O significantly affects the thermal/stress-induced products in β-type titanium alloys. However, the mechanism of O effects on the displacive behaviors involved in the thermal/stress-induced phase transformation and twinning process is still not fully elucidated. The effects of interstitial O on specific orientation moduli and thermal/stress-induced products in bcc Ti–Mo alloys were investigated through first-principles calculations combined with microstructural observations. The addition of O decreased the formation energy of the supercell and formed the Mo–O and Ti–O bonds with the increase in the bonding electron number, thereby enhancing the β phase stability. The specific orientation moduli such as Young’s modulus (E100), tetragonal shear modulus (C′), and shear moduli (G111 and G113) were increased, which was attributed to the formation of Mo–O and Ti–O bonds along <100>β direction and the strengthened Ti–Ti bonds along <110>β, <111>β and <113>β directions, respectively. The addition of O suppressed the thermal-induced ω phase, corresponding to its structural change from hexagonal to tripartite, and the predominant stress-induced product of α" martensite was inhibited due to the increase in moduli of G111, C′, and E100. This study deepens the understanding of the role of O in phase transformation and twinning mechanisms.
