Effect of molybdenum concentration on ductile-to-brittle transition in Ti-Mo Alloys

The stability of β-phase in titanium-molybdenum (Ti-Mo) alloys, controlled by Mo concentration, directly affects the deformation mechanisms, thereby imposing significant effects on their ductile-to-brittle transition (DBT) behaviors. However, systematic investigations of this relationship remain unexplored. In this work, we employed the small punch test to investigate the DBT behavior of model Ti-xMo ( x = 3, 15, 25, 32 wt.%) alloys. The Ti-Mo alloys exhibit pronounced temperature-dependent deformability when β-phase stability surpasses the critical threshold required for maintaining a single-phase structure. The β-Ti-Mo alloys display an anomalous DBT governed by the synergistic effects of Mo concentration and temperature on deformation mechanisms. Interestingly, Ti-Mo alloys demonstrate three distinct toughness regimes: a brittle state characterized by long, straight screw dislocations; a ductile state linked to high-density entangled dislocations that blunt crack tips and enable coordinated deformation; and a tough state induced by the combined activation of twinning and dislocation slip. Notably, twinning effectively alleviates low-temperature brittleness and simultaneously enhances high-temperature toughness. Twin boundaries not only hinder dislocation motion but also act as dislocation sources to enhance plasticity, thereby achieving strength-toughness synergy. These findings clarify the role of Mo concentration in DBT of Ti-Mo alloys and establish guidelines for designing of high-performance Ti alloys.