Abstract
Oxidation studies have been conducted on cast Co-22Cr-11Al (CoCrAl) coating alloy in air at temperatures between 700 and 1000 °C. To investigate the role of oxygen-active element additions on the oxidation behavior of the MCrAlY-type coatings, some of the CoCrAl specimens were ion implanted with either yttrium, hafnium or cobalt prior to oxidation. The oxidized specimens were subsequently examined by various electron optical techniques including scanning transmission electron microscopy and electron microprobe analysis. It was observed that voids formed in the coating alloy at the metaloxide interface during oxidation. The average size and density of these interfacial voids were dependent on temperature and time. Ion-implanted yttrium or hafnium greatly reduced the rate of void growth for all experimental conditions; cobalt implantation had little effect. This behavior is explained by a vacancy kinetic model which invloves the preferential diffusion of either metal or oxygen ions through the growing oxide scale. The results of the present study have significant implications concerning the oxidation kinetics and the adherence of the oxide scale to the coating alloy.
Published Version
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