| Outdoor high-voltage isolation switch is an important electrical equipment in power system. Electrical contact parts often fail owing to overheating, which causes enormous economic losses. In this paper, silver coating and silver graphite self-lubricating composite coating were prepared by electrodeposition, respectively. Surface morphology, composition, binding force, corrosion resistance, sulfur resistance, thermal stability, wear and growth mechanisms of the silver coating and composite coatings were investigated by scanning electron microscopy(SEM), field emission scanning electron microscopy(FESEM), X-ray diffraction(XRD), energy dispersive spectroscopy(EDS), thermal gravimetric/differential thermal analysis(TG/DTA), infrared carbon and sulfur analysis, neutral salt spray test, Tafel curve, friction and wear tests, scans wear outline, et.The results showed that: porosity of the composite coating is higher than that of the silver coating, due to the presence of tip discharge effect on graphite and diffusion layer, silver growth get restricted, presenting a preferred orientation of the linear connection growth pattern. According to GB/T 5270-2005, peeling and abscission don’t exist on the fracture of silver coating and composite coating which bonding force is good on the interface. According to GB/T6461-2002, both of coating don’t appeare surface pits, corrosion resistance reaches grade ten in the neutral salt spray test. According to QJ485-1988, both of coatings soak for half an hour in Na2 S solution are not changing color, anti-tarnish property reach the requirements of aviation criterion.Silver coating was oxidized at about 120 ℃, and the oxide film decomposed sustainedly from 120 ℃ to 664 ℃. The air desorption of the silver-graphite coating stage occurred from room temperature and ends at 48 ℃, the evaporation of water at 48-130 ℃. The graphite intercalation compounds was oxidized from 160 ℃ to 521 ℃. The carbon skeleton of graphite was oxidized from 521 ℃ to 740 ℃. The friction and wear experiment showed that the friction coefficient of the sterling silver coating and the silver-graphite coating were 0.342 and 0.075, respectively(under load of 260g). Abrasive wear was the main form below load of 260 g. Fatigue wear began to appear from 260 to 860 load, and become the main part. The friction coefficient of the silver-graphite coating was below the 0.1 with the reduction of abrasive wear.With the increase of deposition current density, graphite content in composite coating increased, corrosion current density increases in 1 M H2SO4 solution, the wear resistance increased firstly and then decreased. The coating had high ability to resist wear under the current density of 0.3A/dm2. With the increase of stirring speed, the graphite content in composite coatings and corrosion current density increased firstly and then decreased in 1 M H2SO4 solution. The wear rate was the lowest for 8.13×10-14 m-3/N·m at the stirring speed of 420 r/min. |
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