Abstract
Several model Fe- and Ni-based alloys with increased content (up to 30 at.-%) of protecting scale forming elements were developed. High temperature corrosion resistance of bulk alloys as well as thermally sprayed coatings and welded overlays were investigated under the waste power plants simulated atmosphere (500 °C, 100 hours, 75N2-20O2-4.9Ar-0.1Cl2). Arc and HVOF spraying as well as PTA overlay welding were used to produce the coatings. After an exposure the samples were examined with electron probe micro-analysis (EPMA). It was shown that the protection behaviour of overlay welds depends on the content of alloying elements, although the last is limited because of weldability decrease by high alloying level. High temperature corrosion resistance of thermally sprayed coatings is determined by their porosity, which can be varied over a very broad range depending on the applied spray method. The arc sprayed coatings need an additional post-treatment to close a porosity. Two methods were applied, pre-oxidation treatment in the air and sealing with the commercial sealant. Newly developed iron-based coatings with increased aluminium content (< 20 wt- %) sprayed with HVOF-spraying with powders obtained by means of high energy ball milling demonstrate high corrosion resistance. Selected coatings were evaluated for 1000 h exposure under chlorine-containing salt deposits at the higher temperature (600 °C).
