Grain rotation in nanocrystalline layers under influence of swift heavy ions

Significant changes in texture occur in nanocrystalline Ti, TiN and NiO layers during irradiation with 350 MeV Au ions. The angle between ion beam and layer normal ΘΘ was between 30° and 70°. The major effect is a collective rotation of the nanocrystals. In case of ωω layers the texture rotated by more than 70° at an ion fluence Φt=3×1015Au/cm2. In addition to grain rotation, the layers exhibit a shear motion like that observed previously with amorphous materials. Below about 1×1015Au/cm2 the grain growth is small and grain rotation is reversible, i.e. reversing the sign of ΘΘ and applying the same ΦtΦt, the grains roll back into their original orientation. The second observed effect is the alignment of the grains, whose coalescence eventually leads to a mosaic crystal. However, grain rotation is absent or immeasurably small in micro-crystalline titanium. An attempt to understand the processes in nanocrystalline materials in terms of amorphous grain boundaries, as well as the disclination dipole diffusion along the grain boundary was made.