Defects Induced by Helium Ion Irradiation in Aluminum Alloys

Ion irradiation experiments were carried out on pure Al and on a solid solution of Al-wt.4%Cu in order to study the influence of composition on the irradiation effects. The experiments were carried out with a 20 keV He ions at room temperature up to a maximum fluence of about 1.5 x 1017ions.cm-2. The changes in the microstructure were analyzed by transmission electron microscopy (TEM) and the evolution of the irradiated surface was studied combining scanning electron microscopy (SEM) and atomic force microscopy (AFM). In pure Al, homogeneous blistering was observed and small He bubbles with diameters in the range of 1 to 2 nm were formed in the bulk, close to the irradiated surface. In Al-Cu no He bubbles were observed following irradiation. However, after subsequent annealing at 250°C, a homogeneous distribution of He bubbles was observed in the bulk, together with larger bubbles located on the interfaces between the matrix and equilibrium θ phase (Al2Cu) precipitates.