THE TEMPERATURE AND STRAIN-RATE DEPENDENCE OF THE FLOW-STRESS OF ICOSAHEDRAL ALPDMN SINGLE-QUASI-CRYSTALS

To study the deformation characteristics of icosahedral Al70.4Pd20.8Mn 8.8 single-quasicrystals flow-stress measurements by compression tests have been performed in the temperature rang 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 Delta H calculated from these data are: (i) considerably smaller than the dat a known until now from the literature and (ii) exhibit a step at about 1050 K indicating different mechanisms for dislocation motion in AlPd Mn with Delta H congruent to 3.7 eV below and Delta H congruent to 5.5 eV above 1050 K. In both regimes Delta H increases proportional to T suggesting different pre-exponential factors if an Arrhenius behaviour is assumed for the strain rate. From the slopes of the Delta H-T curv es values for Delta S can be deduced which amount to 13k below and 27k above 1055 K. The results are interpreted on the basis of present mod els of dislocation motion in quasicrystals. (C) 1997 Elsevier Science S.A.