The Growth of Bubbles in Pure Aluminum During and After Irradiation with 600 MeV Protons

Abstract

Pure aluminum specimens have been irradiated in the PIREX facility installed in the 600 MeV proton accelerator of the Paul Scherrer Institut. Proton beams of current densities between 3 and 11 μA/mm2 have been used to obtain doses between 0.9 and 6 dpa at various irradiation temperatures from 390 to 750 K. The specimens were observed after irradiation in a transmission electron microscope (TEM). The helium bubble distributions formed as a function of dose and irradiation temperature have been systematically determined. In the range of temperature between 390 and 520 K. there is very little dependence of the bubble number density or diameter with dose. The average value for bubble diameter is 3 nm and number density is about 1022 m-3. There is a linear dependence between the inverse of the absolute irradiation temperature and bubble density; the corresponding apparent activation energy is 0.35 ± 0.04 eV. For irradiation temperatures above 520 K, a stronger dependence of bubble growth on temperature and dose is observed with bubble diameters about 12 nm after 2.2 dpa at 750 K and 80 nm after 6 dpa at 700 K. The response of the bubble structure to post-irradiation annealing has also been established for annealing temperatures between 820 and 900 K. The results show a remarkable stability of the bubbles, even at the highest annealing temperatures (0.97 Tm). The mean bubble diameter changed from 4.6 to 7.6 nm after annealing for 25 h at 900 K while the number density decreased from 6.6 × 1021m-3 to 2.8 × 1021m-3. The bubble growth results are discussed in terms of current models. For in-beam growth, this work shows that up to 520 K, the structure is controlled by nucleation and that the diatomic nucleation model, as proposed by Trinkaus, applies. At higher temperatures, bubble growth is controlling the bubble distribution, but which diffusion mechanism is dominant is not clear. In the case of post-irradiation growth, the results are interpreted in terms of bubble coalescence.