Surface stresses and the hardness of ion implanted aluminium

The stresses resulting from the implantation of nitrogen into aluminium were measured using a strain gauge technique. The strains resulting from 400 keV and 200 keV N+ implantation were measured at doses of between 5 x 1015 and 2 x 1017 ions cm-2 and the corresponding stresses were calculated. The stresses were observed to increase linearly with dose up to about 4 x 1016 ions cm-2 above which they relieved. No corresponding drop in hardness was observed. The relief of stress at high doses is considered to result from plastic yielding of the implanted materials and not blistering or bubble formation as reported by other research workers. For the 400 keV N+ implant there was a gradual increase in stress after the stress relief, suggesting the operation of work hardening mechanisms. (author)