Considering the service safety for TiAl alloy under thermal shock, the effect of thermal shock temperature and cycles on micro-structural degeneration and mechanical properties were studied. The results show that the vertical decomposition of α→β phase transition occurs in α lamellae if the single thermal shock temperature increases to 1000 °C or the thermal shock cycle increases to 10 times at 900 °C. Cracks form during the thermal shock progress as the single thermal shock temperature increases to 1000 °C or the number of thermal shocks is 5 times at 900 °C. Simultaneously, the flexural strength of samples decreases to 70% of the initial flexural strength under the same condition. It indicates that Ti–45Al–4Nb–1Mo-0.1B alloy fails as the single thermal shock temperature is above 1000 °C or the number of thermal shocks exceeds 5 times at 900 °C, and cracks generated during the thermal shock progress cause the dramatic deterioration in flexural strength. Meanwhile, the formed cracks are coarse, and the propagation path is relatively straight, which further deteriorates the flexural strength of the Ti–45Al–4Nb–1Mo-0.1B alloy. Besides, the nucleation and propagation of cracks change with the thermal shock temperature and cycles were analyzed. When the single thermal shock temperature is 1000 °C, the nucleation of cracks is not only in lamellar colony boundaries but also in α/γ lamellar interfaces and the propagation path of cracks is relatively straight compared with the formation of cracks after 5 thermal shocks at 900 °C, because the thermal stress increases, and then cracks directly pass through lamellar colonies when the angle between lamellar orientation and crack propagation direction is about 90°.

中文翻译：

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层状TiAl合金热震过程中的微观组织损伤和力学响应

考虑到TiAl合金在热冲击下的使用安全性，研究了热冲击温度和循环次数对TiAl合金显微组织退化和力学性能的影响。结果表明，当单次热震温度升高到1000℃或热震循环在900℃时增加到10次时，α片层中会发生α→β相变的垂直分解。当单次热冲击温度升高到1000℃或在900℃时热冲击次数达到5次时，在热冲击过程中会形成裂纹。同时，样品的弯曲强度下降至相同条件下初始弯曲强度的70%。这表明Ti-45Al-4Nb-1Mo-0.1B合金在单次热冲击温度高于1000℃或900℃时热冲击次数超过5次时发生失效，热冲击过程中产生的裂纹导致了合金的失效。弯曲强度急剧恶化。同时，形成的裂纹较粗，扩展路径相对较直，进一步降低了Ti-45Al-4Nb-1Mo-0.1B合金的抗弯强度。此外，还分析了裂纹的形核和扩展随热震温度和循环次数的变化。当单次热震温度为1000℃时，裂纹的形核不仅发生在层状团界，而且发生在α/γ层状界面，与5次热震后形成的裂纹相比，裂纹的扩展路径相对较直。 900℃时，由于热应力增大，当层状取向与裂纹扩展方向夹角约为90°时，裂纹直接穿过层状集落。