Void Nucleation and Growth at the (Pd,Ni)Al Coating/Alumina Scale Interface During High Temperature Oxidation and Relation to Oxide Scale Spallation

摘要

β-NiAl (B2-structure) is used as a bond coat in TBC systems because it offers a good resistance to high temperature oxidation with the formation of a compact alumina scale. Pt has been added to NiAl to increase the resistance to hot corrosion and to improve the scale adherence. Pd-modified β-NiAl coatings were also developed with a cost reduction objective and to reduce the precipitation of brittle intermetallic phases. All these coatings may form prismatic voids at the metal/oxide interface during oxidation. This work reports SEM observations of such interfacial voids in palladium-modified nickel aluminide oxidation. The effect of the coating grain crystallographic orientation on underscale void shape and on scale spalling is presented. The substrate surface of the void under the scale together with the oxide inner surface has been detailed.