Handbook of Turbomachinery Second Edition Revised - Ventech!

1. High-temperature capability, about 2,200 8F, as compared with
1,900 8F for single crystals and other nickel-based superalloys. The thermal
conductivity of ceramics is better than that of the alloys used in blade
manufacture. These two characteristics eliminate cooling flow requirements
in many vanes. The thermal efficiency of the engine and its power output
improve compared with those of engines using metallic alloys for the
application. The projected replacement rate of ceramic nozzles is only 10%
of that of metal.
2. Very good dimensional stability, the coefficient of thermal
expansion being about half that of metal. The low expansion coefficient
reduces thermal stresses when compared with that of metal with the same
temperature distribution. In addition, ceramic is less subject to warping,
corrosion, and erosion.
3. Lower density/lower rotational inertia and reduced stresses. The
density of ceramics is about 60% of that of the best nickel alloys. This leads
to a reduced centrifugal load, smaller stresses at the fir-tree attachments, and
a thinner container ring requirement.
4. Increased life due to reduced creep, fatigue, and erosion. Moreover,
corrosive agents in the hot gases do not damage ceramics as seriously
as they do metallic alloys.
As opposed to these advantages, there are certain disadvantages that
need to be taken into account.
Figure 18 FAA accelerated mission test.
Copyright © 2003 Marcel Dekker, Inc.