Investigation Of Plasma Sprayed Mo/Al₂O₃-TiO₂ Coating On Hydraulic Cylinder Piston Rod

This topic for the hydraulic cylinder piston rod commonly used 40 Cr steel, Al₂O₃-TiO₂ coating and Mo / Al₂O₃-TiO₂ composite coating was prepared on 40 Cr steel surface by plasma spray technique.First of all,on the basis of bonding strength, using the orthogonal experiment method, affecting the quality of plasma spraying coating’s four process parameters（power of spraying, spraying distance, primary air flow rate, feeding rate） was optimized. And do a statistical analysis for Mo/Al₂O₃-TiO₂ composite coating on bonding strength.At the same time, utilizing the means such as SEM, EDS, XRD, metallograph, I observed and analyzed the structure, organization, element distribution of substrate and coatings. Then, I performanced a series of tests to verific the property of the composite coatings, for instance: thermal shock test, hardness and wear test, corrosion test, etc.The results shows that:For Al₂O₃-TiO₂ coatings,powder feed rate and spray distance had a great influence on bonding strength, while the main gas flow and spray power were not. After process optimization, bonding strength can be 39.58 MPa, interface of coating and substrate is the weakest part of the entire coating; For Mo/Al₂O₃-TiO₂ composite coating, spray distance had a great influence on bonding strength, while the main gas flow,powder feed rate and spray power were not. After process optimization, bonding strength can be 29.68 MPa,which was less than the bonding strength of the coating and substrate,interface of Mo coating and ceramic coating was the weakness of the entire coatings.The bonding strength of Mo/A12O3-Ti O2 composite coatings was in line with Weibull distribution and normal distribution.Thermal shock damage typically begins at the corner of coating weaknesses. Thermal shock damage process mainly consists of crack initiation, crack propagation, coating off. Coating thermal shock damage mainly dued to thermal stress. One was a transient thermal stress dued to the temperature difference between inside and outside during the heating and cooling process.The other was interface heat mismatch strain dued to difference in coefficient of thermal expansion.they lead to failure of the coating off. thermal shock resistance of Mo/Al₂O₃-TiO₂ composite coating was better than Al₂O₃-TiO₂ coatings.Coating quality were significantly improved,which was prepared by the optimizedprocess parameters. Coating was dense,porosity was lower, each interface linked together closely and bonding strength increased.Mo was a single Mo phase before and after spraying, Al₂O₃-TiO₂ powder before spraying was A12O3 and TiO2 phase, and changed to A12O3 and Al2TiO5 phase after spraying.With the increase of load and the linear velocity, average coefficient of friction of Mo/Al₂O₃-TiO₂ composite coatings will increase.The wear coating process can be divided into three phases. Friction coefficient of the last phase fell between 0.5 and 0.6. There was a big dispersion in the microhardness of Mo/Al₂O₃-TiO₂ composite coating,but finally they was in line with Weibull distribution and normal distribution.Plasma spray Mo/Al₂O₃-TiO₂ coating can improve the corrosion resistance compared to 40 Cr substrate.Sealing with paraffincan further improved the corrosion resistance.