Depth distribution of 20-keV helium ion irradiation induced cavities in nickel

Abstract

Transmission electron microscopy has been used to study the effect of total dose on the depth distribution of cavities (voids or bubbles) in nickel irradiated at 500°C with 20-keV 4He + ions. A transverse sectioning technique allowed us to obtain the entire depth distribution of cavities from a single specimen. The diameter, number density and volume fraction of cavities were measured as a function of depth from micrographs taken from samples sectioned parallel to the direction of the incident beam. The results for the doses at 2.9 x 10 15 and 2.9 x 1016 ions/;m 2 show an increase in the average cavity diameter, number density and volume fraction with increasing dose. A further increase in dose from 2.9 x 10^ to 2.9 x 10*7 ions/cm 2 also shows an increase in the average cavity diameter but a decrease in the number density. This observation is interpreted as evidence for the coalescence of cavities.1.