Effect Of WC Size On The Performances Of WC-10Co-4Cr Coatings By HVOF

ABSTRACT:Four kinds of WC-10Co-4Cr coatings deposited on45#steel substrate were fabricated by HVOF. The cemented carbide feedstock powders containing different WC particle size were produced by the granulating and speedy high temperature sintering process. The microstructures, physical properties, wear resistance and corrosion resistance of the coatings were studied, especially focusing on the effect of WC size on wear resistance and corrosion resistance of WC-10Co-4Cr coatings and the mechanisms. The conclusions can be shown as follows:(1) WC-10Co-4Cr coatings consist of WC, Co and W2C phase. With WC particle size decreasing, specific surface area and the diffusion of C into the Co phase become larger, leading more easily to react in Co phase between C and O, accelerating the oxidation and decarbonization.(2) With decreasing WC particle size, the bonding strength among the layers reduces, so it is easy to form the layered structure in which pores and cracks mainly distribute. When increasing the WC particle size, pores and cracks mainly distribute in the interface between WC particles and Co phase. The coatings containing two WC particles with different size present lower porosity and higher microhardness.(3) The effects of WC particle size on wear resistance of the coatings obey the parabola criterion. Even through WC particle with small size has the favorable protectiveness for Co phase, it is easy to fall off due to the slightly pinning off; when increasing the WC particle size, the distance between the WC particles is so large that the Co phase is easy to grind, WC particles are also easy to fall off.(4) Electrochemical corrosion mechanism of the coatings in5%NaCl solution is galvanic corrosion between hard phase WC and binder phase Co. The low Co potential results in the prior corrosion of Co phase. Along with the process of corrosion, WC particles shedding, the pitting phenomenon occurs. The Multimodal coatings which contain two kinds of WC have a relatively low porosity, resulting in the corrosion resistance being superior, especially the coating containing15%0.5～0.6μm WC and 70%1～2μm WC.