Early stage phase separation in ternary alloys: A test of continuum simulations

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Phase separation in the γ−γ’ alloy 5.2%Al–14.2%Cr-Ni at 873.15 K has been investigated by three-dimensional phase-field simulations, employing a model where both thermodynamic and kinetic parameters were experimentally verified. 510 individual nuclei corresponding to a density of 1024 m−3 were introduced in accordance with classical nucleation theory, and the microstructural evolution was simulated up to a time of 32 h. The microstructural evolution was characterized, and regimes were identified according to the dominant mechanisms for microstructural evolution, where the final regime was found to be a coarsening regime obeying well-known power laws for the particle density and the average γ’ particle radius. The evolution of the volume-averaged composition of the particles was found to follow a complicated trajectory, while the composition of individual particles were found to depart significantly from the average. The simulations were compared to experimental results from the literature based on atom probe tomography, and in general good qualitative correspondence was found, albeit with quantitative differences. These are discussed in terms of the assumptions inherent to the phase-field model, and by extension to most common continuum models of diffusive phase transformations.