Deformation by grain rotations in nanocrystalline fcc-metals

Creep deformation at room temperature in high-density nanocrystalline ( n-) Au and n-Cu proceeds by localized grain boundary sliding (LGBS) but not by diffusion creep such as the Coble or Ashby creep. In order to clarify the underlying mechanism of the creep deformation, changes in the surface morphology and the crystallographic texture of n-Au and n-Cu have been investigated and discussed together with the anelastic data reported previously. The reason why a diffusion creep process does not work in n-Au and n-Cu is that there is no local concentration of internal stress; the concentration of internal stress is suppressed by the internal stress relaxation due to the grain boundary anelastic process activated above 200 K. The surface morphology and the crystallographic texture observed after creep deformation indicate that rotational motions of crystallites take place along the LGBS during creep deformation. The present work demonstrates that the characteristic creep deformation process is commonly observed in n-fcc-metals.