The operating unit in Gainesville, Virginia, is devoted to the production of continuous fiber composite preforms using automated 3D-Through-The-Thickness (TM) braiding machines.
Amercom, located in Chatsworth, California, the third operating unit of the ARC Advanced Materials Division, is the subject of this article. Amercom was established in 1969 for research, development, and production of metal and ceramic composite materials. Metal matrix composites are made using hot-pressed diffusion bonding or the pressure casting technique.
The ceramic matrix composites are manufactured using the Chemical Vapor Infiltration (CVI) process.
A similar process, Chemical Vapor Deposition (CVD), is also used in the production of ceramic fibers which are used in the manufacture of both metal matrix and ceramic matrix composites. CVI SiC deposition and/or infiltration is a mature process that has been used extensively by Amercom for over 12 years to fabricate representative parts (graphic, 65k) for test and evaluation.
Amercom CFCC Team
Amercom established a team of original equipment manufacturers, end item users and technical specialists to conduct the CFCC program. The companies that make up the Amercom CFCC team are ABB Combustion Engineering, Detroit Diesel Company, Inc., Industrial Pump & Filter Manufacturing Co., Solar Turbine Inc., Surface Combustion, Material Science Corporation, MSNW, Inc., and The University of Virginia.
Phase I
In CFCC Phase I, the focus of the program was in two areas. The first direction was the identification of technical hurdles to the commercialization of CVI SiC ceramic matrix composites.
Although the CVI SiC process is a fairly mature process, the resulting ceramic composite material has some features which tend to limit usefulness in several of the applications for which it would otherwise be ideal.
Temperature and Chemistry
One of these features is the need for a tooling approach which will survive the CVI process conditions of temperature and chemistry at least through the initial rigidization step. This is referred to as hot tooling. Graphite, which functions quite well as such a tool material, is relatively expensive and usually not reusable. Hence the tooling of the CFCC component can represent a large percentage of the component cost.
Cold Tooling Process
In Phase I of the program, the feasibility of a reusable, cold tooling technique using steel or aluminum tools to form and rigidize the part was demonstrated. The cold tooling process is being further developed in Phase II with a reduction in cost to less than half of that for hot tooling for many complex shapes.
Another feature of current generation ceramic composites that limits utility in applications requiring extended operation in air at elevated temperatures is stability of the fiber and the fiber/matrix interface.
The Amercom CFCC program is developing an air-stable fiber/matrix interface for applications involving temperatures greater than 1000 degrees C. Fiber development is being addressed by other programs (e.g., the NASA High Speed Civil Transport and the ARPA Fiber Development Consortium).
Benefits
The second focus of the program was the assessment of potential industrial applications of the CVI ceramic composite materials and the benefits to those applications that would accrue due to the use of the CFCC components. The assessment was performed by each of the industrial team members in their respective product and business areas.
Hot cleanup for the new advanced Integrated Gasification Combined Cycle and Pressurized Fluidized Bed Combustion processes for coal-fired electric power generation could greatly improve efficiency and economics. The same is true for the retrofit of Atmospheric Fluidized Bed Combustion systems. For these systems the potential benefits are:
In Phase II, the process development for cold tooling, controlled porosity preforms, graded matrix and nonoxidizing interfaces which was begun in Phase I will continue.
In addition, detail designs will be developed for each of the selected applications. Test specimens, subelement parts, and representative components will be fabricated for test and evaluation. Component testing will be done by the respective OEM team members.
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Comments to: mgc@ornl.gov
Revised: July 5, 1995
