Aluminide coating on Mar-M246 nickel superalloy by halide activated pack cementation (HAPC)

Abstract

Nickel based superalloys are widely applied in high temperatures systems because they have excellent mechanical properties. However their use over long period can lead to excessive degradation oxidation and corrosion. Protective aluminum-based coatings increase the oxidation resistance of these alloys which may be achieved using the Halide Activated Pack Cementation (HAPC) technique. In this study, the Mar-M246 nickel superalloy was coated with aluminum rich intermetallic layers, obtained by the HAPC process at 700 °C, 800 °C, 900 °C and 1000 °C, for treatment duration of 9 h. Thermodynamic calculations have been carried out previously to determine process parameters, such as the choice of the activator and the suitable temperature. The microstructural characterization of the coatings was performed by SEM and EDS analysis. The coatings obtained were uniform and homogeneous in terms composition, and free of failures and cracks containing Ni2Al3 and/or NiAl3 phases. The efficiency of the coatings to enhance the oxidation resistance of the substrate was proved through the oxidation tests carried out at 1000 °C for about 240 h in which there was the formation of protective Al2O3 scale.