In-situ TEM observation of nanobubbles evolution in helium-irradiated aluminium upon tensile stressing

Abstract Polished high-purity aluminium was irradiated by 500 keV helium ions to a fluence of 3 × 1016 ions/cm2 at 450 °C. Then a micro-tensile sample was prepared by focused ion beam. The evolution of nanobubbles in irradiated aluminium upon stressing was investigated by employing in-situ tensile testing in a transmission electron microscope. In the case of helium-ions irradiation, dense bubbles with similar sizes are formed in a certain depth region from the irradiated surface. Upon tensile stressing, it was found that bubbles disappeared in the crack tip, and bubble coalescence occurred along the crack-propagation direction, which both contributed to the decrease of bubble number, whereas bubble sizes as well as bubble number showed almost no changes in the region far away the crack tip. This was caused by the non-uniform stresses in the stress fields, in which bubble migration occurred under the stress gradients while bubble evolution was hardly caused in a much low stressed region. Moreover, bubble sizes increased on the grain boundary and bubbles close to the grain boundary gradually disappeared upon stressing. This can be explained by the migration of helium bubbles toward the grain boundary under the stress gradients near the grain boundary.