Platinum Substitutes and Two-Phase-Glass Overlayers as Low Cost Alternatives to Platinum Aluminide Coatings

The feasibility of processing less-expensive alternative coatings to platinum aluminide was examined. Three approaches were followed: 1) enhancement of nickel-aluminide coatings by application of sol-gel derived two-phase-glass (TPG) overlayers, 2) evaluation of TPG coatings on bare IN 738LC, and 3) substitution of Pt with a less expensive platinum group metal (palladium). Accordingly, IN 738LC coupons were tested with several coatings including TPG, aluminide coatings (platinum aluminide, palladium aluminide, and conventional nickel aluminide), and TPG overlayers on the aluminide coatings. Isothermal-oxidation, cyclic-oxidation, and hot-corrosion tests were conducted at 900°C for 500 hours to evaluate the coatings. The results showed that the TPG by itself provided superior protection compared to the platinum-aluminide coatings under both oxidation and hot-corrosion conditions. The TPG coating also showed promise as an overcoat on aluminide coatings.Copyright © 1996 by ASME