Zhou X W
Sandia National Laboratories Livermore California 94550 USA
RSC Adv. 2023 Aug 1;13(33):23236-23243. doi: 10.1039/d3ra03969b. eCollection 2023 Jul 26.
The growth of helium bubbles impacts structural integrity of materials in nuclear applications. Understanding helium bubble nucleation and growth mechanisms is critical for improved material applications and aging predictions. Systematic molecular dynamics simulations have been performed to study helium bubble nucleation and growth mechanisms in FeNiCr stainless steels. First, helium cluster diffusivities are calculated at a variety of helium cluster sizes and temperatures for systems with and without dislocations. Second, the process of diffusion of helium atoms to join existing helium bubbles is not deterministic and is hence studied using ensemble simulations for systems with and without vacancies, interstitials, and dislocations. We find that bubble nucleation depends on diffusion of not only single helium atoms, but also small helium clusters. Defects such as vacancies and dislocations can significantly impact the diffusion kinetics due to the trapping effects. Vacancies always increase the time for helium atoms to join existing bubbles due to the short-range trapping effect. This promotes bubble nucleation as opposed to bubble growth. Interestingly, dislocations can create a long-range trapping effect that reduces the time for helium atoms to join existing bubbles. This can promote bubble growth within a certain region near dislocations.
氦气泡的生长会影响核应用中材料的结构完整性。了解氦气泡的成核和生长机制对于改进材料应用和老化预测至关重要。已进行了系统的分子动力学模拟，以研究FeNiCr不锈钢中氦气泡的成核和生长机制。首先，针对有位错和无位错的系统，计算了各种氦团簇尺寸和温度下的氦团簇扩散率。其次，氦原子扩散加入现有氦气泡的过程是不确定的，因此使用有无空位、间隙原子和位错的系统进行系综模拟来研究该过程。我们发现气泡成核不仅取决于单个氦原子的扩散，还取决于小氦团簇的扩散。空位和位错等缺陷由于捕获效应会显著影响扩散动力学。由于短程捕获效应，空位总是会增加氦原子加入现有气泡的时间。这促进了气泡成核而非气泡生长。有趣的是，位错会产生长程捕获效应，减少氦原子加入现有气泡的时间。这可以促进位错附近特定区域内的气泡生长。
