Underlying mechanisms for unique elastic properties of nanocrystalline Au

Abstract

Abstract In order to get an insight into the grain boundaries (GBs) in nanocrystalline (n-) metal, we prepared the high-density n-Au with ρ / ρ 0 >99% by the gas-deposition method and carried out the vibrating reed measurements, where ρ / ρ 0 is the relative density referring to the bulk density. The strain amplitude dependence (SAMD) of the resonant frequency ( f ) and the internal friction ( Q −1 ) was measured for the strain ( e ) amplitude between 10 −6 and 2×10 −3 and for temperature between 5 and 300 K. No plastic deformations are detected for the present strain range, where f decreases for e up to 10 −4 and then turns to increase, showing saturation for e between 10 −4 and 2×10 −3 . The low temperature irradiation by 2 MeV electrons or 20 MeV protons causes an increase in the Young’s modulus at 6 K, which is surmised to reflect a modification of the anelastic process in the GB regions. In contrast, the SAMD of f is hardly modified by irradiation, suggesting that it is indicative of a collective motion of atoms in n-Au.