Temperature-Dependent Swelling in Helium Ion Irradiated Vanadium

Vanadium is a typical low-activation metal and has the advantages of lower neutron irradiation activation, better mechanical properties at high temperature, and higher compatibility with the liquid lithium blanket. However, the effect of helium on the formation of irradiation defects in vanadium has not been adequately explored at low temperatures (below 723 K). Helium ion irradiations of 18 keV up to 0.54 displacement per atom were employed to study the temperature-dependent behavior of irradiation defects in vanadium at 523, 623, and 723 K. Helium bubbles were observed in vanadium under irradiations at all temperatures, but no dislocation loops were observed. With the increase of irradiation temperature, the average size of helium bubbles and swelling increased, and the density of helium bubbles decreased. It is noteworthy that the average size of helium bubbles and swelling increased significantly when the irradiation temperature increased from 623  to 723 K. In addition, pentagonal helium bubbles, helium bubbles nucleated at the grain boundary, and combinations between helium bubbles were observed.