Papers by Keyword: Quasicrystal

Abstract: The composite studied here consisted of a geopolymer matrix reinforced with quasicrystal powders. Quasicrystals are complex metal alloys with atypical structures. Due to their physical, mechanical and surface properties, quasicrystals have been widely studied. Nowadays quasicrystalline powders are proposed to be incorporated in ductile matrices. The geopolymers are inorganic polymers with excellent thermal performance and interesting adhesive properties. The quasicrystalline alloys were prepared by induction melting the constituents under argon atmosphere in a water-cooled copper crucible. In this work the adhesion of composites with 5, 10 and 15% of quasicrystal powder in aluminum joints was investigated. In addition, the influence of the curing time was taken in to account and tests were performed in samples with 7 and 28 days of cure. The results indicate an improvement in adherence with the inclusion of quasicrystal. The best adherence was obtained when the curing time was 28 days.

Abstract: A brief review is presented of quasicrystal surfaces and their use as templates for exotic epitaxial structures. The review is illustrated with several examples from the work of the Liverpool quasicrystal group.

Abstract: The Packing Features of Mackay and Pseudo Mackay Clusters in Al Based Approximants to Icosahedral Phases Are Surveyed. The Cubic Approximants of α-AlMnSi, AlReSi, and α-(Al,Si)CuFe Indicate Typical Mackay Clusters Composed by the Dense Icosahedral Shell Packing. On the other Hand, the Cubic Approximants of α-Alcuru and α-(Al,Si)CuFe and the Non-Cubic Approximants of Ir₉Al₂₈, χ-AlPdRe, and R-AlPdCo Shows so-Called Pseudo Mackay Clusters in which the Icosahedral Packing Feature Is Disappeared at their First Shells. The Distorted First Shells Represent a Variation of Pseudo Mackay Clusters, which Could Be Classified into Three Subgroups Based on the Symmetry.

Abstract: Microstructure of rapidly solidified Al₉₁Mn₇Fe₂ (at.%) alloy was investigated using SEM and TEM techniques. Quasicrystalline particles of different shapes and sizes embedded in the aluminium matrix were observed. Quasilattice constant was calculated as 0.461 Å. Additionally orientation relationships between matrix and quasicrystals particles were found based on electron diffraction patterns and high resolution images, such that: five-fold axis lie along [011] or [001] axes of the α-Al crystallographic direction.

Abstract: Composite based on Al–Cu–Co alloy obtained by directional solidification, were characterized. The quasicrystalline decagonal D phase of Al₆₄Cu₂₀Co₁₆ was the reinforcement and the singlecrystalline tetragonal T phase of Al₇₂Cu₂₇Co₁ was the matrix of the composite. The phases were identified by powder X-ray diffraction (XRD). The composite was analysed by light optical microscope and electron microscopes. The SEM and TEM techniques were used. Additionally the Laue method was used. The results of the study showed that the reinforcement has a form of parallel fibres of 20-40 μm diameter. Quasicrystal structure of fibres contained the phason strain. The quasicrystalline phase in the form of decagonal columns was also present inside composite pores.

Abstract: Microstructure of terminal area of Al₆₅Cu_32.9Co_2.1 ingots (numbers indicate at.%), obtained via directional solidification was studied. Scanning Electron Microscopy, Transmission Electron Microscopy and X-ray powder diffraction were applied. Point microanalysis by Scanning Electron Microscope was used for examination of chemical compositions of alloy phases. It was found that tetragonal θ phase of Al₂Cu stoichiometric formula was the dominate phase (matrix). Additionally the alloy contained orthogonal set of nanofibres of Al₇Cu₂Co T phase with the average diameter of 50-500 nm and oval areas of hexagonal Al₃(Cu,Co)₂ H-phase, surrounded by monoclinic AlCu η₁ phase rim. Inside some areas of H-phase cores of decagonal quasicrystalline D phase were observed.

Abstract: The as-cast and semi-solid microstructures of quasicrystal reinforced AZ91 alloys were investigated. The results show that the main phases of as-cast AZ91ZY1 and AZ91ZY2 alloys are all α-Mg, I-phase, Mg17Al12 and Al2Y phase. The grain boundary phases contents increase with increasing Y and Zn contents. The better semi-solid processing technological parameters of AZ91ZY1 and AZ91ZY2 alloys are 580 °C, 30 min and 560 °C, 30 min respectively. The better semi-solid processing temperature of AZ91ZY2 alloy is lower than the one of AZ91ZY1 alloy is mainly attributed to the higher contents of the grain boundary phases in the AZ91ZY2 alloy.

Abstract: The discovery of the icosahedral quasicrystalline phase (i-phase) in as-cast Ti_40.83Zr_40.83-xSc_xNi_18.34 (x = 0~2.0) alloys is described herein. The effect of Sc on the structure and mechanical properties of the bulk quasicrystalline alloys is investigated. The results show that the phase structure of the as-cast alloys are mainly composed of icosahedral phase accompanied by minor C14 Laves phase (L-phase), and the mechanical properties of the bulk quasicrystalline alloys have been examined at room temperature, the compressive fracture strength first increased and then decreased with increasing x from 0.4 to 2.0, and the highest strength is near 1400 MPa when x =1.2, it was 380 MPa higher than the without Sc alloy. The bulk quasicrystalline alloy exhibits the elastic deformation by the compressive test, and the fracture mode was brittle cleavage fracture.

Abstract: The microstructures and mechanical properties of quasicrystal reinforced Mg-Al-Zn-Y alloys with different Y and Zn contents were investigated. The results show that I-phases and Mg₁₇Al₁₂ phases form in all alloys. When Y content exceeds 1.0 at.%, the blocky Al2Y particles form, and it is disadvantageous to improve tensile strength and elongation rate. The tensile failure modes of Mg-Al-Zn-Y alloys are quasi-cleavage fracture. The tensile strength and elongation rate increase firstly and then decrease with increasing Y and Zn contents. When Y content reaches 1.0 at.%, the tensile strength and elongation rate achieve the highest values.

Abstract: We first discuss several aspects of group theory for reformulating the group-subgroup re-lations in quasicrystals to crystals transformations based on the original approach proposed by D.Mermin and his group on indiscernability groups. In the second part of the paper, we discuss ways ofdetermining the possible space-groups of approximants of quasicrystals as generated by the perpen-dicular shear technique.