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414 results on '"Yamanaka, Kenta"'

12. Corrosion behavior of a Co−Cr−Mo−Si alloy in pure Al and Al−Si melt

Author

Yamanaka Kenta, Mori Manami, Yoshida Kazuo, Tunthawiroon Phacharaphon, and Chiba Akihiko

Subjects
phase change material, aluminum, corrosion, co−cr−mo alloys, Technology, Chemical technology, TP1-1185, Chemicals: Manufacture, use, etc., TP200-248
Abstract

Metallic phase change materials (MPCMs) are attracting considerable attention for their application in thermal energy storage. Al–Si alloys are considered potential MPCMs; however, to develop storage systems/modules, it is crucial to fabricate corrosion-resistant materials for MPCMs. In this study, the corrosion behavior of Co−28Cr−6Mo−1.5Si (wt%) alloy was examined via immersion tests in commercial Al−Si alloy (ADC12) melt at 700°C for 10 h. The results were compared to those obtained for pure Al. Substrate thickness loss measurements revealed that the liquid metal corrosion was more severe in the Al−Si melt than that in pure Al, suggesting an increased reactivity due to Si addition. Interfacial analysis elucidated a direct reaction between the alloy substrate and molten Al in both cases. Furthermore, the formation of oxides such as Al2O3 and SiO2 did not contribute to corrosion resistance.

Published
2023
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33. Non-equilibrium solidification behavior associated with powder characteristics during electron beam additive manufacturing

Author

Yufan Zhao, Huakang Bian, Hao Wang, Aoyagi Kenta, Yamanaka Kenta, and Akihiko Chiba

Subjects
Powder bed fusion with electron beam, CoCrMo alloy, Heat flow and solidification, Microsegregation, Multi-scale simulations, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

For components built by powder bed fusion with electron beam (PBF-EB), the resulting microstructure arising from non-equilibrium solidification, microsegregation and the formation of interdendritic phases significantly affects the material properties. Notably, the powder characteristics influence the heat absorption and conduction, thereby altering the molten pool behavior and solidification parameters. However, the effect of the powder feedstock on solidification during PBF has not been widely investigated. In this study, a CoCrMo alloy was fabricated using powders prepared by gas-atomization (GA) and plasma rotating electrode process (PREP). Under the given operating conditions, samples built using the two powders were characterized and compared. By performing multi-scale numerical simulations, melting and solidification were visualized and analyzed to elucidate the mechanism through which the powder characteristics influence the non-equilibrium solidification behavior during PBF-EB. The study revealed that after appropriate size control, compared with the GA powder, the PREP powder had a smaller specific surface area and higher sphericity; thus, the generated powder layer exhibited higher heat absorption and dissipation rates. Therefore, a high solidification rate was facilitated, thereby suppressing microsegregation. These findings contribute to PBF knowledge related to feedstock, proving to be an essential reference for selecting and optimizing metallic powders applicable to additive manufacturing.

Published
2022
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42. Reaching unconventionally large Hall-Petch coefficients in face-centered cubic high-entropy alloys.

Author

Li, Jiaxiang, Yamanaka, Kenta, Zhang, Yongjie, Furuhara, Tadashi, Cao, Guoqin, Hu, Junhua, and Chiba, Akihiko

Subjects
FACE centered cubic structure
Abstract

The Hall-Petch strengthening coefficient of face-centered cubic alloys has the potential to increase. Herein, we experimentally determined an unconventionally large Hall-Petch coefficient equal to 1100 MPa·µm1/2 and a large lattice friction stress for novel Co0.95Cr0.8Fe0.25Ni1.8Mo0.475 high-entropy alloys (Mo0.475 HEAs). Detailed microstructural characterizations showed Mo segregation at grain boundaries (GBs) and no apparent nano-clustering in the matrix. With the increased Mo content, Mo segregating at GBs is an unexpected outcome. The unconventionally large Hall-Petch coefficient is ascribed to the newly generated effect due to Mo segregation at GBs, besides the factors in the grain interior, e.g. the increased solid-solution strengthening. This study is dedicated to enriching the diversity of Hall-Petch strengthening mechanisms for the development of high-strength materials. [ABSTRACT FROM AUTHOR]

Published
2024
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