Morphology and Microstructure of NiCoCrAlYRe Coatings after Thermal Aging and Growth of an Al2O3-Rich Oxide Scale

The surface of metal parts operating at high temperature in energy production and aerospace industry is typically exposed to thermal stresses and oxidation phenomena. To this aim, plasma spraying was employed to deposit NiCoCrAlYRe coatings on metal substrates. The effects of early-stage oxidation, at ~1100 °C, on their microstructure were investigated. The partial infiltration of oxygen through some open pores and microcracks embedded in coating microstructure locally assisted the formation of a stable Al2O3 scale at the splat boundary, while the diffusion of Cr and Ni and the following growth of Cr2O3, Ni(Cr,Al)2O4 and NiO were restricted to Al depleted isolated areas. At the same time, continuous, dense and well adherent Al2O3 layer grew on the top-surface, and was somewhere supported by a thin mixed oxide scale mainly composed of Cr2O3 and spinels. Based on these results, the addition of Re to the NiCoCrAlY alloy is able to enhance the oxidation resistance.