The effect of neutron irradiation on vanadium containing 50 to 800 weight ppm oxygen was studied using electrical resistivity, internal friction, and mechanical property measurements. The resistivity and internal friction specimens were irradiated to 3 × 1018 neutrons/cm2 (E > 1 MeV) at −190 C(−310 F) and the tension test specimens were irradiated to 1.2 x 1019 neutrons/cm2 (E > 1 MeV) at 106 C (223 F). Postirradiation annealing treatments were performed up to 220 C (428 F) for the resistivity and internal friction specimens and up to 520 C (968 F) for the tension test specimens.
Isochronal resistivity annealing measurements exhibited annealing stages at 170 C (338 F), 30 C (86 F), and −105 C(−157 F). The highest temperature stage (near 0.2 Tm, where Tm is the melting temperature) is attributed to the motion of interstitial oxygen to radiation-produced defect clusters and loops, where the oxygen is effectively removed from solid solution. This conclusion is based on the observations that: (a) the annealing activation energy is 1.1 ± 0.1 eV, close to the oxygen migration energy of 1.23 eV; (b) the magnitude of the annealing stage increased with increasing oxygen concentration; and (c) the decreases in oxygen concentration in solid solution upon annealing deduced from the decrease in resistivity and the decrease in the oxygen internal friction peak are in substantial agreement. The origins of the two lower temperature peaks are unknown, although it is speculated that hydrogen may be involved in the peak at -105 C (−157 F).
The yield stress measurements indicate that radiation exposure at 106 C (223 F) results in greater radiation hardening for specimens with larger oxygen concentration. Also, the further increase in strength upon postirradiation annealing (radiation-anneal hardening) is enhanced by increasing interstitial impurity concentrations.