Flow softening and microstructural evolution of near β titanium alloy Ti-35421 during hot compression deformation in the α+β region

Flow softening and microstructural evolution of a novel near β titanium alloy Ti–3Al–5Mo–4Cr–2Zr–1Fe (Ti-35421) with tensile strength beyond 1200 MPa have been investigated at temperatures of 710∼800 °C in the α+β region with strain rates of 0.001∼1 s⁻¹ during hot deformation. The established Arrhenius constitutive model embedded softening mechanism and deformations can predict the flow stress and match the experimental data well. Two mechanisms of dynamic recrystallization (DRX) including the continuous dynamic recrystallization (CDRX) of subgrains rotating and the discontinuous dynamic recrystallization (DDRX) of grain boundaries bulging govern the hot deformation and microstructural evolution. Both CDRX and DDRX occur at high true strains and the number of DRX grains increases with increasing true strain. An obvious flow softening phenomenon presents during thermal compression at the low temperature and low strain rates in the α+β region, which might be attributed to the bending and fragmentation of α phases, inverse change of the texture intensity between α and β phases, and the formation of the new grains from DRX.