Study On The Corrosion,Tribological Behavior And Mechanism Of Graphite-like Coatings In Deep Sea Environment

The tribocorrosion and failure of key friction pair materials in deep-sea equipment seriously threaten the operation reliability and long-life service safety.It is an effective technical measure to prepare a surface protective coating with good anti-friction,lubrication and corrosion resistance onto the surface of the friction pair material.Thanks to the outstanding advantages of high hardness,low friction coefficient,good chemical inertness and multi-environment adaptability,Graphite-like carbon(GLC)coating is an ideal choice for surface protection materials for water-lubricated moving parts.However,due to the lack of research tools and platforms,the study of corrosion and frictional failure mechanisms of GLC coatings has been limited to atmospheric environments,and the service behavior in deep sea environments has rarely been reported.Therefore,we combined the advantages of the platforms of several research units to pave the way for the technical bottleneck.The study of corrosion and tribological behavior of GLC coating in deep-sea environments has been systematically carried out.By combining laboratory simulations of deep-sea and exposure tests in the field site of the Pacific Ocean,the corrosion behavior and mechanism of GLC coatings in deep-sea environments have been elucidated,and meanwhile the intrinsic mechanism of GLC coating performance degradation has been explained thoroughly.The issue of the pathways through which hydrostatic pressure affects the tribological properties of coating materials is carefully analyzed.The results of this study lay a solid foundation for understanding the failure mechanisms of GLC coatings and providing feedback to optimize coating designs.The main findings of the study are as follows:1.Through the combination of laboratory simulation on the high pressure artifial seawater and filed site exposure tests in the Pacific Ocean searwater,the internal failure mechanism of multilayer Cr/GLC coating induced by hydrostatic pressure was deeply explored.Laboratory simulation experiments show that the penetrating defect in the Cr/GLC multilayered coating is the cause of the corrosion of the coating.Due to direct exposure of the substrate,penetrating defects act as a channel for rapid diffusion of seawater.Hydrostatic pressure promotes the diffusion of corrosive species through coating defects,causing severe corrosion of the substrate metal.The experimental results of the field site exposure further prove that the local corrosion induced by the penetrating defect causes the peeling of the coating,indicating that the corrosion occurs at the interface at the same time.Due to the occurrence of interfacial corrosion,the adhesive performance of the coating is significantly deteriorated,which in turn leads to premature peeling and failure of the coating.2.The effect of hydrostatic pressure on the tribological properties of GLC coating is achieved by changing the frictional contact surface.The hydrostatic pressure essentially changes the true contact area of the friction pair surface by generating additional expansion load.That is,increasing the hydrostatic pressure will have a similar effect as increasing the load.With the increase of hydrostatic pressure and load,the trend of grinding and smoothing becomes more and more obvious.The obvious graphitization transfer film and silicon-based reaction products on the friction surface are the lubrication mechanism of the solid-solid contact zone.3.Owing to the higher dissociation rate and ion energy of the carbon atoms,the GLC coatings deposited by Hi PIMS technology has a significantly higher percentage of sp3 hybrid bonds and a smoother and flatter surface.The increase in sp3 carbon bonding has resulted in a higher hardness and modulus of elasticity of the GLC coating,which in turn gives it superior load-bearing and anti-wear properties.Also,the GLC coating fabricated with Hi PIMS own a denser structure,which enables the GLC coating to possess stable corrosion protection in 30 MPa deep sea environments.The results show that the GLC coating prepared by Hi PIMS technology has an apparent advantage of strong and dense integration.At the meantime,Hi PIMS is proved to be an effective technical means to design and prepare high performance anti-wear and self-lubricating amorphous carbon coatings for deep-sea environments.