Void formation in ion bombarded niobium

Transmission electron microscopy has been used to study void formation in high-purity niobium which has been bombarded with 7.5 MeV Ta+++ ions at elevated temperatures. The swelling due to voids increases with ion dose in the range 1 to 100 dpa (atom displacements per atom) at both 800°C and 900°C. Above 100 dpa, the swelling begins to saturate and approaches a value of 4.5% at 800°C and between 7–10% and 900°C for a maximum dose of 300 dpa. The saturation is coincident with the formation of a bcc void lattice. The void lattice is somewhat temperature dependent being much better defined at 800°C than at 900°C.