Irregular growth of the γ′ phase in a Ni-based superalloys under slow cooling rate

The effects of cooling rate on the evolution of γ′ phase were investigated by homogenization treatments performed at the γ′ super-solvus temperature (1160 ℃) with the soaking time of 30 h, following cooled by furnace cooling. Irregular growth and morphological instability of the γ′ phase under slow cooling condition was identified. The shape of γ′ phase was mixture of cubic, octets and dendrites in this process. The growth of the γ′ phases during cooling was consistent with a diffusion-controlled mechanism. Therefore, chemical composition of γ′ phase and γ matrix was analyses, it is found that the γ′ phase was enriched in Al, Ti, Ni and poor in Co, Cr, Fe. Based on the experimental results, the irregular growth process of γ′ phases was discussed, and supersaturation and sufficient diffusivity are the dominated mechanisms of this process.