Effect Of Tungsten Contents On Tribological Properties Of CrWN Coatings Under Different Lubrication Conditions

Piston rings,the key components of the engine,are often exposed to the harsh working conditions of high temperature and high pressure,and the friction and wear between the cylinder liners results in reduced service life and increased energy consumption,which restricts the efficient development of the engine.Therefore,the use of surface modification technology to improve the mechanical properties of the piston ring material and the selection of suitable lubricants to improve the lubrication environment are the two main ways to improve the tribological performance of the piston ring.CrN coatings are widely used for surface protection of piston rings and mechanical components.In order to further improve its comprehensive performance,the CrWN coatings with different W contents were prepared on the steel surface by using IBAD technology.The SRV-4 tribometer were used to investigate the friction and wear behavior of CrWN coatings under dry friction,PAO,PAO+MoDTC/ZDDP/MoDTC+ZDDP,respectively.The results are as follows:?1?With the increase of W content,the crystal structure of CrWN coating changes from a dense columnar crystal to a coarse columnar crystal and a dense fibrous crystal.The hardness,H/E,and H³/E*² increase first and then decrease.The CrW_9.96N coating has the best mechanical properties.?2?With the increase of W content,the friction coefficient,the wear rate of CrWN coating and its counter ball under the five kinds of lubrication conditions change different,the rules are as follows:Under dry friction,the friction coefficient first decreases and doping W has little effect on the wear rate;Under the PAO and PAO+ZDDP oils,they all decreased gradually,and the high W content coatings exhibited better tribological performance;under the PAO+MoDTC and PAO+MoDTC+ZDDP oils,all of them decrease first and then increase.The CrW_9.96N coating has the best friction and wear properties.?3?Under dry friction,doping W atoms increases the hardness and H³/E*² of coatings,which is conducive to friction reduction.Under PAO,the high activity and microporosity on the surface of W-doped coatings promote the adsorption of oil film,which is beneficial to antifriction and wear resistance;Under PAO+MoDTC,the key to friction reduction is that W element promotes the decomposition of MoDTC to produce a friction reaction film containing a high MoS₂/MoO₃ ratio.The key to anti-wear is the high H³/E*² ratio of the coating and the tribofilm;Under PAO+ZDDP,the excellent abrasion resistance of the W-doped coating lies in its high surface activity,which promotes the adsorption,decomposition,and depolymerization of long-chain phosphates of ZDDP.In addition,the tungstate tribofilm formed at a high W content also help to reduce friction and wear;Under PAO+MoDTC+ZDDP,with the W content increases,the reasons for increased tribological properties include:high surface activity,high hardness,high wear resistance of the tribofilm.