Preparation Of VAlN-based Coatings And Study On Lubrication Mechanism Of Wide Temperature Range

With the development of engine technology,the start-up and operation of some parts are facing the transformation process of room temperature and high temperature.In addition,frequent start and stop or overload conditions will cause serious damage to the equipment.Long-time friction will not only cause damage to the contact surface,affect the service life of core machines such as engines and gas turbines,reduce wear and realize energy conservation and emission reduction.Therefore,it is urgent to prepare a coating with high hardness and wide temperature range self-lubricating performance.Based on valn,using three target magnetron co-sputtering technology,v-al-c-n nanocomposite coatings with different C content were prepared by changing the sputtering power of graphite target and adjusting the ratio of different lubricating phases.The mechanical and friction properties of the coatings were tested by a nanoindentation instrument and a high-temperature friction tester.The microstructure and friction and wear surface morphology of the coating was observed by transmission electron microscope and scanning electron microscope,and its wear mechanism was analyzed.Subsequently,the VAl N Ag coating was preliminarily explored.By adjusting the power of the graphite target,six groups of valcn nanocomposite coatings with different C content were successfully prepared.The mechanical properties of the coating have been significantly improved after adding C.the hardness and elastic modulus of S5 are the best in a series,with values of 36 ± 2.24 GPA and 337 ± 15.5 GPA respectively.The coating has excellent plastic deformation resistance and cracks resistance.The coating is mainly composed of V(C,n)nanocrystalline and amorphous C,and grows along the preferred orientation of the(200)plane.The addition of C can effectively reduce the roughness of the coating and improve the film base bonding force to a certain extent.The friction tests of the above six groups of coatings at RT,300 ? and 650 ? were carried out.It was found that the lowest friction coefficients of S5 samples with 29.04% C content were0.43,0.72 and 0.35 respectively at three temperatures.TEM analysis of the wear marks of S 5samples after friction at 300 ? shows that C introduced by graphite target sputtering not only combines with V to form VC but also exists in the coating in the form of amorphous carbon.The result of amorphous wrapping nanocrystals is conducive to the wear reduction and lubrication of the coating.There are many cracks in the coating under RT,but the wear marks are shallow,and the main wear mechanism is mechanical wear;At 300 ?,the lubrication is mainly provided by amorphous C,mainly oxidative wear and adhesive wear;At 650 ?,due to the existence of various magn é Li phase oxides,a transfer lubrication film is formed between the coating and the opposite grinding ball,which avoids the direct contact between the coating and the opposite grinding pair,and then shows a low and stable friction coefficient.The tribological properties of VAl N-Ag coating were preliminarily explored.It was found that the surface roughness of the coating decreased after adding AG,and the roughness did not increase with the increase of Ag content.The reason is that the content of Ag is less,and Ag is compounded in the gap of VAl N columnar crystals,which can improve the compactness of the coating.And there are many large particles on the surface of VAl N-Ag coating,which is that a large number of Ag particles gather on the surface,which effectively reduces the friction coefficient of the coating at medium and low temperatures.The overall performance is that the higher the temperature,the lower the friction coefficient of the coating,because the higher the temperature,the stronger the diffusion effect of Ag.Compared with VAl N coating,the friction coefficient at room temperature is reduced by 18%,because the main wear form of the coating is mechanical wear;At 300 ?,the friction coefficient first decreased and then increased,because the diffused AG was not enough to complete the whole process of lubrication so that VAl N was worn later.The friction coefficient of 650 ? coating is as low as 0.27,which is due to the synergistic lubrication of vanadium and silver oxide.A variety of wear forms are combined,mainly oxidative wear.