高温合金定向凝固过程中枝晶生长与溶质对流数值模拟

目的 针对高温合金叶片在定向凝固过程中容易出现雀斑缺陷，从而导致叶片报废的问题，对定向凝固枝晶生长与溶质对流进行模拟研究，以揭示雀斑缺陷的形成规律。方法 针对CM247LC合金定向凝固过程，采用相场模型模拟凝固过程枝晶生长，采用格子Boltzmann模型模拟溶质浓度差引起的自然对流。采用基于双重网格的GPU并行算法对相场-格子Boltzmann模型进行数值求解。研究在不同晶体取向角度与取向差条件下的枝晶形貌、对流速度及溶质羽流的演变规律。结果 当晶体取向角度不同时，在枝晶生长过程中，液相区域的平均对流速度均表现为周期性变化。当晶体取向角度较大时，随着晶体取向角度的变大，一次枝晶臂间距变大。当枝晶间存在晶体取向差时，溶质羽流倾向于在发散型晶界附近发起;随着晶体取向差的增大，溶质羽流发起时间提前。溶质羽流的形成阻碍了枝晶尖端及附近枝晶侧臂的生长。结论 晶体取向角度对溶质羽流形成的影响较小，较大的晶体取向差对溶质羽流的形成有促进作用。

Numerical Simulation of Dendrite Growth and Solute Convection during Directional Solidification of Superalloy

Superalloy blades are prone to freckle defects during directional solidification, which leads to scrap. Therefore, the work aims to simulate the dendrite growth and solute convection during directional solidification to reveal the formation of freckle defects. The dendrite growth of CM247LC alloy was simulated by phase field model and natural convection caused by solute concentration difference was simulated by the lattice Boltzmann model. The phase field-lattice Boltzmann model was solved by GPU-based parallel algorithm based on two different meshes. The dendrite morphology, convection velocity and evolution of solute plumes under different crystal orientation angles and orientation differences were studied. The average fluid velocity in the liquid phase during dendrite growth varied periodically with different crystal orientation angles. When the crystal orientation angle was large, the distance between the primary dendrite arm spacings increased with the increase of the crystal orientation angle. When there was a difference in crystal orientation between dendrites, solute plumes tended to start near divergent grain boundaries. With the increase of crystal orientation difference, the onset time of solute plume advanced. The formation of solute plumes inhibited the growth of dendrite tips and adjacent dendrite side arms. The angle of crystal orientation has slight effect on the formation of solute plumes, and the larger difference of crystal orientation can promote the formation of solute plumes.