Abstract
Due to their excellent mechanical properties, Co-based alloys are one of the main candidates to replace Ni-based alloys in high temperature application. Knowledge about oxidation resistance of Co-based alloy MAR M-509 and the extent of its aluminizing on its oxidation resistance is limited. Therefore, in the present study, an aluminide layer was manufactured by low activity chemical vapor deposition (LA-CVD) on MAR M-509. Aluminized and uncoated alloys were investigated in terms of oxidation kinetics and oxidation resistance during isothermal and cyclic oxidation at 1000 and 1100 °C. Material in the as-cast and after exposure was analyzed using scanning electron microscopy (SEM), thermogravimetry (TG) and glow-discharge optical emission spectrometry (GD-OES). Obtained results allowed for elucidating of degradation mechanism including nitridation process of carbides for MAR M-509. It was found that aluminizing of MAR M-509 significantly decreases its oxidation kinetics by the factor of 2.5 and 1.5 at 1000 and 1100 °C respectively. Moreover, the suppression of identified degradation mechanism in case of aluminized alloy was found until occurrence of breakaway oxidation of the aluminide layer. It was also proposed that further increase in oxidation resistance can be successively achieved by an increase in aluminide layer thickness.
Highlights
Alloys used in aircraft engines or in stationary gas turbines (SGT) face harsh conditions, such as high temperature, aggressive gases and cyclic thermal loading
A Co-based superalloy MAR M-509, with the chemical composition given in Table 1, was investigated in terms of high temperature oxidation resistance
A similar trend was observed during exposure at 1100 ◦ C, namely, for uncoated MAR M-509, an oxide scale spallation was observed, while for the aluminized sample, oxidation kinetics were decreased by a factor of 1.5
Summary
Alloys used in aircraft engines or in stationary gas turbines (SGT) face harsh conditions, such as high temperature, aggressive gases and cyclic thermal loading. They need to possess good combinations of mechanical strength, microstructural stability and oxidation resistance. Ni-based alloys are the most common materials used in the hottest part of the gas turbines nowadays. The constant need of increase in gas turbines efficiency demands increasing of inlet gases temperature [1]. This in turn implies difficulties due to material limitation, which is mainly its melting temperature. To ensure increased oxidation resistance, the protective coatings are applied on the surface of elements manufactured from
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