| Diesel engine is an important power equipment,and the wear of the inner surface of the cylinder liner will lead to problems such as weakened power output,increased fuel consumption,and increased exhaust emissions.In the manufacturing and maintenance process of diesel engines,the preparation of wear-resistant coatings can effectively reduce wear,extend service life,improve the power of diesel engines,reduce fuel consumption and exhaust emissions,and reduce environmental pollution.Plasma spraying coating has the advantages of dense structure,good wear resistance,strong corrosion resistance,wide applicability,high production efficiency and low cost,and the use of plasma spraying to prepare wear-resistant coating on the inner surface of diesel engine cylinder liner has important economic,environmental and social significance.Based on the research status and application of wear-resistant coatings prepared by the inner wall of diesel engine liners at home and abroad,this paper proposes to use atmospheric plasma spraying to prepare three ceramic composite coatings,Cr2O3-Al2O3,Cr2O3-TiO2 and Cr2O3-Y2O3,characterize the microstructure,phase composition and microhardness of the coating,simulate the lubrication mode of the inner wall of the cylinder liner during operation,study the sliding friction characteristics of the coating under dry friction and boundary lubrication conditions,and analyze the wear mechanism.The experimental and analysis results show that the three ceramic composite coatings prepared by atmospheric plasma spraying have obvious layered structure,sufficient melting of ceramic particles,good flattening,tight bonding between particles,and low porosity.For Cr2O3-Al2O3 coatings,the added hard phase greatly improves the microhardness of the coating and reduces the brittleness of the ceramic.Cr2O3-TiO2 coating has good compactness,TiO2 refinement effect is obvious,and higher microhardness and lower porosity can be obtained by increasing hydrogen flow.The hardness value of Cr2O3-Y2O3 coating decreased,and the Y2O3 content had a great influence on the microstructure of the coating,and the porosity was the lowest and the hardness value was the highest when the Y2O3 content was 10%.The phase composition of Cr2O3-Al2O3 coating is Cr2O3 phase and α-Al2O3 phase,both of which are corundum structures,which can improve the toughness and mechanical properties of the coating.Under the condition of changing the hydrogen flow,the phase composition of Cr2O3TiO2 coating was Cr2O3 phase,rutile TixOy and Cr-Ti oxide,which increased the hydrogen flow rate to make the ceramic particles melt more fully and the solid solution content increased.The phase composition of Cr2O3-Y2O3 coating is Cr2O3 phase and Y2O3 phase,there is chemical inertness between the particles,and the binding method is mechanical bonding.Under dry grinding conditions,the friction curves of five groups of Cr2O3-Al2O3 coatings have undergone a stage of rapid rise and stability in a short period of time,and the final friction coefficient is between 0.28～0.33,among which the friction curve of CA20 coating has the most stable fluctuation,and the friction coefficient and wear rate are the lowest.The wear mechanism at this time is mainly abrasive wear caused by brittle fracture and micro-convex body cutting;The friction curves of the five groups of coatings under boundary lubrication conditions slowly increased within 0-12000 s,and then entered the stable oil lubrication stage,with the addition of Al2O3 content,the transition time to dry friction state gradually increased,among which CA20 coating showed the best boundary lubrication performance,the duration was 48000 s,when the Al2O3 content continued to increase,the transition time was greatly shortened,and when the Al2O3 addition was 20%,the coating could obtain the best boundary lubrication performance.The wear mechanism is micro-polishing based on abrasive wear.The friction characteristics of Cr2O3-TiO2 coatings are greatly affected by hydrogen flow,and the friction coefficient curves of the three groups of coatings fluctuate greatly under dry grinding conditions.The average friction coefficient of CT65-6 and CT65-8 coatings(0.32 and 0.31)is slightly lower than that of CT65-4 coatings(0.36),with the increase of hydrogen flow,the wear rate of CT65 coatings gradually decreases,the wear resistance increases,the wear mechanism changes from abrasive wear to adhesive wear,and the incomplete friction film is mainly composed of material transfer of dual parts and solid solution in the coating;CT65 coatings deposited with high hydrogen flow under boundary lubrication conditions change from oil lubrication to dry friction later,and the transition time is 10000,respectively s,25000 s,28000 s,the boundary lubrication performance is significantly improved.The friction film mixed with oil and transfer Si has a lubricating effect,hinders the direct contact between the coating and the grinding ball,reduces material loss,and the lubricating film has a high viscosity and adheres firmly to the surface of the wear mark.The wear mechanism is mainly micro-cutting of adhesive wear and grinding chips.The friction characteristics of different contents of Cr2O3-Y2O3 coatings were significantly different,and the friction coefficients of the five groups of coatings tended to be flat after slowly rising under dry friction conditions,and finally stabilized between 0.29～0.40,the lowest and highest friction coefficients were CY10 and CY50 coatings,and CY10 coating wear rate and wear depth were the lowest.The addition of Y2O3 changes the wear mechanism,and the wear mechanism is mainly the abrasive wear generated by the particle refining process when the content is low,and the adhesion wear involved in the transfer of grinding ball materials at higher content.Under boundary lubrication conditions,all five groups of coatings underwent a transition from oil lubrication to dry friction,with CY10 coating with the longest transition time of about 45,000 s.The addition of Y2O3 improves the ability of Cr2O3 ceramic composite coating to resist high hard joint cutting under boundary lubrication conditions,the wear mechanism changes from abrasive wear to adhesive wear,and the lubrication medium includes Si3N4 material transfer and Y2O3 grinding chip mixed friction film in addition to engine oil. |
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