Refractory metal high-entropy superalloys (RSA), which possess a nanoscale microstructure of B2 and bcc phases, have been developed to offer high temperature capabilities beyond conventional Ni-based alloys. Despite showing a number of excellent attributes, to date there has been little consideration of their microstructural stability, which is an essential feature of any material employed in high temperature service. Here, the stability of the exemplar RSA AlMo0.5NbTa0.5TiZr is studied following 1000 h exposures at 1200, 1000 and 800 °C. Crucially, the initial nanoscale cuboidal B2 + bcc microstructure was found to be unstable following the thermal exposures. Extensive intragranular precipitation of a hexagonal Al-Zr-rich intermetallic occurred at all temperatures and, where present, the bcc and B2 phases had coarsened and changed morphology. This microstructural evolution will concomitantly change both the mechanical and environmental properties and is likely to be detrimental to the in-service performance of the alloy.

中文翻译：

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AlMo0.5NbTa0.5TiZr 难熔金属高熵高温合金在高温下的微观结构退化


难熔金属高熵高温合金 (RSA) 具有 B2 和 bcc 相的纳米级微观结构，已开发出超越传统镍基合金的高温性能。尽管显示出许多优异的属性，但迄今为止，人们很少考虑其微观结构稳定性，而微观结构稳定性是高温应用中使用的任何材料的基本特征。在此，研究了示例 RSA AlMo0.5NbTa0.5TiZr 在 1200、1000 和 800 °C 下暴露 1000 小时后的稳定性。至关重要的是，最初的纳米级立方体 B2 + bcc 微观结构在热暴露后被发现不稳定。在所有温度下都会发生六方晶系富 Al-Zr 金属间化合物的广泛晶内沉淀，并且在存在的情况下，bcc 相和 B2 相已粗化并改变了形态。这种微观结构的演变将同时改变机械和环境性能，并且可能不利于合金的使用性能。