Growth behavior of γ′ phase in a powder metallurgy nickel-based superalloy under interrupted cooling process

The morphological evolution of the γ′ precipitate in a powder metallurgy nickel-based superalloy under interrupted cooling was investigated. Through deep electrolytic etching, the 3-D morphology of the γ′ precipitate of the alloy was characterized. At 1150–1090 °C, the γ′ precipitate nucleated with a spherical shape. The subsequent cooling to 1050 °C would lead to a morphological transition of the γ′ precipitate into an eight-primary-branch pattern with a preferred growth direction along . As the cooling proceeded, the secondary arms developed from each primary branch. The solute was trapped inside the concave area between different arms, and an atomically sharp order–disorder transition zone exhibited in the vicinity of the γ/γ′ interface. Accordingly, an anisotropy function accounting for both elastic and surface-energy anisotropies was developed and coupled into the phase field model to simulate the morphological evolution of the γ′ precipitate. Good agreement was found between the simulation and experiment results.