耐熱合金の高温酸化膜に及ぼすSiの影響

抄録

The present authors studied, by using the transmission-electron diffraction method, the initial oxide films of A.I.S.I. Type 302 B (2.45%Si), 19-9 DL (0.50%Si), Durimet 20 (1.27%Si) and Nichrome (JIS No.1, 0.5∼1.5%Si) oxidized in air at 700∼900°C. A solution of bromine in methanol (1:50 by vol.) was satisfactorily used for isolating the oxide films from these alloys. The electron-diffraction patterns obtained from initial oxide films (700∼900°C) of the alloys showed the existence of rhombohedral-type (mainly Cr₂O₃ or α-(Cr, Fe)₂O₃) and spinel-type oxides, and no such special oxides as SiO₂ could be observed in the patterns. However, α-cristobalite crystals were detected when the films were heated at 1200°C for 1∼3 hr. Thereby the authors clarified experimentally that the special heat-resisting films consisting of amorphous SiO₂ are formed on the surfaces of alloys in the eariest stage of oxidation.