Helium trapping and surface deformation of helium-ion-implanted aluminium

Helium ions accelerated to 20 keV were implanted into Al samples at room temperature. The formation of blisters and flakes at the surface was observed as a function of He + irradiation fluence by scanning electron microscopy and the number of He trapped in the Al was also determined. To examine the influence of microstructure studies were carried out for 400°C, 2 h (well-annealed) samples, 300°C, 0.5 h (moderately-annealed) samples, and compared to previous results for as-received (cold-rolled) Al. The number of trapped He varies in a saw-toothed form with He ion fluence for the samples with flakes and the surface deformation is predominantly by flaking for the well-annealed samples. The moderately-annealed samples undergo blistering and flaking. Results are discussed from the viewpoint of a correlation between the predominant surface deformation mode and the near-surface microstructural condition.