Effect of Nb content on microstructure and corrosion resistance of Inconel 625 coating formed by laser cladding

The Inconel 625 coatings with Nb addition of 0 %, 1.5 %, 3 % and 5 % were prepared by laser cladding technology. The effects of different contents of Nb on the phase composition, microstructure and corrosion resistance of the coatings were investigated by XRD, SEM, electrochemical test and other techniques. The results show that with the increase of the Nb content, the surface structure of the coating changes from dendrites to cellular crystals. Because of the consumption of C in γ-Ni phase by forming NbC, more Cr was released from its carbide state and solidly dissolved in γ-Ni phase, which improves its passivation capacity in the electrolyte. The increase of Nb also promotes more Nb and Mo elements to participate in the oxidation process. The plugging of pitting holes by corrosion products reduces the corrosion rate of coatings. The 3Nb coating exhibited the best corrosion resistance in 3.5%NaCl solution. The addition of an appropriate amount of Nb is an effective way to optimize the coating's microstructure, improve its corrosion resistance and microhardness.