Morphology and microstructure of NiCoCrAlYRe coatings after thermal aging and growth of an Al 2 O 3 -Rich oxide scale

Abstract

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 Al 2 O 3 scale at the splat boundary, while the diffusion of Cr and Ni and the following growth of Cr 2 O 3 , Ni(Cr,Al) 2 O 4 and NiO were restricted to Al depleted isolated areas. At the same time, a continuous, dense and well adherent Al 2 O 3 layer grew on the top-surface, and was somewhere supported by a thin mixed oxide scale mainly composed of Cr 2 O 3 and spinels. Based on these results, the addition of Re to the NiCoCrAlY alloy is able to enhance the oxidation resistance.