COMPUTER-SIMULATIONS AND TRANSMISSION ELECTRON-MICROSCOPY INVESTIGATIONS OF NITROGEN IMPLANTED INTO ALUMINUM AT HIGH-TEMPERATURE

The study of nitrogen diffusion in metals has mostly been investigated from a post-implantation point of view. Several authors have studied the behaviour of nitrogen ions during annealing treatment which followed the implantation procedure. In the case of aluminium in particular, no significant changes were seen in the nitrogen distributions. Nevertheless we have recently shown that when nitrogen is implanted into aluminium at temperatures equal to or above 300-degrees-C, some of the ions diffuse to the surface. This process is followed by trapping phenomena at a depth of 1 x 10(17) atoms cm-2, leading to the formation of a nitrogen sub-surface peak. The aim of this study was to discover the mechanisms responsible for the migration and trapping of ions under the surface. The different mechanisms involved in the implantation process were simulated with the help of the IMPL computer program. This allows the calculation of ion beam mixing, sputtering, phase precipitation and dissolution, matrix compositional changes, thermal diffusion, etc. Our paper shows that an enhancement in the concentration of the precipitation sites at the surface can induce a nitrogen migration. Assuming this we have successfully reproduced the experimental data. The nature of these sites was investigated through plan view and cross-sectional transmission electron microscopy.