화학공학소재연구정보센터
Materials Science Forum, Vol.461-464, 553-560, 2004
The use of plasma sprayed laser remelted corrosion resistant metallic coatings to inhibit metal dusting
Metal dusting is a catastrophic carburisation phenomenon that occurs in carbon-rich atmospheres at temperatures between 450degreesC and 850degreesC, conditions encountered in steam reforming and similar processes. Material loss occurs as the bulk metal is converted into fine particles via the deposition of carbon and subsequent growth of graphite. The present research is intended to examine the potential of plasma sprayed corrosion resistant coatings (NiCrAlY and 50:50 Ni:Cr) to improve the metal dusting resistance of Alloy 800H. In addition, a CO2 laser has been used to remelt the as-sprayed coated layer. This laser treatment has several aims: to consolidate the coated layer by eliminating porosity from the as-sprayed structure, to refine the microstructure and, thus, enhance diffusion of chromium and aluminium to the surface to aid the formation of protective oxides and to improve adhesion of the coating to the substrate. Coated, uncoated and laser remelted coated samples have been exposed to a mixed gas environment of 80%CO, 20%H-2 at 650degreesC and inspected at intervals. The extents of degradation have been estimated by weight change data while the damaged surfaces have been characterised by optical and scanning electron microscopy / energy dispersive X-ray analysis in plan and cross section. The results are discussed in terms of improvements to corrosion resistance in this essentially metal dusting environment.