Y添加によるFe-20Cr合金の高温耐酸化性改善効果

Abstract

The isothermal oxidation behavior of Fe-20Cr alloys with addition of 0.1,0.2,0.5,0.7,1.0 and 1.4 wt%Y was studied in air over the temperature range of 1273∼1373 K by weight gain measurement, scanning electron microscopy, X-ray diffraction, electron probe microanalysis and ion microanalysis.It was found that 0.1%Y addition or more increased oxidation resistance at 1273 K and 0.7%Y or more remarkably at 1323 and 1373 K compared to the base Fe-20Cr binary alloy. Generally an addition of 0.7%Y gave the best improvement in the oxidation resistance. Cr2O3 was the major oxide formed on the alloys which exhibited a good oxidation resistance. Internal oxidation layer of Y2O3 was observed beneath the Cr2O3 scale of Y containing alloys. The growth of internal oxidation layer depth obeyed a parabolic rate law and the rate increased with increasing oxidation temperature and decreased with increasing Y content in the alloys.The ion microanalyser was used to analyse Y2O3 and Fe2O3 contents in Cr2O3 scales formed on Fe-20Cr-Y alloys after 1h oxidation. Y2O3 content increased, while Fe2O3 content remarkably decreased with increasing Y content in the alloy and slightly increased again over 0.7%Y. The Fe2O3 content in the scale formed after 1h oxidation and the weight gain of Fe-20Cr-Y alloys after 20h oxidation showed the same dependency on Y content in the alloys.The improvement effects of Y addition on the oxidation resistance of Fe-20Cr alloy were discussed from the view points of stabilization of Cr2O3 with dissolving Y2O3 and enrichment of internally oxidized particles beneath the scale.