| HN Mirror

> The engine has one CMC component, a turbine shroud lining its hottest zone, so it can operate at up to 2400 F. The CMC needs less cooling air than nickel-based super-alloys and is part of a suite of technologies that contribute to 15 percent fuel savings for LEAP over its predecessor, the CFM 56 engine. > GE’s CMC is made of silicon carbide (SiC) ceramic fibers (containing silicon and carbon in equal amounts) coated with a proprietary material containing boron nitride. The coated fibers are shaped into a “preform” that is embedded in SiC containing 10–15 percent silicon.

While you are right about the limited applications for this material, the reason cannot be creep, which should be negligible in this kind of ceramic even at the working temperature. Certainly it must be better regarding creep than the alternative metallic alloys.

In a rotating part, subject to high centrifugal forces and vibrations and shocks, I think that the risk of unpredictable fractures may be too high for a ceramic, even a composite one.

Silicon carbide ceramic has low toughness. A composite should be better, but still far from metallic alloys.

I have seen mentions of research about the feasibility of using silicon carbide composite ceramics for rotating parts, with the goal of reducing their mass and increasing their working temperature, in comparison with metallic parts, but it is unlikely that this has reached the stage of being used in production engines.

Ceramics, e.g. derivatives of zirconia, are frequently used for turbine blades, but only as ceramic thermal barrier coatings on metallic blades, not for the body of the blades.