A COMPREHENSIVE REVIEW ON COMBATING THE ELEVATED-TEMPERATURE SURFACE DEGRADATION BY MCrAlX COATINGS

Abstract

Surface degradation (oxidation/corrosion/erosion) at elevated temperature is encountered commonly in engineering industries like gas turbines and thermal power plants. MCrAlX coatings which came into the picture in 1960s were used widely for surface protection in the elevated-temperature section of the gas turbine engines and in boilers to combat oxidation/corrosion/erosion. Among them, MCrAlY ([Formula: see text], Co or [Formula: see text]) were developed to be used as the overlay coatings and bond coat (BC), which offer a combination of multiple features such as oxidation, corrosion and ductility. MCrAlY coatings form a second layer of aluminum oxide beneath the chromium oxide layer at elevated temperatures which minimizes the oxidation/corrosion/erosive wear rates. But the desire to increase combustion efficiencies of power plants and gas turbine engines along with lower CO2 emissions poses a significant challenge for coating design. As the temperature surpasses 900∘C, NiCrAlY coating degrades quickly due to nonregeneration of chromia or alumina. The research and development (R&D) efforts are focusing continuously on improving the existing MCrAlX coatings or developing new sustainable MCrAlX coatings with improved oxidation performance. In this review, the roles of the alloying elements, microstructures, post-deposition treatment techniques and different deposition processes in the elevated-temperature oxidation/corrosion performance of MCrAlX-based alloys have been explored in detail.