Plastic deformation of icosahedral Al-Pd-Mn single quasicrystals to large strains I. Experiments

Icosahedral Al-Pd-Mn single quasicrystals, grown by the Czochralski method, were deformed in compression along a twofold direction to large strains. The true stress versus true strain curves showed three stages: the initial work-hardening stage, a large work-softening stage followed by a weak workhardening stage. The minimum flow stress was about half the maximum flow stress. The stress relaxation experiments showed temperature-dependent activation volume versus applied stress relations. Assuming that the flow stress is composed of the effective stress, the temperature-dependent dragging stress and the internal stress, the effective stress dependence of the activation enthalpy was analysed for both the maximum-flow-stress state and the minimum-flow-stress state. The activation enthalpy of the latter state was found to be about 20% smaller than the former state, and the work softening is due to a decrease in the activation enthalpy with increasing plastic strain.