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

The morphological evolution of the precipitate in a powder metallurgy nickel-based superalloy under interrupted cooling was investigated. Through deep electrolytic etching, the 3-D morphology of the precipitate of the alloy was characterized. At 1150-1090 degrees C, the precipitate nucleated with a spherical shape. The subsequent cooling to 1050 degrees C would lead to a morphological transition of the precipitate into an eight-primary-branch pattern with a preferred growth direction along < 111 >. As the cooling proceeded, the secondary arms developed from each < 111 > 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 / 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 precipitate. Good agreement was found between the simulation and experiment results.