Defects and Diffusion in d-AINiCo-Quasicrystals - Application of Mechanical Spectroscopy

摘要

Mechanical loss (internal friction) measurements were applied to polycrystalline d-AlNiCo quasicrystals for compositions ranging from Al_(72.8)Ni_(7.5)Co_(19.7) to Al_(71.1)Ni_(18)Co_(10.9) and to an Al(71.3)Ni_(13.4)Co_(15.3) mono-quasicrystal The measurements were carried out in the temperature range from 290 K up to 1220 K for measuring frequencies between 0.1 Hz 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.