Volume 8, Number 2     March/April 2000

Aeropace Technology Development

Materials Processing Technology Transferred to Industry

Fabrication techniques developed by an international team of researchers for making space age engine exhaust components mean improved performance and gas mileage for tomorrow’s aerospace planes. Structural engineers from NASA’s Glenn Research Center in Cleveland, Ohio, selected a space age, intermetallic alloy material to be used for the truss core portion of the exhaust nozzle of a proposed High-Speed Civil Transport.

Titanium aluminide (TiAl), in sheet form, was chosen because it is lightweight, stiff and strong at high temperatures. The alloy had been difficult to form into usable parts because standard alloy forming processes degraded some of its best features. In addition, its high material and production costs made it unattractive to manufacturers.

The team developed and tested fabrication processes for shaping and joining the thin, 0.6-millimeter (0.025-inch) thick sheets of TiAl, while paying particular attention to reducing production cost. The processes include sheet rolling, relatively low-temperature hot forming, joint brazing and bonding, and heat treatment after machining to relieve stresses around rivet holes.

"The team’s work shows that this intermetallic alloy does not need the costly fabrication processes typically used for intermetallic components," said Paul Bartolotta, Glenn’s principal investigator and team lead for the project. "Our process doesn’t require a vacuum, uses relatively low shaping and forming temperatures and produces more uniform parts than could be produced with other forming methods."

The practicality of the technique was proven when BF Goodrich Aerospace in Chula Vista, California, successfully manufactured the truss core from TiAl sheets in its own plant using its regular production equipment. The result was a truss core with the soundness and strength of similar parts made under the special conditions of a research laboratory. The truss core was made from separately formed corrugations, or hats, covered top and bottom with flat sheets of the same material. In cross section, it looks much like a corrugated box.

"This NASA Glenn contact has greatly assisted us in the development of production processing of this new material system," said John Meaney, BF Goodrich Aerospace project manager for the program.

Cast and wrought TiAl is already being used in high-end, high-performance cars and is being considered for use in commercial aircraft engines. The inexpensive forming techniques may allow the wrought form of this lightweight alloy to be used in valve stems, heat shields and exhaust system components, result-ing in more lightweight and fuel-efficient cars.

The Glenn structures and materials research program is part of NASA’s continuing research effort to provide the materials for tomorrow’s aerospace vehicles. TiAl alloy development was conducted under its High Speed Research Propulsion project with research partners Pratt & Whitney of West Palm Beach, Florida, and Plansee GmbH of Lechbruck, Germany. Technology from that program will be used to help design economical, lightweight TiAl components for next-generation space vehicles such as the reusable launch vehicle, VentureStar.

For more information, contact Dr. Paul Bartolotta at Glenn Research Center. 216/433-3338, Paul.A.Bartolotta@grc.nasa.gov Please mention you read about it in Innovation.