Defects and Diffusion in d-AlNiCo-Quasicrystals - Application of Mechanical Spectroscopy
Mechanical loss (internal friction) measurements were applied to polycrystalline d- AlNiCo quasicrystals for compositions ranging from Al72.8Ni7.5Co19.7 to Al71.1Ni18Co10.9 and to an Al71.3Ni13.4Co15.3 mono-quasicrystal The measurements were carried out in the temperature range from 290 K up to 1220 K for measuring frequencies between 0.1Hz and 10 kHz. A loss maximum of Debye type is observed at ≈ 700 K (2Hz) for both the I-phase and the bCo-phase, which is attributed to local rearrangement of point defects. The activation enthalpy of the peak of H = 1.9 - 2.4 eV is in the range of values obtained from tracer diffusion experiments. This indicates that local defect rearrangement and self diffusion are governed by the same atomic diffusion process.. A high temperature viscoelastic damping background is only observed in polycrystalline samples with H = 2.4 – 3 eV. The background is assigned to viscolealastic relaxation based on intergranular diffusion.
M. Danielewski, R. Filipek, R. Kozubski, W. Kucza, P. Zieba, Z. Zurek
M. Weller et al., "Defects and Diffusion in d-AlNiCo-Quasicrystals - Application of Mechanical Spectroscopy", Defect and Diffusion Forum, Vols. 237-240, pp. 322-327, 2005