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Research and development of high performance metallic materials have increased the number of component elements of new alloys, and also increased the number of materials with various chemical compositions. However, from the viewpoint of recyclability, which is essential to environmental protection, this trend is undesirable. On the other hand, it is well known that some properties of metallic materials are strongly influenced by their microstructure, such as grain size, shape of grains, grain boundary and texture. Furthermore, to reduce apparent density of metallic materials and make the materials soft, fabrication of cellular materials with high porosity is recommended. Development of high performance materials by designing and controlling their microstructure without increasing the number of their component elements, is recommended for excellent recyclability of developed materials. On this basis, we are developing some kinds of high performance materials.
| (Chief) | Mamoru Mabuchi | E-mail: mabuchi@nirin.go.jp |
| Yasuo Yamada | ||
| Naobumi Saito | ||
| Masaru Nakanishi | ||
| Ichinori Shigematsu | ||
| Koji Shimojima | ||
| Yasumasa Chino |
Magnesium is the lightest metallic structural material with a density of about 1.8g/cm3 (two thirds of the density of aluminum). Today Mg-use in some vehicle components is expanding for weight reduction. However, some properties of Mg-alloys, such as strength, workability and toughness, are not high enough to increase the applications.
In this laboratory, high performance Mg-alloys with ultra-fine grains (below 1mm) have been developed with thermo-mechanical treatments. These materials showed excellent mechanical properties at room temperature. Furthermore, high-strain-rate superplasticity and low-temperature superplasticity were attained for these alloys. (During tensile test, maximum elongation to failure of the test pieces was over 600%.) Superplastic forging methods are going to be developed for these Mg alloys to form complex shaped products by single-step-forging.
As well-known, fine Mg powder flames out severely. Therefore, machined chips of Mg alloy must be handled carefully. In this laboratory, recycling methods of these chips by hot extrusion have been developed to produce high performance alloys. That recycled alloy showed higher strength and toughness than original casts.
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| Relationships between 0.2%proof stress and grain size on some magnesium alloys | A transmission electron micrograph of Mg-Zn-Zr alloy with ultra-fine grains processed by hot extrusion |
Reduction in weight of vehicles is effective to reduce CO2 emission, which may cause global warming in the future. Many companies are making efforts to develop lightweight components for vehicles. Use of engineering plastics for those components, which had been promoted in the past, have caused some problems on recycling of plastics. For a last decade, use of light alloy components for vehicles, which can be recycled easily, is expanding rapidly.
In this laboratory, ultra-light cellular metals have been developed. Those are open cellular materials, showing extraordinary high porosities, low apparent densities, excellent shock absorbency. Furthermore, they are recyclable without expensive processes. Apparent density of the ultra-light cellular magnesium alloy, fabricated by precision casting was only 0.05g/cm3. A designing procedure for cellular structures is being developed in this laboratory.
Use of ultra-light cellular metal components in aerospace industries and construction is also expected.
Typical demands for materials to be used in high temperature environments for hydrogen fueled combustion turbines are resistivity against attack by uncombustive hydrogen and complex corrosion by hydrogen-steam mixture. The object of the research which has been conducted in this laboratory is to establish materials technologies of refractory metals to be used in such environments. Studies on tungsten and molybdenum based alloys as the candidates with high resistivity against hydrogen attack, have been carried out mainly. W with dispersion of small amounts of fine oxide particles(0.8wt%,La2O3 particle size of 0.3mm) and W-Ta alloy show excellent mechanical properties at elevated temperatures up to 1973K.
Surface modification methods of molybdenum, titanium and magnesium to improve oxidation resistance and/or hardness, have been studied. A plasma activated sintering (PAS) method was applied to form a Mo-MoSi2 FGM (functionally gradient material) structure on the surface of Mo. Laser beam radiation on Ti members was used to form TixSiy intermetallic compounds and titanium nitrides surface layers to harden their surfaces.
Genetic algorithm was applied to simulation for structural optimization of the surface layers. Designing was carried out to minimize the thermal stress appeared in Mo specimens with FGM surface layers during heating and cooling processes.
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Research Results |
Material Processing Dept. |
Composite Materials Labo. |
Advanced Processing Labo. Innovative Materials Labo. | Interface Control Processing Labo. |