Work

Helium nano-bubbles in copper thin films slows down creep under ion irradiation

Year: 2025

Type: article

Abstract: Neutron irradiation of structural materials in nuclear applications is accompanied by a variety of microstructural changes including generation of helium nano-voids at high doses. When operating under stress, irradiation creep is taking place, leading to change of dimensions of components, relaxation of springs or screw torques. These distortions may have important implications on the performance of the nuclear reactor. Irradiation creep is particularly complicated to investigate and the link between creep rate and microstructure remains partly elusive. Ultra-miniaturized testing of thin films allows using ion irradiation and implantation methods to emulate the effect of in-reactor neutron irradiation. Here, on-chip tests on freestanding copper films reveal much slower irradiation creep of helium implanted copper layers compared with non-implanted copper, with or without ion irradiation hardening prior testing. This effect is due to the presence of the high density of helium bubbles, as evidenced by transmission electron microscopy, that impede dislocation glide and climb, thus limiting irradiation creep. A unified elementary model for moderate to high stress creep under irradiation is proposed showing that the creep law for this range of stress primarily depends on the yield strength which is increased by the presence of helium bubbles.

Source: Acta Materialia

DOI: 10.1016/j.actamat.2025.120854

Authors: Nargisse Khiara, Michaël Coulombier, Jean-Pierre Raskin, Yves Bréchet, Thomas Pardoen, Fabien Onimus