Abstract The valence electron concentration (VEC) is an important physical factor for phase formation. A high VEC is conducive to forming an FCC phase and improving an alloy's ductility, while a low VEC is beneficial in forming a BCC phase that improves an alloy's strength. This is demonstrated for two HEAs, CoCrCuFeNi (FCC) and AlCoCrFeNi (BCC), that were designed as matrix alloys, where Ni and Mo are alloyed. The microstructure, phase evolution, and the mechanical properties for (AlCoCrFeNi) 100- x Ni x and (CoCrCuFeNi) 100- x Mo x were systematically investigated. As the phase structure for the (AlCoCrFeNi) 100- x Ni x high entropy alloy (HEA) transformed from a BCC to an FCC crystal structure as the Ni content increased from 0 at.% to 16 at.%, the FCC volume fraction increased from 0% to 85%, its compressive fracture strain increased from 25% to 40%, its VEC increased from 7.2 to 7.6. As the phase structure for the (CoCrCuFeNi) 100- x Mo x HEA transformed from FCC to BCC as the Mo content increased from 0 at.% to 16 at.%, the BCC volume fraction increased from 0% to 65%, its compressive yield strength increased from 260 MPa to 928 MPa, its VEC decreased from 8.8 to 8.3. Selecting an element based upon an alloy's VEC is a practical method for designing compositions for HEAs that balance strength and ductility. According to the needs of practical applications, balancing both strength and plasticity requires the following criteria for selecting an element for incorporation into an HEA system: matrix strength is improved by selecting an element with a VEC lower than the average VEC of the matrix, while ductility is improved by selecting another element with a VEC higher than the average VEC for the matrix.

中文翻译：

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利用价电子浓度平衡强度和延展性的高熵合金成分设计

摘要 价电子浓度（VEC）是相形成的重要物理因素。高VEC有利于形成FCC相并提高合金的延展性，而低VEC有利于形成提高合金强度的BCC相。这在两种 HEA 中得到了证明，CoCrCuFeNi (FCC) 和 AlCoCrFeNi (BCC)，它们被设计为基体合金，其中 Ni 和 Mo 被合金化。系统地研究了 (AlCoCrFeNi) 100- x Ni x 和 (CoCrCuFeNi) 100- x Mo x 的微观结构、相演变和机械性能。当 (AlCoCrFeNi) 100- x Ni x 高熵合金 (HEA) 的相结构从 BCC 转变为 FCC 晶体结构时，随着 Ni 含量从 0 at.% 增加到 16 at.%，FCC 体积分数增加从 0% 到 85%，其压缩断裂应变从25%增加到40%，其VEC从7.2增加到7.6。随着 (CoCrCuFeNi) 100- x Mo x HEA 的相结构从 FCC 转变为 BCC，随着 Mo 含量从 0 at.% 增加到 16 at.%，BCC 体积分数从 0% 增加到 65%，其压缩屈服强度从260 MPa提高到928 MPa，VEC从8.8降低到8.3。根据合金的 VEC 选择元素是设计 HEA 成分以平衡强度和延展性的实用方法。根据实际应用的需要，平衡强度和塑性需要以下标准来选择加入 HEA 体系的元素：通过选择 VEC 低于基体平均 VEC 的元素来提高基体强度，