Atomistic modeling of long-range ordering in FCC Ni-Cr-Fe alloys

This study examines the thermodynamics and kinetics of the face-centered cubic Ni-Cr-Fe system, focusing on the order-disorder phase transformation in Ni${}_{0.67(1-x)}$Cr${}_{0.33(1-x)}$Fe_x ($x=0$ – 0.1) alloys. A pair interaction model (PIM) is developed, with a significant portion based on density functional theory (DFT) calculations and CALPHAD models for binary Ni-Cr and Ni-Fe alloys and further adjusted using experimental order-disorder transformation temperatures and diffusion data. Monte Carlo simulations using this PIM yield detailed phase diagrams and kinetic insights into the ordering process. The simulations reveal that adding up to 10 at.% Fe extends the incubation time by slowing down the atomic diffusion, while slight deviations in Ni-Cr ratio have minimal impact on the ordering kinetics. Although additional experimental data would be required—especially at low temperature and high Fe content—for further validation of the model, our results match reasonably well with the available experimental data on ordering incubation times, capturing the alloy's key characteristics.