Aerospace Materials
industry, including GE Aviation, continued using nickel-based superalloys for the hottest parts of their turbine engines and worked to refine methods of cooling the alloys. What makes CMC different from some other potentially game-changing materials (such as buckypaper, discussed in these pages in March 2013) is that after two decades of development, including over a million hours of testing, it’s actually ready to go into commercial aerospace production: In November GE Aviation broke ground for a new 170,000 ft2 (15,810 m2
) CMC factory near Asheville, NC, which will make a high-pressure turbine shroud for the LEAP engine, marking the first time CMCs will be used for a commercial application. The LEAP, a product of CFM International, a joint company of GE and France’s Snecma SA, will enter airline service in 2016 and will power the Airbus A320neo, Boeing 737 MAX and China’s Comac C919.
In other words, as Billy Ocean might put it; CMCs are finally getting out of our dreams and into our planes.
The turbine shroud, in a container, is placed in an autoclave at GE Aviation’s Newark, DE, micro factory.
Which makes this a good time to ask two questions: First, just how does this stuff work? And second, just what happened in the two decades between its groundbreaking discovery and the groundbreaking ceremony for the Asheville production facility? Jeff Wessels, GE Aviation’s plant leader for the Newark, DE, CMC microfactory, recently spoke to Manufacturing Engineering Media to answer both questions and to walk us through how CMCs are made at GE.
The Recipe
According to Wessels, the process for making CMC components begins in Japan at a Tokyo-based company called NGS Advanced Fibers—a joint venture of GE, Safran, and Nippon Carbon Co. that makes silicon carbide (SiC) continuous fiber or Nicalon. GE, at its Newark, DE, facility, puts several layers of “a very proprietary” coating onto the fiber via chemical vapor deposition. This coating does two things, Wessels says: “It provides the toughness needed later on in the process, when the silicon car- bide fiber needs to slide within a matrix, and it provides protection that the fiber will need in downstream processes, which will involve a lot of high tempera- tures.” Others at GE refer to it as “the secret recipe.”
That coated fiber is then turned into a prepreg tape, in a process that will
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ManufacturingEngineeringMedia.com | February 2014
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