The phase constituent, phase stability, microstructure, and hardness of seven arc melted Al_xCr_2-xCoFeNi (x = 0.25~1.75) high-entropy alloys, in as-cast and 800 or 1000°C annealed states, were investigated using XRD, SEM, EDS and DSC. With the increase of Al content, the FCC phase disappeared in the as-cast Al_xCr_2-xCoFeNi alloys. As for the as-cast alloys with 25~30 at.%Al, the composition difference between the former and the later solidified B2 phase can be clearly identified. As for the Al_xCr_2-xCoFeNi (x = 0.25~1.0) alloys, the σ phase formed at above 576°C and decomposed at 912~1033°C. Fine FCC, BCC, B2 and σ phases existed in the 800°C annealed Al_xCr_2-xCoFeNi (x = 0.25~1.25) alloys. And the hardness became higher than that of the as-cast alloys. When the Al content was 25 at.%, the hardness of the alloy decreased significantly with the disappearance of the σ phase. After annealing at 1000°C, the σ phase only existed in the Al_0.25Cr_1.75CoFeNi and Al_0.5Cr_1.5CoFeNi alloys. With the increase of Al content, the alloy hardness also increased. Prolonging the annealing time, from 120 h to 480 h, can decrease the Al content in precipitated FCC or BCC phases and coarsen the phase grains, which will decrease of the alloy hardness. In all, the change of hardness after annealing depends on the contributions of formation of the harder σ phase or the softer FCC/BCC phases and the grain size of the precipitates. The results will help design the composition and treatment process of Al-Co-Cr-Fe-Ni high-entropy alloys.

7 种电弧熔炼的 Al _x Cr _2-x CoFeNi (x = 0.25~1.75) 高熵合金在铸态和 800 或 1000°C 退火状态下的相组成、相稳定性、微观结构和硬度进行了研究。 XRD、SEM、EDS 和 DSC。随着Al含量的增加，铸态Al _x Cr _2-x CoFeNi合金中FCC相消失。对于含 25~30 at.%Al 的铸态合金，可以清楚地识别出前者和后者凝固的 B2 相之间的成分差异。对于 Al _x Cr _2-x CoFeNi (x = 0.25~1.0) 合金，σ 相在 576°C 以上形成并在 912~1033°C 分解。800°C退火的Al _x Cr中存在精细的FCC、BCC、B2和σ相_2-x CoFeNi (x = 0.25~1.25) 合金。并且硬度变得高于铸态合金的硬度。当Al含量为25at.%时，随着σ相的消失，合金的硬度显着降低。1000℃退火后，σ相仅存在于Al _0.25 Cr _1.75 CoFeNi和Al _0.5 Cr _1.5CoFeNi合金。随着Al含量的增加，合金硬度也随之增加。延长退火时间，从 120 h 到 480 h，可以降低析出的 FCC 或 BCC 相中的 Al 含量，使相晶粒粗化，从而降低合金硬度。总之，退火后硬度的变化取决于较硬的σ相或较软的FCC/BCC相的形成和析出物晶粒尺寸的贡献。研究结果将有助于设计 Al-Co-Cr-Fe-Ni 高熵合金的成分和处理工艺。