温度和氧含量对Ti-2Al合金拉伸力学行为和断裂方式的耦合影响

研究高氧含量(0.30%，质量分数，下同)、工业水平氧含量(0.16%)和极低氧含量(0.06%) 3种Ti-2Al合金在低温(77 K)、室温和高温(673 K)下的拉伸力学行为。结果表明：低温和室温下，随着氧含量的升高，材料强度提高，塑性降低。然而，高温673 K下，不同氧含量Ti-2Al合金强度和塑性基本相同，材料强度和塑性对氧含量的依赖性显著降低。氧含量较低时，温度对Ti-2Al合金塑性影响很小。微观组织观察表明，随着温度的升高，工业水平及高氧含量Ti-2Al合金拉伸断口由脆性解理转变为延性韧窝。高温环境下，固溶氧原子扩散速率提高使Cottrel气团对位错滑移的阻碍减弱，均匀变形的结果导致高氧含量Ti-2Al合金延性改善。

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.