H) and Young's modulus (E) after HPT were measured. H increased from 5.1 +/- 0.1 to 6.4 +/- 0.1 GPa with increasing pre-annealing temperature. The steady-state value of torsion torque during HPT also increases from 1533 to 2094 N m. However, the E value remained almost unchanged at 147 +/- 3 GPa. The microhardness of the samples after HPT increased by about two times compared to the annealed samples.