Performance analysis of Fe-N compounds based on valence electron structure

Abstract

In this paper, the valence electron structure and the bond energy of covalent bonds of α-Fe and ε-Fe2N, ε-Fe3N and γ′-Fe4N were calculated by means of the empirical electron theory (EET). It was put forward that the valence electron structure parameter related to hardness is the covalent electron density, the valence electron structure parameters related to plasticity are the lattice electron density and the symmetry factor of the atomic bonding strength, the valence electron structure parameters related to corrosion resistance are the atomic total bonding energy and lattice electron density, and the valence electron structure parameter related to stability is the average atomic total bonding energy. The hardening and corrosion resistance mechanism of ion-based nitriding layer was discussed and the influence of three Fe-N compounds on the hardness, brittleness, corrosion resistance and stability were compared and analyzed from the perspective of electron structure. The calculation results show that the three Fe-N compounds, which have larger covalent electron density and average atomic total bonding energy and smaller lattice electron density than α-Fe, can improve the hardness and corrosion resistance of the iron-based surface. Among the three compounds, ε-Fe2N has the greatest hardness, corrosion resistance and stability, and the least brittleness. Therefore, during the nitriding process, efforts shall be made to prompt the formation of ε-Fe2N as much as possible.