高强韧固溶强化型高熵合金的快速设计与实验验证

Compositionally complex CrMnFeCoNi high-entropy alloy (HEA) has a single fcc solid solution and outstanding damage tolerance and fracture toughness even at 77 K. However, it cannot satisfy the requirement of engineering applications as high performance structural materials due to its poor room-temperature strength. The present proposal will develop rapid and effective alloy design methods that optimize alloy components and their ratios. The EMTO-CPA approach can accurately describe multicomponent and multiphase complex alloys with continuously changed alloy components. This proposal will employ EMTO-CPA method in combination with experimental characterization to investigate (CrMnFeCoNi)yXx (X1= Al, Ti, V, Cu, Zn, Nb, Mo, W; X2=C, N; x1=0-5, x2=0-0.2, y=0-3; x and y values in molar ratio) HEAs considering the competing body-centered cubic (bcc), face-centered cubic (fcc), hexagonal close-packed (hcp), and other ordered crystal structures. Based on the high-speed calculations from the first-principles EMTO-CPA method, we systematically demonstrate the four effects, such as the change of alloy components and its ratios, substitutional and interstitial alloying elements, different crystal structures, and temperature, on the basic physical properties, phase stability, stacking fault energies, elastic moduli, and mechanical properties of HEAs. Furthermore, we reveal the microscopic mechanism responsible for the observed elastic properties and stacking fault energies from first-principles. According to the calculated elastic moduli, we demonstrate the modification of brittle-ductile transition criterion and solid solution strengthening in HEAs. Then, we use the four effects mentioned-above to design and screen high-entropy alloys with best matching of high strength and high toughness. We built a fast theoretical optimization approach for screening high strength and high toughness HEAs. Finally, we prepare, character and verify as-cast high-entropy alloys by experiments. After preparing the designed and optimized high-entropy alloys, we test and analyze their microstructure, strength, toughness and modulus, etc. Finally, we establish the composition-microstructure-properties prediction model of HEAs. The research of this project will provide theoretical and experimental support for the development of high performance high-entropy alloys.

Fcc单相的CrMnFeCoNi高熵合金在77K有优异损伤容限和断裂韧性，但是其室温强度较低无法满足工程应用需求。本项目拟发展优化合金组元及其配比的快速设计方法，利用能够精确描述多组元成分连续变化的第一性原理EMTO-CPA方法和实验表征相结合，针对（（CrMnFeCoNi）yXx （X是掺杂元素）高熵合金，快速研究合金组元及其配比变化、合金化、不同结构相、温度这四种效应对其物性参数、相稳定性、层错能、弹性模量和力学性能的影响规律，并在电子结构层次上揭示影响这些性能的微观机制。以弹性模量为出发点研究高熵合金脆韧性判据的修正值和固溶强化，利用上述四种效应来实现设计具有高强和高韧良好匹配性的高熵合金，建立高强韧高熵合金的快速理论优化途径。通过制备设计优化的高熵合金，对其微观组织与强度、韧性及模量等进行测试与分析，构建高熵合金的成分-组织-性能预测模型，为高性能高熵合金的发展提供理论与实验支持。

高熵合金是近年来物理冶金领域的新热点之一，高熵合金是一类新兴的多主元结构材料。与统合金不同的单一主元不同，高熵合金是由多种主要合金元素组成的固溶体。因此，多主元的特点使高熵合金的种类组合和性能调控出现无限可能性，大大拓展了合金的潜在应用可能；多主元特性也使其表现出与传统合金不同的结构和形变特征。精确的muffin-tin轨道(exact muffin-tin orbitals, EMTO)和相干势近似(coherent potential approximation, CPA)相结合的第一性原理方法能够高效准确地描述高熵合金中的化学无序、结构无序和磁性无序，因此，本项目利用第一性原理EMTO-CPA方法系统地研究了合金化效应对高熵合金的相稳定性、弹性性能、层错能和变形机制等的影响规律，建立了高熵合金的成分-结构-性能的预测模型；利用多组分高熵合金概念设计出具有可回复应变大、转变温度低的性能优异的新型形状记忆合金。这些研究对快速设计和高效筛选具有高性能的高熵合金具有重要的指导意义。.项目共发放表论文10篇（包括1篇Acta Mater.，1篇JMST，1篇MD，1篇PNAS Nexus等），取得的主要研究成果包括：1）考察了合金化效应、结构效应和温度效应对层错能、弹性性能和力学性能的影响规律；2）建立了理论计算的层错能和塑性变形机制之间的关联性，基于负层错能现象提出了形成变形孪晶的相变介导孪晶机制，该机制能够同步提高强度和塑性，不但突破了强度-塑性倒置关系，而且构建了亚稳合金的成分-结构-力学性能的预测模型；3）基于高熵合金的固溶强化效应，提出了筛选具有最佳合金组元配比的低成本高强韧的高熵合金的普适模型。