Predicting the temperature dependence of self-diffusion behavior in Ni-Cr alloys via molecular dynamics

Abstract

Defect-mediated mass transport is a critical phenomenon for many material performance and degradation issues. In the area of stress corrosion cracking, a predictive model of mass transport under realistic, elevated temperatures would be instrumental in predicting crack initiation and propagation tendencies. Molecular simulations can address some of these gaps about underlying processes. In that context, this study presents a robust model that describes self-diffusion at high temperatures in Ni-xCr alloys with varying Cr concentrations. We show that by using a vacancy concentration rescaling factor, it is possible to properly estimate diffusion coefficients in Ni-5Cr, Ni-10Cr and Ni-20Cr. The model reaches its upper limit at 1600 K for Ni-20Cr, because it has been fitted on dilute solute concentrations. Extrapolations at low temperature match experimental trend. Simulations with a theoretical number of vacancies give results comparable to the diffusion coefficients with the rescaling factor. In further simulations of more complex systems, efforts should be made in interstitial formation and migration barrier energy description.