Direct evidence for plastic deformation of quasicrystals by means of a dislocation mechanism

Abstract

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...

Novel Type of Dislocation in an Al-Pd-Mn Quasicrystal Approximant

“…Despite the lack of translational symmetry in quasicrystals dislocations exist in them [1], and as in crystals moving dislocations carry plastic flow. This has been shown in high temperature deformation experiments for quasicrystals of icosahedral [2] and decagonal [3] structure. The structure of a quasicrystal, quasiperiodic in the physical three-dimensional space, can be described as a periodic structure in a higher dimensional hyperspace, which is a six-dimensional (6D) space in the case of an icosahedral quasicrystal.…”

Elasto-Dynamics of Quasicrystals

“…The existence of phason degrees of freedom leads to the essential difference between crystals and quasicrystals. Wollgarten et al used a dislocation mechanism to study plastic deformation of quasicrystals [45]. A model of the plastic deformation of icosahedral quasicrystals was provided by Feuerbacher et al [46] and refined by Messerschmidt et al [47].…”

The remarkable nature of one-dimensional quasicrystal

“…The physical properties, such as the structural, electronic, magnetic, optical and thermal properties, of QCs have been investigated intensively (Socolar et al, 1986;Ronchetti, 1987;Wollgarten et al, 1993). Elasticity is one of the interesting properties of QCs.…”