Copper wire was arc-sprayed in air by using the compressed air as atomizing gas: The structures of the particles collected during fl ying and the coatings formed on a steel substrate were examined. The collected particles and the coatings consisted of a copper phase and a Cu2O phase. The copper splat in the coatings had a fi ne columnar grain structure and was supersaturated with oxygen due to the rapid solidifi cation of the sprayed particles on the substrate. The copper phase in the as-sprayed coating was thermally unstable and decomposed to form a Cu2O phase on heat treatment at 1073K for 10s. Further heat treatment resulted in the coarsening of the Cu2O phase and the formation of continuous Cu2O plates on the splat/splat boundaries. The plate was disintegrated and granulated on heat treatment at 1073K for 28.8ks or at1273K for 7.2ks. The amount of the Cu2O phase in the coating could be decreased by using a nitrogen gas as the atomizing gas. The coating structure was compared with the structure of the iron coating and the nickel-chromium coating that were fabricated by thermal spraying in air.
Thermal spraying has emerged as an important tool of increasingly sophisticated surface engineering technology. Therefore, the demand for technology that is checked non-destructively has become more insistent. This paper presents the nondestructive evaluation of fl aking-resistance in thermal sprayed Al2O3, ZrO2 and TiO2 coating. The full-width at half maximum taken from the X-ray diffraction peak profi le was used as a nondestructive evaluation method in this study. The results by the nondestructive method were compared to the results with scratch test. It was found that nondestructive evaluation of the thermal sprayed ceramic coating was effective.
The relationship between roughness caused by blasting and adhesion of spray coatings on aluminum container substrates was studied through various experiments as part of measures for improving the adhesion of the 75mass%Cr-Fe alloy plasma spray coating for sulfi dation corrosion resistance, which is applied on the inner surface of cylindrical Al containers of high-temperature type NAS batteries. Surface roughness of μmRa2.8 - 7.3 was acquired by using Al2O3 particle size #100 (212 - 75μm) to #46 (600 - 250μm) grit. In order to achieve uniform roughness and a clean surface, a combination of blasting when the nozzle was being inserted from the top of the container, and air blowing when the nozzle was being removed was done. It was determined that when Al2O3 particles of size #100 grit was used, a good anchoring shape was formed throughout with a roughened surface of μmRa 2.8. When the internal surface of 3000 Al cylindrical containers were continually blasted using particle size #100 grit, the initial surface roughness of μmRa3.7 - 3.9 only deteriorated to about μmRa2.6. A 75mass%Cr-Fe alloy spray coating was applied to the Al cylindrical containers that were roughened using particle size #100 grit. This coating showed cracks by a bending test, but no peeling occurred. This coating was examined by a tensile strength test and showed good adhesion at 64 - 66 MPa. Through experiments, it was proven that spray coatings formed on the Al cylindrical containers after receiving optimal blasting with particle size #100 grit had good adhesion and corrosion resistance after being used for NAS batteries that stored electrical power for about nine years.
The sprayed coating containing fl uorine-carbon showed high water repellency (the contact angle for water droplet was 145°). However, the water repellency of the sprayed coating decreased with adsorption of organic materials, NOx, and SOx, which discharged from the automobile. To remove the adsorption compounds from the coating surface, we decide to add titanium oxide (TiO2) in the coating, which could be able to oxidize the surface adsorption compounds photo-catalytically. It was found that the particles dispersion type sprayed coatings prepared by fl ame spray technique using aluminum tubing fi lling with fl uorine-carbon (15.2mass%) and titanium oxide (0.5mass%) had high photo-catalytic activity for liquid phase decomposition of methylene blue without decreasing water- repellency.