EFFECT OF STRUCTURAL-PHASE STATE ON THE DEFORMATION BEHAVIOR AND MECHANICAL PROPERTIES OF NEAR β TITANIUM ALLOY VT22 IN THE TEMPERATURE RANGE 293-823 K

Abstract

This paper investigates the effect of thermomechanical treatments, including deformation by radial shear rolling or severe plastic deformation by abc pressing with subsequent aging at 773 K, on the structural-phase state, deformation behavior and mechanical properties of commercial near β titanium alloy VT22 (Ti-5Al-5Mo-5V-1Cr-1Fe). The structure of the alloy after radial shear rolling and subsequent aging consists of transformed β grains with a lamellar α + β structure and primary α-phase particles. Severe plastic deformation of the alloy followed by aging causes the formation of a grain-subgrain α + β structure with an average characteristic size of 0.23 µm. It is found that after the thermomechanical treatments, the strength characteristics of the alloy at room temperature increase by ~40% compared to the as-received alloy. The alloy after radial shear rolling and aging retains a 40-20% higher strength in the temperature range of 293-823 K. The strength of the alloy after severe plastic deformation and aging becomes lower than that of the as-received alloy already at a temperature of 773 K. Analysis of creep parameters at 743 K shows that the creep deformation of the alloy in the state after radial shear rolling and aging occurs by the motion of dislocations (glide + climb). The creep deformation of the alloy in the state after severe plastic deformation and subsequent aging is largely contributed to by grain boundary sliding.