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by Ralph E. AndersonSix companies have joined together with the Government to conduct a program aimed at implementing titanium matrix composites into large gas turbine engines. The potential benefit to the U.S. aerospace industry could translate into a significant competitive advantage and a market share increase for the U.S. aircraft and engine manufacturers. The potential benefit to the industrial base for metal matrix composites could result in the foundation from which widespread implementation of metal matrix composites could finally become affordable.
In August 1994, a major initiative to pursue and exploit the use of titanium matrix composites in gas turbine engines was begun with the formation of the Titanium Matrix Composite Turbine Engine Composite Consortium (TMCTECC). The consortium consisted of two propulsion companies (General Electric Aircraft Engines and Pratt & Whitney), three manufacturers of titanium matrix composite (TMC) materials (Textron Specialty Materials, Atlantic Research Corporation and 3M) and one aerospace component manufacturer with particular expertise in castings (Howmet). Industrial membership in the TMCTECC team required cost sharing, an agreement to fully share technical data across the team and an assumption of business risk.
The intent of this Title III-funded effort is to establish a stable industrial base that will facilitate continued supplier profitability and material cost reductions. The cost of the TMC materials has historically been the most significant impediment to their usage over the past thirty years. Since the cost of the TMC material is most strongly controlled by the volume of the market, the principal purpose of the TMCTECC program was to help generate the market required for TMC materials that would yield an acceptable cost.
|The TMCTECC program has determined the required size of the
market needed to achieve a cost level required for acceptance of the TMC materials into
engine applications. In addition, the market will have to be of sufficient size to
sustain a healthy industrial base from which the components made with TMC materials could
be purchased. Success in the TMCTECC program would assure availability of TMC
materials throughout the foreseeable future and eliminate the need for continued
Government support of this technology.
The TMCTECC program is seeking to deploy TMC technology that has been developed and demonstrated in previous efforts such as those under the Integrated High Performance Turbine Engine Technology (IHPTET) Joint Technology Demonstrator Engine (JTDE) programs. While the early program emphasis was on the application of TMC materials to large turbo fan engines for commercial and transport applications, the current focus is on large fighter engines such as the F110, F119, F120 and their derivatives (see Figure 1).
In Figure 2 is shown a silicon carbide fiber reinforced hollow titanium fan blade configured to fit into the F110 engine. This component was fabricated as part of the JTDE program under joint sponsorship of the United States Air Force (USAF) and General Electric Aircraft Engines (GEAE).
|Other components that are being evaluated include static components such
as actuator pistons, synchronization rings and connecting links and rotating components
such as shafts and disks (see Figure 3).
Industrial Technology Base
During the last ten years, three methods for manufacturing TMC materials have been matured under Government and industrial resources. These methods each have advantages for particular applications and, as a result, all are being pursued simultaneously under the auspices of the TMCTECC management team.
|At Atlantic Research Corporation (ARC) a batch tape making process has been developed and optimized that can utilize either powder or wire of the titanium alloy matrix composition which is combined with the silicon carbide fibers to form the TMC material. The ARC fabrication method is currently a batch process, as shown in Figure 4. Textron Specialty Materials (TSM) has developed and optimized a continuous tape making process that utilizes titanium alloy powder that is cast onto an array of fibers on a backing tape. This process is shown in Figure 5.|
At 3M, an Electron Beam/Physical Vapor Deposition (EBPVD) process is used to coat each of the individual silicon carbide fibers with the matrix material. The fibers can then be used directly or combined together to form a high density tape product form (see Figure 6). The high density tape is particularly useful where thick sections of TMC material are required to achieve the performance of the component.
Forecast Market for TMC Materials
In order to stabilize the industrial base for TMC materials, a large and varied market for TMC components is needed. To aid in accomplishing this, the TMCTECC team evaluated a large variety of commercial and military applications with respect to the potential performance benefits to the user community and the potential impact on the market for TMC materials. The result of that study projected that the demand for TMC materials could grow over the next ten years to well over the 15,000 pounds per year needed to achieve the cost goal. This level of demand will also provide a sufficient business base to sustain the industrial capability for manufacturing TMC materials and components in the United States.
The current focus of the TMCTECC team is on launching the lower risk applications for TMC materials in the military engines. Putting TMC components into the real production environment will help to validate the cost, quality and performance of these materials and lay the foundation for additional applications to be initiated throughout the aerospace industry.
The following information was extracted from the Winter ,1998, issue
of the technical magazine
AMPTIAC, now known as AMMTIAC,
Permission was granted to ALLSTAR by the magazine to use the preceding materials.
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For more information about this article, please contact, Wade Babcock
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