热带海洋大气环境316不锈钢及其PVD防护涂层的腐蚀行为与性能演变研究OA

A 3.5-year field atmospheric exposure test was conducted on the Yongxing Island,South China Sea,to investigate the corrosion behavior and failure mechanisms of 316 stainless steel(316 SS)and six PVD coatings deposited by multi-arc ion plating.The coatings comprised TiN,TiAlN,TiSiN-Ag,CrN-6 h,CrN-12 h,and a Cr/CrN multilayer.The objective was to provide experimental evidence for the design of protective coatings intended for service in tropical marine environments,where high humidity,salinity,and temperature pose severe challenges to metallic components,and to identify the dominant degradation mechanisms and key factors governing coating performance. 316 SS substrates and the six coatings were exposed at the Yongxing Island corrosion test station for 3.5 years.Coating deposition consisted of target cleaning,substrate etching by Ar+,deposition of the respective coatings,and cooling.For the unexposed 316 SS,nanoindentation,tribological testing,and electrochemical measurements were performed as baselines.For the exposed 316 SS,a comprehensive characterization was performed using SEM/EDS,XPS,CLSM,nanoindentation,tribological testing,and electrochemical measurements in artificial seawater(ASTM D1141-98)to evaluate corrosion morphology,corrosion product composition,tribological properties,and corrosion resistance.For the exposed coatings,a systematic characterization program was carried out,incorporating SEM/EDS for morphological and compositional analysis,tribological testing,and electrochemical measurements. After 3.5 years of exposure,the uncoated 316 SS exhibited typical pitting corrosion,with a maximum pit depth of 8.91 μm and an average depth of approximately 6.70 μm.XPS analysis confirmed that the predominant corrosion products consisted of Fe2O3 and Cr2O3.The exposure led to measurable degradation in surface properties,including mechanical,tribological,and electrochemical aspects:hardness decreased from 5.48 GPa to 4.78 GPa,the H/E ratio declined from 0.024 85 to 0.021 29,and the corrosion current density increased from 4.10×10-6 A/cm2 to 4.57×10-6 A/cm2.Among the PVD coatings,TiN and CrN monolayer coatings suffered from penetrating failure,with dense rust spots and exposure of the underlying steel.In contrast,the Cr/CrN multilayer,TiAlN,and TiSiN-Ag coatings maintained substantially better integrity.Electrochemical measurements after exposure demonstrated that the Cr/CrN multilayer coating retained the lowest corrosion current density(4.47×10-7 A/cm2),outperforming TiAlN(2.66×10-6 A/cm2)and TiSiN-Ag(1.15×10-6 A/cm2)coatings.In severely corroded regions of TiN and CrN monolayer coatings,the corrosion current density escalated to the 10-5 A/cm2 range,indicating near-total loss of protective capability. Cross-sectional SEM examination of failed CrN coatings revealed that large macroparticles,intrinsic to the multi-arc ion plating process,acted as preferential penetration pathways for the chloride-containing electrolyte.The corrosive medium infiltrated along these defect channels to the coating/substrate interface,initiating pitting of the underlying steel.Subsequent lateral propagation of interfacial corrosion,coupled with volume expansion from Fe2O3 and Cr2O3 formation,generated sufficient internal stress to induce coating bulging,collapse,and eventual spallation.For the Cr/CrN multilayer coating,the abundant layer interfaces effectively deflected crack propagation,and the dense structure extended the diffusion path of corrosive media through a tortuous-path effect,thereby imparting superior resistance to penetration and failure.In conclusion,this study identifies macroparticle defects as the primary failure initiation sites,interfacial corrosion as the dominant degradation mechanism,and multilayer architecture as an effective strategy for long-term corrosion protection in aggressive tropical marine environments.