Microstructural response and mechanical properties of α-precipitated Ti–5Al–5Mo–5V–3Cr alloy processed by high-pressure torsion

The aged Ti–5Al–5Mo–5V–3Cr alloy which is composed of acicular α precipitates and β matrix was processed by high-pressure torsion (HPT). The different flow behaviors of these two phases have a great influence on the grain refinement process. The homogenization of microstructure and microhardness along the radial direction is very slow, which is reached after HPT processing of 100 revolutions. And the α precipitates might enhance the refinement. It is shown that HPT processing produces an ultrafine microstructure with a grain size of less than 50 nm and a high dislocation density of approximately 8 × 1016 m−2. The microhardness evolution as a function of equivalent strain follows a bell-shaped curve, for which the hardness initially increases with strain, reaches a peak value (∼450 Hv) and then decreases to a saturated condition (∼413 Hv). The refined β gains, the high density of dislocations and the α grains with a certain size contributes to the peak hardness. But the strengthening caused by α phase will weaken as increasing the strain.