Atomistic modeling of the order–disorder phase transformation in the Ni2Cr model alloy

Mechanical property degradation due to the disorder–order phase transformation is of potential concern for alloys based on the Ni–Cr binary system, particularly in nuclear power applications, where component lifetimes can exceed 80 years. In the present research, a disorder–order phase transformation has been studied in the Ni–33 at.% Cr model alloy by a combined experimental and computational approach. The multiscale modeling framework utilizes grand canonical and kinetic Monte Carlo simulation techniques based upon density functional theory calculations to treat both the thermodynamic and kinetic aspects of the phase transformation. The simulation results are used to generate a simple model for the ordering kinetics based upon the Kolmogorov–Johnson–Mehl–Avrami equation. Experimental measurements of the change in lattice parameter as a function of aging time and temperature are obtained in order to assess the model accuracy. The resulting model shows reasonable agreement with experimental data at 470 and 418 C; however, additional experimental data at longer aging times are needed to confirm the accuracy of the model at lower temperatures. The model predicts that the initiation of the ordering transformation will occur in Ni–33Cr at temperatures and timescales relevant to nuclear power systems, though longer times are required for the transformation to proceed to completion.