Metadislocations: The case of pure glide
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\ Metadislocations: The case of pure glide Marc Heggen and Michael Feuerbacher Forschungszentrum Jülich GmbH, 52425 Jülich, Germany ABSTRACT Metadislocations are highly complex and pivotal defects mediating plastic deformation in complex metallic alloys. Here, we review recent results on the structure of metadislocations in the phases T-Al-Mn-Pd, T-Al-Mn-Fe and o-Al13Co4. In these materials, metadislocation motion is of particular interest as it takes place by pure glide in contrast to most other complex metallic alloys. Recently, novel metadislocations were found in the T-phase [1]. They have Burgers r −n vectors b = ±τ c(0 0 1) (n = 2, 3, 4) and are associated to two, four and six planar defects, respectively. The type of planar defect depends on the deformation geometry. Metadislocation glide creates (1 0 0) stacking faults and climb creates (0 0 1) phason planes. Metadislocation glide was observed in the o-Al13Co4 phase, as well [2]. The close structural relation of metadislocations in the phases T-Al-Mn-Pd, T-Al-Mn-Fe, Al13Co4 and ε6-Al-Pd-Mn is discussed. INTRODUCTION Metadislocations were first observed in the complex metallic alloy (CMA) phase ε6-Al-Pd-Mn [3], later in other ε-type phases in the systems Al-Pd-Mn [4] and Al-Pd-Fe [5] and also in other non ε-type phases like Al13Co4 [7] and T-Al-Mn-Pd and T-Al-Mn-Fe [1,8]. Metadislocations in the phases T-Al-Mn-Pd and T-Al-Mn-Fe are very special as they consist of a complex core and separated but inevitable phason defects which are referred to as escort defects. Upon deformation, the escort defects move ahead and locally transform the T-phase structure for accommodation of the metadislocation core. Metadislocation core and escort defects leave a slab of R-phase in their wake as they move. This mechanism of plastic deformation of a complex material is of special importance, as it provides one of few examples of metadislocation motion in terms of pure glide. Glide is the most common process of dislocation motion in simple materials, but in most complex phases investigated so far metadislocation motion takes place by pure climb. Climb is a non-conservative mode of motion which involves atomic transport. Metadislocation glide is thus a very special phenomenon as it bridges the gap between the mechanisms of plastic deformation in simple and complex alloys. In the present paper metadislocation motion in the phases T-Al-Mn-Pd and T-Al-Mn-Fe is reviewed. Furthermore we will discuss metadislocation motion in the phase Al13Co4, another example where metadislocations move by pure glide. EXPERIMENT The present experiments were carried out using single crystalline samples of composition Al 75 at.% Mn 21 at.% Pd 4 at.%, Al 72 at.% Mn 22 at.% Fe 6 at.%, and Al 77 at.% Co 23 at.%. Single crystalline samples were uniaxially deformed in compression with a modified Zwick Z 050 testing machine at elevated temperature [1,6,7,8]. Bragg-contrast and conventional highresolution TEM was performed in an FEI Tecnai G2 F20. Atomic-resolution STEM was
performed in a probe-corrected FEI
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