Morphological changes of γ′ precipitates in superalloy IN738LC at various cooling rates

The effect of cooling rate from a temperature below the γ′ solvus on morphology of γ′ in a Ni-base superalloy, IN738LC, was investigated. At high cooling rates, γ′ showed solid-state morphological instability and as the cooling rate decreased, γ′ reduced in size and the growth occurred in a stable manner. The morphology changed from a cubic shape to a complex and flower-like shape as the cooling rate increased. The shape changes observed in this study suggested that the cooling rate has a significant impact on the misfit between γ and γ′. The morphological instability of γ′ is believed to be controlled by the degree of supersaturation in the matrix.