In the present work, microstructures of dispersoids in two Al-added high-Cr ODS ferritic steels (including the commercial MA956, and another ODS steel with a similar composition recently developed in Kyoto University) were studied. The study with transmission electron microscopy (TEM) of both the thin-foil specimens and the extraction replica specimens showed that the nano-sized oxides in the two ODS steels consist mainly of a complex Y-Al-O compound (YAlO 3) in a perovskite structure (i.e. YAP), while other oxide particles with different chemical composition or crystalline structures are in significantly lower number density. The comparison between the two kinds of ODS steels shows that the size distribution and the number density of the oxide particles significantly depends on the conditions of fabrication. Mechanisms underlying the processes were discussed.
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