Preparation Of HVOF(HVAF) Sprayed Stellite20/CrN Composite Coating And Study Of Wear And Corrosion Resistance

This study investigates the application of two thermal spray processes,traditional high velocity oxygen fuel(HVOF)and modified high velocity air fuel(HVAF),using Stellite 20 as the feedstock material to prepare HVOFStl20 and HVAFStl20 coatings on 316 stainless steel substrates,with a CrN coating deposited on the surface of the coatings using physical vapor deposition(PVD)technology.The coating samples were characterized and tested using optical microscopy(OM),Vickers hardness tester,scanning electron microscopy(SEM),X-ray diffractometer(XRD),confocal laser scanning microscope(CLSM),friction and wear tester,and electrochemical workstation.The microstructure,mechanical properties,room temperature atmospheric friction and wear,high temperature atmospheric friction and wear,and electrochemical corrosion properties of different coatings were compared and studied.The mechanical properties,wear resistance,and corrosion resistance of HVOFStl20 coating,HVAFStl20 coating,CrN film,HVOFStl20/CrN composite coating,and HVOFStl20/CrN duplex coating were compared and analyzed,and the results show that:(1)For Stellite20 coatings prepared by HVOF and HVAF techniques,compared with the HVOF process,the HVAF spray process can provide faster particle spray speed and lower spraying temperature.In addition,the HVAFStl20 has less decarburization during the spraying process and the obtained coating is more uniform and dense,with a lower friction coefficient and higher hardness.(2)Under ambient temperature wear conditions,the wear phenomenon is mainly abrasive wear and fatigue wear.The HVAFStl20 coating has higher microhardness and lower friction coefficient,making it more wear-resistant.Under high-temperature conditions,the HVOFStl20 coating performs better,as severe adhesive wear is more likely to occur at high temperatures due to the following factors:1)the temperature during spraying is higher,allowing the Ni and Co elements in the raw material to melt better during the spraying process.2)Unmelted alloy particles are tightly wrapped by plastic deformation,making them less likely to peel off.In the 5%H2SO4 medium,both the HVOFStl20 and HVAFStl20 coatings show similar performances.(3)CrN films were prepared on both the substrate and Stellite20 coating surfaces using PVD technology.The films have a dense structure and are tightly bound to the coating.A small amount of droplets was observed on the surface of the film,showing obvious CrN(220)preferred orientation,highest crystallinity,and significantly increased hardness after film preparation.Stellite20 in HVOF and HVAF composite coatings provides good support,making it less prone to fracture under external loads.In the room temperature friction and wear experiments,the CrN film has good hardness and lubrication properties,thus providing good protection for the substrate,HVOFStl20,and HVAFStl20.When the load is increased,the individual CrN film will fracture first.The high temperature friction and wear experiment results showed severe adhesive wear and oxidation wear of the CrN film.In the individual CrN film and HVAFStl20/CrN composite coating,the CrN film on the surface of the wear mark almost completely disappeared,but the CrN film prepared on the surface of HVOFStl20 only peeled off a small part and still provides protection,showing the best high temperature friction performance.In H2SO4 media with a mass fraction of 5%,the CrN film can significantly increase the impedance of the composite coating,reduce the self-corrosion current density,shift the anodic polarisation curve in a positive direction and improve the corrosion resistance of the coating.