Achieving superior grain refinement and mechanical properties in vanadium through high-pressure torsion and subsequent short-term annealing

Commercial purity vanadium with an initial grain size of ~27 μm and a Vickers microhardness of Hv≈85 was processed by high-pressure torsion (HPT) under a pressure of 6.0 GPa at room temperature through 1/2 to 10 turns. After processing through 10 turns, some samples were immediately subjected to a short-term annealing (15 min) at different temperatures from 773 to 1173 K. The microstructures developed in HPT and in HPT plus post-HPT annealing were characterized by electron backscatter diffraction (EBSD). Processing by HPT for 10 turns gave a refined grain size of ~410 nm and an increased hardness of Hv≈240. Post-HPT annealing demonstrated that the ultrafine grained vanadium has good thermal stability up to at least 873 K. Tensile testing at room temperature gave an ultimate tensile strength of ~920 MPa after 10 turns of HPT with an elongation of ~29%. These results show HPT processing produces superior mechanical properties in vanadium by comparison with processing by ECAP or ECAP plus cryorolling.