Samples were neutron-irradiated near 80C, to doses of 7.2 x 10−5, 7.2 x 10−4, 7.2 x 10−3, 0.072 and 0.28dpa. Post-irradiation examination included electrical resistivity and tensile properties measured at room temperature. Microstructure of irradiated specimens was examined by transmission electron microscopy and the defect cluster density and cluster mean size were characterized. Measurements of electrical resistivity and cluster density showed sub-linear defect accumulation behaviour. The mean size of visible defect clusters increased with increasing dose. Yield stress decreased at 7.2 x 10−5 and 7.2 x 10−4dpa, then increased significantly with increasing dose up to 0.072dpa and saturated. It appeared that there was a transition in hardening from weak obstacles to strong obstacles. It was suggested that the formation of sessile defect clusters in neutron-irradiated Mo was mainly associated with diffusive nucleation and growth rather than in-cascade clustering.

Defect Cluster Formation and Radiation Hardening in Molybdenum Neutron-Irradiated at 80C. M.Li, N.Hashimoto, T.S.Byun, L.L.Snead, S.J.Zinkle: Journal of Nuclear Materials, 2007, 367-370[1], 817-22