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Author: search.filters.author.Tunthawiroon, PhacharaphonSubject: search.filters.subject.Co-Cr-Mo alloys

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    Corrosion behavior of a Co-Cr-Mo-Si alloy in pure Al and Al-Si melt
    (2023-01-01)
    Yamanaka, Kenta
    ;
    Mori, Manami
    ;
    Yoshida, Kazuo
    ;
    Tunthawiroon, Phacharaphon
    ;
    Chiba, Akihiko
    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.
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    Xps analysis of oxide formed on the surface of co-28cr-6mo-1si alloy oxidized at 550 ºc
    (2020-01-01)
    Tunthawiroon, Phacharaphon
    ;
    Kitiwan, Mettaya
    ;
    Wongpromrat, Patthranit
    ;
    Chiba, Akihiko
    This work investigated the influence of oxidation durations on the formation of oxide on the surface of wrought Co-28Cr-6Mo-1Si alloy. The iso-thermal oxidation was individually performed in air at 550ºC for 4, 12 and 24 h. For comparison, the surface of the non-oxidized Co-28Cr-6Mo-1Si alloy was concurrently examined. The chemical compositions of the non-oxidized and oxidized alloys were principally analyzed via X-ray photoelectron spectroscopy (XPS). The XPS results revealed that the surface of the non-oxidized alloy enriched in Cr-oxide. After oxidation treatment, the Co-oxide, existing as Co<sup>2+</sup> state was observed coexisting with two Cr-oxide states, Cr<sup>3+</sup> and Cr<sup>4+</sup>. The low concentrations of Mo<sup>6+</sup> were also observed on the oxidized alloy surface. With the increase in oxidation durations, the Co-oxide was suppressed by Cr-oxide. The XPS depth profile analysis indicated that the thickness of the oxide film increased with increasing the oxidation duration.