Low temperature deformation mechanisms of icosahedral AlPdMn quasicrystals.
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Low temperature deformation mechanisms of icosahedral AlPdMn quasicrystals. Michael Texier, Joël Bonneville, Anne Proult, Jacques Rabier, Ludovic Thilly Université de Poitiers, LMP, UMR-CNRS 6630, SP2MI, BP 30179 F-86962 Futuroscope-Chasseneuil Cedex, FRANCE. ABSTRACT Confining pressure techniques, that superimpose a shear stress on an isostatic component, allowed us to plastically deform AlPdMn specimens at temperatures below the brittle-to-ductile transition temperature obtained using conventional uniaxial deformation tests at usual strainrates. Microstructural observations associated with these low deformation temperatures are reported. They provide new insights on the elementary deformation mechanisms that control plasticity in this non-periodic structure. INTRODUCTION It has been unambiguously established that plastic deformation of AlPdMn quasicrystals, like in periodic structure, results from dislocation movement [1]. However, the microscopic mechanism by which dislocations move in AlPdMn, that is, in a non-periodic structure, is still a subject of debate (for a review see [2]). As recently emphasised in [3], it is not yet clearly established whether dislocations move by pure glide either pure climb or a process that combines both mechanisms. The very high brittle-to-ductile transition temperature (BDTT) of AlPdMn quasicrystals, i.e., higher than 0.7 Tm (Tm is the melting temperature) for strain-rates ranging between 10-4 and 10-6 s-1, suggests that diffusion processes are involved in the plastic deformation of this alloy. It has been proposed that in quasicrystalline structures diffusion may influence plasticity by various manners [4]. Like in usual crystals, diffusion may directly contributes to dislocation climb but, as proposed in [5] for non-periodic structures, diffusion can also enhance dislocation movement by spreading the stacking-fault-like disorder, which is inherently created in the wake of moving dislocations. It is therefore of prime importance to study the low temperature dependence of AlPdMn plastic flow, in particular to establish if plastic deformation can occur in this quasicrystalline alloy without the occurrence of diffusion. Such an investigation can be completed using deformation techniques, which superimpose a shear stress on an isostatic component. These techniques have been proved to be efficient for investigating the mechanical properties of materials at temperatures at which they are usually brittle in conventional deformation tests, such as for instance covalent semiconductors [6], ceramics [7] and to a less extend AlCuFe polyquasicrystals [8]. This paper reports experimental results on the plastic behaviour and related microstructures of AlPdMn poly and single quasicrystals in the temperature range (300K- 750K), which were obtained using two different confining pressure techniques. The post mortem microstructures were examined by transmission electron microscopy (TEM) and particular attention was paid to determine the planes of dislocation movements as well as the involv
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