The swelling, microstructure, and hardening of wrought LCAC, TZM, and ODS molybdenum following neutron irradiation

TEM examinations and swelling measurements were performed on commercially available wrought Low Carbon Arc Cast (LCAC), La-oxide Oxide Dispersion Strengthened (ODS), and TZM molybdenum alloys following irradiation in the High Flux Isotope Reactor (HFIR) at 300 °C, 600 °C, and 900 °C to neutron fluences between 1.05 and 24.7 × 1025 n/m2 (E > 0.1 MeV), or 0.6–13.1 dpa. The defect structure, hardening, and swelling were shown to be strongly dependent on irradiation temperature and starting microstructure. Irradiation at 300 °C results in the formation of a high number density of fine loops and voids (∼1 nm) that produce significant hardening and low swelling that is comparable for all alloys. Irradiation at 600 °C–784 °C produces a high number density of larger voids (5–6 nm) that results in significant hardening with the highest swelling. A low number density of the largest void sizes (8–30 nm) are formed for the 900 °C irradiation that result in low hardening and less swelling than observed for the 600 °C irradiation. The fine grain size of ODS Mo results in a higher concentration of denuded zones along grain boundaries and improved ductile-laminate toughening that results in improved resistance to irradiation embrittlement for the 600 °C irradiations. Irradiation-induced formation of precipitates rich in transmutation products is observed at the highest dose, and it is likely that these features exert an influence on subsequent void growth.

Graphical abstractTEM examinations and swelling measurements were performed on commercially available wrought Low Carbon Arc Cast (LCAC), La-oxide Oxide Dispersion Strengthened (ODS), and TZM molybdenum alloys following irradiation in the High Flux Isotope Reactor (HFIR) at 300 °C, 600 °C, and 900 °C to neutron fluences between 1.05 and 24.7 × 1025 n/m2 (E > 0.1 MeV), or 0.6–13.1 dpa. The defect structure, hardening, and swelling were shown to be strongly dependent on irradiation temperature and starting microstructure. Irradiation at 300 °C results in the formation of a high number density of fine loops and voids (∼1 nm) that produce significant hardening and low swelling that is comparable for all alloys. Irradiation at 600–784 °C produces a high number density of larger voids (5–6 nm) that results in significant hardening with the highest swelling. A low number density of the largest void sizes (8–30 nm) are formed for the 900 °C irradiation that result in low hardening and less swelling than observed for the 600 °C irradiation. The fine grain size of ODS Mo results in a higher concentration of denuded zones along grain boundaries and improved ductile-laminate toughening that results in improved resistance to irradiation embrittlement for the 600 °C irradiations. Irradiation-induced formation of precipitates rich in transmutation products is observed at the highest dose, and it is likely that these features exert an influence on subsequent void growth.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Irradiation at 300 °C forms a high number density of small voids and loops (∼1 nm). ► Irradiation at 600 °C forms a high number density of larger voids (5–6 nm) with no loops. ► Only a low number density of large voids (8–30 nm) are formed at 900C. ► The fine grain size for ODS Mo results in a lower post-irradiated DBTT. ► Irradiation-induced precipitates were formed at the highest dose.