Effects of interstitial O on specific orientation moduli and thermal/stress-induced products in bcc Ti–Mo alloys

Abstract

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.