STRUCTURE AND HIGH-TEMPERATURE PERFORMANCE OF VARIOUS PALLADIUM-MODIFIED ALUMINIDE COATINGS - A LOW-COST ALTERNATIVE TO PLATINUM ALUMINIDES

Of the protective coatings applied to turbine hot stage components (generally superalloys), platinum-modified aluminide coatings have proved to be satisfactorily hot corrosion resistant (type I hot corrosion). More recently, cost-saving measures have motivated studies on the replacement of platinum by a cheaper metal: palladium. The structures of three different types of palladium-modified aluminide coating on Inconel 100 (IN 100) substrates are described; it is shown that the integrity of the coatings critically relies on an adequate processing route (preventing hydrogen embrittlement). Cyclic oxidation tests at 1100-degrees-C and 850-degrees-C hot corrosion tests (in air and air plus 0.01% SO2) have been performed on simple aluminides, commercial RT22 platinum-modified coatings and palladium-modified coatings applied to IN 100. Palladium not only stabilizes the protective aluminia scale formed in cyclic oxidation, but also dramatically increases the hot corrosion resistance of the coatings. Indeed, the performance of palladium-modified coatings compares very well with that of commercial platinum-modified coatings in terms of hot corrosion resistance.