Plastic behaviour of icosahedral Al–Cu–Fe quasicrystals: experiment and modelling

Abstract

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) 2815].