Effect of in-situ NbC content on the microstructure and mechanical properties of Ni625 composite coating by laser cladding

To improve the mechanical properties of Ni625 coatings, different contents of Nb powder and Ni-coated graphite particles were added to Ni625 powder for in-situ generation of NbC particles. The effects of different NbC contents on the microstructure, hardness, wear resistance and corrosion resistance of Ni625 coatings were investigated. The results show that the highest XRD phase diffraction peaks of NbC in the coating are obtained with the addition of 15 % (Nb 9.9 %, Ni-coated graphite particles 5.1 %), and the coating exhibits a hardness of 441.9 HV, which is 1.53 times greater than that of the coating with the addition of 0 %. Furthermore, the wear coefficient (mu) of the coating is 0.4804, and the wear volume is 0.0042 mm3, representing a reduction of 23.5 % and 64.1 %, respectively, in comparison to the coating with 0 % additive. However, the coating with an addition of 20 % does not generate more NbC phase, and the hardness and wear resistance are not further improved. The coating with an addition of 10 % has the best corrosion resistance, with a corrosion current density of 2.1829E10 A/cm2. Further additions do not result in an enhanced corrosion resistance of the coating. Therefore, appropriate amount of in-situ generation of NbC within the Ni625 coating during the laser cladding process can effectively enhance the mechanical properties of the Ni625 coating.