Atomistic Mechanisms of Binary Alloy Surface Segregation from Nanoseconds to Seconds Using Accelerated Dynamics
Atomistic Mechanisms of Binary Alloy Surface Segregation from Nanoseconds to Seconds Using Accelerated Dynamics
复制标题
使用加速动力学从纳秒到秒的二元合金表面偏析的原子机制
DOI：
10.1021/acs.jctc.2c00303
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发表时间：
2022
影响因子：
5.5
通讯作者：
Saidi, Wissam A.
中科院分区：
文献类型：
--
作者：
Garza, Richard B.;Lee, Jiyoung;Nguyen, Mai H.;Garmon, Andrew;Perez, Danny;Li, Meng;Yang, Judith C.;Henkelman, Graeme;Saidi, Wissam A.
虽然许多合金表面的平衡成分已经被很好地理解，但退火过程中瞬态表面偏析的速率尚不清楚，尽管它对合金腐蚀和在重叠时间尺度上发生的催化反应有重要影响。本文采用原子模拟的方法，对具有（100）个表面面的CuNi双金属合金进行真空退火，观察空位扩散对表面分离的影响。我们采用多时间尺度方法对分离过程中板坯表面的早期瞬态、中间态和平衡态进行采样，包括标准MD以及三种执行原子性、长时间动力学的方法：平行轨迹拼接（ParSplice）、自适应动力学蒙特卡罗（AKMC）和动力学蒙特卡罗（KMC）。从纳秒（ns）到秒的时间尺度，我们的多尺度计算方法可以观察到标准MD通常看不到的罕见随机事件，缩小了表面分离的计算和实验时间尺度之间的差距。这四种方法都能在几十纳秒内解决空位向板坯的快速扩散问题。然而，在两种KMC方法中，空位随机重新进入地下仅在微秒时间尺度上可见。讨论了表面动力学空位俘获及其对偏析速率的影响。据估计，在退火过程中偏析后CuNi的平衡成分分布发生在KMC确定的秒级时间尺度上，结果直接可与纳米级实验相媲美。
Although the equilibrium composition of many alloy surfaces is well understood, the rate of transient surface segregation during annealing is not known, despite its crucial effect on alloy corrosion and catalytic reactions occurring on overlapping timescales. In this work, CuNi bimetallic alloys representing (100) surface facets are annealed in vacuum using atomistic simulations to observe the effect of vacancy diffusion on surface separation. We employ multi-timescale methods to sample the early transient, intermediate, and equilibrium states of slab surfaces during the separation process, including standard MD as well as three methods to perform atomistic, long-time dynamics: parallel trajectory splicing (ParSplice), adaptive kinetic Monte Carlo (AKMC), and kinetic Monte Carlo (KMC). From nanosecond (ns) to second timescales, our multiscale computational methodology can observe rare stochastic events not typically seen with standard MD, closing the gap between computational and experimental timescales for surface segregation. Rapid diffusion of a vacancy to the slab is resolved by all four methods in tens of nanoseconds. Stochastic re-entry of vacancies into the subsurface, however, is only seen on the microsecond timescale in the two KMC methods. Kinetic vacancy trapping on the surface and its effect on the segregation rate are discussed. The equilibrium composition profile of CuNi after segregation during annealing is estimated to occur on a timescale of seconds as determined by KMC, a result directly comparable to nanoscale experiments.