Preparation And Tribological Performance Of Flame-sprayed Self-lubricating And Wear-resistant Ni-based Coatings

Ni-based coatings have good comprehensive properties and are widely used in industry.Among them,Ni-coated graphite coatings has been successfully applied in the field of aerospace.However,low surface hardness and poor wear resistance limit its tribological application.In order to improve the tribological performance of Ni-coated graphite coatings,WC particles and Ni60/WC composite particles were introduced into the coatings by flame spraying technology respectively.Then various Ni-based graphite/WC composite coatings were prepared.The effects of different particles on the microstructure and the tribological performance of Ni-coated graphite coatings were studied.WC particles were added into Ni-coated graphite coatings.The results show that the hardness and bonding strength of the coatings can be improved by adding appropriate amount of WC.When the content of WC is 30 wt.%,the friction coefficient of the coatings is only slightly increased,but the wear resistance is obviously enhanced.WC has good compatibility with Ni-based coatings,which is not easy to peel off in the process of friction.At the same time,it can inhibit the crack growth and reduce the fatigue wear of Ni-coated graphite coatings.However,when the content of WC is too high,the content of metal bonding phase in the coatings is relatively low,the hardness of the coatings is reduced and the tribological performance is poor.Ni60/WC composite particles,including the Ni60-coated WC particles and the Ni60-mixed WC particles,were added into Ni-coated graphite coatings respectively.The results show that the composite coatings prepared with the Ni60-coated WC particles has low surface roughness,uniform phase distribution and high density.When the content of the coated particles is less than 30 wt.%,the composite coatings can form a complete selflubricating film in the friction process,and the friction coefficient is low.Compared with Ni-coated graphite coatings with the single addition of WC particles,the content of metal binding phase in the composite coatings is more sufficient,the strengthening effect of WC is good and the wear resistance is significantly improved.The distribution of graphite and WC in the composite coatings prepared with the Ni60-mixed WC particles is uneven and it is difficult to form a complete self-lubricating film in the friction process.The friction coefficient and wear rate of the coatings are high.Compared with the composite coatings prepared with the mixed particles,Ni-based graphite/WC composite coatings prepared with the coated particles has better tribological performance.The high temperature tribological performance of Ni-coated graphites coating and Nibased graphite/WC composite coatings were studied.The results show that the friction coefficient of the two coatings reaches the maximum at low and medium temperature(200 ?~300 ?).Then the friction coefficient decreases with the increase of temperature.This is because although the lubrication effect of graphite decreases with the increase of temperature,the oxide with lubrication effect is formed on the coatings surface at higher temperature.In high temperature environment,the wear resistance of the two coatings decreased to some extent.Due to the strengthening effect of WC,the wear rate of Ni-based graphite/WC composite coatings is lower than that of Ni-coated graphite coatings at medium and high temperature(above 300 ?).