Abstract Thermally stable high-entropy alloys (HEAs) consisting of a high density of coherent precipitates show a great potential for high-temperature applications. In this work, we systematically investigated the phase stability and coarsening kinetics of L12-type coherent precipitates in a Ni-30Co-13Fe-15Cr-6Al-6Ti-0.1B (at.%) HEA isothermally aged at 800, 900 and 1000 °C. Aged microstructures in the grain interiors under this temperature range were essentially dominated by the uniform precipitation of multicomponent L12 (Ni, Co, Fe, Cr)3(Ti, Al)-type precipitates. The coarsening kinetics of these intragranular L12 precipitates were quantitatively determined, which were adequately characterized by the classical Lifshitz-Slyozov-Wagner model. The activation energy for coarsening was determined to be 378 kJ/mol, which is relatively higher than that of conventional Ni or Co-based superalloys, suggesting a slow elemental diffusion in the HEA matrix. More importantly, the heterogeneous precipitation and the associated metastable phase transformation mechanism along grain boundaries (GBs) were carefully analyzed. Localized chemical heterogeneity was identified within the discontinuous L12 phase at the GBs, which thermodynamically destabilizes the L12 structure and encourages the formation of brittle Heusler phase. Finally, we establish a unique duplex-aging strategy that can be efficiently utilized for GB stabilization, by which these detrimental intergranular heterostructures can be greatly eliminated, leading to an exceptional resistance to intermediate-temperature embrittlement, along with enhanced tensile strengths. These findings will not only shed light on the precipitation mechanisms in compositionally complex HEAs but also generate new opportunities to the interfacial design of HEAs for advanced high-temperature applications with superior properties.

中文翻译：

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多组分高熵合金中纳米级析出和中温脆化的控制

摘要 由高密度相干析出物组成的热稳定高熵合金 (HEA) 在高温应用中显示出巨大的潜力。在这项工作中，我们系统地研究了 Ni-30Co-13Fe-15Cr-6Al-6Ti-0.1B (at.%) HEA 在 800、900 和 1000 ° 等温时效中 L12 型相干析出物的相稳定性和粗化动力学C。在该温度范围内，晶粒内部的时效显微组织主要由多组分 L12（Ni、Co、Fe、Cr）3（Ti、Al）型析出物的均匀析出主导。这些晶内 L12 析出物的粗化动力学被定量测定，这已被经典的 Lifshitz-Slyozov-Wagner 模型充分表征。粗化活化能确定为 378 kJ/mol，这相对高于传统的镍或钴基高温合金，表明 HEA 基体中的元素扩散缓慢。更重要的是，仔细分析了沿晶界（GBs）的非均相沉淀和相关的亚稳态相变机制。在 GB 的不连续 L12 相内发现了局部化学异质性，这在热力学上破坏了 L12 结构并促进了脆性 Heusler 相的形成。最后，我们建立了一种独特的双相时效策略，可以有效地用于 GB 稳定，通过这种策略可以大大消除这些有害的晶间异质结构，从而导致对中温脆化的卓越抵抗力，以及增强的拉伸强度。