Simulation and Experimental Investigation of a Combined Control Method for Stray Grain During Single Crystal Blade Solidification

It is of great significance to effectively prevent the stray grain defect at the edge plate of nickel-based superalloy single crystal blades. In this study, the evolution of the mushy zone and the growth of grain adjacent to the edge plate was first simulated by the temperature field and cellular automaton-finite element (CAFÉ) model, combined with a single crystal blade solidification experiment; it was proved that modifying the withdrawal rate alone was insufficient to prevent the stray grain formation. Then, the formation reason of the heat barrier zone and the irregular distribution pattern of the mold shell thickness were revealed by quantifying the present mold shell thickness near the edge plate through an industrial conical beam computed tomography. Based on these results, a combined control method for stray grain was proposed, which involves the use of precise measures such as non-uniform mold design, exact addition of process bars, and variable withdrawal rate. Simulation analysis demonstrated that this method can substantially reduce the undercooling range and average undercooling at the edge plate by 45.5% and 31.6%, respectively, and then eliminate the isolated undercooling zone. The macrostructure and microstructure of the blade cast by this method verified the effectiveness in inhibiting stray grain, and it will be a promising approach to manufacturing single crystal blades.