Understanding homogeneous nucleation in solidification of aluminum by molecular dynamics simulations
Understanding homogeneous nucleation in solidification of aluminum by molecular dynamics simulations
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DOI：
10.1088/1361-651x/aa9f36
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发表时间：
2018-02-01
影响因子：
1.8
通讯作者：
Baskes, Michael I.
中科院分区：
文献类型：
--
作者：
Mahata, Avik;Zaeem, Mohsen Asle;Baskes, Michael I.
利用改进的次近邻嵌入原子方法势，用百万原子分子动力学模拟方法研究了铝熔体的均匀形核。在不受压力、自由表面效应和杂质影响的情况下，铝熔体产生了自然的、均匀的形核。研究了过冷熔体在不同恒温条件下的初始等温结晶形核，以及过热铝熔体在不同冷却速度下的淬火过程。确定了晶核的晶体结构、临界晶核尺寸、均相成核的临界温度、诱导时间和成核率。淬火模拟清楚地揭示了三个温度区域：亚临界形核、超临界形核和固态晶粒长大区域。主晶相为面心立方，但也存在六方密排(HCP)和非晶固相。在Al熔体凝固过程中，由于层错的形成，产生了HCP相。随着冷却速度的减慢，HCP相和非晶相的体积分数降低。在箱体完全实心后，模拟了晶粒长大，确定了不同温度下的晶粒长大指数。
Homogeneous nucleation from aluminum (Al) melt was investigated by million-atom molecular dynamics simulations utilizing the second nearest neighbor modified embedded atom method potentials. The natural spontaneous homogenous nucleation from the Al melt was produced without any influence of pressure, free surface effects and impurities. Initially isothermal crystal nucleation from undercooled melt was studied at different constant temperatures, and later superheated Al melt was quenched with different cooling rates. The crystal structure of nuclei, critical nucleus size, critical temperature for homogenous nucleation, induction time, and nucleation rate were determined. The quenching simulations clearly revealed three temperature regimes: sub-critical nucleation, super-critical nucleation, and solid-state grain growth regimes. The main crystalline phase was identified as face-centered cubic, but a hexagonal close-packed (hcp) and an amorphous solid phase were also detected. The hcp phase was created due to the formation of stacking faults during solidification of Al melt. By slowing down the cooling rate, the volume fraction of hcp and amorphous phases decreased. After the box was completely solid, grain growth was simulated and the grain growth exponent was determined for different annealing temperatures.