Study Of Plasma Sprayed NiCrMo Based Metal Ceramic Coating Ceramic Coating And Its Antifriction Wear And Corrosion Resistance Properties

Cylinder liner is the core component of diesel engine.The outer wall of cylinder liner bears the influence of cooling water corrosion and cavitation,and the inner surface also has serious friction,wear and corrosion,which leads to premature failure of cylinder liner.Therefore,it is urgent to study new wear and corrosion resistant protective coating to extend the service life of cylinder liner.In this paper,NiCrMo as the research object,using atmospheric plasma spraying technology to prepare Cr₃C₂reinforced NiCrMo composite coating.Some valuable results have been obtained,which provides a theoretical basis for its application in cylinder liner.This paper mainly draws the following conclusions:（1）The preparation process and electrochemical corrosion properties of plasma sprayed NiCrMo coating were studied.The microstructure of plasma sprayed NiCrMo coating is compact and a few pores exist.The coating is composed of a singleγ-Ni phase,and the spraying process parameters have no obvious effect on the phase composition of the coating.The process parameters of NiCrMo coating prepared by plasma spraying were optimized as follows:spraying power:36 k W,main gas（Ar）flow:35L/min,powder feeding rate:35g/min,and hardness of the prepared coating:328（HV200 gf）.The average binding strength was 65.1MPa,and the porosity was3.19%.The corrosion voltage and current density of plasma sprayed NiCrMo coating in Na Cl solution environment are-37.8 m V and 1.080×10^-6A/cm²,respectively,indicating that the NiCrMo coating has excellent electrochemical corrosion resistance.（2）The effects of doping content of Cr₃C₂on the microstructure and friction and wear properties of NiCrMo-Cr₃C₂composite coatings were studied.With the increase of Cr₃C₂content,the porosity and hardness of NiCrMo-Cr₃C₂composite coating increase,while the bonding strength decreases.The coating is mainly composed of binder phaseγ-Ni（Cr,Mo）,Ni Cr phase and ceramic phase Cr₃C₂,and the doping content of Cr₃C₂has no obvious effect on the phase composition of the coating.The wear rate of the composite coating decreases with the increase of Cr₃C₂content.At room temperature and 300℃,the wear mechanism of the composite coating is mainly adhesive wear and oxidation wear,and there is a slight abrasive wear.The friction coefficient of NiCrMo-Cr₃C₂composite coating doped with 22.5%Cr₃C₂is 0.517,and the wear rate is only 2.06×10^-5mm³/N ·m.The friction coefficient of the composite coating is significantly reduced in the presence of lubricating oil at room temperature,and the main wear mechanisms of the coating are abrasive wear and fatigue wear.（3）The oxidation and corrosion resistance of NiCrMo-Cr₃C₂composite coating at 700℃was studied and its oxidation and corrosion mechanism was revealed.Cr₃C₂doping concentration has no obvious effect on the phase composition of NiCrMo-Cr₃C₂composite coating oxidized at 700℃,and the main oxidation products are Ni O、Cr₂O₃and Ni Cr₂O₄.When Na₂SO₄and Na₂SO₄co-exist at 700℃,the oxidation of the composite coating is accelerated,but the complement of oxidation products is almost unchanged.As the doping content of Cr₃C₂increases,the unit weight gain of the composite coating decreases first and then increases.When the doping concentration of Cr₃C₂is 22.5%,the composite coating has the best oxidation resistance.The oxidation rate of NiCrMo-22.5%Cr₃C₂composite coating at 700℃and Na₂SO₄is 0.18886mg^-2 ·cm^-4 ·h^-1.In 700℃sulfate environment,mechanism of oxidation-corrosion resistance of coatings:Coating and the area of contact sulfate can form is far lower than the melting point of sulfate in local area,low melting eutectic salt coating of chromium and molybdenum in the process of hot corrosion formation of oxide inhibits the Ni O dissolved in the eutectic salt makes hot corrosion cannot proceed,ultimately to protect matrix.