Zr65Cu17.5Ni10Al7.5 as well as Zr69.5Cu12Ni11Al7.5 belong to the best glass forming alloys known. Glass transition temperatures of melt-spun ribbons are 372 and 360 °C, respectively. TEM and x-ray analysis of samples annealed above the glass transition temperature exhibit the formation of quasicrystalline microstructures with small amounts of crystalline phases. The metastable icosahedral phase is primitive with a quasilattice constant a=0.253 nm; its composition as determined by EDX is close to Zr69.5Cu12Ni11Al7.5. In both glasses, growth of the quasicrystals has been observed to be time-dependent (r∝t1/2), thus indicating a diffusion controlled transformation.

Single quasicrystals of Al?oPd2iMn9 were plastically deformed by 25% under compression at 750°C. Both these samples as well as control samples of as-grown and heat-treated material were investigated by transmission electron microscopy. It was found that upon deformation the dislocation density increases by about 2 orders of magnitude. This provides the first direct evidence for quasicrystal deformation by a dislocation mechanism. The dislocations were found to have twofold and fivefold Burgers vector directions in physical space.PACS numbers: 61.44.+p, 6L66.Dk, 61.72.Bb, 62.20.Fe In a number of ternary aluminum-transition metal alloy systems thermodynamically stable quasicrystalline phases occur which can be produced with high structural perfection [l]. Of these alloys Al-Pd-Mn is particularly attractive. It contains an icosahedral phase of F-type lattice structure, of which single quasicrystals can be grown by the Czochralski technique [2,3]. After the first observation of lattice defects in the form of dislocations in decagonal AI65CU20C015 and icosahedral Al65Cu2oFei5, similar observations were reported for other stable quasicrystalline phases [4][5][6][7][8][9]. These observations raised the question of the origin of the dislocations, in particular, whether they can be induced by plastic deformation. Indeed hardness and compression tests demonstrated a relatively high ductility which increases with temperature [10][11][12][13][14][15]. With the exception of a hardness test at room temperature [10], these studies were all carried out in polyquasicrystalline material. We are reporting here on the first high-temperature single quasicrystal deformation experiments. Transmission electron microscopy of deformed and undeformed single quasicrystals of Al7 0 Pd2r Mn9 indicates an increase in dislocation density by about 2 orders of magnitude after plastic deformation, providing the first direct evidence for quasicrystal deformation by a dislocation mechanism.A master alloy of composition Al7 0 Pd2iMn9 was prepared in an induction furnace under an Ar atmosphere. Employing the Czochralski technique the resulting ingot was used to grow a single quasicrystal 7 cm in length and 1 cm in diameter of [0/0,0/0,0/2] orientation (notation of Cahn, Schechtman, and Gratias [16]). Small columns of 3x3x7 mm 3 were cut from this with their long axis parallel to [0/0,0/0,0/2]. Deformation under compression along this axis was performed at 750 °C in an INSTRON 1122 machine in air at a deformation velocity of 0.05 mm/min. A second sample was placed on the lower piston of the machine in order to serve as a reference. Because of a reduced length it was not deformed but went through the same temperature program as the deformation sample. In the following this sample is referred to as the heat-treated sample. After a deformation of 25% the load was released and the samples were quenched in water. Specimens for investigation in the transmission electron microscope (TEM) were prepared from the deformed and the heat-treated samples was well...

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Transmission electron microscopy (TEM) has been used to study the twin structures of monoclinic Al13Fe4 phase annealed at high temperature as well as in the as‐cast state. The main selected‐area electron‐diffraction (SAED) patterns, which might imply an orthorhombic symmetry, have been explained to be from repeated (001) microtwins of monoclinic Al13Fe4. The relationship between these microtwins and the high‐temperature orthorhombic Al13Fe4 phase (Ellner 1995) is discussed. In addition, structural models for (100)—(201) fivefold twins are proposed which are somewhat different from the previous one. Zwillinge wurden in monoklinem Al13Fe4 sowohl in abgegossenen als auch in bei hohen Temperaturen geglühten Proben elektronenmikroskopisch analysiert. Die Elektronenbeugungsbilder, die eine orthorhombische Symmetrie vortäuschen, werden mit einer wiederholten (001) Mikroverzwillingung von monoklinem Al13Fe4 erklärt. Die Beziehung zwischen diesen Mikrozwillingen und der von Ellner (1995) beschriebenen orthorhombischen Hochtemperaturphase wird diskutiert. Zusätzlich werden Strukturmodelle für eine weitere fünfzählige (100)—(201) Verzwillingung vorgeschlagen.

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