Evolution of microstructures at a wide range of solidification cooling rate in a Ni-based superalloy

The evolution of microstructures at a wide range of solidification cooling rate in a Ni-based superalloy was investigated by employing conventional casting, spray casting and melt spinning processes. Depending on solidification cooling rate, microstructures sequentially show planar, cellular, dendritic, the dendritic growth suppressed features (in melt spinning process) and the shapes of γ′ precipitates progressively exhibit irregular (planar and cellular growth), cuboidal (dendritic growth) and spherical (dendritic growth suppressed) patterns. Moreover, in dendritic growth conditions, γ′ shapes experience irregular cuboidal, regular cuboidal and near cuboidal patterns with increasing cooling rate. γ′ precipitates in dendritic cores show more and less regular morphology than those in interdendritic regions in lower and higher cooling rate range, respectively. The size scale of γ′ precipitates decreases with solidification cooling rate in cellular and dendritic growth conditions and γ′ precipitates are obviously smaller in crystallizing (cellular or dendritic) cores than those in interval regions.