Research On Microstructure And Properties Of Co-WC Composite Wear-resistant Coatings Desposited By Ptaw

With consideration of the damages of mechanical equipment in die industry and metallurgy, improving the wear and corrosion properties of the workpiece is an important way to increase their service life. The PTAW deposited resistant overlays is the key direction at present. In present paper, orthogonal experiment is used to explore the influence of process parameters on deposited overlays. The influence of the tungsten carbide particle addition on the microstructure, microhardness and wear behavior of PTAW coatings deposited on Q235steel substrate has been reported, and the strengthening mechanism is analyzed.The study found that the larger the Mass Energy (The average energy for unit mass of powder and shadowed substrate) is, the dilution rate of coatings is higher.a good forming of coating can be achieved with the Mass Energy of110~133J/g. With the νg (spray velocity) at80~120mm/min, the increasing of Mass Energy induces three evolutions of coatings: Firstly, the Co6W6C, Fe6W6C in W-rich phase gradually disappears. Secondly, with the degree of WC melting increases, M23C6precipitates a major precipitation of hardening phase. Thirdly, with the degree of iron melting increases, Laves phase of Fe2Si precipitates with oriented grown. The main factors of wear resistance, hardness, dilution rate of the coatings are studied by the orthogonal experiment. Optimal parameters for wear resistanced coating is gived below: spray current:60A, powder flow:23.5g/min, νg:80mm/min.When WC content is lower than20%wt.%, the solid solution will be formed first, followed by the precipitation of the eutectic crystallization with the shape of small dendritic inside the solution. With the increase of WC content, the WC as nucleation sites, the proportion of heterogeneous nucleation crystallization with WC increases, the eutectic precipitation outside the solution increases; The matrix gradually precipitates with the shape of flower clusters, followed by the eutectic precipitated in the boundary. The phases of the coatings consist of the solid solution, the eutectic, W-rich phase. The solid solutions are mainly Co3Fe7, CoFe, FeNi and Ni-Cr-Fe. With WC content increases, the eutectic of M23C6, MC, M12C, Fe23(C, B)6, Cr3Si gradually precipitates, and the ratio increases. W-rich phases transform from Co6W6C, Fe6W6C to WC with the increasing WC content. The eutectic and W-rich phase can be reflowed by solution treatment; then the eutectic reprecipitates and disperses discontinuously in the boundary of matrix, and the W-rich phases are reformed with higher distribution degree after800℃×4h aging treatment。The wear resistance of coating is improved by solution strengthening and precipitation strengthening. Solid solution strengthening mainly depends onαCo supersaturated solid solution with W dissolved. The carbide, silicide are the main strengthening phase; And the morphology of rich W-phase is mainly related to the W content. With the content of W increaseing, the evolution process of the shape was the amorphousâ†'damascene shapeâ†'shape of starâ†'the polygonal. The composition of W-rich phase depends on C content available within the crystalline regions. When W content is from39to53wt.%, the W-rich phase is uniformly distributed with the shape of the damascene or star. Coatings with WC of30%or40%have uniformly distributed WC and have better wear performance than others. spray layer has a fixed shape and uniform distribution of the W-rich phase, wear the best performance; with WC content increaseing, wear resistance of coatings is improved significantly, the wear type between grinding ring and coatings is mainly adhesive wear and small part of abrasive wear.