npj: 高熵合金——机制、模拟与预测
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高熵合金（HEAs）材料应用前景广阔，学界对其兴趣浓厚而持续，尽管大多数HEA的元素比例相等或近等，但其性能在该比例下并非最佳。为了改善特定HEAs的性能，拓展其应用，必须探索合金原子组分、单元素对HEA性能的影响，阐明有关的物理冶金机制，以便高效地设计合金。遗憾的是相关机制（如在低温下的迟滞扩散效应和微孪晶的形成）大多至今尚未阐明。来自韩国浦项科技大学李秉珠领导的研究小组，采用各种模拟技术（蒙特卡洛方法、分子动力学和分子静力学）研究了原子在一系列无序高熵合金中的运动，探讨了各元素对等原子比例的经典合金CoCrFeMnNi固溶度的影响。他们发现，具有高迁移势垒、能量稳定的大量晶格空穴存在于HEA中，且导致了动力学上的迟滞扩散效应；而在低温下，六方密堆积结构的能量更为稳定，是微孪晶形成的根本原因。模拟结果很好地预测了合金效应中的临界分切应力，进而通过调整元素比例设计出了一种性能更好的高熵合金。这种高熵合金设计的计算方法，既可帮助开发更为复杂的合金，又能实现更好的性能。
该文近期发表于npj Computational Materials 4: 1 (2018); doi:10.1038/s41524-017-0060-9。英文标题与摘要如下，点击阅读原文可以自由获取论文PDF。
Understanding the physical metallurgy of the CoCrFeMnNi high-entropy alloy: an atomistic simulation study
Won-Mi Choi, Yong Hee Jo, Seok Su Sohn, Sunghak Lee & Byeong-Joo Lee
Abstract Although high-entropy alloys (HEAs) are attracting interest, the physical metallurgical mechanisms related to their properties have mostly not been clarified, and this limits wider industrial applications, in addition to the high alloy costs. We clarify the physical metallurgical reasons for the materials phenomena (sluggish diffusion and micro-twining at cryogenic temperatures) and investigate the effect of individual elements on solid solution hardening for the equiatomic CoCrFeMnNi HEA based on atomistic simulations (Monte Carlo, molecular dynamics and molecular statics). A significant number of stable vacant lattice sites with high migration energy barriers exists and is thought to cause the sluggish diffusion. We predict that the hexagonal close-packed (hcp) structure is more stable than the face-centered cubic (fcc) structure at 0 K, which we propose as the fundamental reason for the micro-twinning at cryogenic temperatures. The alloying effect on the critical resolved shear stress (CRSS) is well predicted by the atomistic simulation, used for a design of non-equiatomic fcc HEAs with improved strength, and is experimentally verified. This study demonstrates the applicability of the proposed atomistic approach combined with a thermodynamic calculation technique to a computational design of advanced HEAs.
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