The temperature and strain-rate dependence of the flow stress of icosahedral AlPdMn single-quasicrystals

To study the deformation characteristics of icosahedral Al70.4Pd20.8Mn8.8 single-quasicrystals flow-stress measurements by compression tests have been performed in the temperature range 990–1105 K. Each test was combined with a stress relaxation experiment to determine the strain-rate sensitivity of the flow stress. The activation enthalpies ΔH calculated from these data are: (i) considerably smaller than the data known until now from the literature and (ii) exhibit a step at about 1050 K indicating different mechanisms for dislocation motion in AlPdMn with ΔH ≅ 3.7 eV below and ΔH ≅ 5.5 eV above 1050 K. In both regimes ΔH increases proportional to T suggesting different pre-exponential factors if an Arrhenius behaviour is assumed for the strain rate. From the slopes of the ΔH-T curves values for ΔS can be deduced which amount to 13k below and 27k above 1055 K. The results are interpreted on the basis of present models of dislocation motion in quasicrystals.