The influence of interstitial distribution on phase stability and properties of hexagonal ε-Fe6Cx, ε-Fe6Ny and ε-Fe6CxNy phases: A first-principles calculation

By using the first-principles projector-augmented wave method, the phase stability together with the bulk modulus and magnetic moment have been investigated in binary and ternary interstitial phases ε-Fe6Cx, ε-Fe6Ny and ε-Fe6CxNy (x, y = 0, 1, 2, 3 and x + y ⩽ 3) with a hexagonal structure. The predicted bulk modulus and volume of the ε phases increase with increasing the interstitial content, while the calculated magnetic moment decreases. The present work indicates that the longer the distance between the interstitial atoms, the lower the energy of the ε phases, i.e. the interaction between the interstitial atoms is of repulsive nature. The presently predicted phase stability of the ε-Fe6CxNy phases provides helpful insights into understanding the processes occurring during carbonitriding in steel and the further development of magnetic (carbo)nitrides.