Mechanical properties of molybdenum neutron-irradiated at a high temperature

Molybdenum specimens prepared by two processes, powder-metallurgy (PM) and electron-beam melting (EB), were irradiated to a fast neutron fluence of 2.74 × 10²⁴n/m² (E_n? 1 MeV) at about 600°C (873 K), and their mechanical properties were studied in detail. It was shown that the degree of irradiation embrittlement in EB-Mo was smaller than that in PM-Mo, which might be caused by stronger grain-boundaries and probably smaller irradiation-hardening in the former. From the relation between the recovery of ductility and microstructural changes in post-irradiation annealed PM-Mo at 800 (1073 K), 1000 (1273 K) and 1200°C (1473 K), it was concluded that the recovery resulted from a decrease of irradiation hardening due to a rearrangement and a disappearance of depleted-zones, dislocation-loops and voids in order with increasing annealing temperature. An anomalous mode of fracture was observed in as-irradiated specimens, which consisted of inhomogeneous deformation, then brittle fracture not at the center but at the root of the deformation neck. This mode was observed in a narrow temperature range near the DBTT. A possible mechanism is discussed.