On the role of increasing O concentration and room-temperature aging in modulating the mechanical behavior and deformation mechanisms of Ti-12Mo alloy

This study investigates the influence of O concentration (0.04 versus 0.12 wt.%) and room-temperature aging on the mechanical behavior and deformation mechanisms of a metastable β-type Ti–12Mo (wt.%) alloy. Following solution treatment in the β phase region and subsequent quenching, the alloy exhibits equiaxed β grains containing nanometer-sized ω particles. Atom probe tomography analysis reveals that in the Ti–12Mo–0.04O alloy, 30 days of room-temperature aging increases the number density of ω particles from 3.4 × 10²⁴ m^-3 to 4.4 × 10²⁴ m^-3, indicating a β→ω transformation during room-temperature aging. Conversely, this transformation is suppressed in the Ti–12Mo–0.12O alloy, where the ω particle number density remains nearly unchanged at 4.1 × 10²⁴ m^-3, highlighting the role of O in hindering β→ω transformation during room-temperature aging. During plastic deformation, stress-induced β→α″ martensitic transformation (SIMT) and {112}<111>_β, {455}<522>_β, and {332}<113>_β twinning are activated in Ti–12Mo–0.04O, whereas SIMT as well as {112}<111>_β and {455}<522>_β twinning are suppressed in Ti–12Mo–0.12O due to the higher O concentration. After room-temperature aging, SIMT and all three twinning modes persist in Ti–12Mo–0.04O, though SIMT is inhibited below ∼10 % true strain. In contrast, the aged Ti–12Mo–0.12O alloy shows little change in deformation behavior due to suppressed β→ω transformation. The role of O addition and room-temperature aging in modulating deformation mechanisms is discussed in relation to the elastic stability of the β matrix and the twinning behavior of α″ martensite.