Effect of hydrogen on the low-temperature deformation properties of neutron-irradiated vanadium

Abstract

The influence of hydrogen on the low temperature deformation characteristics of neutron-irradiated vanadium single crystals has been investigated in compression in the temperature range from 77 to 550 K. The addition of hydrogen to neutron-irradiated vanadium causes a local perturbation in the temperature dependence of yield stress that is similar to unirradiated vanadium. A mechanism based on the stress induced reorientation of small hydrides by the stress fields of moving dislocations has been put forward to account for this observation. In contrast, the presence of hydrogen prior to irradiation results only in a general rise in the yield stress. The disappearance of the local perturbation is attributed to the trapping of hydrogen atoms to form stable complexes during irradiation, thereby eliminating the phenomenon of stress-induced reorientation of hydrides. The fact that the hydrogen does not reduce the thermal component of the yield stress implies that the cancellation of neutron-produced defects by hydrogen is unlikely. The effect of prestraining prior to neutron irradiation resulted in a reduction of the increase in the yield stress due to the neutron irradiation. This reduction is probably due to the fact that the additional dislocations provide an increased sink density.