Papers by Author: Tokimasa Kawabata

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Authors: Kaname Fujii, Tokimasa Kawabata, Kenji Matsuda, Susumu Ikeno
Abstract: Changes in the mechanical properties on AZ91 Mg alloy cast into sand mold caused by heat-treatment and its microstructure were investigated by the tensile test and observation using optical and scanning electron microscopes, and chemical composition analysis. Tensile test results show that the specimens aged at 441K have larger elongation than those of aged at 489K, although they had same proof stress. The fracture surface observation reveal the cleavage fracture of aged specimen caused by the nodular structure as well as the formation of micro void around the coarse spheroidal Al-Mn-(Fe) phase.
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Authors: Kenji Matsuda, Tokimasa Kawabata, Yasuhiro Uetani, Susumu Ikeno
375
Authors: Kenji Matsuda, Tokimasa Kawabata, Tomoyuki Sakai, Tatsuo Sato, Akihiko Kamio, Susumu Ikeno
1119
Authors: Kenji Matsuda, Tokimasa Kawabata, Yasuhiro Uetani, Tatsuo Sato, Akihiko Kamio, Susumu Ikeno
989
Authors: Tokimasa Kawabata, Toshiyuki Matsuno, Kenji Matsuda, Shigeharu Kamado, Yo Kojima, Susumu Ikeno
Abstract: High resolution transmission electron microscopy(HRTEM)observation was performed to clarify morphology of precipitates at early stage of aging in Mg-Gd-Zr alloy. In the specimen aged at 423K, monolayer was observed on {1100}Mg planes. With increasing aging time, the monolayer and β” phase grew along the <1120>Mg directions. Arrangement of bright dots corresponding to {020}β’ except for the monolayer and β” phase was observed before peak aging stage. β’ phases formed at the same aging stage. Thus, these precipitates co-existed before peak aging stage. The monolayer, β” phase and β’ phase still co-existed in the peak aged specimen. The β’ phase was dominated in the peak hardness. It is revealed that the monolayer lying on {1100}Mg act as precursor of β” phase and β’ phase.
303
Authors: Kosuke Kido, K. Matsuda, Tokimasa Kawabata, T. Sato, Susumu Ikeno
953
Authors: Toshiyuki Matsuno, Tokimasa Kawabata, Kenji Matsuda, Shigeharu Kamado, Yo Kojima, Susumu Ikeno
Abstract: The TEM observation was performed to investigate the precipitation hardening in Mg-Gd-Zr alloy. Both the β’ and the β” phase coexist in the specimen aged at 473K for 16h. In the specimen aged at 523K, the β’ phase which has base centered orthorhombic (bco) structure was observed at early stage during aging. The β’ phase has a globular shape and four atomic layer periodicity in the [1100]Mg. The β’ phase grew with increasing aging time mainly along the [0001]Mg and the [1100]Mg.
445
Authors: Kunio Fukumori, Tokimasa Kawabata, Kenji Matsuda, Susumu Ikeno
307
Authors: Shogo Mori, Tokimasa Kawabata, Kenji Matsuda, Susumu Ikeno
Abstract: The age hardening precipitates of Mg-4.7mass%Zn alloy aged at 423K,473K were studied by using high-resolution transmission electron microscope (HRTEM). Contrasts of mono layers were confirmed to exist on the (0001) and (1100) matrix planes. It was considered that the contrast of mono layer was plate-like shape, and identified as pre-precipitates from as-quenched stage to early stage of aging at 473K for 32h . In the peak aged specimen of aged at 473K, the β1’ phase was observed. The β1’ phase has a rod-like shape and parallel to c-axis of Mg matrix. It can be observed orientation relationship between Mg matrix and β1’phase has not only same parts to previous reports but also different parts in one β1’ phase .
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Authors: Tokimasa Kawabata, Yuya Fukuda, Kenji Matsuda, Shigeharu Kamado, Yo Kojima, Susumu Ikeno
Abstract: The high resolution transmission electron microscope (HRTEM) observation was carried out to investigate the microstructure of precipitates in Mg-Gd-Y-Zr alloy. In the early stage of aging at 423K, monoatomic layers were observed along the (1 1 00)Mg plane. After 64h aging at 423K, the contrast of β” phase based on ordered D019 hexagonal super lattice structure was appeared. The monoatomic layers, two layers spaced by (1 1 00) Mg planes and β’ phase based on bco-structure were observed in the specimen aged for 128h. In the peak- aged specimen, the β’ phase and monoatomic layers were observed.
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