Activation parameters of plastic flow in icosahedral Al-Cu-Fe

Poly-quasicrystalline samples of an icosahedral Al-Cu-Fe alloy have been de formed in compression tests under constant-strain-rate conditions at temper atures ranging from room temperature up to 1020 K (m approximate to 1150 K, where T-m is the melting temperature). The activation volumes, which were measured by performing load relaxation experiments, were found to be small and reveal that two different thermally activated mechanisms belonging to t wo different temperature regimes, are responsible for plastic flow of icosa hedral Al-Cu-Fe; the first mechanisms operates between 770 and 960 K, and t he second at higher temperatures. The activation enthalpy Delta H has been determined for the low-temperature regime. Under the assumption that the en tropy term arises mainly from the variation in the shear modulus with tempe rature, the activation Gibbs free energy Delta G has been deduced for the c orresponding rate-controlling mechanism.