Plastic behaviour of icosahedral Al-Cu-Fe quasicrystals: Experiment and modelling

Constant strain-rate and creep tests have been performed on poly-quasicrystalline specimens of the icosahedral Al-Cu-Fe system. Three temperatures (870, 960 and 1000 K) have been investigated by creep for samples predeformed at constant strain-rate before and beyond the upper yield stress, over the stress range 30-320 MPa. The influence of the creep stress level and plastic strain amount on the stress-strain curve has also been studied when the samples are deformed again at constant strain rate. Depending on temperature, stress and initial predeformation states, single or two-stage creep curves have been observed. When performed before the upper yield stress, in the high work-hardening portion of the stress-strain curve, only a primary stage of continuous decreasing creep rate is observed. At higher stresses, close to the upper yield stress, the primary stage is followed by a second stage of work-softening leading to an increasing strain-rate. The shape of the constant strain-rate and creep curves, as well as the transients observed when creep is switched-back to constant strain-rate conditions, are in fair agreement with the predictions of the dislocation model recently proposed by Guyot and Canova on the basis of an irreversible strain dependent friction stress [P. Guyol, G. Canova, Phil. Mag. A 79 (1999) 28151]. (C) 2001 Elsevier Science B.V. All rights reserved.