Refinement mechanism of NbC by CeO2 in hypereutectic Fe-Cr-C hardfacing coating

Abstract The lattice misfits of different CeO 2 /NbC interfaces were calculated by Bramfitt two-dimensional lattice misfit degree theory. The interface relationship of CeO 2 (100)/NbC(111) was calculated by first principles, and the possibility of CeO 2 as the heterogeneous nucleus of NbC was analyzed as well. In this paper, hypereutectic Fe-Cr-C hardfacing coating was prepared with NbC and CeO 2 addtion to observe its microstructure by Transmission Electron Microscope (TEM) and optical microscope (OM). The calculated results show that the lattice misfit of CeO 2 (100)/NbC(111) is the smallest (7.85%), which indicates that it is moderately effective for the CeO 2 as the heterogeneous nucleus of NbC. Four interfaces were constructed between CeO 2 and NbC, which are Ce-C, Ce-Nb, O-C, and O-Nb ones. The adhesive works of Ce-C and Ce-Nb interfaces are small, which are negative. And their interface energies are large, which indicates that they are extremely unstable and easy to decompose. The adhesive work of O-Nb interface is the largest, which is positive. Its interface energy is the smallest, so that O-Nb interface is thermodynamically stable. O-C interface is less stable than O-Nb interface. In addition, O-C and O-Nb interfaces contains covalent, metallic and ionic bonds. The experimental results proves that CeO 2 can be as the heterogeneous nucleus of NbC, then refines NbC.