Page 64 - The Jet Engine

Fig. 5-10 Free power contra-rotating turbine.
Fig. 5-11 Section through a dual alloy disc.
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Nozzle guide vanes
25. Due to their static condition. the nozzle guide
vanes do not endure the same rotational stresses as
the turbine blades. Therefore, heat resistance is the
property most required. Nickel alloys are used,
although cooling is required to prevent melting.
Ceramic coatings can enhance the heat resisting
properties and, for the same set of conditions,
reduce the amount of cooling air required, thus
improving engine efficiency.
Turbine discs
26. A turbine disc has to rotate at high speed in a
relatively cool environment and is subjected to large
rotational stresses. The limiting factor which affects
the useful disc life is its resistance to fatigue
cracking.