Mterials Used For Turbine Blades In Jet Engines

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,