A comparative study of Cr7C3, Fe3C and Fe2B in cast iron both from ab initio calculations and experiments

Abstract

The ground state properties of three compounds, Cr7C3, Fe3C and Fe2B, are investigated using ab initio calculations based on density functional theory. Formation enthalpy values indicate that Cr7C3 is the most stable crystal among the three compounds. Fe3C is metastable which has a positive heat of formation value. The calculated bulk modulus, shear modulus and Young's modulus value of Cr7C3 are 311 GPa, 143.8 GPa and 374 GPa, respectively. The bulk modulus values of Fe2B and Fe3C are 194 GPa and 258 GPa. We also find that both the hardness and the stiffness of the Cr7C3 type carbides can be improved by doping with B, W, Mo, etc. The bulk modulus of transition metal doped Fe2B is considerably higher than pure Fe2B. The electronic structures of Fe2B and Fe3C are ferromagnetic and the evaluated average magnetic moment of Fe is 2.09μB/atom for Fe3C and 2.02μB/atom for Fe2B, respectively. Micro-indentation test results indicate that Cr7C3 is the hardest phase among the three phases and shows excellent wear resistance performance under three-body abrasive experiments. The experimental results are in agreement with the theoretical prediction that Cr7C3 is the best both in stability and mechanical performance.