Plasticity of decagonal Al 73 M 10 Co 17 quasicrystals
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Plasticity of decagonal Al73Ni10Co17 quasicrystals Peter Schall1, Michael Feuerbacher, Knut Urban Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany 1 DEAS, Harvard University, Cambridge, MA 02138, U.S.A.
ABSTRACT We present a study of the deformation mechanism of decagonal Al73Ni10Co17 quasicrystals by means of transmission electron microscopy. We performed compression tests on singlequasicrystalline samples in three different orientations: with the compression axis parallel to, inclined by 45 ° and perpendicular to the tenfold axis of the decagonal quasicrystal. The deformed samples reveal characteristic orientation-dependent dislocation structures leading us to the conclusion that fundamentally different deformation mechanisms are involved in plastic deformation in the three deformation geometries. We explicitly identified the Burgers vectors of the dislocations as interatomic vectors in the structure of decagonal Al-Ni-Co.
INTRODUCTION Decagonal phases belong to the class of two-dimensional quasicrystals. Their structure can be described in terms of quasiperiodic planes possessing tenfold rotational symmetry, variants of which are stacked periodically [1]. Hence, these materials possess quasiperiodic as well as periodic lattice directions, making them interesting candidates for plastic deformation studies. The investigation of the plastic properties in different deformation geometries permits influences of both periodicity and quasiperiodicity on the plastic behavior to be studied on a single material. In the Al-Ni-Co and Al-Cu-Co alloy systems, the decagonal phase has been grown in the form of large single quasicrystals [2-4]. In these systems, the deformation behavior of the decagonal phase has been studied previously in macroscopic deformation tests on single quasicrystalline samples [3,5,6]. In macroscopic tests, single crystallinity of the deformation samples is crucial for the interpretation of the deformation behavior, since obviously in polycrystalline samples, only average values over different spatial directions of the decagonal phase would be obtained. Distinct anisotropies have been observed in stress-strain curves as well as in thermodynamic activation parameters. Up until now, not much work has been devoted to the study of the microstructure of deformed samples, which is a key to a reliable interpretation of the observed deformation behavior. Dislocations have been reported to exhibit Burgers vectors parallel to the periodic as well as quasiperiodic directions [7-9]. In our experiments, we recently found a third type of a dislocation in decagonal Al-Ni-Co with a Burgers vector possessing components in both the periodic as well as the quasiperiodic direction [11]. These dislocations, which we termed mixed dislocations, were found to exhibit reactions with the periodic dislocations. In this paper we present results of microstructural studies performed on decagonal Al-Ni-Co single quasicrystals deformed in different orientations. The studies allow us to
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