Density-functional theory (DFT) is used to identify phase-equilibria in multi-principal-element and high-entropy alloys (MPEAs/HEAs), including duplex-phase and eutectic microstructures. A combination of composition-dependent formation energy and electronic-structure-based ordering parameters were used to identify a transition from FCC to BCC favoring mixtures, and these predictions experimentally validated in the Al-Co-Cr-Cu-Fe-Ni system. A sharp crossover in lattice structure and dual-phase stability as a function of composition were predicted via DFT and validated experimentally. The impact of solidification kinetics and thermodynamic stability was explored experimentally using a range of techniques, from slow (castings) to rapid (laser remelting), which showed a decoupling of phase fraction from thermal history, i.e., phase fraction was found to be solidification rate-independent, enabling tuning of a multi-modal cell and grain size ranging from nanoscale through macroscale. Strength and ductility tradeoffs for select processing parameters were investigated via uniaxial tension and small-punch testing on specimens manufactured via powder-based additive manufacturing (directed-energy deposition). This work establishes a pathway for design and optimization of next-generation multiphase superalloys via tailoring of structural and chemical ordering in concentrated solid solutions.

中文翻译：

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双相多主元合金的理论指导设计

密度泛函理论 (DFT) 用于识别多主元素和高熵合金 (MPEA/HEA) 中的相平衡，包括双相和共晶微观结构。组合依赖于组成的形成能和基于电子结构的排序参数被用来识别从 FCC 到 BCC 有利于混合物的转变，并且这些预测在 Al-Co-Cr-Cu-Fe-Ni 系统中得到了实验验证。通过 DFT 预测了晶格结构和双相稳定性作为成分函数的急剧交叉，并通过实验进行了验证。使用一系列技术，从慢速（铸件）到快速（激光重熔），通过实验探索了凝固动力学和热力学稳定性的影响，这表明相分数与热历史的解耦，即相分数被发现是凝固速率-独立，能够调节从纳米级到宏观级的多模态细胞和晶粒尺寸。通过对粉末增材制造（定向能量沉积）制造的样品进行单轴拉伸和小冲头测试，研究了选定加工参数的强度和延展性权衡。这项工作通过定制浓固溶体中的结构和化学顺序，为下一代多相高温合金的设计和优化建立了一条途径。