| With the rapid development of the engine manufacturing industry,diesel engines have been widely used as a mechanical core power component.The cylinder liner is one of the important parts of diesel engines,which often works under high temperature,high pressure,and poor lubrication conditions.The friction between the inner surface and the piston will cause the cylinder liner to wear easily.Therefore,it is very important to reduce the cost of diesel cylinder liners.Plasma spraying technology is of great significance for extending the service life of cylinder liners.Based on the research progresses and existing problems of the inner wall coating of cylinder liners,this thesis proposed to prepare NiCrBSi-YSZ,Al2O3/13%TiO2(AT13)and Al2O3/13%TiO2-Mo(AT13-Mo)coatings on the substrate by atmospheric plasma spraying technology.The microhardness,microstructure and phase composition of the coatings were analyzed.According to the three working conditions of the cylinder liner inner wall during actual service,i.e.oil lubrication,boundary lubrication and dry friction conditions,the tribological properties of the coating were studied,and the wear mechanism was studied.Friction and wear conditions had an important effect on the friction coefficient and wear rate of the coatings.Under dry friction conditions,the friction coefficient of three NiCrBSi-YSZ composite coatings was stable between 0.6 and 0.7.It was found that the wear rate of the NiCrBSi-20%YSZ composite coating is the lowest(2.77×10-5 mm3/N·m).The tribofilm formed on the coating surface during the friction process played a good role in reducing wear and abrasion.The wear mechanism was mainly abrasive wear.The choice of the matching pair and load had a great impact on the dry friction of AT 13-based coatings.The materials with the same nature are prone to adhesive wear during friction,and the wear damage was worse.AT13 coating paired with a tungsten steel ball and AT13-Mo coating paired with a Si3N4 ball both showed excellent wear resistance.Under the oil-lubricated condition,the friction coefficients of NiCrBSi-YSZ composite coatings rise with the increase of the amount of YSZ doping,which was stable between 0.115 and 0.135.The wear rate of the composite coating doped with 10%YSZ was the lowest at 4.86×10-8 mm3/(N·m).The friction coefficient of AT13-Mo coating was lower than that of AT13 coating,which was 0.123 and 0.127,respectively,and the wear rates were 2.28×10-8 mm3/(N·m)and 5.38×10-8 m3/(N·m).The tribological performance of AT13-Mo coating was better under oil-lubricated lubrication,which was related to the doped Mo alloy in the coating.The coating wear mechanism was mainly abrasive wear.Under the boundary lubrication condition?AT13-based coatings have undergone the transition from boundary lubrication to dry friction.Compared with AT13 coatings,AT 13-Mo coating had a longer transition time.The improvement of wear-resistance of AT13-Mo coating is attributed to the chemical reaction between Mo element of coating and S element of lubricating oil to form self-lubricating film MoS2,which can effectively withstand part of the load.In addition,MoO2 generated in the sliding process and oil film covering the surface of the wear track can synergistically improve the wear resistance of coatings and effectively extend the boundary lubrication time.The wear mechanisms of coatings were mainly adhesive and abrasive wear. |
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