The impurity effect of light elements (carbon, nitrogen, and oxygen) on nickel crystallization in the triple junction region of grain boundaries is studied by the molecular dynamics method. The tilt grain boundaries with disorientation axis 〈111〉 are considered as grain boundaries. The computational cell is a cylinder, the axis of which coincided with the triple junction and the disorientation axis of grains. Periodic boundary conditions are imposed along the cylinder axis; the atoms on the lateral surface of the cylinder are stationary. To simulate crystallization, the computational cell was melted by heating to a temperature significantly higher than the melting point of nickel. After the simulated polycrystal became liquid, the thermostat was turned on and the polycrystal was kept at a constant temperature less than melting point. In this case, the rigid boundary conditions on the lateral surface of a cylindrical computational cell simulated the crystallization fronts from three crystallization centers. The area near the triple junction crystallized in the last turn. Defects and free volume are concentrated in this area. The impurities significantly slowed down the crystallization rate. The addition of 10% impurity atoms slowed down the rate of the crystallization front by several times. The impurity effect on the crystallization rate increased in the direction C–N–O. This is due to the difference in the deformation of the crystal lattice caused by impurity atoms: the greater this deformation, the more impurity atoms slow down the crystallization front. Impurity carbon atoms formed aggregates of crystal grains at rather high concentrations. Crystallization front remained on these aggregates. Oxygen atoms and nitrogen atoms did not form aggregates; nevertheless, they distorted the crystal lattice and significantly slowed down the crystallization front.

中文翻译：

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轻元素杂质对晶界三重结区镍结晶的影响：分子动力学模拟

采用分子动力学方法研究轻元素（碳、氮、氧）杂质对晶界三结区镍结晶的影响。具有取向轴<111>的倾斜晶界被认为是晶界。计算单元是一个圆柱体，其轴与三重结点和晶粒的错位轴重合。沿圆柱轴施加周期性边界条件；圆柱体侧面的原子是静止的。为了模拟结晶，计算单元通过加热到明显高于镍熔点的温度而熔化。模拟多晶变成液体后，打开恒温器，将多晶保持在低于熔点的恒温。在这种情况下，圆柱形计算单元侧面的刚性边界条件模拟了来自三个结晶中心的结晶前沿。三重结附近的区域在最后一圈结晶。缺陷和自由体积集中在这个区域。杂质显着减慢结晶速率。添加 10% 的杂质原子使结晶前沿的速度减慢了数倍。杂质对结晶速率的影响在 C-N-O 方向上增加。这是由于杂质原子引起的晶格变形的差异：这种变形越大，杂质原子就越慢结晶前沿。杂质碳原子以相当高的浓度形成晶粒的聚集体。结晶前沿保留在这些聚集体上。氧原子和氮原子没有形成聚集体；然而，它们扭曲了晶格并显着减慢了结晶前沿。