Various components, such as turbine buckets for gas turbine engines, are often formed by directional solidification (DS)/single crystal (SC) casting techniques. More specifically, many components are often formed by a casting “withdrawal” technique where a melt-filled investment mold is withdrawn from a casting furnace. Withdrawing the melt-filled investment mold from the casting furnace permits a molten metal or alloy in the mold to cool and solidify, forming the component within the mold.
As the molten metal or alloy cools a thermal gradient across the solid/liquid interface which is too low, or an incline of the interface compared to the horizontal which is too high, may lead to the formation of freckle grains. Freckle grains are formed due to interdendritic fluid flow, which may result in equiaxed phases surrounded by eutectic phases. Freckle grains are considered undesirable features and may have unacceptable weakness, particularly in the form of reduced fatigue strength.