Preparation And Performance Of Metal-Ceramic Coating/Carbon,Nitride Based Thin Film Duplex System

The friction and wear problems of key moving parts operating under harsh conditions（high load,corrosion,and high temperature）heavily affect the reliability and service life of mechanical equipment.This dissertation focuses on advanced protective coatings and their preparation technology for metal moving parts under harsh working conditions,including high-load wear,corrosion wear,and high-temperature wear.To overcome brittleness,high internal stress,low adhesion strength,and insufficient bearing capacity of traditional PVD/CVD hard thin films on the steel substrate,the high-bearing and high-wear-resistant Cr₃C₂-NiCr/DLC duplex coating,high-bearing and corrosion-resistant Cr₃C₂-NiCr/Si-DLC duplex coating,high-temperature and wear-resistant Cr₃C₂-NiCr/TiN and Cr₃C₂-NiCr/TiSiN-CrAlN duplex coatings are designed.They are constructed by introducing high-velocity oxygen-fuel spraying Cr₃C₂-NiCr metal-ceramic coating as the intermediate bearing layer and based on the synergetic effect of two different technologies.The behavior of duplex coatings under harsh working conditions is deeply explored,and the related damage mechanisms are analyzed.It provides theoretical guidance for the design and development of advanced protective coatings.The main research content and conclusions are as follows:（1）To reduce the wear under high-load conditions,a duplex Cr₃C₂-NiCr/DLC coating was prepared on steel substrates by combining a hard,self-lubricating DLC film top functional layer and thick Cr₃C₂-NiCr metal-ceramic coating intermediate bearing layer.The microstructure,mechanical properties,and tribological properties of the duplex coating were systematically studied under varying loads.The results show that the Cr₃C₂-NiCr/DLC duplex coating has good bonding reliability and high bearing capacity.The friction coefficient of the duplex coating is low and stable（less than 0.1）under high-load conditions and decreases with the increase of load,which can be explained by the Hertz elastic contact model.The wear rate of the duplex coating is less than 2.5×10^-7mm³·N^-1·m^-1,showing excellent tribological performance.（2）To meet corrosion wear conditions,Si-DLC films with different Si content were studied by their microstructure,mechanical properties,tribological properties,and corrosion resistance.Si-DLC films with high wear and corrosion resistance in strongly corrosive media were solved by preparing a Cr₃C₂-NiCr/Si-DLC duplex coating,consisting of an intermediate Cr₃C₂-NiCr cermet coating and a Si-DLC top functional layer.The results show that the microstructure and corrosion resistance of Si-DLC films can be effectively improved by controlling Si content.The films present a dense microstructure when the Si content is about 15.32 at.%,which provides the best corrosion resistance in 1M HCl aqueous solution.Along with the strong support of the Cr₃C₂-NiCr cermet coating,the high corrosion resistance of the top layer Si-DLC film in Cr₃C₂-NiCr/Si-DLC duplex coating also achieves excellent wear resistance in strong corrosion media.The wear rate of Si-DLC films is as low as9.0×10^-8mm³·N^-1·m^-1under a load of 10 N.（3）Towards high load and high-temperature conditions,Cr₃C₂-NiCr/TiN duplex coating was prepared using TiN film as the top functional layer by arc ion plating method and Cr₃C₂-NiCr metal-ceramic coating as the intermediate bearing layer.The microstructure,mechanical properties,and tribological behavior of the duplex coating were studied at different temperatures.The results show that the hardness and elastic modulus of the Cr₃C₂-NiCr/TiN duplex coating are as high as 32.3±0.9 GPa and402.5±35.5 GPa,respectively.The coating shows good fracture toughness and high bearing capacity.Low wear rate is obtained in the temperature range from room temperature to 500℃,showing good high-temperature wear resistance.The wear mechanism at high temperatures is mainly dominated by oxidation wear,accompanied by abrasive and adhesive wear.（4）To improve the friction and wear at higher temperatures（>500°C）and to elevate the service temperature limitation of TiN films,TiSiN-CrAlN nanomultilayer film with better high temperature and oxidation resistance was prepared as the top functional layer by arc ion plating technology.The Cr₃C₂-NiCr/TiSiN-CrAlN duplex coating was produced by plating Cr₃C₂-NiCr metal-ceramic coating as an intermediate bearing layer.The microstructure,mechanical properties,and tribological properties were studied in the temperature range from room temperature to 900℃.The results show that Cr₃C₂-NiCr/TiSiN-CrAlN duplex coating can prevent plastic deformation of steel substrate under high-temperature conditions.This effectively reduces the stress concentration at the film/coating interface and prevents the brittle fractures and peeling of hard film,showing excellent high-temperature wear resistance.The duplex coating is mainly subjected to abrasive wear below 500℃but is controlled by oxidative wear at 700℃and 900℃.A tribo-film formed at the friction interface is mainly composed of TiO₂and Cr₂O₃.