Effects of nano-CeO2 on microstructure and properties of Ni625 alloy prepared by laser cladding

In this study, nano-CeO2 particles as nucleating agents were incorporated into Ni625 alloy powder by ball milling method, with the aim of inhibiting occurrence of liquation crack during Ni625 alloy laser cladding. The differences in microstructure, electrochemical performance and tribological performance between Ni625 and Ni625 + 0.2 wt%CeO2 cladding layers were studied and compared. The results from scanning electron microscope (SEM) and electron backscattered diffraction (EBSD) analyses clearly revealed that liquation crack in the lap zone between scanning tracks of the Ni625 cladding layer was caused by successive γ + Laves eutectic structure at the boundary of coarse grains. CeO2 with high melting point and low Gibbs free energy had good stability, and the two-dimensional disregistry between CeO2 and Ni625 alloy was 5.9%, which made the nano-CeO2 particles promote the heterogeneous nucleation of Ni625 alloy. Benefiting from heterogeneous nucleation, the Ni625 + 0.2 wt%CeO2 cladding layer was without liquation crack and had larger equiaxed zone and finer grains. Moreover, the γ + Laves eutectic structure at grain boundary changed from successive distribution to discrete distribution and its content reduced, which indicated that elemental segregation of Mo and Nb during solidification was improved. The results of electrochemistry, microhardness and friction wear tests showed that the Ni625 + 0.2 wt%CeO2 cladding layer had large charge transfer resistance, higher microhardness and less wear mass loss, which signified that it had better corrosion resistance and wear resistance.