Cyclic oxidation-induced deleterious effects of Ru on the surface rumpling of a Pt-modified aluminide coating

Abstract

Generally, surface rumpling is detrimental to high temperature protective coatings as it leads to adhesion losses and Ru can suppress rumpling behaviour in most Pt-modified aluminide (Pt-Al) coatings during the cyclic oxidation. However, in this study, we found that this suppression is related to the cyclic oxidation cycles of Pt-Al-coated superalloys: Ru suppresses rumpling behaviour with cyclic oxidation for more than 200 cycles at 1100 °C but aggravates it with cyclic oxidation from 50 to 150 cycles. The aggravation of rumpling behaviour was turned out to be associated with coating oxidation. Microstructure observation indicated that Ru participates in oxidation and deteriorates the oxidation resistance via destroying the integrity of the Al2O3 oxide film. More Al atoms are depleted owing to oxidation degradation, attributing to partial β-NiAl phases transformation towards the L10 martensitic phases, which exacerbates volume shrinkage and the driving force of rumpling behaviour. The Ru diffusion process during cyclic oxidation has also been studied. Furthermore, the relationship among martensite transformation, rumpling behaviour and cyclic oxidation in Pt-Al coated Ru-containing superalloy was ascertained to provide a guideline for integrated design of Pt-Al coating/high-generation SX superalloys and propose an investigation strategy for rumpling behaviour of the Pt-Al coating.