Influence of Annealing on the Structure and Mechanical Properties of Ultrafine-Grained VT22 Titanium Alloy

Studies of the evolution of the structural-phase state and changes in the mechanical properties of the ultrafine-grained alloy VT22 after annealing in the temperature interval 773-1073 K have been carried out. It has been shown that after annealing at 773 K practically no decrease in the density of deformation defects and practically no changes in the average size of the elements of the grain-subgrain structure and the mechanical properties of the alloy are observed. However, the structural-phase state of the alloy under these conditions is thermally unstable. There take place a generation of new grains with sizes less than 0.1 mu m and growth of individual grains up to sizes on the order of 1 mu m, and also a change in the volume fractions of the alpha- and beta-phases. At higher annealing temperatures, there is observed a decrease in the density of deformation defects, growth of existing grains, a transition of the grain boundaries to a more equilibrium state, and, as a consequence, a substantial deterioration of the mechanical properties at room temperature. Under these conditions, alpha-beta-phase transformations actively develop, leading to an increase in the volume fraction of the beta-phase with increasing temperature. Estimates of the activation energy of grain growth were performed. It is shown that its value is 145 kJ/mol.