Overview of FGM Research in Japan
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Outline of the Research Project To efficiently promote the establishment of fundamental FGM technologies, the goal was set to develop materials for use in thermal environments (at temperatures up to 2000 K and temperature differences as great as 1000 K) which space planes might encounter in the future. The project aimed to complete small test pieces of 30 mm diameter in Phase I and 300 mm square test pieces in Phase II. As a framework for promoting research and development, an organization was established with a database as a nucleus. The organization consists of three technical departments working independently of one another, as shown in Figure 2. The
MRS BULLETIN/JANUARY 1995
Materials Design Department determines the optimum gradient composition for minimizing thermal stress and gives design instructions to the Structure Control Department, which then works to develop functionally gradient materials by making
Relaxation funclion for thermal stress
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Introduction Space planes require high-performance heat-resistant materials which can withstand ultrahigh temperatures and extremely large temperature gradients. To meet these needs, functionally gradient materials (FGMs) were proposed about 10 years ago in Japan. Figure 1 shows a conceptual diagram of functionally gradient materials, taking into account the relaxation of thermal stress. For the surface that contacts hightemperature gases at thousands of degrees, ceramics are used to provide adequate heat resistance. For the surface that provides cooling, metallic materials are used to furnish the necessary thermal conductivity and mechanical strength. In addition, the composition of these materials is formulated to provide optimum distribution of composition, structure, and porosity to effectively relax thermal stress. Since fiscal 1987, an R&D project entitled "Research on Fundamental Techniques to Develop Functionally Gradient Materials for Relaxation of Thermal Stress,"1 which aimed to develop ultra heat-resistant materials, had been carried out with special coordination funds from the Science and Technology Agency. The five-year project had two phases; Phase I was carried out from 1987 to 1989, and Phase II from 1990 to 1991.
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Figure 1. Conceptual diagram of functionally gradient materials.
Figure 2. Research organization for the functionally gradient materials research project.
best use of various innovative synthesis technologies. Then the Characterization Department characterizes test pieces using various evaluation tests, and these results are reflected in the new material design. The data obtained from these three departments are collected in the FGM database, which promotes R&D through a close linkage among three departments. Results of the Research Project23 Phase I emphasized basic research of materials design and synthesis techniques. These results were used to develop large test pieces in
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