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We present a new niche application of quasicrystalline powders that leads to a commercially successful development of polymer-matrix composites. The process is based upon selective laser sintering, which is one of the current most powerful additive manufacturing technologies in use in the mechanical industries. Characteristics of the materials produced, such as porosity, friction and wear against hard steel, are evaluated and compared to the state of the art. Insight into the production of metal-matrix composites, using a variant of the technology, is also given. [ABSTRACT FROM AUTHOR]

The atomic and electronic structures of the (100) and (001) surfaces of the Al5Co2 complex metallic alloy are studied by ab initio calculations. The relative stability of the possible surface planes built from bulk truncation is calculated and the influence of the atomic surface density, the interlayer spacing and the surface chemical composition on the plane selection is discussed. In addition, we show that the simulated images of scanning tunnelling microscopy for each possible termination present a specific signature that appears to be sufficient to experimentally identify the surface plane. [ABSTRACT FROM AUTHOR]

Although the industrial development of complex metallic alloys (CMAs) and quasicrystals (QCs) has remained quite limited so far, these materials exhibit interesting and sometimes unexpected properties in terms of technological applications. A few selected examples of the most promising properties and trends for potential applications are presented. [ABSTRACT FROM AUTHOR]

Twenty-five years after the historic discovery of a real material exhibiting fivefold symmetry, the scientific field opened as a result is still robust and active. On the experimental side, it has been strengthened in recent years by new inputs coming from studies of transport properties, surface physics, coating technology, catalysis, etc. Its future probably relies upon combining these very exotic, but now extremely well documented materials with more conventional materials in composites, or challenging the discovery of new, or more exciting properties in a systematic screening of intermetallics compounds with untried compositions. An effort towards making quasicrystals better understood outside our own community has become mandatory with a view to developing the field. [ABSTRACT FROM AUTHOR]

We report on the formation of a new crystalline approximant phase of the icosahedral (i-)Al-Cu-Fe quasicrystal. This phase is formed during sintering of Al-based composites reinforced with i-AlCuFeB quasicrystalline particles. The structure of this phase has been characterized by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). TEM revealed that it is a B-centred orthorhombic phase with lattice parameters a = 1.166 nm, b = 1.195 nm and c = 3.44 nm. Its chemical composition, as determined by electron energy loss spectroscopy (EELS), is close to Al76.9Cu2.7Fe20.4, with an average number of valence electrons per atom e/a of 1.92, similar to the value in all other approximants of the i-phase discovered thus far. Initial results on local atomic arrangements along one of its pseudo-5-fold axes are also presented. [ABSTRACT FROM AUTHOR]

Al-based composites reinforced by icosahedral (i-) Al59Cu25.5Fe12.5B3 quasicrystalline particles were prepared by solid-state sintering. It was found that Al diffusion from the matrix to the quasicrystalline particles induces phase transformation into the ω-Al7Cu2Fe tetragonal phase. In order to preserve the i phase, we used an oxidation pre-treatment of the particles and studied its influence on the kinetics of the phase transformation (Al + i → ω) as a function of temperature by high energy X-ray diffraction. The oxide layer acts as a barrier, reducing efficiently the diffusion of Al up to a sintering temperature of 823 K, allowing the control of the phases in the composites. The mechanical properties and the friction behaviour of the composites were investigated and show the negative influence of the oxide on the interface strength. [ABSTRACT FROM AUTHOR]

This article attempts to understand better the origin of low friction and zero solid–solid adhesion observed on quasicrystals placed in vacuum. We present an ensemble of experimental data that allows us on the one hand to estimate the true surface energy of unoxidized quasicrystals and approximants and on the other hand to point out a correlation with electronic densities of states. [ABSTRACT FROM AUTHOR]

This paper reports a vacuum or space related effect, which is referred to as “cold welding”, “adhesion” or “sticking”. This effect is studied for bulk quasicrystal (J.M. Dubois, Useful Quasicrystals (World Scientific, Singapore, 2005)) versus different kinds of counterparts (steel, aluminium, titanium, hard metals). Full series of samples, prepared either by crystal-pulling techniques (single crystals) or by sintering (multi-grain samples) were analysed by fretting tests. Four alloy systems were investigated: Al–Pd–Mn, Al–Cr–Fe–B, Al–Cu–B and Al–Cu–Fe–B, with different crystallographic structures and nominal compositions. These materials, especially icosahedral phases, exhibit the absence of cold-welding in vacuum versus certain steels. [ABSTRACT FROM AUTHOR]

