Numerical simulation of temperature field and grain texture during casting single crystal superalloy DD403 with liquid metal cooling

The temperature field and grain texture during the directional solidification of Ni-base single crystal superalloy DD403 has been simulated by ProCAST& CAFE model. The effect of withdrawal rate on stray grains formation and shape as well as location of the solid-liquid interface of the casting between its platform and transition region (airfoil) was analyzed. Critical withdrawal rates (Vc), which are maximum withdrawal rates of no stray grains formation in the single crystal casting, were obtained with two methods. It is found that the liquid isotherm moves from center to edge at the platform region for liquid metal cooling (LMC) method at a rate of 150 μm/s, inhibiting the formation of stray grains. However, the edge of platform for high rate solidification (HRS) approach with the same withdrawal rate is cooled earlier than the center, and great undercooling of the edge of the platform may occur, which results in stray grains formation there. In this study, Vc cannot be more than 125 μm/s for HRS method; it is recommended the maximum withdrawal rate for LMC approach cannot exceed 150 jxm/s, otherwise new grains may occur at the pigtail or platform region. When the withdrawal rate is 150 μm/s, the LMC process can create axial thermal gradient (Ga) at airfoil more than double the HRS process with a 1/3-1/2 refinement in primary dendrite arm spacing (PDAS). In addition, Ga and PDAS are more uniform along the axis of the castings compared with HRS method. As withdrawal rate increases in the range of 50 to 200 μm/s, the solid-liquid interface at airfoil remains flat and moves to the middle of the thermal baffle for LMC method; however, it becomes more concave and moves to the underside of the baffle for HRS approach.