Comparison of oxidation resistance of NiCoCrAlTaY-coated and -uncoated Mar-M247 superalloys in the air at 1150 °C

Oxidation resistance of NiCoCrAlTaY coated and uncoated Mar-M247 superalloys were compared experimentally in the air at 1150 °C. It was found that the oxidation behavior of the NiCoCrAlTaY coated and uncoated Mar-M247 superalloys generally followed the parabolic kinetics with the rate of 1.5 and 9.8 × 10−3 mg2/cm4 h for each one. Microstructural observation and elemental analysis indicated that after 200 h the uncoated alloy covered with an oxide scale of 6–10 times thicker than the coated one, beneath which a fairly continuous and relatively thin α-Al2O3 could be found along the interface close to the substrate. Comparatively, the NiCoCrAlTaY coated alloy uniformly produced the continuous, dense and thick α-Al2O3 layer adhesive to the coating to prevent the metal elements against excessive oxidation, and finally formed the steady oxide scales: outer (Ni, Co)(Al, Cr)2O4 spinels, NiO, (Al, Cr)2Ni3; inner protective α-Al2O3 with a little Cr2O3. On the surface of the uncoated alloy, however, it mainly formed the Ni-rich oxides in which a large quantity of cracks propagated to result in the more oxidation.