DD6单晶精铸薄壁试样定向凝固过程数值模拟

Numerical Simulation on Directional Solidification Process of DD6 Single Crystal Superalloy Thin-walled Specimen

摘要：针对单晶高温合金精铸薄壁试样制备困难的问题，建立了薄壁板形试样的有限元模型，采用ProCAST数值模拟的方法模拟DD6单晶精铸薄壁板形试样的定向凝固过程，研究了几何形状和工艺参数对定向凝固过程中温度场、温度梯度场及糊状区的影响。结果表明：薄壁板形试样中间部位工作端的温度梯度在60～65℃cm范围内，糊状区固相线较为平直，液相线的位置在近炉壁一侧较低，远炉壁一侧较高。几何形状对单晶高温合金试样定向凝固过程有重要影响，提高浇注温度或降低抽拉速率有助于薄壁板形试样固液界面前沿液相温度梯度增大、糊状区宽度减小。单晶高温合金精铸薄壁试样定向凝固过程数值模拟结果与实际浇注结果吻合，凝固过程数值模拟为单晶精铸薄壁试样的制备提供了技术支持。

For the difficulty in preparation of thin-walled specimen of DD6 single crystal superalloy, the finite element model of thin-walled slab specimen was established to simulate the directional solidification process of investment casting thin-walled slab specimen using a numerical simulation software ProCAST. The effects of specimen shape and solidification parameters on temperature field, temperature gradient field and mushy zone were investigated. The results show that temperature gradient at the working end of the thin-walled slab specimen's centre location ranges from 60/cm to 65/cm. The solidus isotherm of mushy zone is relatively flat, but liquidus isotherm closed to furnace wall is slightly lower than that far away from furnace wall. Geometrical shape has great effect on the directional solidification process of single crystal superalloy specimen. Increasing the pouring temperature or decreasing the withdrawal rate helps to increase the temperature gradient in solid/liquid interface front and reduce the mushy zone width. The numerical simulation results of the directional solidification are consistent with that of the actual casting results. The solidification simulation can provide the technical support for the preparation of thin-walled specimen.