Grain growth kinetics in submicrometer-scale molecular dynamics simulation
Grain growth kinetics in submicrometer-scale molecular dynamics simulation
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DOI：
10.1016/j.actamat.2018.04.060
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发表时间：
2018-07-01
期刊：
影响因子：
9.4
通讯作者：
Shibuta, Yasushi
中科院分区：
文献类型：
--
作者：
Okita, Shin;Miyoshi, Eisuke;Shibuta, Yasushi
采用大尺度长时间分子动力学（MD）模拟了亚微米尺度体系中晶界各向异性晶粒的成核、凝固和晶粒长大过程，研究了晶粒生长动力学。过冷铁熔体经均匀形核得到的显微组织由大约1500个晶粒组成，晶粒数量通过晶粒生长过程减少到原来的十分之一。由于晶界特性的各向异性效应固有地包含在晶界模拟中，因此由MD模拟得到的晶粒生长指数偏离理想值。结果表明，降低迁移率（即固有晶界迁移率与晶界能的乘积）的减小是导致晶粒偏离理想生长的主要因素。晶粒间定向失向角的分布偏离Mackenzie函数，说明晶界能小的晶界在晶粒生长过程中发生优先选择。这增强了晶界性质的各向异性，从而降低了晶界的迁移率。此外，从MD构型出发的多相场模拟结果表明，当降低迁移率为恒定值时，晶粒生长较为理想，验证了降低迁移率的讨论。这项研究中的新见解是首次实现的，这要归功于在GPU丰富的超级计算机上使用128个GPU对一个案例进行了超过50天的多图形处理单元（GPU）并行计算。(C) 2018材料学报Elsevier Ltd.出版。版权所有。
Grain growth kinetics under the anisotropic grain boundary properties is investigated by large-scale and long-time molecular dynamics (MD) simulations of contentious processes of nucleation, solidification and grain growth in a submicrometer-scale system. Microstructures obtained via homogeneous nucleation from undercooled melt iron consists of approximately 1500 grains and the number of grains decreases to one tenth of the number via the grain growth process. The grain growth exponent obtained from the MD simulation deviates from the ideal value since anisotropic effects in the grain boundary properties are inherently included in MD simulations. It is confirmed that the decrease of the reduced mobility (i.e., the product of the intrinsic grain boundary mobility and the grain boundary energy) is a dominant factor for the deviation from the ideal grain growth. The deviation from the Mackenzie function for the distribution of the disorientation angle between neighboring grains implies that the preferential selection of grain boundaries with small grain boundary energies occurs during the grain growth. This enhances the anisotropy in grain boundary properties and therefore decreases the reduced mobility of the grain boundary. Moreover, a multi-phase-field simulation starting from a MD configuration results in an ideal grain growth when a constant value of the reduced mobility is employed, which validates the discussion on the reduced mobility. The new insight in this study is achieved for the first time owing to a multi-graphics processing unit (GPU) parallel computation over 50 days for one case using 128 GPUs on the GPU-rich supercomputer. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.