Journal of the Japan Society of Powder and Powder Metallurgy
Online ISSN : 1880-9014
Print ISSN : 0532-8799
ISSN-L : 0532-8799
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April
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  • Microstructures in Heat Treated LPBF Ti-6Al-4V Alloys after α′phase Decomposition and their Mechanical Properties
    Reita ANAN, Shota KARIYA, Shufeng LI, Yafeng YANG, Junko UMEDA, Katsuy ...
    2025 Volume 72 Issue 4 Pages 79-84
    Published: April 15, 2025
    Released on J-STAGE: April 15, 2025
    Advance online publication: March 07, 2025
    DOIhttps://doi.org/10.2497/jjspm.25-00001
    JOURNAL OPEN ACCESS
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    Alloys formed by laser power bed fusion (LPBF) contain high residual stress and strain due to the cyclic heating process, which decreases ductility. Therefore, many researchers have investigated heat treatments to improve ductility by removing residual stress and forming α + β phase structures. However, in this study the ductility of some heat-treated samples was found to decrease below that of as-built samples. This study investigated the heat treatment of LPBF at different temperatures to decompose α′ grains to α grains and understand the resulting microstructure and mechanical properties. Specifically, the influence of microstructural factors on ductility was examined. In the samples heat treated at 500°C, α′ was found to decompose into α with elevated strain and finer β grains, which increased yield strength at the cost of ductility. Meanwhile, in the samples heat treated at 700°C, coarser β phase was precipitated, and greater ductility was supported by the transfer of the slip deformation between α phase grains.

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  • Establishment of Conduction Mechanism for ZnO Varistors Based on Solid State Chemistry
    Hideyuki OKINAKA, Wataru SAKAMOTO
    2025 Volume 72 Issue 4 Pages 85-95
    Published: April 15, 2025
    Released on J-STAGE: April 15, 2025
    Advance online publication: March 08, 2025
    DOIhttps://doi.org/10.2497/jjspm.25-00004
    JOURNAL OPEN ACCESS
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    The tunneling effect model between Schottky-type energy barriers, currently the best-known conduction mechanism for ZnO varistors, is based on the assumption that energy barriers of uniform height exist at the interface inside the ZnO grains. This conduction model does not adequately reflect the compositional heterogeneity and microstructural complexity of actual varistor devices. Therefore, considering newly obtained analytical data on various phenomena, we discuss the “composite barrier model” based on tunneling effects in grain boundary insulating layers with scattered “holes” where ZnO grains come into contact with each other. By calculating each element in the microstructure (thickness of the thin grain boundary layer between ZnO grains, size and occurrence density of “holes” in the grain boundary layer, etc.) and correlating them with electron microscopy observation data and E-J characteristics, the remarkable temperature dependence of E-J characteristics in ZnO varistors can be quantitatively understood. This result cannot be satisfied by conventional models.

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