What are superalloys and where are they used in aerospace?

Superalloys are high-performance alloys designed for extreme temperature service. Types: Nickel-based - Most common (Inconel 718, Waspaloy, Rene alloys), excellent high-temperature strength, oxidation resistance; Cobalt-based - Better hot corrosion resistance (Haynes 188), used in combustors; Iron-based - Lower cost (A286), moderate temperatures. Properties: Retain strength at high temperatures (up to 1100C), Excellent creep resistance, Oxidation and corrosion resistant, and Fatigue resistance at temperature. Applications: Turbine discs - High strength, fatigue resistance (Inconel 718); Turbine blades - Creep and oxidation resistance (single crystal alloys); Combustor liners - Hot corrosion resistance; and Afterburner components. Processing: Investment casting (single crystal for blades), Powder metallurgy (discs for fine grain), and Forging. Cost is high, machining is difficult (work hardening), but no alternatives exist for hot section components.