Plasticity of quasicrystals and of bulk metallic glasses: An analogy

Despite their antinomic atomic structures, long range ordered but non-periodically for quasicrystals (QC), or disordered for met-glasses (MG), both materials share surprisingly a similar mechanical behaviour: brittleness at low temperature, plasticity at high temperature. Such a-priori surprising results are considered and analysed, focussing on the high temperature ductility. the aperiodic order of the QC atomic structure, the dislocation motion creates a topological and chemical disorder from which a friction stress results. Combining the friction stress–strain reduction with classical dynamic properties of dislocations allows to establish a constitutive equation of the deformation, which reproduces the essential characteristics of the experimental stress–strain and creep curves [7]. In MG, the diffusion of the free volume flow defects [9] is at the origin of the high temperature plastic strain. Their flow equation, where time and strain variations of the flow carriers density are introduced, leads to a satisfactory description of experimental observations: scaling of the glass viscosity with strain-rate and temperature, transient regimes occurring during specimen loading/unloading or strain-rate changes. features underlying the constitutive equation of the high temperature deformation of both materials are emphasized and discussed.