Plastic deformation and hardness in Mg-Zn-(Y,Ho) icosahedral quasicrystals

High-quality icosahedral poly-quasicrystalline samples have been produced f or Mg30Zn60Y10 and Mg30Zn60H10 to alloys by melting and annealing the const ituent elements in a sealed tantalum ampoule. Compression tests with a cons tant crosshead speed and stress-relaxation tests at about 10% compressive s train have been performed at high temperatures. The Vickers hardness has al so been measured at high temperatures for undeformed and compressed samples . The thermal activation analysis of plastic deformation has been successfu lly performed by estimating the dragging stresses at various temperatures f rom the stress dependence of the activation volume; the total activation en thalpy is about 2.5 eV in both alloys. The higher the plastic strain, the l ower is the Vickers hardness at high temperature. This work softening pheno menon is interpreted to be caused by the effects of the deformation-induced phason strain on the dislocation motion. (C) 2000 Elsevier Science B.V. Al l rights reserved.