Effect of CeO2 addition on microstructure and mechanical properties of in-situ (Ti, Nb)C/Ni coating

As a surface repair and strengthening technology, (Ti, Nb)C/Ni coatings with different amount of CeO2 were fabricated to repair the automobile dies. The phase constitution, microstructure, texture characteristics of oriented growth, micro-hardness, tensile properties and the action mechanism of CeO2 were investigated. The results showed that the diffraction peaks of γ-Ni(Fe), (Ti, Nb)C, Cr7C3 and Cr23C6 drifted slightly as a result of solute atoms incorporation. The compact and homogenized microstructure of coatings was dominated by small striped precipitated phases and particles according to SEM and TEM results. The size of (Ti, Nb)C particles were suppressed by rare earth element Ce, which was prone to accumulate at the interface of grain boundary or crystalline phases. The unmelted CeO2 can also become the heterogeneous nucleation basement of (Ti, Nb)C, Cr23C6 and Cr7C3 particles. EBSD results showed that the grain growth orientation of coatings was changed by the effect of CeO2 on the fluidity of molten pool, as well as the growth of particles. In addition, the tensile properties of coatings were improved, and the fracture behavior was transformed from the quasi-cleavage fracture to brittle fracture with the increase of CeO2 addition.