Heterogeneous nuclei effect of MgAl2O4 on NbC in Fe matrix MMC coating

Niobium carbide (NbC) reinforced metal matrix composite (MMC) coatings have been widely applied for surface strengthening, and the precipitation of granular primary NbC may be a feasible way to improve the wear resistance of coating. In this work, MgAl2O4 was selected to promote the precipitation of granular primary NbC, and a combination of experimental observations and first-principles modelling were carried out to investigate it. The calculation results show that, misfit between MgAl2O4 and NbC is 8.7%, which indicates that the MgAl2O4 nucleating effecting on NbC is structurally potent. In order to eliminate the interference combination between different elements, the MgAl2O4 (1 1 1)/NbC (1 1 1) interface overlaps were selected, and four different element matches are designed: O(Mg)Nb, Al(Mg)Nb, Al(Mg)C and Mg(O)C. From the interfacial adhesion work and interfacial energy, the stability order of the four models can be found: O(Mg)Nb > Al(Mg)C > Al(Mg) Nb > Mg(O)C. Moreover, mixture bonding of metal bonds, ionic bonds and covalent bonds are formed at the interface of O(Mg)Nb, Al(Mg)Nb, Al(Mg)C and Mg(O)C. From the experimental results, core-shell primary NbC carbides can be observed in M-1 (0.5 wt% AlMg alloy powder) coating and the core of carbide is identified to be MgAl2O4. Besides, the wear loss of M-1 coating is decreased, compared to M-0 coating.