Coupling effect of testing temperature and oxygen concentration on tensile mechanical behavior and fracture mode of Ti-2Al alloy

The tensile mechanical behavior of Ti-2Al alloys containing 0.06% (extremely low content; mass fraction, similarly hereinafter), 0.16% (industrial content) and 0.30% (high content) oxygen at low temperature (77 K), room temperature and elevated temperature (673 K) was investigated. Results show that Ti-2Al-0.06O, Ti-2Al-0.16O and Ti-2Al-0.30O exhibit significant variation in strength and ductility. The strength was increased but the ductility was decreased with increasing of the oxygen concentration at room temperature and low temperature. However, there was not an obvious effect of oxygen concentration on both the strength and the ductility of these alloys at 673 K. In addition, the ductility of Ti-2Al-0.06O remained nearly invariable at different temperatures. In other words, ductility was independent on the testing temperature in the alloy with low oxygen concentration. This indicates that deterioration in ductility of Ti-2Al alloy is mainly due to excess absorption of oxygen. SEM observations reveal that a transition of fracture from brittle cleavage to dimple occurred in Ti-2Al-0.30O and Ti-2Al-0.16O as the testing temperature increased. Improvement in ductility of these alloys with high oxygen concentration can be attributed to increase in diffusivity of oxygen atoms, which leads to escape of the constrained dislocation from Cottrel atmosphere at the elevated temperature.