Abnormal feather-like grains induced by the thin-wall effect in a polycrystalline nickel-based superalloy

•Abnormal feather-like grains with high-angle grain boundaries were detected in a thin-walled polycrystalline superalloy.•The quantity of the feather-like recrystallized grains was increased with the decrease of the specimen thickness.•The formation mechanism of the abnormal feather-like grains was revealed. The effect of wall thickness on the casting microstructures of polycrystalline Ni-based superalloy K465 was investigated. Abnormal feather-like grains with high-angle grain boundaries (HAGBs) were detected. The quantity of the feather-like grains increased with the decrease of the specimen thickness. Experimental investigation and numerical simulation results showed the cooling rate and the residual stress increased with the decrease of the specimen thickness. The increased residual stress and the heat treatment resulted from the sand box with elevated temperature induced the formation of the abnormal feather-like recrystallized grains. This work provides a guidance for producing turbine blades made of cast superalloys.