Study On Friction And Corrosion Characteristics Of CrMoCn Based Coatings With High Mo Content

Serious friction,wear and corrosion problems occur in parts of mechanical equipment in high temperature,humidity and salinity environment for long term.The surface protection of parts by multi-component coatings with high Mo content can effectively improve their wear and corrosion resistance.In this thesis,CrMoCN and Cr Mo Si CN coatings with high Mo content were prepared on TC4 alloy substrate and Si(100)by controlling Mo target currents using a closed-field unbalanced magnetron sputtering ion coating equipment.XRD,XPS,and SEM were used to characterize and test the microphase structure,chemical bond composition as well as surface and cross-section morphology of CrMoCN-based coatings,respectively.Then,several properties were tested,such as elastic modulus,hardness before and after corrosion at different times(i.e.7 days,14 days,and 21 days),corrosion resistance and adhesion of the coating to the substrate.The friction and wear experiments of CrMoCN-based coatings with high Mo content were carried out with Si C and YG6 in air,deionized water and seawater respectively using"ball-disk"friction and wear tester to test the tribological properties of coatings.The study shows that:(1)Mo in CrMoCN-based coatings replace Cr in CrN to form(Cr,Mo)N solid solution.The increase of Mo content is conducive to the formation of solid solution in coatings,which can reduce the surface grain size of coatings,improve the roughness of coatings,and make the structure of coatings denser and more compact.Coatings with high Mo content have better mechanical properties,stronger film-base binding ability and better crack resistance.In addition,the doping of Si elements can further improve the mechanical properties of coatings to a certain extent.(2)In the air environment,wear mechanisms are mainly of adhesive wear and abrasive wear.With limited corrosion wear,due to the presence of hard particles,friction coefficient fluctuates are stronger with Si C balls compared with YG6 balls.So,it is hard to reach the steady state and the wear rate is higher.However,the friction and wear performance of coatings with high Mo content is more excellent.In the deionized water environment,wear mechanisms are mainly of corrosive wear and adhesive wear.With abrasive wear and friction,the abrasive is discharged in time with the flow of the liquid,which can reduce the damage and stabilize the friction coefficient.The frictional chemical reaction generates Si O₂·2H₂O and the lubricant layer MoO₃,which can reduce the wear rate of the coating.In the seawater environment,wear mechanism is mainly of corrosive wear.The progress of the tribochemical reaction can reduce the friction coefficient more than in the deionized water environment.Si elements in Cr Mo Si CN coatings also participate in the reaction to improve the tribological properties of coatings.(3)The CrMoCN-based coatings are easy to react with water,and the soaking corrosion promotes the chemical reaction.The coating corrosion starts from the small holes on the surface,and the corrosion product fills the gap of the columnar structure of coatings.The original morphology of coatings'surface is destroyed,but the structure is denser,which does not damage the hardness and other mechanical properties of coatings,and at the same time prevents the seawater from contacting the matrix through the pores.On the other hand,the reaction generates Mo O₃,Ca CO₃ and Mg(OH)₂,which are attached to the surface of coatings.They can prevent the continuous occurrence of corrosion,improve the corrosion resistance and the protection of coatings.