Initial investigation on joining ods alloy using friction stir welding for Gen IV nuclear reactor heat exchanger applications

To investigate the possibility of joining oxide-dispersionstrengthened (ODS) alloys while preserving the dispersion for high temperature strength in potential applications to Gen IV nuclear reactor compact heat exchanger, solid-state welding of ODS alloy sheets using friction stir welding (FSW) was studied. Butt weld was successfully produced, and the weld and base metals were characterized using optical, scanning electronic, and transmission electronic microscopes, as well as energy dispersion x-ray spectrum. Microhardness mapping was also conducted over the weld region. Analyses indicate that the distribution of the strengthening oxides was preserved in the weld. Decrease in microhardness of the weld was observed but was insignificant. The preliminary results seem to confirm the envisioned feasibility of FSW application to ODS alloy joining. Further investigation activities are suggested for providing better mechanistic understanding and processing control for applications to Gen IV nuclear reactor systems.