The observation of mechanical relaxation in a quasicrystalline Al₇₅Cu₁₅V₁₀ alloy

We measured dynamic mechanical properties, such as the storage modulus E′ and loss tangent tan δ, i.e. the internal friction, a quasicrystalline Al₇₅Cu₁₅V₁₀ alloy between 393 and 773 K by a forced oscillation method. A tan δ peak appears distinctly at 439 K in the temperature-dependent measurements for a frequency of 62.8 rad s^-1. The loss peak exhibits frequency dependence which is a feature of relaxation. We have thus confirmed experimentally the existence of the mechanical relaxation system at high temperatures in quasicrystals for the first time. The activation energy for the relaxation obtained from the frequency-dependent measurements is 110 kJ mol^-1. The distribution of the relaxation time is much broader than that of the Debye peak of the single relaxation time. The occurrence of relaxation is ascribed to phasons.