“If the past is prologue, the future of materials will be quite exciting,” said Robert Schafrik, retired general manager of the Materials and Process Engineering Department of General Electric Aviation.
Fifty years ago, when Schafrik was an undergraduate, General Electric was developing a new class of jet engines for the new Air Force C-5A strategic airlifter program. The TF39 engine was very successful, and its CF6 commercial derivative is still flying today on many wide-bodied aircraft,1 as are similar engines designed by Pratt & Whitney and Rolls-Royce. The engine had a 25 percent improvement in fuel efficiency over early turbojet engines, based in part on a new architecture known as a high-bypass engine and in part on the implementation of many new materials. Since then fuel efficiencies have continued to improve by an average of 1 percent per year. When Schafrik asked the design engineers what proportion of that improvement was due to new materials as opposed to other engineering changes their estimate was one-third to one-half
To further boost fuel efficiencies, the compression ratio and burning temperature in the engine have to increase. However, the temperature in the turbine of today’s jet engines is already several hundred degrees above the incipient melting point of the turbines’ nickel superalloys. But engineers have found ways to “fool the metal to think the environment is cooler,” Schafrik said. The turbine blades are essentially radiators with many internal cooling passages. In addition, they have cooling air flowing over the surface and an insulating layer of ceramic.
1 Applications for the CF6 include the Airbus A300, A310, A330; Boeing 747 and 767; McDonnell Douglas DC-10 and MD-11; and the C-5M. To date, all models of the engine have accumulated 400 million flight-hours.
Nevertheless, “designing [and] developing a new turbine blade alloy is really hard,” Schafrik said. “There definitely are limits … to what you can do.”
One way to overcome today’s temperature limits is to make engine parts out of ceramic materials that have much higher operating temperatures. For example, the new LEAP engine that will soon be introduced into service has the first application of ceramic matrix composites (CMC) in the turbine section of an engine, though on the turbine shroud rather than a rotating part of the engine. Other CMC applications are under development.
Another intriguing concept would be to move away from the Brayton thermodynamic cycle to new engine architectures, such as a number of small fans along the leading edge of an airplane’s wing, with each fan powered by electricity carried in a superconducting wire. “Within 50 years, we will know what the answer is,” said Schafrik. But whatever the configuration, “there will be significant challenges in materials.”
What is evident from this look at materials in aviation engines is that societal benefit does result from application of new materials. Materials
developments have transformed nearly every aspect of modern life, from electronics and photonics to the constructed environment, medical equipment, aerospace, and modern energy systems.
SPEEDING UP DEVELOPMENT
The development of new materials has typically taken a long time, Schafrik noted. A new class of materials like an intermetallic or ceramic matrix composite can take 20 to 30 years, and more, to move from concept to use.
He predicted that in the future development will take place in one-third the time, not only for structural materials but across the board. Already, accelerated programs on a selective basis have produced tremendous gains. Recently, a new turbine blade alloy was qualified for flight by the Federal Aviation Administration within two years of starting the program. Normally, the development of that material would have taken at least six years, Schafrik said, but the use of computational tools and an integrated design and manufacturing team greatly sped up the process. That success “gives us a road map for the future on how to conduct an accelerated program and how [to] extend that process into other areas.”
Over the next 50 years, the major materials impetus will be on effectively taking advantage of new materials developments, across all application areas, to fulfill societal needs. The route to get there will involve step increases in the amount of computational modeling and quantum increases in knowledge of the underlying science behind the material that can readily be turned into predictive models. It will also lead to closer collaboration between materials experts, design engineers, and manufacturing experts.
A lot is at stake, Schafrik observed. For instance, new aircraft engines cost $1–2 billion to develop, and a field problem can easily cost hundreds of millions of dollars to solve. Other application domains encounter similar challenges, which add to the reluctance to use a new material. Current computational models are becoming proficient at predicting the properties of new materials, but more scientific research is needed to predict how materials degrade in use. “We need very smart ways to test these materials. This is beyond some of the standard tests in use now, which often are not representative of the environments that we encounter. Over the next 50 years, accelerated tests based on scientific understanding of the relevant degradation modes will enable confident
predictions of long-term performance of materials, greatly reducing the risk of using them.”
THE ROLE OF GOVERNMENT
As Eric Schmidt pointed out during an earlier presentation at the 2014 NAE annual meeting, the government has played a key role in stimulating innovation. That also has been the case with the development of new materials, Schafrik said, and governmental involvement will continue to be critical.
“Going forward, I think a coordinated effort by industry, government, and universities—and this will no doubt happen in the next 50 years—will be essential to accelerate the development of materials across all different spectrums of interest.”
A collaborative ecosystem among sectors can bring experts together to solve problems and satisfy needs, with computational tools facilitating collaborations. “The future for materials is quite exciting,” Schafrik concluded. “We have tremendous opportunity to influence the engineering world.”
The Return of Supersonic Transport?
In response to a question, Schafrik speculated about the possible development of a new supersonic jet. It would be costly, he pointed out, which raises the question of whether a business case exists for such a program. But “if we wanted to do that, we do know how to do it. We could roll up our sleeves… . Will it be economical in 50 years? That is an intriguing possibility.”