IN718高温合金水平定向凝固和真空电弧重熔过程中“黑斑”形成的多组元数值模拟

建立了多组元两相模型来描述IN718高温合金凝固过程中的宏观/微观传输和“黑斑”形成，并应用动态网格算法模拟真空电弧重熔（VAR）过程中的填充过程。首先，使用热力学计算方法求解液相成分随固相分数的变化，并获得多组元合金的枝晶间液相密度。之后模拟了水平定向凝固工艺下形成的“黑斑”，并与实验结果进行对比，研究其形成机理和影响因素。最后，利用所开发的模型来研究工艺参数对工业规模VAR铸锭中“黑斑”的影响。结果表明，元素组成对凝固过程中液相的密度变化有显著影响，“黑斑”的形成伴随着高热溶质对流强度。“黑斑”的生长方向由液相密度差和凝固界面相对重力方向的角度决定。在VAR过程中，熔池形状受电极熔化速率和冷却速率影响。

Multicomponent Modeling of Freckle Formation in IN718 Superalloy During Horizontal Directional Solidification and Vacuum Arc Remelting

A multicomponent two-phase model was established to describe the macro/micro-transportation and the freckle formation during solidification, and the dynamic mesh algorithm was applied to perform the filling process during the vacuum arc remelting (VAR). Firstly, the thermodynamic calculation approach was used to evaluate the liquid composition with the variation of solid fraction during solidification, and the interdendritic liquid density of multicomponent alloys was obtained. Then, the freckle formed during the horizontal directional solidification was simulated and compared with the experiment one to study the freckle formation mechanism and influence factor. Finally, the developed model was used to investigate the influence of process parameters on the freckle formation in the industrial-scale VAR casting. Results show that the element composition has a significant effect on the density change of liquid phase during the solidification. The freckle forms with a high thermosolutal convection strength. The growth direction of freckles is determined by the liquid density difference and the angle between solidified interface and gravity direction. It is also found that the molten pool profile is affected by the electrode melting rate and cooling rate during VAR.