Radiation Response of Oxide Dispersion Strengthened Alloy

Abstract

Ferritic-martensitic (F/M) steels are known to have greater resistance to void swelling, higher thermal conductivities and lower thermal expansion coefficients than austenitic steels do. The strength and swelling resistance of F/M alloys can be further improved through adding fine dispersions of various yttria oxides. The majority of such oxide-dispersion-strengthened (ODS) alloys introduce dispersoids in ferrite phases. However, previous studies have shown that in the absence of dispersoids, the ferrite phase is significantly less swelling resistant than the tempered martensite phase.

A dual-phase 12Cr ODS alloy with improved corrosion and oxidation resistance exhibits promising microstructural stability and void swelling resistance under 3.5 MeV Fe^2+ ion irradiation at elevated temperatures. Dispersoids were originally present in both ferrite and tempered martensite grains, with the latter having a wider range of dispersoid sizes. In both phases dispersoids larger than 10 nm in diameter are incoherent with the matrix, while smaller dispersoids exhibit coherency. Beyond radiation damage of 60 displacements per atom (dpa), dispersoids in both phases appear to approach a near-identical equilibrium size, which depends on irradiation temperature. The evolution of dispersoids under irradiation was found to be related to the interface configuration. Grain morphology was found to be stable under irradiation up to a peak dpa of 800. Compared to other ferritic-martensitic alloys, the ion-induced swelling of this alloy is quite low, arising from swelling resistance associated with both tempered martensite and dispersoids in both phases. The swelling in tempered martensite is an order of magnitude less than in the ferrite phase.