Ni-20Cr焼結合金の高温耐酸化性に及ぼす各種活性金属酸化物分散添加の影響

概要

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The isothermal oxidation behavior of sintered Ni-20Cr alloys with 0.7 mass% dispersion of various reactive metal oxides (Y2O3, La2O3, Gd2O3, Al2O3, ZrO2, TiO2, SiO2, MgO, Ta2O5 and Cr2O3) was investigated in air at 1373 and 1473 K. It was found that the oxidation rate was significantly dependent on the type of the dispersed oxides. The dispersion of MgO, ZrO2, SiO2 and Cr2O3 increased the oxidation rate, while the dispersion of La2O3 and Gd2O3 excellently reduced the oxidation rate of the sintered Ni-20Cr alloy. The oxidation rate of the sintered Ni-20Cr alloy was not reduced by the dispersion of Y2O3, which excellently reduced the oxidation rate of the sintered Fe-2OCr alloy. The scale adhesion was also markedly dependent on the type of the dispersed oxides. The dispersions ofLa2O3 and Gd2O3 excellently improved the scale adhesion. The results of EPMA observation and X-ray diffraction for the scale revealed that the scale generally consisted of inner Cr2O3 scale and outer NiO scale. There was a general tendency that the thickness of the outer NO scale was larger on the alloys which showed larger mass gain. A thin Cr2O3 scale without outer NiO scale was maintained stably on the alloys with La2O3 and Gd2O3. It may be concluded from these results that the additions of La2O3 and Gd2O3 suppress outward migration of Ni ions through the Cr2O3 scale.