As a commonly used process to protect a target material, surface coating technique organically combines the advantages of both the substrate and the coating material for some mechanical properties (such as strength, toughness, etc.) and environmental service demands (such as wear and corrosion resistance， etc.).
Metal-ceramic coating is a composite prepared by appropriate technology from mixed phase of metal or alloy and one or several ceramic phases. With the combination of the high strength, good toughness and good process technology of metal and the superior wear resistance， corrosion resistance and chemical stability of ceramic materials， both adequate strength and excellent corrosion resistance surface could be kept to significantly improve the using performance of the materials.
Cold spray is an effective technique to deposit pure metallic coatings on a variety of substrates，especially for those metals that are apt to oxidation at high temperature.During cold spray， the particles are fed into a supersonic gas stream and accelerated to a high velocity. The intensively deformed spray materials are deposited on the substrate in a solid state.
Laser remelting process is a surface hardening technology combined laser heat treatment technology. Appropriate laser remelting processing can significantly improve the structure and properties of coatings and it has been applied in the post processing technology of thermal spray coatings at present.
In order to explore laser remelting technology for the post processing of cold spray coating， this study combine the cold spray coating technology with the surface laser remelting technology, for better performance. The study used cold spray coating technology to prepare the NiCoCrAIY/ZrC>2 metal-ceramic composite coating on steel substrate and design the scheme of laser remelting processing adopting laser output power and laser scanning rate as the variables of laser processing parameters.
Compared the original NiCoCrAlY/Zr02 metal-ceramic composite coating deposited by cold spraying, the microstructures，phases and performance characteristics of the laser remelting coatings were studied systematically.
Scanning electron microscope (SEM)，energy spectrum analysis (EDS), and x-ray diffraction analysis (XRD) technology were used to analyse microscopic morphology and coating composition. The results showed that the cold spray coating was deposited through intensive plastic deformation of the spray particles by high-speed impact and most of interfaces were physical and mechanical combinations.
After laser remelting process，the outlines of the solid particles gradually fade, the grains of remelted layer were refined， the small pores and loosen tissues were reduced and the coating became more dense and uniform. After laser remelting coatings, element spread and penetrated between coating and substrate that the content of Fe on the coating surface had increased and the A1 elements moved up to the surface. When the laser energy density was high enough, the content of AI2O3，ZrOi and Y2O3 had a significant increase and the content of chromium, iron，cobalt，nickel and other metals had clearly slowed down in the laser melting area.
Performance test results showed that after laser remelting，micro-hardness has been improved significantly, up to 650HV and the micro-hardness of the surface layer was lower than that in the inner layer. The coefficient of friction of composite coating had fallen down to 0.7 from 0.75-0.8.The laser energy density is larger， the coefficient of friction became smaller and the minimum is 0.45 .The wear-resisting performance was improved by laser remelting.
Electrochemical corrosion test results showed that the stable corrosion potential of NiCoCrAlY/Zr02Composite coating by cold spraying is about -0.355v.The corrosion potential positive is higher than that of matrix steel and anodic polarization curves appeared distinct passivation. After laser remelting， the corrosion potentials of coating negative move a certain amount of range and the passivation had become gradually weakening. For the NiCoCrAlY/Zr02 composite coating by cold spraying，seawater was apt to corrode the substrate through small gaps. Laser remelting could reduce the small gaps in coatings and increase the density. Both the oxides formed on the surface and the corrosion products that would fill the micro-gaps could make the penetration of seawater for coating problem. Salt spray test results showed cold spray coating and the coating of laser remelting with low energy density appeared corrosion spot first， the salt spray corrosion resistance was poor； the coatings with high energy density had low levels of corrosion and showed good resistance to salt spray corrosion.
It can be predicted that if choosing the right laser treatment parameters for thick cold spray coating， laser remelting process is a very promising post-treatment methods for cold gas spraying coatings.
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