Pt含有γ-Ni+γ'-Ni_3Al合金の耐酸化性  [in Japanese] Oxidation Resistance of Pt Containing γ-Ni+γ'-Ni_3Al Alloys  [in Japanese]

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    • 泉 岳志 IZUMI Takeshi
    • アイオワ州立大学材料工学科 Department of Materials Science and Engineering, Iowa State University


  The oxidation behavior of Pt+Hf-modified γ-Ni+γ′-Ni<sub>3</sub>Al alloys containing up to 20 at%Pt and either 15 or 20 at%Al was studied by oxidizing the alloys in air at 1150°C under both isothermal and thermal cycling conditions. It was found that the co-addition of Pt and Hf was extremely beneficial to oxidation resistance, to the extent that Ni-20Al-20Pt-0.4Hf and Ni-20Al-10Pt-0.4Hf alloys (all compositions are in at%) oxidized at significantly slower rates than that of a Ni-50Al-15Pt β-NiAl alloy. A Ni-20Al-5Pt-0.3Hf alloy also showed relatively good oxidation resistance, with the oxidation rate being almost the same as that obtained for Ni-50Al-15Pt alloy. Over a period of up to 500 one-hour oxidation cycles, no oxide spallation from the modified γ+γ′ alloys was observed. From cross-sectional SEM examination coupled with X-ray diffraction analyses, it was found that a compact and planar exclusive scale layer of α-Al<sub>2</sub>O<sub>3</sub> formed on the Ni-20Al-20Pt-0.4Hf alloy. By contrast, Ni-20Al-10Pt-0.4Hf and Ni-20Al-5Pt-0.3Hf alloys formed a very thin outer layer of NiAl<sub>2</sub>O<sub>4</sub> and a planar inner layer of α-Al<sub>2</sub>O<sub>3</sub>. The thickness of this inner Al<sub>2</sub>O<sub>3</sub> layer increased with increasing oxidation time relative to that of the NiAl<sub>2</sub>O<sub>4</sub> layer, suggesting that the latter primarily formed during the initial stages of scale formation. Both NiO and NiAl<sub>2</sub>O<sub>4</sub> were found in the outer scales formed on the Ni-20Al-0.3Hf and Ni-15Al-0~10Pt-Hf alloys, with the thickness of these oxide layers decreasing with increasing Pt content in the alloys. Further, it was found that the extent of internal HfO<sub>2</sub> formation decreased significantly with increasing in Pt content, to the extent that no HfO<sub>2</sub> was found in the oxidized Ni-20Al-20Pt-0.4Hf alloy. Inferences for the observed beneficial effects of Pt promoting protective Al<sub>2</sub>O<sub>3</sub> formation and decreasing the tendency for Hf to oxidize in γ+γ′ alloys will be presented.<br>


  • The Journal of the Japan Institute of Metals.A  

    The Journal of the Japan Institute of Metals.A 71(1), 34-40, 2007-01-01 

    The Japan Institute of Metals

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