After examining the possibility of ceramics being used in flight in 2001, scientists from the Institute for Defense Analyses starkly concluded, “There may be more pigs flying than ceramics in the future.” It’s easy to see why when you think of a coffee mug: The material is great for handling heat but breaks catastrophically when met with force.
Less than two decades later, ceramics are the most exciting part of the aviation business, as a series of scientific and manufacturing innovations have combined to create ceramic matrix composites (CMCs), advanced materials that are as tough as metals while being lighter and retaining the superior heat-handling characteristics of glass. At GE, CMC development is the culmination of $1.5 billion in investment and decades of research, which have led to crucial advances in GE engines used in military and civilian aircraft. “We are at generation one with CMCs,” says Gary Mercer, vice president of engineering at GE Aviation.
CMCs are made of silicon carbide (SiC), ceramic fibers and ceramic resin, manufactured through a sophisticated process and further enhanced with proprietary coatings. CMCs are one-third the density of metal alloys and one-third the weight, yet can handle temperatures up to 2,400 degrees Fahrenheit, when most every metallic alloy will begin to soften. This heat resistance means that turbines need less air from the flow path of a jet engine to be diverted to cool the hot-section components. By keeping more air in the flow path instead of cooling parts, the engine runs more efficiently at higher thrust.
That part directing the airflow into the hottest part of the engine — the turbine shroud — has been the first turbine component to be widely manufactured. GE has made more than 40,000, including for the best-selling LEAP turbofan that powers hundreds of single-aisle commercial jetliners. The LEAP is produced by CFM International, a 50/50 joint-venture between GE Aviation and Safran Aircraft Engines.
Engineers started seriously looking at CMCs in the 1970s with funding and encouragement from the U.S. government. By 1986, GE engineers had patented ceramic technology used in large natural gas turbines, which eventually found their way into power plants. Evolving ceramics for use in jet engines led to a decade-long effort by GE to establish America’s first fully integrated CMC supply chain, which includes a network of four interrelated GE production sites in Ohio, Delaware, North Carolina and, most recently in 2018, Alabama. The Alabama plant, located in Huntsville, is where the raw CMC fibers are made in a joint venture among GE, Safran and Nippon Carbon of Japan, an innovator in raw CMC material.
Having control over the whole supply chain means that GE can work on boosting production rates and lower costs through honing the manufacturing process. As CMCs become more integrated in GE jet engine cores, the expectation is that engine thrust will increase by 25% and fuel efficiency by 10%. Additional engine advances are expected too: Not long ago, GE engineers successfully built a military demonstrator engine that achieved the highest jet-engine temperatures ever. GE is also fine-tuning CMC-based rotating parts. The material’s characteristics also mean that CMCs will likely be essential components to spacecraft in coming years.
“As you think of the future of flight, light and hotter are two constants. With the reemergence of supersonic, hypersonic, and reusable space vehicles, it is easy to see how CMCs will add value to future propulsion and airframes alike,” says Mercer.