This document discusses superalloys, which are nickel, cobalt, or iron-based alloys that have excellent strength and corrosion resistance at high temperatures. It classifies superalloys based on their predominant metal, such as iron-based, cobalt-based, or nickel-based alloys. The document states that superalloys are commonly used in turbine blades for jet engines due to their high-temperature properties. They are also used in applications like industrial gas turbines, nuclear reactors, and heat exchangers.