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Ceramic Matrix Composites Allow GE Jet Engines to Fly Longer
CMCs are not your typical cup of tea. If you want to fly non-stop from New York to Sydney, jet engines with parts made from ceramic matrix composites (CMCs) could be your ticket not too far in the future. The light, tough and heat resistant material will allow engineers to build lighter and more efficient engines that can take planes farther and burn less fuel.
Static components made from CMCs are already serving in the newest and most advanced civilian and military engines like the LEAP engine made by CFM International, a joint venture between GE Aviation and France’s Snecma (Safran).
GE Engineers just scored an important breakthrough when they for the first time successfully tested rotating parts made from CMCs inside a jet engine turbine (see below). “Going from nickel alloys to rotating ceramics inside the engine is the really big jump,” says Jonathan Blank, who leads CMC and advanced polymer matrix composite research at GE Aviation. “CMCs allow for a revolutionary change in jet engine design.”
The material has two hugely winning attributes for aviation: it’s one-third the weight of metal, and it’s also heat-resistant and doesn’t need to be air-cooled.
The turbines of most modern jet engines work with surface high temperatures, which can make even advanced alloys grow soft. Engineers use lasers to drill tiny holes in the metal alloy turbine blades to bleed in cooling air and protect their surface from the heat. But the cooling air also reduces engine performance. “More heat means more cooling air, which lowers overall efficiency,” Blank says. “When you drop the need for cooling components, your engine will become aerodynamically more efficient and also more fuel efficient.”
Since the rotating turbine blades made from CMCs are so light, they also allow engineers to reduce the size of the metal disks to which they are attached. “This is pure mechanics,” Blank says. “The lighter blades generate smaller centrifugal force, which means that you can also slim down the disk, bearings and other parts.”
GE just recently finished the world’s first successful test of rotating CMC blades inside an F414 military jet engine, which normally powers F/A-18 Hornet and Super Hornet jets. They were able to run the engine for 500 cycles. (One cycle takes the engine to takeoff thrust and back.) The blades powered through punishing dynamic forces and high temperatures inside the engine’s low-pressure turbine, giving engineer another proof that the heat-resistant technology that can withstand unprecedented conditions. Blank says that thanks to CMCs, GE’s ADVENT adaptive cycle engine had already set the world record for the highest combined compressor and turbine temperatures. It was validated by the Air Force Research Lab (AFRL).
The first application of the blades could be inside new jet engines for “sixth-generation” fighter jets (see below), like the ADVENT. “But we already envision future commercial applications,” Blank says.
GE made the CMC blades for the test at its materials research facility in Newark, Del., but the company has already built a new plant in Asheville, N.C. for high rate production of components made from CMCs.
GE has spent $1 billion over the last two decades to develop the material. Says materials scientist Krishan Luthra who was involved in the project: “I thought it would be the Holy Grail if we could make it work.”
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The Right Stuff: New GE Advanced Manufacturing Plant to Make Next-Gen Ceramic Parts for Jet Engines
People have been using ceramics to store food, drink tea, and tile their homes for millennia. But GE engineers recently upped the ante and started putting high-grade ceramics inside jet engines.
Their version is a light super material that combines silicon with ceramic-coated silicon carbide fibers. It is tough enough to take the heat and forces inside a roaring jet engine and outperform even the most advanced alloys, and light enough to shave hundreds of pounds off a jet engine. “We are pushing ahead in materials technology, which gives us the ability to make jet engines lighter, run them hotter, and cool them less,” says GE Aviation manufacturing executive Michael Kauffman. “As result, we can make the engines, and the planes they’ll power, more efficient and cheaper to operate.”
GE is said today that it would invest $125 million and build a new 125,000 square-foot advanced manufacturing plant in Asheville, N.C., to make parts from the new material, called ceramic matrix composites, or CMCs.
A hot oven “burns out” polymers and leaves a porous lattice made from ceramic-coated silicon carbide fibers in the shape of the desired part. Top image: Parts from ceramic composites will serve inside next-generation jet engines like the LEAP.
The first products will be stationary high pressure turbine parts for the next-generation LEAP jet engine manufactured by CFM International, a joint venture between GE Aviation and France’s Safran. But CMCs, which weigh a third of metal alloys, could also find applications as light-weight turbine blades, rotors, and other parts. “When you start thinking about design, the weight savings multiplier effect is much more than three to one,” Kauffman says. “Your nickel-based superalloy turbine disc does not have to be so beefy to carry all those light blades, and you can slim down the bearings and other parts too because of a smaller centrifugal force. It’s just basic physics.”
Engineers at GE Global Research and GE Aviation’s pilot-scale production facility in Delaware developed the material over the last 20 years. They also designed the machines that manufacture CMCs. Pending final approval from the state of North Carolina, the Asheville facility would be the first of its kind in jet propulsion.
GE plans to use the Delaware facility to apply the highly engineered ceramic coatings onto silicon carbide fibers and then incorporate the fibers into flexible sheets together with polymers and other composite matrix materials. Workers in North Carolina will then cut the sheets into shapes, put them inside molds and compact them in giant pressure cookers called autoclaves, which make the parts take their form.
The parts then travel inside a hot oven that “burns out” the polymers and leaves a porous lattice made from the ceramic-coated silicon carbide fibers in the shape of the desired part.
The workers then melt silicon on top of the lattice and let the silicon wick its way into the shell’s nooks and crannies. “The ceramic coating the fiber is the secret sauce,” Kauffman says. “It allows us to use a relatively simple process to get really good infiltration.”
Finally, the workers will use hard diamond grinders to get the desired part dimensions. “We often use ceramics as metal cutters, so we had to go to one step beyond, to diamond,” Kauffman says. “This is a new process. We generally don’t cut anything as hard as CMCs.”
The company completed design freeze on the first two versions of the LEAP engine in June 2012. The first full LEAP engine, a LEAP-1A for the Airbus A320neo, is on schedule to begin ground testing in September of this year.
Boeing estimates that the world aircraft fleet will double in size over the next 20 years to some 40,000 planes. Much of the growth will come from single-aisle next-gen planes like the A320neo, Boeing’s the 737 MAX, and COMAC’s C919, the LEAP’s target market. CMCs will also serve inside the new GE9X engine selected by Boeing for its future 777X aircraft program.
Southwest, Lion Air, AirAsia, Virgin America, Quantas and dozens of other airlines have already placed orders for more than 4,500 LEAP engines.
GE estimates that the new plant, along with plant and equipment upgrades across GE’s facilities in North Carolina, could create 240 new jobs by 2017.