Qin Qin, Li Weizhuang, Wang Wenrui, Li Dongyue, Xie Lu
School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China.
Materials (Basel). 2024 Dec 11;17(24):6051. doi: 10.3390/ma17246051.
In this study, molecular dynamics (MD) simulations were employed to compare the effects of different solidification conditions on the solidification behaviour, stress distribution, and degree of crystallization of iron. The results indicate significant differences in nucleation and microstructural evolution between the two solidification methods. In the homogeneous temperature field, the solidification of iron is characterized by instantaneous nucleation. The BCC phase surged at 1431 K followed by the phenomenon of latent heat of crystallization. As the temperature continued to decrease, the percentage of the BCC phase continued to increase steadily. Eventually, the atoms aggregated to form a crystal nucleus and grow outward to form polycrystalline structures. During gradient solidification, continuous nucleation of iron leads to a slow increase in the BCC phase. From the initial stage of solidification, the solid-liquid interface moves in the direction of higher temperature and is accompanied by a higher stress distribution. Furthermore, increasing the temperature gradient, particularly the cooling rate, accelerates the transformation efficiency of iron in the gradient solidification process. In addition, increasing the cooling rate or temperature gradient reduces the residual stress and crystallinity of the solidified microstructure. It is worth noting that an increased temperature gradient or cooling rate will produce higher residual stress and uneven microstructure in the boundary region. This study provides an atomic-level understanding of the improvement in the solidification performance of iron.
在本研究中，采用分子动力学（MD）模拟来比较不同凝固条件对铁的凝固行为、应力分布和结晶程度的影响。结果表明，两种凝固方法在形核和微观结构演变方面存在显著差异。在均匀温度场中，铁的凝固以瞬时形核为特征。体心立方（BCC）相在1431 K时激增，随后出现结晶潜热现象。随着温度持续下降，BCC相的百分比持续稳定增加。最终，原子聚集形成晶核并向外生长形成多晶结构。在梯度凝固过程中，铁的连续形核导致BCC相缓慢增加。从凝固初期开始，固液界面向高温方向移动，并伴随着较高的应力分布。此外，增加温度梯度，特别是冷却速率，会加速梯度凝固过程中铁的转变效率。另外，提高冷却速率或温度梯度会降低凝固微观结构的残余应力和结晶度。值得注意的是，增加温度梯度或冷却速率会在边界区域产生更高的残余应力和不均匀的微观结构。本研究为铁凝固性能的改善提供了原子层面的理解。
