Helium bubble formation and swelling in metals

Abstract

The effect of a continuous production of helium on swelling is analyzed using an improved equation of state for gaseous helium that incorporates both a gas-kinetic as well as a static pressure for densely packed helium. In the absence of a bias, bubble swelling is characterized by two temperature regimes. At temperatures below about 550°C, bubble swelling is due to thermally assisted interstitial emission and is of a magnitude determined by the volume occupied by densely packed helium. At higher temperatures, bubbles grow by thermal vacancy emission at dislocations and their absorption at cavities. For high He/dpa ratios, bubbles remain overpressurized, and swelling is less than obtained from the equilibrium assumption. When a modest bias exists, bias-driven swelling or void growth in the low temperature regime is always larger than bubble swelling, and helium has no effect on the swelling rate.