Structural and diffusion studies were made of high-purity nano-crystalline material which had been prepared by cluster compaction to full density, or by severe plastic deformation. The size distribution of atomic free volumes in the interfaces, as studied by means of positron lifetime spectroscopy, varied as a function of the preparation technique. In pure high-density nano-crystalline metal, the crystallites grew rapidly upon annealing; with an activation enthalpy of 1.1eV for material that had been prepared by severe plastic deformation. Rapid atomic diffusivity in the interfaces was studied by using sputter sectioning and Rutherford back-scattering. Diffusion occurred at the interfaces, which migrated during diffusion annealing due to rapid crystallite growth. The diffusivities (table 14) were similar to those in conventional grain boundaries.

Structure and Diffusional Properties of Nano-Crystalline Pd R.Würschum, K.Reimann, S.Grub, A.Kübler, P.Scharwaechter, W.Frank, O.Kruse, H.D.Carstanjen, H.E.Schaefer: Philosophical Magazine B, 1997, 76[4], 407-17

Table 14

Diffusivity in Nano-Crystalline Pd