Off-angle Thermal Spray Of WC-10Ni Cemented Carbide Coatings Using Nickel Layer Capsulized Powders And Characterization Of Coating Microstructure And Properties

Thermally sprayed coatings in air atmosphere are usually subjected to oxidation.Especially decarburization and decomposition will occur in WC based cemented carbide coatings during spraying and thus affecting the coating features and characteristics,including coating porosity,phase composition,microhardness,elastic modulus,fracture toughness and interface bonding strength et al,having a profound influence on the final performance of coatings,such as wear resistance,corrosion resistance and fatigue resistance.At present,the off-angle is indispensable for industrial application.Our recent study revealed that enhanced oxidation happened in HVOF WC-Ni cemented carbide coatings.The coatings are degraded at off-angle spraying,including aggravated decarburization degree,increased porosity and residual tensile stress,reduced microhardness and fracture toughness,which deteriorate the coating wear resistance.Inconsistent results were also reported in spray angle dependence of microhardness,coating density,and wear resistance of coatings.In this study,the features and characteristics of off-angle HVOF WC-10 Ni coatings are modified by nickel electroless plating of WC-10 Ni feedstock powders.Comprehensive study on formation of coating features and characteristics as well as correlative interactions between them is thus facilitated with controllable coating features/characteristics using electroless plating powders,in comparison with as-received commercial powders.Results show that the coatings of HVOF with nickel electroless plated powders,either at normal or off-angle spraying,the degree of oxidation decarburization as well as coating porosity of coating is reduced,and microhardness,fracture toughness and interface bonding strength are all improved.In addition,the wear resistance of coating is improved significantly,increased by about 50% at the spray angle of 90°,about 43% at 60°,and 26% at 45°.The wear mechanism of coating under water lubrication is abrasive wear.Moreover,the obvious abrasive wear under the small spraying angle is changed to the slight abrasive wear under normal spraying angle.Furthermore,the relationship between coating features and characteristics is studied.The coating hardness is mainly influenced by porosity and WC retention rate,and elastic modulus correlates the impact force determined by spraying angle.The coating microhardness and elastic modulus are less influenced on fracture toughness.The coating fracture toughness can be increased by enhancing the bonding force between WC particle and binder.The nickel electroless plating of WC-10 Ni powder can effectively improve the bonding of WC particles and Ni binder,thus increases the WC retention rate and coating density,so as to improve the wear resistance of coatings.