Microstructure of the χ phase in ODS ferritic alloys

Ferritic alloys as core components of a fast neutron reactor are more resistant to swelling in the temperature range 400 to 650 C than austenitic ones but they have usually a poor creep resistance in this temperature range. In order to improve their creep properties, oxide dispersion strengthened (ODS) ferritic alloys can be elaborated by mechanical alloying, a process derived from powder metallurgy, compaction and extrusion. Therefore, two ODS ferritic alloys, DT (DT 2906) and DY (DT2203Y03), containing an intermetallic χ phase, have been developed by CEN/SCK, Belgium. The lattice parameter and the chemical composition of the χ phase have been determined by XR analysis and TEM examinations in two ODS ferritic steels. In both DT and DY alloys it is found that: the χ phase is partially coherent with the ferritic matrix, the stoichiometry of the χ phase is Fe42Cr9Ti5Mo2, and the lattice parameter is 0.886 nm. These results, which are similar to oxide free materials indicate that oxide strengthening do not affect the χ phase composition