Refinement of β Grains and Dynamic Recrystallization of Ti–3Al–5Mo–4Cr–2Zr–1Fe Alloy during Different Passes Hot Deformation in α+β Phase Region

This study systematically investigates the microstructural evolution and flow softening behavior of the near-β alloy Ti–3Al–5Mo–4Cr–2Zr–1Fe under strain rate of 0.01 s⁻¹ in the α+β phase region, during both single-pass and multi-pass deformation. The results show that an increase in temperature led to a reduction in flow stress, fragmentation of the α phase, and dynamic phase transformation from α to β during single-pass compression. During multi-pass hot compression, as the strain increased, a substantial amount of the α phase underwent spheroidization. The β phase was elongated in the direction orthogonal to the compression axis, accompanied by a decrease in average grain size. The orientation of β grains changed from a random distribution to alignment along the <111> and <001> directions parallel to the compression axis. With an increasing number of passes, the size of β grains was refined from 30.35 μm after single-pass deformation to 18.62 μm after 3-pass. The size of the equiaxed α phase increased significantly, and the geometrically necessary dislocation density in the deformed microstructure correspondingly increased. Dislocations progressively accumulated at grain and subgrain boundaries, and the localized internal stresses acted as a driving force for nucleation, promoting dynamic recrystallization and thereby enhancing the degree of recrystallization. The main softening mechanism during single-pass hot compression was continuous dynamic recrystallization (CDRX), while both CDRX and discontinuous dynamic recrystallization coexisted during three-pass compression. The intensities of the deformation textures {001} and {111} decreased with the number of passes, showing a negative correlation with the degree of recrystallization.