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...
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