Interactions of high-temperature coatings in hot corrosion environments

High-temperature coatings such as MCrAlY or aluminide coatings are used to protect metallic substrates from corrosion in various corrosive applications like gas turbines and incinerators. The oxides formed on these coatings are either dependent on the alloy substrate compositions or the processing parameters and chemistries. Aluminide coatings are formed by several processes to protect superalloys and depend primarily on the stability of aluminum oxide for its degree of protection in high-temperature environments. Aluminide coatings that provide excellent oxidation resistance may fail catastrophically in a environment where hot corrosion can occur. Recent efforts to reduce operational costs by using less expensive fuels in marine gas turbines may seriously impact the performance of current and anticipated high-temperature protective coatings. The increasing desire to raise temperatures in different high-temperature applications may require the development and implementation of alternative, more corrosion-resistant coatings. This paper will examine the compositional and structural variations of some of these protective coatings and their interactions with several corrosive species found in gas turbine and/or waste incinerator environments and offer some suggestions to improve the hot corrosion-resistance of protective, barrier coatings.