Platinum Substitutes and Glass Overlayers for Enhancing Nickel Aluminide Coatings

Platinum additions are currently used to enhance the effectivenss of nickel-aluminide coatings under severe service conditions. This study will determine the feasibility of new, less expensive alternatives. Nickel-aluminide coatings protect hot turbine engine parts from the effects of oxidation and hot corrosion. The coatings are protective when the aluminum activity near the surface is maintained at a high level. Aluminum near the surface is depleted through scale formation, and replenished through diffusion from the interior. Platinum additions enhance the protectiveness of nickel-aluminide coatings because they increase the aluminum replenishment rate. The new coatings will use two-phase-glass (TPG) overlayers that will reduce aluminum depletion rates, and less-expensive platinum group (Pg) additions that will maintain increased aluminum replenishment rates over nickel-aluminide coatings. Coupons with TPG overlayers and selected Pg aluminides will be prepared and subjected to short-term, realistic oxidation, hot corrosion, and thermal cycling tests on a laboratory scale. The best coatings will be selected for further testing in Phase II. Phase II will include fatigue studies, burner-fatigue testing plan is also proposed as a Phase I Option.