Fe-C合金凝固枝晶形貌及特性参数的相场模拟

 为了实现对合金凝固过程中枝晶形态的定量表征、揭示凝固前沿溶质分布与过冷度对微观偏析的影响,进而实现对凝固枝晶间液相渗透率的量化研究,采用相场模型探讨了Fe-0.5％C合金凝固过程中的显微组织和特征参数,并引入分形维数和无量纲周长定量分析了枝晶形貌、微观偏析和其糊状区的渗透性。结果表明,分形维数和无量纲周长可用于定量描述枝晶形态的复杂性。当过冷度从20增加到27 K时,分形维数从1.28增加到 1.791,无量纲周长从2.39增加到12.6;随着过冷度的增加,枝晶中心轴和固/液界面的溶质浓度均增加,并且枝晶尖端的扩散层厚度减小,即枝晶之间的偏析率增大。此外,利用分形维数和无量纲周长作为凝固过程中枝晶曲折因子实现了凝固过程枝晶间糊状区渗透率的量化计算。其中,与分形维数相比,利用无量纲周长作为曲折因子估测的渗透率与试验结果更为吻合,其在不同过冷度下数值为1.36×10-15~1.75×10-13 m2。

Dendritic morphology and characteristic parameters during solidification of Fe-C alloy with phase field model

In order to realize the quantitative characterization of the dendrite morphology during the alloy solidification process,reveal the influence of solute distribution and undercooling on the microsegregation in the solidification front,and then carry out the quantitative study of the liquid phase permeability between solidification dendrites,the phase field model is adopted to discuss the microstructure and characteristic parameters of Fe-0.5%C alloy during solidification,and the fractal dimension and dimensionless circumference were introduced to quantitatively analyze the dendrite morphology,microsegregation and mush zone permeability.The results show that the fractal dimension and dimensionless circumference can be used to estimate the complexity of dendrite morphology quantitatively.The fractal dimension increases from 1.28 to 1.791,and the dimensionless circumference increases from 2.39 to 12.6 when the undercooling increases from 20 to 27 K.With increasing undercooling,the solute concentration in both the central axis of dendrite and the solid/liquid interface increase,and the diffusion layer thickness at the dendrite tip decreases,i.e.,the segregation ratio between dendrites increases.Taking as the tortuosity factors of the dendrite in liquid,the fractal dimension and dimensionless circumference were used to estimate the mush permeability during solidification.Compared the fractal dimension,the dimensionless circumference is reliable in estimating the permeability with the value of 1.36×10^-15-1.75×10^-13m² for the given undercoolings.