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对细晶Ti-2Al-2.5Zr合金进行了室温/低温(77 K)疲劳实验及微观组织观察.结果表明:室温低应变幅△εt/2(= 0.5%,1.0%)下,合金表现为循环软化;室温高应变幅(1.5%,2.0%)下,则表现为循环应力饱和;77 K时,不同应变幅下均表现为循环硬化,且随应变幅升高,循环硬化程度增强.疲劳寿命测试结果表明:低温疲劳寿命始终高于室温,断口SEM观察表明,室温和低温下,疲劳裂纹扩展区均有明显的疲劳条纹,疲劳裂纹以穿晶方式扩展,室温下伴随有大量二次裂纹,低温下的二次裂纹数量明显减少.TEM观察表明:低温下孪生是合金主要的变形方式,包括(10■1)和(11■1)型孪晶.疲劳变形位错组态为:室温较低应变幅(0.5%,1.0%)下,形成位错线和局部位错缠结;室温下应变幅提高到1.5%和2.0时,{10■0}柱面和{11■1}锥面滑移同时开动,位错组态演化为亚晶和明显的位错胞.77 K下,应变幅2.0%时形成沿柱面平行分布的位错带:77 K下应变幅升高到4.5%时,多滑移形成相互垂直的位错线.低温诱发形变孪晶是Ti-2Al-2.5Zr低温疲劳寿命升高的原因.
At room temperature / low temperature (77 K) fatigue test and microstructure observation of the fine grain Ti-2Al-2.5Zr alloy, the results show that the alloy exhibits a low strain rate of ε εt / 2 (= 0.5%, 1.0% The cyclic strain was saturated at room temperature with high strain amplitude (1.5%, 2.0%), while cyclic strain was observed under different strain amplitude at 77 K. The fatigue strength increased with the increase of strain amplitude The results of life test show that the fatigue life at low temperature is always higher than room temperature. SEM observation of the fracture shows that there are obvious fatigue streaks in the fatigue crack growth zone at room temperature and low temperature, the fatigue crack propagates by transgranular growth, accompanied by a large number of secondary cracks , The number of secondary cracks at low temperature was significantly reduced.The TEM observations showed that the twin is the main deformation mode at low temperature, including (10 ■ 1) and (11 ■ 1) type twins.The fatigue deformation dislocation configuration is: room temperature Dislocation lines and local dislocation tangles were formed at lower strain amplitudes (0.5%, 1.0%). At room temperature, when strain amplitude increased to 1.5% and 2.0, {10 ■ 0} cylinders and {11 ■ 1} cones Surface slip at the same time, the dislocation configuration evolves into subgrain and obvious dislocation cells.When the strain amplitude is 2.0% at 77 K, it forms parallel to the cylinder Offset strip: 77 K when the strain amplitude was raised to 4.5%, formation of multiple slip dislocation lines perpendicular to each other low temperature induced deformation twins reason Ti-2Al-2.5Zr increased low temperature fatigue life.