Pseudo-binary IQC 100- x DQC x alloys made from mixing Al 62 Cu 25.5 Fe 12.5 icosahedral quasicrystal (IQC) and Al 70 Co 15 Ni 15 decagonal quasicrystal (DQC) together in progressively increased proportions were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDAX). In this way the transition from IQC to DQC was manifested by the evolution of their constituent phases. The formation of these phases was found to follow the evolution of their valence electron concentration per atom ( e/a ) lines in the Al–(Cu,Ni)–(Fe,Co) pseudo-ternary phase diagram. An Al–Cu–Co type decagonal phase was found in the annealed IQC 80 DQC 20 alloy. This phase is characterized by transmission electron microscopy (TEM) and by high-resolution electron microscopy (HREM). The study proved that it is a superstructure of the DQC phase. The possible origin of its formation was discussed according to the variation of its DQC formation e/a -constant line in the Al–(Cu,Ni)–(Fe,Co) alloy system. [ABSTRACT FROM AUTHOR]

We used X-ray emission spectroscopy to investigate the electronic structure of various catalysts obtained by leaching a quasicrystalline Al–Cu–Fe compound in 5% Na 2 CO 3 aqueous solution. The study of Al states confirmed that Al is almost totally oxidized in the catalysts. Fe is not as much oxidized probably because it is embedded in Cu–Al 2 O 3 grains. Cu is only partly oxidized. However, it is not excluded that the catalytic activity could be due to a size effect that prevents the formation of a band as in metallic Cu, and gives to the electronic structure an atomic-like character. New measurements should be done from fresh specimens in order avoid further oxidation interference with the Cu spectral distributions. [ABSTRACT FROM AUTHOR]

We present new results concerning the formation of Al-based composites reinforced by icosahedral i -Al 59 Cu 25.5 Fe 12.5 B 3 quasicrystalline particles. The issue is to limit the diffusion of Al from the matrix to the quasicrystalline particles during sintering in order to overcome the transformation of the i -phase into the ?-Al 7 Cu 2 Fe tetragonal phase. Here we have investigated the influence of an oxidation pre-treatment of the quasicrystalline particles onto the kinetics of this phase transformation by high energy X-ray diffraction. The quasicrystalline particles were annealed either in vacuum or in air, leading to a different thickness of the oxide layer. We show that the oxide barrier efficiently reduces the kinetics of Al diffusion, enabling the formation of composite materials with no phase transformation during the sintering process. The dependence of the tribological properties of these composites is investigated as a function of the volume fraction of i -AlCuFeB particles. [ABSTRACT FROM AUTHOR]

Microstructures and morphological features of a series of sintered quasicrystalline Al62.5-xCu25.3Fe12.2Bx alloys, with x ranging from 0 to 5 at.% were studied using x-ray diffraction, scanning electron microscopy, x-ray mapping, and electron probe microanalysis. Electron backscattering diffraction (EBSD) was also used to get information about the structures of some phases and identify the crystalline relationship in-between phases. Increasing x results in the change of the nature of extra phases. These secondary phases are all less than 1% in volume of the total matter except for the β phase at 5% of boron. Whatever the percentage of boron considered, boron seems to concentrate essentially in the parasite phases confirming doubts found in literature about the solubility of boron inside the face-centered-icosahedral Al-Cu-Fe phase. No special crystallographic relationship in between the tested phases could be spotted. EBSD is thus also confirmed as an excellent technique to get quasicrystalline grains orientations. [ABSTRACT FROM AUTHOR]

Using the Soft X-ray Emission Spectroscopy technique, we have investigated the electronic structure of a series of Al-Cu-Fe compounds in which Al atoms have been substituted by Be atoms. Changes in the shape of Al 3s,d spectral curves are clearly visible in the energy region extending over 2 eV below the Fermi level. Calculation of the moments of orders 1 and 2 of the partial electronic distributions show that there is a slight decrease of the contribution of Fe 3d states to the total energy of the system and that there are changes in Fe hybridisation that tend to enhance the localised character of the Al states in the vicinity of the Fermi level. Yet, the shape of the pseudo-gap does not change. [ABSTRACT FROM AUTHOR]

