GE integrates ceramic matrix composites in LEAP engine
CMC materials are tough, lightweight and capable of withstanding extreme temperatures, making them well suited for aircraft engine components.
Over the last couple of decades, there has been a significant shift in the materials used for aircraft components. With the push to become more energy efficient, manufacturers have been forced to rethink design and material choice.
Ceramic matrix composite (CMC) materials llre first developed through a program at the U.S. Department of Energy, led by DOE’s Oak Ridge National Laboratory.
CMC materials are made of coated ceramic fibers surrounded by a ceramic matrix. These materials are tough, lightweight and capable of withstanding extreme temperatures (300-400°F hotter than metal alloys), making them preferable for use in turbine engine components.
And that’s exactly what CFM International, a 50/50 joint venture of Safran and GE, is doing with their LEAP aircraft engine.
The engine has one component that uses CMC, 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.
In August 2016, the first LEAP engine started flying commercially on Airbus A320neo. Other LEAP engines will fly on the Boeing 737 MAX in 2017.
“The materials developed in the DOE program became the foundation for the material now going into aircraft engines,” explains Krishan Luthra, who led GE Global Research’s development of CMCs for 25 years.
GE’s CMC is made of silicon carbide (SiC) ceramic fibres 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.
“A ceramic matrix composite is different than almost all other composites because the matrix is ceramic and the fiber is ceramic,” says ORNL’s Rick Lowden.
Typically, combining two brittle materials yields a brittle material, he explains. But altering the bond between fiber and matrix allows the material to act more like a piece of wood. Cracks don’t propagate into the fibers from the matrix around them. The fibers hold the material together and carry the load while slowly pulling from the matrix, adding toughness.
The development of CMC materials continues. ORNL is working to develop materials with different fibres, interfacial coatings and matrices. And as researchers develop these materials to better suit industrial market demands, CMC materials will be integrated more and more into aerospace component design.
“We were working toward a common goal of getting ceramic matrix composites into industrial applications including high-pressure heat exchangers, land-based turbines, carburizing furnaces and radiant burners,” Lowden adds.
Currently, Luthra hopes GE will integrate components using CMCs everywhere the engine gets hot—blades, nozzles, liners. One of the challenges will be to develop a manufacturing processes that, unlike melt infiltration, do not produce excess silicon that can volatilize and form cracks in the matrix.
“Every decade we have increased [the heat metals can take] by about 50 degrees,” Luthra noted. Today CMC material can take up to 2400°F, but Luthra would like the next generation to reach 2700°F. “This is going to be as challenging as the development of the first ceramic composite,” he said.
GE is pushing the limits for aerospace component design by partnering with industry leaders to develop the latest materials, including CMC materials. With a vision in mind, the company hopes to advance the next generation of CMCs to improve efficiency and decrease emissions in aircraft components.