Effects of matrix microstructure on oxide nanoparticles in 9Cr F/M and 12Cr ferritic ODS steels

Abstract

Fe–Cr ODS steels are considered as promising materials for the fusion reactor blankets and the cladding of sodium-cooled fast reactors. For 9Cr ferritic/martensitic (F/M) (Fe–9Cr–0.14C–2W–0.23Ti–0.37Y₂O₃) and 12Cr ferritic (Fe–12Cr–0.027C–2W–0.23Ti–0.24Y₂O₃) ODS steels, the morphology of matrix grains and nanoparticles, as well as crystal & interface structures of nano-oxides were studied by TEM, STEM and HRTEM. For 9Cr F/M ODS steel, the particle dispersion morphology of the residual ferrite is much better than that of tempered martensite. The proportions of coherent/semi-coherent particles in residual ferrite of 9Cr F/M ODS steel and matrix of12Cr ferritic ODS steel are ∼83.7 % and ∼87.5 %, respectively, and however, for tempered martensite of 9Cr F/M ODS steel, the proportion is only ∼7.9 %, which explains the facts that the oxide particle dispersion morphology of ferritic matrix (i.e., residual ferrite of 9Cr F/M ODS steel and the matrix of 12Cr ferritic ODS steel) is much better than that of tempered martensite of 9Cr F/M ODS steel. Moreover, the results of first-principles calculations indicate that Y₂TiO₅ and Y₂Ti₂O₇ oxides have excellent kinetic and thermal stability, which contribute to the high-temperature stability of both ODS steels. The findings provide valuable insights for the optimization and development of advanced ODS steels.