The term “superalloys” means alloys that are superior in heat and corrosion resistance, and maintain superior properties even at elevated temperatures. Thus, superalloys are synonymous with “hightemperature alloys.” Traditionally, superalloys are basically classi™ed into three types according to their base element: iron-based superalloys, nickel-based superalloys, and cobalt-based superalloys. Presently, however, in a more broad sense, alloys that have the capability of preserving their mechanical, physical, and chemical stabilities at high temperatures and in severe corrosive environments are all called superalloys.