Preparation And Performance Study On The Composite Coating Of Hydraulic Cylinder Piston Rod In Ocean Splash Zone

The impact factors,including serve corrosive environment of high humidity,high salt and high oxygen content and the frequent impact of ocean waves in the ocean splash area（OSA）,put forward strict requirements for the service performance of Marine equipment.Hydraulic cylinder piston rod,as an important actuator of Marine equipment,is exposed in the harsh conditions above mentioned for a long time,which results in the occurrence of surface damages,such as corrosion,wear,fatigue crack.Thus,the problems,for instance hydraulic cylinder failure,hydraulic cylinder instability and other problems,are prone to occur.Laser cladding,thermal spraying and other surface treatment technologies are often used to improve the surface service performance of parts in harsh environments.However,the traditional single coating technology cannot meet the requirements of the combination property of corrosion,wear and fatigue resistance for the piston rod in the OSA.Therefore,developing a new surface technology to improve the comprehensive service performance of piston rod has become a research focus of domestic and foreign scholars.According to the different connection strategy of metallurgical combination-mechanical combination,the present paper proposes a laser cladding（LC）and high velocity oxygen spraying（HVOF）complex function coating structure.In present paper,the research mainly focus on the LC bonding layer,HVOF working layer,the design and development of compound function coating,and reliability analysis and validation of complex coating,respectively.The purpose is to provide theoretical and technical basis for improving the comprehensive service performance of wear-corrosion-fatigue resistance for hydraulic piston rod.The preparation technology and properties of laser cladding coatings are studied and analyzed.The key parameters affecting the coating quality are analyzed,and the evolution of microstructure and property of 316L and Ni625 coatings under different energy densities are studied.Combination the tests of NSS and ball-disk wear,the damage behavior and mechanism of 316L and Ni625 coatings under multi-factor coupling conditions of fatigue,corrosion and wear conditions are revealed.Furthermore,solution treatment process on the diffusion behavior of corrosion resistant elements and the effects of solution treatment on microstructure and properties of 316L coating are both studied.The interaction and acceleration effect of coating damage behavior under the coupling condition of multiple environmental factors are experimentally verified,which manifests the improvement mechanism of solution treatment on microstructure and properties of316L coating.The preparation technology and properties of high velocity oxygen fuel coatings are studied and analyzed.Using the nonlinear regression analysis method,a mathematical model is established between the bonding properties of Cr₃C₂-Ni Cr coating and the 3D surface morphology parameters of sandblasting surface.Moreover,the influence mechanism of sandblasting process parameters on the key morphology parameters is explored.According to the four points bending,immersion corrosion and erosion wear testing methods,the properties of the Cr₃C₂-Ni Cr coating,such as fatigue,corrosion,wear resistance,are studied as response,clarifying the failure behavior and mechanism of the fatigue,corrosion and wear.Basing on the curing mechanism of epoxy resin,a new formulation of pore sealing agent is developed,and the influence of Cr₃C₂-Ni Cr coating sufferred sealing treatment is subsequently studied on the cossosion resistanceThe structure design and properties of"laser cladding-high velocity oxygen fuel"composite coatings are studied and analyzed.Depending on the"metallurgical combination and mechanical combination"differential connection strategy,a composite coating which is composed of LC Ni625 bonding laser and HVOF Cr₃C₂-Ni Cr working coating is following designed.Electrochemical and four points bending tests are carried out for the composite coatings to explain the corrosion and fatigue failure behavior and damage mechanism,respectively.Meanwhile,the accelerated failure behavior of composite coatings under the coupling conditions of fatigue,corrosion and wear is studied.The mechanism of crack initiation and propagation,pitting corrosion formation and growth of composite coating are both described basing on the test results.Furthermore,the service performance improvement method of hydraulic piston rod in OSA is correspondingly clarified.The stress fatigue reliability of hydraulic cylinder piston rod is studied and analyzed.The parametric modeling of hydraulic cylinder piston rod structure under conventional conditions and corrosion conditions is established,and a four-point bending test model is used to load the piston rod.Based on the above model,the structure is simulated and analyzed.Furthermore,the reliability and sensitivity of the piston rod are analyzed according to the structure-strength interference theory,and the influence of the structural parameters of the piston rod on its reliability and life is discussed.A four-point bending test bench was set up to test the reliability of hydraulic cylinder piston rod,verifying the correctness of the simulation model and the reliability of the hydraulic cylinder piston rod.