Post-irradiation fracture toughness of unalloyed molybdenum, ODS molybdenum, and TZM molybdenum following irradiation at 244 °C to 507 °C

Commercially available unalloyed molybdenum (Low Carbon Arc Cast (LCAC)), Oxide Dispersion Strengthened (ODS) molybdenum, and TZM molybdenum were subject to fracture toughness testing following neutron irradiation at temperatures of nominally 244 °C, 407 °C, and 509 °C to neutron fluences between 1.0 and 4.6 × 1025 n/m2 (E > 0.1 MeV). All alloys exhibited a Ductile to Brittle Transition Temperature that was defined to occur at 30 ± 4 MPa m. The highest post-irradiated fracture toughness values (26–107 MPa m) and lowest DBTT (100–150 °C) was observed for ODS molybdenum in the longitudinal orientation. The results for ODS molybdenum are anisotropic with lower post-irradiated toughness values (20–30 MPa m) and higher DBTT (450–600 °C) in the transverse (T-L) orientation. The results for ODS molybdenum are better than those for LCAC molybdenum (21–71 MPa m and 450–800 °C DBTT). The fracture toughness values measured for LCAC and T-L ODS molybdenum at temperatures below the DBTT were determined to be 8–18 MPa m. The role of microstructure and grain size on post-irradiated fracture toughness was evaluated.