Revealing the real structure of M7C3 by high-throughput DFT calculations

Abstract

High-throughput first-principles calculations and statistic mechanics simulations were performed to study the thermodynamics property of M7C3 carbide. The formation enthalpy of 407 distinguished FexCr7-xC3 configurations were determined, which shows that the previous reported Fe3Cr4C3 and Fe5Cr2C3 are on the convex hull of the 0 K formation enthalpy. Then, a cluster expansion was fitted. The formation enthalpy predicted by the cluster expansion and determined by first-principles calculations were compared, which proves the accuracy and effectiveness of the cluster expansion. Finally, the Gibbs free energy of M7C3 at elevated temperatures were determined by Monte Carlo simulations, which shows that M7C3 is an infinite solid solution with Fe and Cr atoms replacing each other in infinite proportions. Thus, the real structure of M7C3 is revealed.