Zhou Xinran, He Sicong, Marian Jaime
Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095, USA.
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095, USA.
Materials (Basel). 2022 Aug 8;15(15):5468. doi: 10.3390/ma15155468.
In this work, we study vacancy energetics in the equiatomic Nb-Mo-Ta-W alloy, especially vacancy formation and migration energies, using molecular statics calculations based on a spectral neighbor analysis potential specifically developed for Nb-Mo-Ta-W. We consider vacancy properties in bulk environments as well as near edge dislocation cores, including the effect of short-range order (SRO) by preparing supercells through Metropolis Monte-Carlo relaxations and temperature on the calculation. The nudged elastic band (NEB) method is applied to study vacancy migration energies. Our results show that both vacancy formation energies and vacancy migration energies are statistically distributed with a wide spread, on the order of 1.0 eV in some cases, and display a noticeable dependence on SRO. We find that, in some cases, vacancies can form with very low energies at edge dislocation cores, from which we hypothesize the formation of stable 'superjogs' on edge dislocation lines. Moreover, the large spread in vacancy formation energies results in an asymmetric thermal sampling of the formation energy distribution towards lower values. This gives rise to vacancy formation energies that are noticeably lower than the distribution averages. We study the effect that this phenomenon has on the vacancy diffusivity in the alloy and discuss the implications of our findings on the structural features of Nb-Mo-Ta-W.
在这项工作中，我们使用基于专门为Nb-Mo-Ta-W开发的光谱邻域分析势的分子静力学计算方法，研究等原子Nb-Mo-Ta-W合金中的空位能量学，特别是空位形成能和迁移能。我们考虑了体环境以及近位错核心处的空位性质，包括通过Metropolis蒙特卡罗弛豫制备超胞以及温度对计算的影响来考虑短程有序（SRO）的作用。采用推挤弹性带（NEB）方法研究空位迁移能。我们的结果表明，空位形成能和空位迁移能都呈统计分布，分布范围很广，在某些情况下可达1.0 eV左右，并且对SRO有明显的依赖性。我们发现，在某些情况下，空位可以在边缘位错核心处以非常低的能量形成，由此我们推测在边缘位错线上形成了稳定的“超级扭折”。此外，空位形成能的广泛分布导致形成能分布向较低值的不对称热采样。这使得空位形成能明显低于分布平均值。我们研究了这种现象对合金中空位扩散率的影响，并讨论了我们的发现对Nb-Mo-Ta-W结构特征的意义。
