Background:

• Alumina (Al₂O₃) scale adherence to the underlying metallic bond coating is typically the weak link in reliability and durability of electron beam-physical vapor deposition (EB-PVD) TBC systems.
• It is generally agreed that oxide scale adherence is degraded by S impurities in alloys that do not contain appropriate reactive element additions.
• Single-phase (Ni,Pt)Al coatings, produced by Pt electroplating and chemical vapor deposition (CVD) aluminizing, have become widely accepted as a premiere bond coating for higher-temperature EB-PVD TBC applications.
• Although Pt-modified aluminide coatings have been in commercial service for over two decades, there is little understanding of the mechanism by which Pt improves oxide adherence.  Thus, it is difficult to devise methods to maximize the effectiveness of this effect or even to define the limits.

Objectives:

• Attain an improved understanding of the role of Pt to improve oxide adherence to single-phase CVD aluminide bond coatings
• Fabricate CVD NiAl & NiPtAl coatings on high-S & low-S superalloys
• Evaluate S & Pt influences on oxide scale growth and adherence
• Characterize coating & Al₂O₃ microstructures & microchemistries

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