Superalloys - A Technical Guide
Superalloys provide the most reliable and cost-effective means of achieving high operating temperature and stress conditions in aircraft and industrial gas turbines and in a wide variety of other applications.
In recent years, superalloys have been widespread usage in aerospace gas turbine engine parts. The main reason of it is that these materials have high yield, ultimate tensile strength, and very good corrosion/oxidation resistance, and they combine these good properties with an excellent creep resistance at elevated temperatures. In spite of their outstanding properties, superalloys can lose their mechanical strength because of wear, tear, and crack formation when they are exposed to high-service temperatures and heavy working conditions. Moreover, corrosion is another important issue for superalloys because the materials of gas turbine engine parts are exposed to harsh engine environments, which consist of many pollutants and hot gases.
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Properties of superalloys
Superalloys are intended for use in high-temperature applications, which means they need to maintain their shape at elevated temperatures close to their melting points (above 650 °C or 1200°F). When alloyed with certain elements, at extreme temperatures superalloys can maintain high strength, stability, and corrosion and oxidation resistance
Superalloys are classified into three main categories:
Nickel-based superalloys
- High strength
- High thermal resistance
- High corrosion resistance
- Machinability
- Shape memory
- Low coefficient of thermal expansion
Cobalt-based superalloys
- Higher melting point compared to nickel- or iron-based alloys
- Superior hot corrosion resistance compared to nickel- or iron-based alloys
- Higher thermal fatigue resistance and weldability compared to nickel-based alloys
Iron-based superalloys
- High strength at room temperature
- High resistance to creep, oxidation, corrosion, and wear