Flow Softening and Microstructural Evolution of Metastable Β Titanium Alloy Ti-35421 During Hot Compression Deformation in the Α+Β Region

Abstract: Flow softening and microstructural evolution of a novel metastable β titanium alloy Ti-3Al-5Mo-4Cr-2Zr-1Fe (Ti-35421) newly-developed with tensile strength beyond 1200 MPa have been investigated. Hot deformation was performed at temperatures of 710~800 ℃ in the α+β region with strain rates of 0.001~1 s -1 . 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 phase, inverse change of the texture intensity between α and β phases and the formation of the new grains from dynamic recrystallization. The Arrhenius constitutive model has been established to discern the softening mechanism and predict the flow stresses. According to the results, predicted stress matches well with experimental data. Two mechanisms of dynamic recrystallization (DRX) including the continuous dynamic recrystallization (CDRX) with subgrains rotating and the discontinuous dynamic recrystallization (DDRX) with grain boundaries bulging govern the hot deformation and microstructural evolution. Both CDRX and DDRX occur at high true strains and low strain rates simultaneously. In addition, the DRX occurs after the α phase appears and the number of DRX grains increases with increasing true strain