Study On The Microstructures And Performances Of AlCoCrFeNi High-entropy Alloy Coatings Deposited By Plasma Spray-physical Vapor Deposition

High-entropy alloys?HEAs?have many excellent properties with the potentials to be a kind of novel coating materials.Plasma spray-physical vapor deposition?PS-PVD?is a new thermal spraying technology developed at the end of the 20th century.It has been successfully used for the preparation and application of functional coatings such as thermal barrier coatings,oxygen-permeable filter coatings,and nuclear reactor wall coatings,which is expected to further expand its application fields,preparing higher-performance coatings.In this dissertation,the AlCoCrFeNi high-entropy alloys?HEACs?were prepared by the PS-PVD process.The HEA particles deposited by different spraying parameters were collected on the polished 316L stainless steel substrates to analyze the relationship between the spraying parameters and deposition behaviors.Laser particle size analyzer,scanning electron microscope?SEM?,energy dispersive spectrometer?EDS?,and X-ray diffraction?XRD?were used to analyze and characterize the particle size of HEA powders and the morphology,composition,phase,and microstructure of the coatings.The bonding strength,hardness,wear resistance,and high-temperature oxidation performance of the HEACs were tested.The effects of spraying parameters such as spraying current and spraying distance on the coatings'structures and properties were investigated.The research results are as follows.The phases of AlCoCrFeNi HEA powder are BCC and B2 phase with an average particle size of 22.567?m and an average grain size of 36.52 nm.The HEACs prepared by PS-PVD have BCC,B2,FCC mixed structures,and their grain size is reduced compared with HEA powder.The heating and melting stage,flying atomization stage,and collision and deposition stage of AlCoCrFeNi HEA powder particles occurred during the spraying process.Their morphologies after being deposited on the surfaces of 316L stainless steel substrates are mainly disc-like and sunflower-like.And many“antennary”morphologies appeared on the periphery of deposited particles,indicating an obvious liquid-deposition characteristic.When the spraying distance was 475 mm,with the increase of the spraying current,the bonding strength of the HEACs increased first and then decreased,meanwhile,the surface hardness decreased and then increased while the volume wear rate increased and decreased as well.When the spraying current was 1800 A,the bonding strength increased with the increasing spraying distance,and the surface hardness decreased first and then increased,the volume wear decreased gradually.When the spraying current was 1800 A and the spraying distance was 550mm,the coating had the highest bonding strength?71.5±2.1 MPa?and surface hardness?526±17 HV?,showing a good wear resistance with a volume wear rate of?1.72±0.14?×10^-4mm³/?N·m?.With the increase of spraying current and spraying distance,the total weight gain and average oxidation rate of HEACs showed a trend of decreasing first and then increasing.In summary,when the spraying current was 1800 A and the spraying distance was 475 mm,the HEACs had relatively better comprehensive performance.The coatings'average deposition rate under this parameter was 14.25?15.58?m/time,the thickness of coatings was 179±8?m with a high bonding strength of 49.5±0.7 MPa.The coatings showed a good oxidation resistance with the average oxidation rates of 0.075 g?m^-2·h^-1,0.045 g?m^-2·h^-1,0.115 g?m^-2·h^-1respectively at 800?,900?,and 1000?.An oxide film with?-Al₂O₃as the main component was formed on the surface of coatings.The coatings exhibited complete anti-oxidation ability at 800?and 900?while anti-oxidation level at 1000?.