Superalloys: A Vital Element in the Aircraft Engine Industry
Aircraft are expected to function in incredibly harsh conditions; they experience extreme temperatures, shock loads, friction and vibration. This can jeopardize the integrity of the aircraft’s components, but these challenges can be addressed with the use of specialist alloys and high-performance materials.
Superalloys are metallic materials for service at high temperatures, particularly in the hot zones of gas turbines. Such materials allow the turbine to operate more efficiently by withstanding higher temperatures. Turbine Inlet Temperature (TIT) depends on the temperature capability of 1st stage high-pressure turbine blade made of Ni-base superalloys exclusively.
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One of the most important superalloy properties is high temperature creep resistance. Other crucial material properties are fatigue life, phase stability, as well as oxidation and corrosion resistance.
Superalloys develop high-temperature strength through solid solution strengthening. Oxidation and corrosion resistance is provided by the formation of a protective oxide layer which is formed when the metal is exposed to oxygen and encapsulates the material protecting the rest of the component. Oxidation or corrosion resistance is provided by elements such as aluminum and chromium.
Innovation
Powder metallurgical alloys, giving a finer carbide dispersion and smaller grain size, have superior properties to cast alloys. Further process development by hot isostatic pressing has even further improved the properties by removal of possible failure sites.
Casting is important for cobalt-based alloys and directionally solidified alloys have led to increased rupture strength and thermal fatigue resistance.
Even further improvements in strength and temperature resistance have been achieved by the development of single crystal alloys. These trends have allowed the development of higher thrust jet engines which operate at even higher temperatures.