Microstructural evolution and mechanical properties of Ti-6Al-20Mo alloy after hot rolling deformation

This study aimed to evaluate the effects of the different hot rolling deformation process on the structural evolution and mechanical properties of a novel metastable β-type Ti-6Al-20Mo alloy. The microstructural and mechanical properties of the studied alloy under the different conditions were investigated by X-ray diffraction, optical microscopic, scanning electron microscopy, transmission electron microscopy, tensile testing, and microhardness testing. The results demonstrate that hot rolling in the α+β region consistently produces a dual-phase (α+β) microstructure with significant amount of fine intragranular α precipitates, and at 85% deformation the precipitated α-phase size increases significantly from 0.15 to 0.45 μm during the rolling temperature increasing from 700 to 800 °C. In contrast, β-phase-field rolling exclusively retains β grains and triggers discontinuous dynamic recrystallization, and exists the elongated β grains and the equiaxed small-sized grains (∼20 μm). The mechanical properties of the studied alloy are critically modulated by rolling parameters: tensile strength and microhardness decline with rising rolling temperature, whereas both properties increase with greater rolling reduction. The peak mechanical properties emerge after hot rolling at 700 °C with an 85% reduction, i.e. 1301 MPa yield strength, 1320 MPa ultimate tensile strength, and 394 HV0.2 microhardness. Meanwhile, with the fracture mode of the alloy changes from brittle fracture to ductile fracture with the rolling temperatures increasing.