An analysis of interatomic potentials for vacancy diffusion simulation in concentrated Fe-Cr alloys

Abstract

The study tested correctness of three interatomic potentials available in the scientific literature in reproducing a vacancy diffusion in concentrated Fe-Cr alloys by molecular dynamic simulations. It was necessary for further detailed study of vacancy diffusion mechanism in these alloys with Cr content 5-25 at.% at temperatures in the range of 600-1000 K. The analysis of the potentials was performed on alloys models with Cr content 10, 20, 50 at.%. The consideration of the model with chromium content 50 at.% was necessary for further study of diffusion processes in chromium-rich precipitates in these alloys. The formation energies and the atomic mobilities of iron and chromium atoms were calculated and analyzed in the alloys via an artificially created vacancy for all used potentials. A time dependence of mean squared displacement of atoms was chosen as а main characteristic for the analysis of atomic mobilities. The simulation of vacancy formation energies didnt show qualitative differences between the investigated potentials. The study of atomic mobilities showed a poor reproduction of vacancy diffusion in the simulated alloys by the concentration-dependent model (CDM), which strongly underestimated the mobility of chromium atoms via vacancy in the investigated range of temperature and chromium content. Also it was established, that the two-band model (2BM) of potentials in its original and modified version doesnt have such drawbacks. This allows one to use these potentials in simulations of vacancy diffusion mechanism in Fe-Cr alloys. Both potentials show a significant dependence of the ratio of chromium and iron atomic mobilities on temperature and Cr content in simulated alloys. The quantitative data of the diffusion coefficients of atoms obtained by these potentials also differ significantly.

Keywords

• molecular dynamics
• vacancy diffusion
• Fe–Cr alloys
• interatomic potentials