ANELASTIC AND THERMAL-PROPERTIES OF NANOSTRUCTURED ALUMINUM PREPARED BY MECHANICAL ATTRITION

Elastic energy dissipation coefficient and dynamic elasticity moduli measurements have been performed by a vibrating reed technique on nanocrystalline aluminium prepared by mechanical attrition through ball milling and cold consolidation. Thermal analysis of the aluminium powders was made with differential scanning calorimetry (DSC). A strong dependence of the anelastic parameters and of the DSC spectra on the sample grain sizes was experienced. A maximum in the stored enthalpy occurs at grain sizes of 25-30 nm. An anomalous modulus behaviour in the 400-600 K region depending on grain size with a corresponding small exotherm in the DSC spectra are observed and attributed to structural relaxation in the nanophase. Anelastic relaxation with an activation energy of about 0.8 eV occurs before extensive grain growth set-up.