The change in tensile properties of wrought LCAC molybdenum irradiated with neutrons

Molybdenum alloys are known to be most susceptible to neutron radiation damage at radiation temperatures <800 °C, a condition which has limited their broader use in nuclear applications. Manipulation of alloy microstructure through the optimization of carbon and oxygen contents, and mechanical working were investigated as means to mitigate the undesirable effects of irradiation. Low carbon arc cast (LCAC) molybdenum sheet specimens were irradiated in the high flux isotope reactor (HFIR) at temperatures ranging from 270 to 1100 °C and at neutron fluences between 10.5 and 64.4 × 1024 n/m2 (E>0.1 MeV). Irradiation of LCAC molybdenum at nominal temperatures of 935–1100 °C produced only moderate changes in tensile strength, tensile elongation, and no change in the ductile to brittle transition temperature (DBTT) as inferred from tensile fracture surfaces. Irradiation of LCAC molybdenum at either 270 or 605 °C resulted in a significant increase in yield strength, a decrease in tensile elongation, and an increase in DBTT. This behavior is characteristic of that reported for pure molybdenum following irradiation at temperatures <800 °C. The use of arc-cast processing, a low oxygen content, and high carbon to oxygen ratio to produce the LCAC molybdenum used in this work results in strong grain boundaries that are not the preferred fracture path.