Mechanical Properties of Neutron-Irradiated Niobium

Abstract

Commercial purity polycrystalline niobium was irradiated in the JMTR to neutron fluences of 3.5 x 1018 and 6.9 × 1018 n/cm2 (E>1 MeV) and then deformed in tension at temperatures between 77 and 340°K in order to investigate the mechanical properties, particularly the temperature dependence of yield stress and the activation volume and activation energy for thermal activated motion of dislocations. From the force acting on radiation-produced defects, it was deduced that the radiation defects observed by trans-mission electron microscopy do not account for the thermal component of yield stress because of the extremely large defect sizes. In addition, a comparison was made between the athermal component of yield stress and the stress which was derived from the defect distribution as determined by transmission electron microscopy. The measured data amount to about 1.4 and 2 times larger than the calculated values. These discrepancies may be ascribed to the interaction between interstitial impurities and the radiation defects. In the room temperature deformation, dislocation channeling was observed in the specimens irradiated to 6.9 × 1018 n/cm2 but not to 3.5 × 1018 n/cm2.