Isothermal and Cyclic Oxidation Behavior of the Nanostructured MCrAlY Coatings Deposited by Thermal Spraying Process

Conventional and nanostructured NiCoCrAlY coatings were deposited developed using the high-velocity oxy- fuel (HVOF) thermal spraying technique. The nanostructured NiCoCrAlY powder feedstock for the coatings was produced by the ball milling method. In this regard, the ball-milling method was used to produce the nanostructured NiCoCrAlY powder feedstock. The microstructures examinations of the as-received and nanostructured powders as well as their developed coatings were analyzed investigated by using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) equipped with energy-dispersive electron dispersed X-ray spectroscopy (EDS), and a transmission electron microscope (TEM). Due to the evaluation of the oxidation kinetics, the free-standing coating specimens were subjected to the isothermal and cyclic oxidation testing at 1000 and 1100 ºC respectively, under a laboratory air atmosphere. The results indicated that the as- received NiCoCrAlY coating had a parabolic oxidation behavior in short- and long-term oxidation exposure tests. For the nanostructured NiCoCrAlY coating, in contrast, the long-term oxidation kinetics deviated from parabolic behavior and showed instead sub-parabolic rate behavior. The obtained results also exemplified revealed that the nanostructured NiCoCrAlY coating had a greater oxidation resistance for to both cases of isothermal and cyclic conditions on account of the formation of a dense and slow-growing Al2O3 layer on the coating surface.