Effects of Al and Fe on the metastable phase and deformation mode in β-type Ti-Mo alloys

The effects of Al (1, 1.5, 2, 2.5, 3 wt%) and Fe (0, 1, 2, 3, 4 wt%) addition on the evolution of metastable phase and transition of deformation mode in Ti-11Mo (wt.%) alloys are systematically studied. The tetragonal shear modulus (Cʹ), Youngʹs modulus (E100), and shear modulus (G111) of Ti-11.8 Mo (wt.%) alloys under the addition of Al (3.4 wt%) and Fe (6.8 wt%) are obtained by first-principles calculations. The results reveal that with the addition of Al, the α″-martensite is enhanced, while the ω-phase is suppressed owing to the decreased values of E100 and Cʹ. The decrease in the value of E100 is higher than that of Cʹ, so the deformation mode undergoes a transition from {332} twinning combined with stress-induced α″-martensitic transformation to stress-induced α″-martensitic transformation. With the addition of Fe, both the α″-martensite and ω-phase are suppressed due to the increase in the values of E100 and G111, and the increased Cʹ leads to the suppression of {332} twinning.