| Budget Amount *help |
¥14,900,000 (Direct Cost: ¥14,900,000)
Fiscal Year 2003: ¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2002: ¥4,800,000 (Direct Cost: ¥4,800,000)
Fiscal Year 2001: ¥6,700,000 (Direct Cost: ¥6,700,000)
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| Research Abstract |
This research has been done in an attempt to develop a new type of aluminum-base metal matrix composites (MMCs) with particulate ceramic reinforcements as advanced high-temperature structural materials. Paying special attention to different roles of ceramic particles with much different sizes in conventional particulate-reinforced MMCs and dispersion-strengthened alloys, we have planed to examine, toward the design of novel 'hybrid' particulate MMCs, the effects of particle size on elevated-temperature stiffness and creep resistance in MMCs which contain either one or both of fine (<1μm) and coarse (【approximately equal】10μm) ceramic particles. To this end, the present work begins with reactive synthesis of TiB_2 /Al MMCs from Al-Ti-B mixed elemental powders because this reactive powder processing can produce submicron-size TiB_2 particulates in situ in aluminum matrices. Here, we are much involved in a problem as to the undesirable compound Al_3Ti that forms intermediately and often r
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emains in final products under the usual processing conditions with heating temperatures of up to 1000℃. Our detailed study has shown that two intermediate compounds AlB_2 and Al_3Ti, known previously, can decompose in the presence of molten aluminun, forming TiB_2 and Al, i.e. AlB_2 +Al_3Ti→ TiB_2+4Al. This reveals a proper range of reactant compositions, xAl-Ti-2B with x【greater than or equal】4 for making the desired TiB_2 /Al two-phase MMCs, the critical composition x=4 corresponding to a maximum of 27.9 vol.% TiB_2. Then, the work proceeds to the fabrication of three different 20 vol.% TiB_2/Al MMCs wherein the particulate reinforcement is either one of very fine (<1μm) in situ and coarse (【approximately equal】10μm) 'ex situ' formed TiB_2, or both of these at equal amounts (10 vol,%). All the three have been successfully fabricated under essentially the same processing condition, and thereby our final experimental work on the measurement of temperature dependence of dynamic tensile modulus and creep tests is satisfactorily accomplished. Results are analyzed in detail in light of our micromechanics-based description of high-temperature deformation of MMCs, wherein the importance of strongly size-dependent stress relaxation of reinforcing particles is emphasized. The 'hybrid' particulate design and reactive synthesis route to fabrication is promising as advanced technology of high-temperature MMCs. Less
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