Abstract
The formation mechanism and coarsening behavior of fan-type structures in a new Ni–Cr–Co-based powder metallurgy superalloy were investigated by means of field scanning electron microscope, transmission electron microscope, electron backscattered diffraction, and differential scanning calorimetry. The results show that the fan-type structures consist of finger-shaped γ′ dendrites and γ matrix between them. They nucleate in the chemical segregation regions on grain boundaries and grow by diffusion. There are three types of solute atoms flow: (a) rapid diffusion along grain boundary; (b) the diffusion from supersaturated γ matrix to fan-type γ′ phases; and (c) short-distance diffusion from the previous formed γ′ phases at high temperature to γ′ phases formed at low temperature within the branches of fan-type structures. These γ′ dendrites are perpendicular to grain boundaries and grow asymmetrically, resulting in grain boundary serration. In addition, the fan-type structures coarsen within the γ′ depletion zone after the standard aging treatment.
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