| Surface modification techniques play an important role in improving properties and extending the life of materials.Electrodeposited nickel matrix coatings have been developed for a variety of applications due to their high hardness,excellent wear,and corrosion resistance.Duplex coating,which takes advantage of the individual coating structures to further improve the overall performance,has gradually become the focus in the field of electrodeposition.In this paper,Ni-Mo and Ni-P coatings were prepared based on the substrate of pure copper by pulsed electrodeposition,and the effects of different solute element contents on the structure and properties of the coatings were analyzed.Based on the optimization process,the amorphous structure Ni-P coating was selected as the inner layer,and the nanocrystalline structure Ni-Mo coating was designed as the outer layer to prepare a duplex structure coating（Ni-P/Ni-Mo）.Additionally,Zr O2 nanoparticles were selected to further enhance the relevant properties of the structural coatings.The relationship between the morphological and structural transformation of the coating and the mechanical properties,corrosion,and wear properties was investigated,and the mechanism of co-deposition of the second phase nanoparticles with the Ni-P/Ni-Mo duplex structural coating was discussed.The results show that the crystallite size decreases and gradually transforms into the nanocrystalline structure as the Mo content of the Ni-Mo coating increases from 9.79 wt.%to34.50 wt.%,with a homogeneous cellular cluster structure at the 28.34 wt.%Mo content.The increase in molybdenum content significantly improves the wear resistance of the coating,and the Ni-28.34 wt.%Mo coating being the hardest（736 HV）with the lowest wear rate(5.212×10-4mm3/N·m).Additionally,it has been investigated the influence of sodium hypophosphite concentration on the morphological structure and corrosion resistance of Ni-P coatings,which exhibit a dense amorphous structure at a high phosphorus content of 12.22 wt.%.The corrosion current density of the coating was 6.9794×10-7 A/cm2 and the polarization resistance was 4.09times higher than that of the Ni-Mo coating,providing excellent corrosion resistance.The amorphous structure without surface inhomogeneity and the surface protection coating formed by the enrichment of phosphorus elements has a positive effect on reducing the corrosion rate and positively transferring the corrosion potential in the active corrosion region.The morphology and properties of the Ni-P/Ni-Mo and Ni-P/Ni-Mo-Zr O2 duplex coatings were analyzed.The interface between the“substrate/coating”and“coating/coating”is well bonded.Compared with the Ni-Mo coating,the Ni-P/Ni-Mo coating shows the 68.75%reduction in corrosion current density and an increase in polarization resistance to 308 kΩ·cm2.The mismatch of the interlayer defects causes a deviation in the corrosion path,resulting in a transformation from longitudinal pinhole corrosion to extended transverse corrosion,which effectively strengthens the corrosion resistance of the coating while maintaining the high hardness and low wear rate of its outer coating.The incorporation of nanoparticles in the coating increases the hardness of the coating to 810 HV and reduces the wear rate to 4.317×10-4mm3/N·m.The particles carry stress and transfer loads during the wear process,which improves the wear resistance of the coating.The design of Ni-P/Ni-Mo-Zr O2 duplex coating takes advantage of the properties of the different structures and incorporates second-phase reinforcing particles to improve the wear and corrosion resistance of the coating. |
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