Abstract
The beneficial effect of yttrium in high temperature protective coatings applied by EB–PVD and vacuum plasma spray against oxidation and hot corrosion has been recognized in many studies. In this study, the feasibility of adding yttrium into aluminide coatings has been successfully demonstrated by the conventional pack cementation process. It was found that yttrium oxide was the only practical inert filler material among the oxides investigated. Yttrium can be added into the aluminide coating either prior to or after the pack aluminizing process. Specimens prepared by the different pack cementation sequences were evaluated at 1000 °C for cyclic oxidation resistance up to 250 cycles. The yttriumized IN 738 and the yttriumized/aluminized IN 738 specimens showed very poor resistance compared to either the uncoated or the straight aluminized IN 738 specimens. Gross internal oxidation was found in the yttriumized/aluminized coating. On the other hand, the aluminized/yttriumized IN 738 showed marginal improvement over the straight aluminized IN 738. The aluminized/yttriumized coating had an yttrium rich outer oxide scale and an aluminum oxide inner scale, while the straight aluminized coating had a chromium rich outer oxide scale and an aluminum oxide inner scale.
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Schedule a callMore From: Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films
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