The deformation behaviour of grain boundary regions polycrystalline aluminium

The deformation pattern at grain boundaries and at triple junctions in polycrystalline high purity aluminium (99.999%) has been studied by electron back scattering pattern (EBSP) observations. Specimens of two different grain sizes rolled to give 5% and 30% reductions have been examined by these different EBSP scans: (i) scans across grain boundaries, (ii) scans along grain boundaries and (iii) two-dimensional scans near triple junctions. These scans are carried out in small steps (1-5 mu m) over long distances (up to 50 mu m). The EBSP measurements show that the level of perturbations increases with strain and that enhanced zones of perturbations are observed at grain boundaries and especially near triple junctions. In specimens deformed by 30%, such zones of large perturbation are observed at most of the grain boundaries, and in the specimens deformed by 5%, at some triple junctions. The EBSP measurements are compared to previous microstructural observations by transmission electron microscopy and the effect of the zones of enhanced perturbations is discussed with relation to the mechanical and thermal behaviour at highly deformed polycrystalline metals.