Essay About Such Materials And High Temperatures

Mterials Used For Turbine Blades In Jet Engines
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Turbine blades used in jet engines can be made from such materials as nickel-based
superalloys. We can, in principle, even use ceramic materials such as zirconia or other alloys
based on steels. In some cases, the blades may have to be coated with a thermal barrier coating
(TBC) to minimize exposure of the blade material to high temperatures. What design parameters
would you consider in selecting a material for the turbine blade and for the coating that would
work successfully in a turbine engine? Note that different parts of the engine are exposed to
different temperatures, and not all blades are exposed to relatively high operating temperatures.
What problems might occur? Consider the factors such as temperature and humidity in the
environment that the turbine blades must function.
For such an application, one must consider a material with a very stable
microstructure. High temperatures may induce grain boundary creep. High humidity
environments can induce corrosion and be detrimental to materials with high water
absorption rates. Optimally, the material may exhibit a single crystal structure (reference
Group 8 HW 2). However, additional design criteria must be examined. Environmental
conditions such as temperature changes; corrosive environments such as salt, fog, sand
and dust can affect material selection. Designers must also consider operational vibration
spectra, bird strikes, operating temperatures, and atmospheric pressure changes. While
most of the mentioned criteria refer to engine operation, the designer must also consider
the effects of maintenance fluids that might come into contact with blades such as
ethylene glycol used to de-ice airplanes and Skydrol a hydraulic fluid (otherwise known
in the aircraft industry as fluid susceptibility). Materials are also subjected to scrutiny
for expected service life, routine maintenance requirements (maintenance schedule
RTCA DO-160 is an environmental test procedure used by the aircraft industry to define
the minimum environmental requirements aircraft components must meet in order to be
installed on aircraft). (Reference: www.rtca.org/aboutrtca.asp)
Obviously a high strength, light weight material that is corrosion resistant would
be desirable. The internal sections of a material have to be light, strong and fatigue
resistant. They have to be able to handle multiple loads. The external sections of a
material outside have to focus on corrosion, thermal conductivity, and thermal expansion.
Such materials common in the industry include titanium and nickel superalloys. While
these materials may exhibit a relatively high heat and corrosion resistance, a postsecondary
coating may be needed to further protect blades which may be subjected to the
highest levels of heat. Materials such as sputter coated Alumina (Al2O3) or proprietary
electrodeposited Trobomet® MCrAlY (nickel, cobalt, chromium,