Papers by Author: Hidehiro Yoshida

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Authors: Taketo Sakuma, Zhang Lian Hong, Hidehiro Yoshida, Yuichi Ikuhara, Toshiyasu Nishimura, Mamoru Mitomo
279
Authors: Byung Nam Kim, Keijiro Hiraga, Koji Morita, Hidehiro Yoshida
Abstract: For steady-state deformation caused by grain-boundary diffusion and viscous grain-boundary sliding, the creep rate of regular polyhedral grains is analyzed by the energy-balance method. For the microstructure, the grain-grain interaction increases the degree of symmetry of diffusional field, resulting in a decrease of the effective diffusion distance. Meanwhile, the viscous grain-boundary sliding is found to decrease the creep rate. The present analysis reveals that the grain-size exponent is dependent on the grain size and the grain-boundary viscosity: the exponent becomes unity for small grain sizes and/or high viscosity, while it is three for large grain sizes and/or low viscosity.
565
Authors: Byung Nam Kim, Keijiro Hiraga, Koji Morita, Hidehiro Yoshida
Abstract: When the sliding of the grain boundary containing hexagonal particles is accommodated by grain-boundary diffusion, we evaluate the sliding rate and the stress distribution on the boundary, by taking the particle rotation and the intrinsic boundary viscosity into account. The sliding rate was obtained by the energy-balance method, and the particle-rotation rate by a condition of minimum energy-dissipation. With increasing boundary viscosity, the rotation rate increases and then decreases after a maximum. The sliding rate is enhanced by the particle rotation, and decreases with the boundary viscosity.
305
Authors: S. Watanabe, Hidehiro Yoshida, Taketo Sakuma
67
Authors: Koji Morita, Byung Nam Kim, Hidehiro Yoshida, Keijiro Hiraga
Abstract: The densification mechanism in park-plasma-sintering (SPS) processing was examined in MgAl2O4 spinel. As the relative density ρt increases, that is, as the effective stress σeff decreases, stress exponent n evaluated from effective stress-densification rate relationship continuously varies from n  4 to n  1. TEM observation shows that significant stacking faults caused by partial dislocations are frequently observed in the low ρt region. The results suggest that, for spinel, the predominant densification mechanism in SPS processing changes with ρt from plastic flow by a partial dislocation motion in the low ρt region (n  4) to diffusion-related creep in the high ρt region (n  1).
1986
Authors: Koji Morita, Byung Nam Kim, Hidehiro Yoshida, Keijiro Hiraga, Yoshio Sakka
Abstract: The densification mechanism during the park-plasma-sintering (SPS) processing was examined in high purity MgAl2O4 spinel. As the density ρt increases, that is, as the effective stress σeff decreases, stress exponent n evaluated from σeff dependence of densification rate varies from n ≥ 4 in the low ρt region, n ≈ 2 in the intermediate ρt region to n ≈ 1 in the high ρt region. TEM observation shows that significant stacking faults caused by partial dislocations are observed in the low ρt region, but limited in the high ρt region. The ρt dependent densification behavior and microstructure suggest that the predominant densification mechanism during the SPS processing changes with ρt from plastic flow by partial dislocation motion for the low ρt region (n ≥ 4) to diffusion-related creep for the high ρt region (n ≈ 1).
62
Authors: Yoritoshi Minamino, Hidehiro Yoshida, Seung Boo Jung, Kiyoshi Hirao, Toshimi Yamane
257
Authors: Hidehiro Yoshida, Katsuyuki Matsunaga, Takahisa Yamamoto, Yuichi Ikuhara
299
Authors: Keijiro Hiraga, Hidehiro Yoshida, Koji Morita, Byung Nam Kim
Abstract: In tetragonal zirconia, possibility is investigated of densification with finer grain sizes under the combination of doping and sintering in air. The materials used are CIP'ed compacts of 3-mol%-yttria-stabilized tetragonal zirconia (3Y-TZP) doped with a small amount of cations. For a given sintering temperature and initial density of the compacts, while the doped cations enhances densification in the latest stage of sintering, the effect is different in grain growth during densification: a doped cation tended to enhance grain growth, whereas the other cations tended to suppress grain growth. As a result, the doping of the latter cations brings about a grain size finer than that of the undoped 3Y-TZP for a given relative density.
227
Authors: Hidehiro Yoshida, Koji Morita, Byung Nam Kim, Keijiro Hiraga, Takahisa Yamamoto, Taketo Sakuma
997
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