Superalloys - Intro Flashcards
Define a superalloy
A superalloy is an alloy developed specifically for elevated temperature service.
What are usually the bases of super alloys?
Nickel or Cobalt
High temperature materials are characterised by which three properties?
High operating Temps (Homologous temp >0.6)
Resistance to mechanical degredation over long period of time at high temps
Tolerance of severe operating temperatures
Why are superalloys needed more and more?
As jet engine cores get smaller to increase the bypass ratio and efficiency, the core is spinning faster leading to higher temperatures
Which part of the core engine is the hottest?
Turbine entry
What are the 4 reasons Nickel is so suitable as a base element?
FCC structure - both tough and ductile
Stability of FCC structure - unlike Titanium
High alloy tolerance - a good solvent
Low self diffusion - good for creep
Define Creep
the time dependant plastic deformation of materials under contstant load.
When does creep become relevant?
When the homologous temperature is above 0.4-0.5. Supperalloys operate at 0.75.
What is the homologous temperature?
The ratio of operating temperature to melting temperature.
What is the Larson-Miller parameter?
A parameter to rank the creep performance of materials. The great the value the better.
