ABSTRACT

Stability of hydrogen clusters at crystallographic defects in Ni has been recently reported in a number of density functional theory investigations at 0 K. It has been suggested that hydrogen atoms can accumulate at such defects as vacancies and grain boundaries in a form of a cluster containing up to six hydrogen atoms and that the formation of the hydrogen agglomerations can have a significant impact on the hydrogen embrittlement processes in Ni-base alloys. In this work, we employ a combination of density functional theory calculations and embedded atom method simulations to investigate the stability of hydrogen clusters at 0 K as well as finite temperatures. At 0 K, comprehensive calculations for stability of hydrogen clusters have shown that the vacancy of Ni exhibits as a stronger binding than grain boundary for hydrogen atoms, both the vacancies and grain boundaries are able to trap a certain amount of hydrogen atoms respectively. However, at the finite temperatures, our results show that stability of hydrogen clusters at crystallographic defects of Ni is limited to temperatures below 300 K and that their appearance at the ambient temperature and therefore an impact on possible hydrogen embrittlement mechanisms is unlikely.

摘要

Ni在0 K的密度泛函理论研究中最近报道了Ni的晶体缺陷处的氢簇的稳定性。有人提出氢原子可以以诸如包含空位和晶界的簇的形式聚集在空位和晶界等缺陷处。氢原子团数为六个，并且氢团聚的形成会对镍基合金中的氢脆化过程产生重大影响。在这项工作中，我们结合使用密度泛函理论计算和嵌入式原子方法模拟来研究氢簇在0 K和有限温度下的稳定性。在0 K时，对氢簇稳定性的综合计算表明，与氢原子的晶界相比，Ni的空位表现出比晶界更强的结合力，空位和晶界都能够分别捕获一定量的氢原子。然而，在有限的温度下，我们的结果表明，在Ni的晶体缺陷处氢簇的稳定性仅限于300 K以下的温度，并且它们在环境温度下的出现并不大可能对氢脆化机制产生影响。