SUPERALLOYS

SUPERALLOYS

1. Superalloys are complex, high-performance alloys, which have a high tolerance of oxidising environments and high temperatures.

2. They are typically classified according to their predominant matrix element; nickel, cobalt, or iron, and they contain multiple alloying elements including the refractory metals (Nb, Mo, W, Ta), chromium, and titanium.

3. They exhibit high mechanical strength, creep resistance and corrosion resistance, especially at high temperatures.

4. Superalloys are the primary materials used in the hot portions of jet turbine engines, such as the blades, vanes and combustion chambers, constituting over 50 % of the engine weight .

5. Superalloys are produced as wrought, cast and powder metallurgy product forms. Some superalloys are strengthened by precipitation hardening mechanisms, while others are strengthened by solid solution hardening.

6. Nickel based superalloys

   • Nickel based superalloys are the most complex of the superalloys and are used in the hottest parts of aircraft engines, constituting over 50% of the engine weight.
     • High strength, High thermal resistance, High corrosion resistance, Machinability, Shape memory, Low coefficient of thermal expansion

7. Iron–Nickel Based Superalloys

   • The iron–nickel based superalloys originally evolved from austenitic stainless steels with at least 25% nickel required to stabilize the FCC austenitic matrix. Most of them contain 25–45% nickel and 15–60% iron. C
     • Exceptional strength, High heat resistance, Corrosion resistance, Machinability

8. Cobalt Based Superalloys

   • Unalloyed cobalt has a hexagonal close-packed matrix at temperatures below 780 °F that then transforms to an FCC structure at higher temperatures; however, nickel alloying additions are used to stabilize the FCC austenitic structure between room temperature and the melting point.
     • * 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 nickelbased alloys

9. PROCESS OF FABRICATION

   • Vacuum Induction Melting (VIM)
   • Powder Metallurgy
   • Heat Treatment
   • Forging
   • Machining
   • Directional solidification
   • Coating Technology
   • Joining

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