This work compares the oxidation behaviour of CoNiCrAlY coatings manufactured by the HVOF, APS and CGDS processes when submitted to temperatures of 1000°C and 1100°C. The as-sprayed coating microstructural features were characterised using SEM and XRD analysis before being subjected to isothermal heat treatments in an air furnace. Oxide scale composition was determined using XRD, SEM and EDS analysis while the oxide growth rates were obtained using mass gain measurements. The as-sprayed HVOF and CGDS coatings exhibit similar microstructures while the APS samples have a significantly higher porosity and oxide content levels. Results from the oxidation experiments indicated that the oxide growth rate of HVOF and CGDS were lower than that of the APS samples. The results also indicated that samples oxidised at 1100°C have a lower oxide growth rate than those oxidised at 1000°C. Analysis of the oxidation process up to 100 hours indicates that the formation of dense α-Al 2 O 3 is more favourable at 1100°C while a transition alumina, θ-Al 2 O 3 is more favourable at 1000°C. Furthermore, the surface profile of the samples oxidised at 1100°C were more uniform and free of protrusions.

This paper examines the oxidation behaviour of CoNiCrAlY coatings manufactured by APS, HVOF and CGDS deposition techniques when subjected to isothermal heat treatments. Comparison of the as-deposited coating microstructures is achieved by means of scanning electron microscopy (SEM). Investigation of the oxide compositions and growth dynamics is achieved by SEM, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Oxide growth rates were determined by a series of mass gain measurements. Results from this study demonstrate that lower coating porosity and oxide contents lead to lower oxide growth rates. Results also demonstrate that low-temperature processing of CoNiCrAlY bond coats is beneficial to their oxidation behaviour as it favours the formation of alumina in preference to other detrimental fast-growing mixed oxides.