The application and component designs of single crystal superalloys are restricted by the precipitation of topologically closed packed (TCP) phases, which can deteriorate the microstructural stability of the alloys severely. Limited researches concerning the type and morphology evolution of TCP phases under elevated temperature conditions have been reported previously. In the present work, three Re-containing single crystal alloys were designed to investigate TCP phase evolution via long term isothermal exposure tests at 1120 °C while the effects of Re on the microstructural characteristic and elements segregation were also clarified. The results showed that the addition of Re increased the instability of the alloys and the volume fraction of the TCP phases exceeded 5 vol% when the Re content reached 3 wt%. The increasing Re content had also raised the precipitation temperature of TCP phases but it did not change the type of them after long term aging; all the TCP particles were identified as μ phase in this study. Moreover, the elements segregation became considerably serious as Re addition increased constantly, which brought about various morphologies of the μ phase in the experimental alloys. In particular, the rod-like and needle-like μ phases demonstrated the typical orientation within γ matrix while the blocky μ phase was dispersedly distributed in the space. No specific orientation relationship could be observed in the μ phase when the addition of Re exceeded certain threshold value.

中文翻译：

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几种含余单晶高温合金在长期热暴露期间TCP相的演变

单晶高温合金的应用和零件设计受到拓扑密堆积（TCP）相沉淀的限制，这会严重降低合金的显微组织稳定性。先前已经报道了关于在高温条件下TCP相的类型和形态演变的有限研究。在目前的工作中，设计了三种含Re的单晶合金，以通过在1120°C下进行的长期等温暴露试验研究TCP相的演变，同时还弄清了Re对微结构特征和元素偏析的影响。结果表明，当Re含量达到3 wt％时，添加Re增加了合金的不稳定性，TCP相的体积分数超过5 vol％。Re含量的增加也提高了TCP相的析出温度，但经过长时间的老化后并没有改变它们的类型。所有的TCP粒子都被标识为本研究中的μ相。此外，随着Re的添加不断增加，元素的偏析变得相当严重，这导致了实验合金中μ相的各种形态。特别是，棒状和针状μ相表现出γ矩阵内的典型取向，而块状μ相则分散在空间中。当Re的添加超过一定阈值时，在μ相中未观察到特定的取向关系。