First-principles study on the interfacial electronic structure and analysis of the bonding properties of NbC/Fe composites

Abstract

This paper investigated the bonding mode and atoms’ surface energy in the α-Fe and NbC bulk phases in NbC/Fe composites using the first-principles calculation of density functional theory. Different interface models were established to evaluate the interface bonding strength and stability considering the total interface energy and work of adhesion. After structural optimization, four interface models were established, α-Fe(100)/NbC(100) at the C-terminus, α-Fe(100)/NbC(100) at the Nb-terminus, α-Fe(100)/NbC(111) at the C-terminus, and α-Fe(100)/NbC(111) at the Nb-terminus, defined as interfaces I, II, III, and IV, respectively. The results show that the interface adhesion of the C-terminal interface is higher than the Nb-terminal interface. The minimum total energy of interface I and the maximum adhesion work are − 1.80 × 104 eV and 5.31 J/m2, respectively, indicating the most stable interfacial bonding method. The effects of different terminal atoms on the electronic structure and bonding characteristics of the α-Fe(100)/NbC(100) interface were analyzed. The bonding characteristics of the atomic interfaces I and II of the two interface models demonstrated covalent binding of different intensities. Interface I depends on the covalent-ionic bond formed by Fe and C atoms, while interface II relies on metal bonds formed by Fe and Nb atoms and weaker Fe-C bonds. Mulliken's analysis revealed that the bond population of Fe-Nb at interfaces I and II were negative, indicating an intense anti-bonding state between Fe and Nb atoms and a severe anti-bonding effect of Fe-Nb at interface II, resulting in its structural instability. Moreover, because of the covalent bonding (Fe-C) at interface I, the binding strength of the interface was higher with a stable interface.