| Ceramic particles reinforced metal matrix composite coating possesses not only strength and toughness of metal material, but also good corrosion resistance, high temperature resistance, wear resistance and oxidation resistance of ceramic material. Strengthing phase in ceramic particles reinforced metal matrix composite coating fabricated by in situ reaction possesses many advantages:1) the size of the ceramic particles is very small;2)the distribution of the ceramic particles is dispersed; 3) no surface pollution; 4) good wettability with metal substrate; 5) good interface combination with the bonding metal.This paper studied the change law of coating microstructure, phase composition, brittleness, microhardness, friction and wear properties of the coating with different ratio of Ni25/(WO3+C) alloy powder. The wear mechanisms of the coating were also analyzed. The phase of compositions, micro-structure, and chemical compositions of the coatings were analyzed by XRD, SEM and EDS respectively. The hardness and brittleness of the coatings were measured by microhardness tester and coating adhesion scratch tester.The results showed that:(l)When the thickness of preset powder was 1.5mm, the best technological parameters were:current 300A, pulse width 1.6ms, frequency 30Hz, scanning speed 2mm/s. The coating shows low dilution rate, good combination with the substrate, smooth surface. The thickness of the coating is about 200-300μm.(2) The microstructures of the coating are tiny dendritic and equiaxed crystal at the top part, dendritic and cellular crystal with different direction at the middle part, planar crystal at the bottom. The cladding layers are composed by (Fe)Ni solid solution, Cr7C3, Cr23C6, Fe3W3C, W2C, WC and so on. The size of the WxC particles is about 0.5-2μm. The shapes of the WxC particles are granular, rectangle, triangle. No defects and cracks can be sen in the WxC particles.The combination between the WxC particles and the surrounding matrix is good.(3) The hardness of the coating is obviously higher than the substrate and increases with the (WO3+C) proportion. The highest hardness can reach 704 HV0.2, which is about 3.5 times of the 45 steel substrate.(4) The coating have smaller friction coefficient compared with 45 steel. When the content of (WO3+C) in the composite powder is lower than 40%, the friction coefficient gradually reduce with the increase of the content of (WO3+C). But the friction coefficient increases when the content of (WO3+C) increases to 50%. The friction coefficient of 40% (WO3+C) coating is similar to that of Crl5Mo3 and shows a good anti-friction effect.(5) Lots of pits and abrasive dust at the wear area of 10%-30%(WO3+C) coating indicate that the main wear mechanism are abrasive wear and adhesive wear. Micro cracks and some wear debris at the wear area of 40%(WO3+C) and 50%(WO3+C) coating indicate that the main wear mechanism are abrasive wear and brittle flaking.(6) The thermit reaction occurred between the powders of Ni25, WO3, Al and C by laser cladding. Reaction products composed of WC, W2C, W3C and Al2O3, which are white granuliform with size less than 200 nm. Most WxC particles distributed at the grain boundary of (Fe)Ni solid solution, only a small amount of WxC distributed in the intracrystalline. Cladding layer is uniform, no defects such as cracks and holes. The highest hardness of cladding layer is 900 HV0.2,4.5 times that of the substrate. |
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