Abstract
The present study was undertaken for the purpose of clarifying the effects of Ce additions on the microstructures and high temperature corrosion resistance of Fe-30 mass%Cr-5 mass%Al alloys. The microstructures of two alloys, Fe-27Cr-4Al-0.25Ce and Fe-29Cr-4Al-0.76Ce (mass%), were examined using optical microscopy, X-ray diffraction, electron probe microanalysis and transmission electron microscopy (TEM).
The microstructure of the 0.25% Ce alloy showed the precipitation of CeO2 and grain boundary carbide of (Cr, Fe)23C6, while that of the 0.76%Ce was characterized by the formation of CeO2 and coarse precipitates of a Ce-enriched intermetallic compound. TEM along with STEM/EDX analysis identified this compound with the Ce2(Fe, Cr, Al, Si)17 phase having the Th2Zn17 type structure.
High temperature corrosion tests in 80%Na2SO4-20%NaCl were made on both the Ce-containing alloys used for the metallographic examinations. The test results showed that the surface scale formed on the tested sample was observed to decrease in thickness as the Ce-content increased. Also, Ce addition improved the adherence of the surface scale. The 0.25% Ce alloy has predominantly developed α-Al2O3, while a duplex oxide layer consisting of Cr2O3 and α-Al2O3 was occasionally observed on the tested sample. In contrast, the 0.76% Ce alloy developed only a thin scale of α-Al2O3 which was continuous and apparently adherent to the underlying metal. The role of Ce in the improvement of corrosion resistance of the Ce-containing alloys was discussed.
