The Research On Preparation And Tribocorrosion Behavior Of Cr₃C₂-NiCr/DLC Duplex Coating

Marine equipment metal parts are subject to different degrees of corrosion and wear and their interaction during the service process,which reduces the service performance of the material and accelerates the material failure.The self-lubricating solid DLC films prepared by physical vapor deposition（PVD）technology are widely used as surface protection films for marine metal equipment due to their excellent chemical inertness,mechanical properties,and wear resistance.However,the poor stiffness,thermal stress,and structural mismatch between DLC films and substrates lead to their weak load-bearing capacity and poor toughness under severe environments such as corrosion and high load,which are pro ne to cracking and peeling,limiting their application in harsh conditions.Cr₃C₂-NiCr cermet coatings prepared by high velocity oxygen fuel（HVOF）have high hardness,high strength and low porosity and are widely used as wear and corrosion resistant protective coatings for metallic materials.The introduction of the Cr₃C₂-NiCr interlayer also avoids the degradation of the film properties caused by the dissolution of the substrate due to the penetration of corrosive media into the film-substrate bonding interface.In this study,the Cr₃C₂-NiCr cermet interlayer was prepared using HVOF on 316L stainless steel substrate based on the design idea of PVD/HVOF duplex coating,and the Cr₃C₂-NiCr/DLC duplex coating was prepared using a closed filed unbalanced magnetron sputtering（CFUBMS）with DLC film.The electrochemical behavior,tribological behavior under the medium and the corrosion-wear interaction behavior were studied.The specific research results are as follows:（1）The introduction of Cr₃C₂-NiCr interlayer did not change the organization of the top DLC film,the top DLC film was well bonded with the Cr ₃C₂-NiCr interlayer,no large cracks and pores were found on the surface of the Cr ₃C₂-NiCr/DLC duplex coating,the porosity was only 1.3%,the surface was island-like,and the presence of the Cr₃C₂-NiCr coating that was not covered by the top DLC film.（2）The introduction of Cr₃C₂-NiCr coating increased the roughness of the top DLC film and the wetting angle of the aqueous NaCl solution,and the Cr ₃C₂-NiCr intermediate layer provided good mechanical support for the top DLC film,improved the bearing capacity of the top film,and enhanced the toughness of the DLC film.The hardness,elasticity and plastic factor are significantly improved compared with single DLC film and single Cr₃C₂-NiCr coating.（3）The introduction of Cr₃C₂-NiCr intermediate layer prolongs the time for the corrosive medium to penetrate into the substrate through the defects of the duplex coating,and substantially improves the corrosion resistance of the top DLC film with a positive shift in corrosion potential and about 10 times lower corrosion current density than that of the single DLC film.Corrosion occurs at the island-like boundary on the surface of the Cr₃C₂-NiCr/DLC duplex coating and the exposed Cr₃C₂-NiCr firstly Cr₂O₃ and Ni O are the main corrosion products.（4）The Cr₃C₂-NiCr/DLC duplex coating has better load-bearing capacity and toughness than the single DLC film and is less susceptible to plastic deformation at a load of 20 N and a sliding contact time of 90 min and still maintains excellent wear and friction reduction performance.The introduction of the Cr ₃C₂-NiCr intermediate layer achieves the stress gradient transition,improves the overall mechanical properties of the Cr₃C₂-NiCr/DLC duplex coating,promotes the graphitization of the top DLC film,and its wear rate is reduced by about one order of magnitude compared with that of the single DLC film.（5）In 3.5 wt.%NaCl solution,the tribocorrosion resistance of the Cr₃C₂-NiCr/DLC duplex coating was higher than that of the single DLC film,and the single Cr₃C₂-NiCr/DLC duplex coating was optimal with the lowest total material loss rate.The introduction of the Cr₃C₂-NiCr intermediate layer increased the coupling between corrosion and wear,and the top DLC film in the duplex system played a major role in the resistance of tribocorrosion and mechanical wear dominates the material loss of the Cr₃C₂-NiCr/DLC duplex coating.