Study On Thermal Spraying Cr₃C₂-NiCr Composite Coating For Power Plant Boiler Pipeline

In this paper,the Cr₃C₂-NiCr Composite Coating doped with Y₂O₃ and SiC was prepared on G20 boiler steel substrate by using oxygen propane supersonic flame spraying technology.These coatings were designed to prolong the service life of the boiler pipe by improve the corrosion resistance and wear resistance of metal-ceramic layer.The microstructure,microhardness,bond strength and wear property were systematically studied by X-ray diffractometer?XRD?,scanning electron microscope?SEM?,microhardness tester,tensile testing machine,ball on disk friction wear tester and step profiler.The results showed that the main phase of HVOF sprayed Cr₃C₂-NiCr coatings were NiCr and Cr₃C₂.The composite coating doped with Y₂O₃ shows better microhardness and bonding strength than the coating without Y₂O₃ because of the grain refinement and purification of Yttrium.And the coating shows the best comprehensive performance when the addition of Y₂O₃ was 1wt.%.The comprehensive mechanical properties of the coating doped with SiC are also better than that of the Cr₃C₂-NiCr coating without SiC in which the performance of the coating doped with 1wt.%SiC was the best.The reason was that with the increase of SiC doping,the increase of porosity makes the comprehensive performance decrease slightly.Under the condition of 400?degrees Celsius and 10 N wear loading,the wear resistance of the composite coating was improved by doping Y₂O₃ and SiC,but the friction coefficient increases with the increase of doping amount.The wear resistance of the composite coating was the best and the lowest wear rate when the doping amount of Y₂O₃ and SiC was 1wt.%and 5wt.%.The main corrosion products on the surface of the Cr₃C₂-NiCr-Y₂O₃composite coating corroded moltem salt at 650?were NiCr₂O₄ and Cr₂O₃.The Y element inhibits the oxidation of the molten salt at the grain boundary,refines the grain of the oxide film,and promotes the rapid formation of the continuous oxide film.The hot corrosion performance of the 1%Y₂O₃ composite coating was optimal.The Cr₂O₃ oxide film formed on the surface of the Cr₃C₂-NiCr-SiC composite coating was accompanied by the formation of SiO₂ which increased the hot corrosion resistance for its good barrier effect on oxygen.The exfoliation of the oxide film was more serious with the increase of the amount of doping for the coefficient of thermal expansion of SiO₂ varies greatly at high temperature.The results showed that the hot corrosion performance of the 5%SiC composite coating was optimal.