SiC fibers find their way into aircraft engines
New material promises lighter, stronger components
YOSHIFUMI UESAKA, Nikkei staff writer
TOKYO A new type of fiber is finding its way into jet engines, promising greater fuel efficiency for some of the biggest aircraft crisscrossing the skies.
Components requiring high heat resistance, like aircraft engine parts, currently rely on nickel-based superalloys. Using silicon carbide (SiC) fibers made in Japan, manufacturers have found a way to make ceramic matrix composites that are twice as strong and 20% more heat resistant than these alloys, despite being two-thirds lighter.
General Electric has adopted SiC fiber-based ceramics for its latest jetliner engines, and the material is already being used in the compact Airbus A320neo, which went into service last year.
The A320neo owes its high fuel efficiency to engines supplied by two companies. One of them is CFM International, a joint venture between GE Aviation and France's Safran Aircraft Engines. CFM is the first company to include SiC fiber-based ceramics in its engines. The material is currently used in only a few parts, but its introduction may herald a growing trend in aircraft engine manufacturing.
SiC fibers are made by melting a compound of carbon and silicon -- called polycarbosilane -- and forcing it through a nozzle, which shapes it into fibers with a diameter of about 10 micrometers. These fibers are then subjected to a special electron beam as part of an anoxic treatment to prevent degradation when exposed to extremely high temperatures. Finally, the fibers are woven into clothlike sheets that can be used in ceramic matrix composites -- light, highly heat-resistant ceramics able to withstand the high temperatures inside jetliner engines.
Currently, Japan's Ube Industries and Nippon Carbon are the only companies in the world that can manufacture SiC fibers. U.S. chemical giants Dow Chemical and Corning have failed in their attempts to produce the material commercially.
RIGHT TIME, RIGHT MATERIAL In the late 1980s, there were few applications for SiC fibers and Nippon Carbon's SiC fiber business was in the red. Around that time, however, GE, the world's largest aircraft engine manufacturer, began considering replacing nickel alloys with SiC fiber-based ceramics in certain engine parts. Sensing an opening, Nippon Carbon attempted to raise the heat resistance of its SiC fibers from 1,300 C to above 1,500 C -- the range necessary for use in aircraft engines.
The technological challenges were daunting, but the company overcame them by increasing the molecular mass of the carbon fibers by exposing them to electron beams. Since then, the company has developed SiC fibers able to withstand temperatures up to 1,900 C, enough to convince GE that the fibers are suitable for aircraft engines.
Unlike nickel alloys, which can only withstand temperatures up to 1,600 C, SiC fibers do not require air cooling. This enables jetliners to use air more efficiently for propulsion, resulting in higher fuel efficiency.
GE is employing SiC fiber-based ceramics for its GE9X engines, which will power Boeing's next generation of massive jetliners. Four main components of the GE9X engines, including blades and nozzles in the high-pressure turbines, will be made of SiC fiber-based ceramics instead of nickel alloys. This alone will improve fuel efficiency by 2%.
The main impediment to wider commercial use of SiC fibers is their price: They are 100 times more expensive than carbon fibers, which go for 3,000 yen to 10,000 yen ($27 to $90) per kilogram. Demand for the new fibers will go up only when their cost comes down. Improving manufacturing technology will prove crucial to this goal.