It was recalled that in nanocrystalline materials, unlike conventional polycrystals, the volume fraction of matter in the core region of the grain boundaries tended to approach the share of matter in the interior of the nm-sized grains since it scaled as 1/L. The discovery of room-temperature grain growth in nanocrystalline Pd made it possible to monitor the coarsening of the microstructure and to measure simultaneously, or even in situ, the concomitant evolution of the properties. From the resulting scaling behavior of properties interface elastic moduli were deduced using ultrasonic techniques. In particular, a 30% shear-softening of grain boundaries was found and its relationship to the shear softening observed in bulk metallic glasses was considered.

Shear Softening of Grain Boundaries in Nanocrystalline Pd. M.Grewer, J.Markmann, R.Karos, W.Arnold, R.Birringer: Acta Materialia, 2011, 59[4], 1523-9