Department of Mechanical Engineering, Faculty of Engineering, The University of Hong Kong, Hong Kong 999077, China.
Shenzhen Institute of Research and Innovation, The University of Hong Kong, Shenzhen 518057, China.
Proc Natl Acad Sci U S A. 2023 Mar 21;120(12):e2209188120. doi: 10.1073/pnas.2209188120. Epub 2023 Mar 13.
Local chemical short-range ordering (SRO) and spatial fluctuations of planar fault energy are important features of multi-element and metastable complex concentrated alloys (CCAs). Arising from them, dislocations in such alloys are distinctively wavy in both static and migrating conditions; yet, such effects on strength have remained unknown. In this work, molecular dynamics simulations are used to show that the wavy configurations of dislocations and their jumpy motion in a prototypic CCA of NiCoCr are due to the local fluctuations of the energy of SRO shear-faulting that accompanies dislocation motion, with the dislocation getting pinned at sites of hard atomic motifs (HAMs) associated with high local shear-fault energies. Unlike the global averaged shear-fault energy which in general will subdue on successive dislocation passes, the local fluctuations in the fault energy always remain in a CCA, thus offering a strength contribution that is unique in such alloys. Analysis of the magnitude of this form of dislocation resistance shows that this is dominating over contributions due to elastic misfit of alloying elements and is in good agreement with strengths predicted from molecular dynamics simulations and experiments. This work has unfolded the physical basis of strength in CCAs, which is important for the development of these alloys into useful structural materials.
局部化学短程有序（SRO）和平面位错能的空间涨落是多组元和亚稳复杂浓化合金（CCA）的重要特征。由此产生的结果是，这些合金中的位错在静态和迁移状态下都具有明显的波浪形；然而，其对位错强度的影响仍然未知。在这项工作中，分子动力学模拟表明，NiCoCr 原型 CCA 中位错的波浪形构型及其跳跃式运动是由于伴随位错运动的 SRO 剪切位错能的局部涨落引起的，位错在与高局部剪切位错能相关的硬原子图案（HAM）位置被钉扎。与通常会在连续位错通过时减弱的全局平均剪切位错能不同，位错能的局部涨落在 CCA 中始终存在，从而为这些合金提供了独特的强度贡献。对这种位错阻力形式的大小进行分析表明，这一形式的位错阻力主导了合金元素弹性失配的贡献，并且与从分子动力学模拟和实验预测的强度很好地吻合。这项工作揭示了 CCA 强度的物理基础，这对于将这些合金开发成有用的结构材料非常重要。
