Study of dendrite growth with natural convection in superalloy directional solidification via a multiphase-field-lattice Boltzmann model

The natural convection is able to change dendrite morphology and cause freckles formation in alloy solidification. Though great progress has been made in in-situ observation techniques and numerical models, the interaction between the melt flow and the growing dendrite in directionally solidified superalloy has not been well understood. In this study, the dendrite growth with natural convection in directional solidified nickel-based superalloy was investigated using a developed multiphase-field-lattice Boltzmann model. The PanNickel thermodynamic database was used to present realistic data for the multicomponent superalloy solidification simulation. A range of temperature gradients and pulling velocities were applied to investigate the effects of solidification conditions on dendrite growth and melt flow. First, the microsegregation pattern of each alloy component was obtained, and the simulation results were compared with the experimental results. Then, the dendrite morphology change and the variation of fluid velocity in the mushy zone under different solidification conditions were analyzed. The normalized average fluid velocity in the mushy zone was obtained and can be used to predict freckle formation. Finally, the effects of grain orientation on the dendrite morphology and melt convection were studied and the results were analyzed.