Microstructure modifications induced by sliding a WC-Co indenter in scratch tests on the surface of a single-phase Al-Cu-Fe icosahedral quasicrystal (IQC) was studied by scanning electron microscopy and transmission electron microscopy. The scratch track was shown to consist of many smaller tracks. Dislocations were discovered to emerge from the edges of the smaller scratch tracks. Along a small track where the shear stress is concentrated, a phase transition from an IQC to a bcc phase with lattice parameter a = 0.29 nm was found to occur. A modulated quasicrystal state as well as a deformation twin of IQC were determined in the region beneath the scratch. [ABSTRACT FROM AUTHOR]

Brillouin-zone widths are deduced from fivefold electron diffraction patterns for a quasicrystalline sample of Al59Cu25.5Fe12.5B3. Optical measurements in the infrared were also performed on the same alloy. The results were analysed by the Kramers-Kro nig method in order to obtain the absorption coefficient as a function of the energy. The optical study allows the observation of critical energies that are directly correlated to singularities in the density of states at the edge of Brillouin zones. Recurrent pseudogaps in the density of states are discussed in terms of the hierarchical nature of Brillouin zones, in agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

By investigating the magnetism of spins on a quasiperiodic lattice, we present an experimental study of static and dynamic magnetic properties, specific heat, and magnetic entropy of the Gd3Au13Sn4 quasicrystalline approximant. The magnetic sublattice of Gd3Au13Sn4 is a periodic arrangement of nonoverlapping spin clusters of almost perfect icosahedral symmetry, where gadolinium localized f magnetic moments are distributed on equilateral triangles. The absence of disorder on the magnetic sublattice and the antiferromagnetic (AFM) interactions between the nearest-neighbor spins distributed on triangles result in geometrical frustration of spin-spin interactions. Thus, the Gd3Au13Sn4 phase can be viewed as a prototype site-ordered, geometrically frustrated spin system on icosahedral clusters. The zero-field-cooled and field-cooled magnetic susceptibilities, the alternating current susceptibility, the thermoremanent magnetization, the memory effect, the magnetic specific heat, and the magnetic entropy all show that the spin system undergoes at low temperatures a transition to a nonergodic state at the spin freezing temperature Tf ≈ 2.8 K. Below this, the ergodicity is broken on the experimental timescale, because the thermally activated correlation times for the spin reorientations become macroscopically long. The magnetic state achieved at low temperatures by continuous cooling in low magnetic fields is likely a superposition of (1) metastable states with randomly frozen spins that have no long- range order yet undergo gradual spin-freezing dynamics and (2) an AFM-like magnetically ordered state with critical slowing dynamics. The magnetic properties of the site-ordered, geometrically frustrated Gd3Au13Sn4 system are discussed in comparison to site-disordered spin glasses that contain both randomness and frustration. [ABSTRACT FROM AUTHOR]

By applying the alloy design concept that stable intermetallic phases between two immiscible elements can be formed by adding a third element that forms stable compounds with both elements, we have synthesized the first known stable intermetallic compound of Cu, Gd, and Ca, where copper acts as the mediating element between the immiscible Gd and Ca. A compound with the composition Cu84Gd9Ca7 (equivalent to Cu5Gd0.54Ca0.42) was synthesized by the Czochralski technique in the form of a large single crystal of high structural perfection, and the structural model was determined by x-ray diffraction (XRD). The compound crystallizes in the hexagonal system, space group P6/mmm, and the crystal structure is isotypic to the Cu5.44Tb0.78. The unit cell contains inherent disorder due to partial occupation of the Cu3 site and the substitutional disorder at the Gd/Ca mixed site located at the vertices of the hexagonal unit cell, where Gd and Ca randomly substitute each other. The random substitution of magnetic Gd by nonmagnetic Ca atoms makes the magnetic Gd lattice disordered, which leads to interesting magnetic ordering at low temperatures that occurs below TC=24K in zero and low external magnetic fields. By performing a large set of complementary experiments along two perpendicular crystallographic directions (the [001] hexagonal-axis direction and the [100] hexagonal-plane direction), we show that the zero-field collective magnetic state can be described as a random-anisotropy ferromagnetic state, where random magnetic anisotropies originate from the magnetic dipole interactions between the Gd moments in the magnetically disordered lattice. The random-anisotropy ferromagnetic state in the Cu84Gd9Ca7 is characterized by randomness and frustration of magnetic interactions, which are the two ingredients that allow classifying this state into the generic class of spin glasses. Our paper opens the possibility to search for new ternary intermetallic phases in the Cu-Gd-Ca phase diagram, including structurally complex phases and quasicrystals. [ABSTRACT FROM AUTHOR]