An overview of the microstructural and mechanical properties of Al-Co-Cr-Fe-Ni-Ti high entropy alloys (HEAs) at high temperatures is presented. With exceptional properties at high temperature and high dissolution temperature of the L12 phase (γ′), HEAs exhibit excellent wear resistance, thermal stability, high hardness and strength, superior corrosion resistance, and remarkable electrical and magnetic properties, which position them as ideal candidates to replace traditional superalloys. Refractory high entropy alloys (RHEAs) offer excellent mechanical properties at high temperatures. However, reducing price and weight without sacrificing mechanical properties is an essential requirement for broadening the applications of RHEAs. Among varieties of HEA systems, Al-Co-Cr-Fe-Ni-Ti has proven to be an optimum choice for high-temperature applications considering price and weight. The development of strength in this alloy system primarily depends on optimizing its chemical components regarding various phases and their phase fractions. An increase in Al+Ti content increases the formation of Ni3(Ti, Al) or γ′ and, consequently, the strength of the alloy. Conversely, Cr and Fe must be carefully balanced to prevent the formation of brittle phases. Exceeding the limiting values of Co, Cr, and Fe can lead to the formation of brittle phases like Heusler,β,η, and σ. In order to achieve better mechanical properties, the optimized [Al+Ti]-content should be around 15–16 at%. At elevated temperatures, valence electron concentration (VEC) closely aligns with the corresponding microstructure, suggesting that VEC can be utilized to predict the microstructure. Superior oxidation resistance at elevated temperatures (higher than that of Ni-based superalloys) promotes Al-Co-Cr-Fe-Ni-Ti HEAs for high-temperature applications.

中文翻译：

---

Al-Co-Cr-Fe-Ni-Ti 高熵合金：高温下微观结构和机械性能综述


概述了 Al-Co-Cr-Fe-Ni-Ti 高熵合金 （HEA） 在高温下的微观结构和机械性能。HEA 在 L12 相 （γ′） 的高温和高溶解温度下具有优异的性能，表现出优异的耐磨性、热稳定性、高硬度和强度、卓越的耐腐蚀性以及卓越的电学和磁性能，这使它们成为替代传统高温合金的理想选择。难熔高熵合金 （RHEA） 在高温下具有优异的机械性能。然而，在不牺牲机械性能的情况下降低价格和重量是扩大 RHEA 应用的基本要求。在各种高熵合金系统中，考虑到价格和重量，Al-Co-Cr-Fe-Ni-Ti 已被证明是高温应用的最佳选择。该合金系统的强度发展主要取决于优化其化学成分的各种相及其相分数。Al+Ti 含量的增加会增加 Ni3（Ti， Al） 或 γ' 的形成，从而增加合金的强度。相反，Cr 和 Fe 必须仔细平衡，以防止形成脆性相。超过 Co、Cr 和 Fe 的极限值会导致形成脆性相，如 Heusler、β、η 和 σ。为了获得更好的机械性能，优化的 [Al+Ti] 含量应在 15-16 at% 左右。在高温下，价电子浓度 （VEC） 与相应的微观结构紧密一致，表明 VEC 可用于预测微观结构。 在高温下卓越的抗氧化性（高于镍基高温合金）促进了 Al-Co-Cr-Fe-Ni-Ti HEA 在高温应用中的应用。