Cyclic oxidation characteristics of HVOF thermal-sprayed NiCoCrAlY and CoNiCrAlY coatings at 1000 °C

Highlights: • NiCoCrAlY coating is more resistant to 1000 °C air-oxidation than CoNiCrAlY. • The initial generated phase on CoNiCrAlY during oxidation is θ-Alumina. • Unlike the CoNiCrAlY, the main protecting phase on NiCoCrAlY coating is α-Alumina. • Oxidation rate of CoNiCrAlY obeys two consecutive sub-parabolic and parabolic law. Thermal-sprayed MCrAlY coatings have become widespread in various industries such as power plants, aeronautics, and oil and gas firms. High-temperature oxidation behavior of these coatings is therefore of significance. Spraying of two prevalent MCrAlY powders (NiCoCrAlY and CoNiCrAlY) on Hastelloy substrate by high velocity oxygen and fuel method and exposing them to 1000 °C air for resolving of their cyclic oxidation behavior are presented in this paper. The coatings were characterized by x-ray diffraction, scanning electron microscopy and energy-dispersive x-ray spectroscopy. The obtained oxidation kinetic indicated that at 1000 °C, the thermally sprayed NiCoCrAlY coating has greater resistance to oxidation than CoNiCrAlY. While oxidation rate of the former follows a parabolic rate equation with specific rate of 5.1 × 10⁻³ (μm)² h⁻¹ at 1000 °C, the oxidation rate for the latter has a specific rate of 12.1 × 10⁻³ (μm)² h⁻¹.