Effect of Molybdenum on the Oxide Films and Scales on Ni-Cr-Base Alloys

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  • Imai Yûnoshin
    The Research Institute for Iron, Steel and Other Metals, Tohoku University
  • Nishi Yoshizum
    1st Research Center, The Technical Research and Development Institute, Defence Agency

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  • Ni-Cr基合金の高温酸化被膜およびスケールにおよぼすMoの影響
  • Ni-Crキ ゴウキン ノ コウオン サンカ ヒマク オヨビ スケール ニ オヨボス Mo ノ エイキョウ

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Abstract

Oxide films and scales formed on Ni-Cr-Mo and Ni-Cr-Co-Mo alloys containing about 19%Cr were studied by electron and X-ray diffraction methods. The following results were obtained. (1) In Ni-Cr-Mo alloys, the rate of formation of spinel phase NiOCr2O3 rose as the molybdenum content was increased, during the early part of oxidation at temperatures of 850° and 1000°C. (2) In the scales of Ni-Cr-Mo alloys, Cr2O3, NiOCr2O3, NiO and NiOMoO3 were formed above 1000°C. NiOMoO3 formed on Ni-Cr-Mo alloys decomposed, releasing MoO3 above 1200°C, and fused at the temperature of oxidation-resistance limit, 1350°C. (3) In Ni-Cr-Co-Mo alloy, formation of spinel phase (Ni, Co)OCr2O3 was expedited, owing to the cobalt content, and the formation of (Ni, Co)OMoO3 was hindered thereby. At the temperature of oxidation-resistance limit of Ni-Cr-Co-Mo alloy, (Ni, Co)OMoO3 was formed and fused.

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