Single Quasicrystalline Research Articles

A wear-resistant Al85Cu6Fe3Cr6 spray-formed quasicrystalline composite

An Al-based quasicrystalline composite has been processed by spray-forming resulting in a microstructure containing α-Al and a decagonal quasicrystalline phases as the major constituents. Microstructural characterization was performed by scanning and transmission electron microscopy, including detailed analyses of single quasicrystalline particles. In addition, the unlubricated sliding wear behavior of the composite was studied by pin-on-disk tests using several testing parameters, with normal loads ranging from 5 to 20 N and sliding wear velocities ranging from 0.05 to 0.2 m/s. For comparison basis, an Al-Si A380 commercial alloy was tested under the same wear parameters. The quasicrystalline composite showed a significantly higher wear resistance when tested with normal loads in the range of 5 to 10 N, with wear rates ranging from 4 to 6 × 10−4 mm3/N.m against 1 to 2 × 10−3 mm3/N.m for the Al-Si alloy. When tested under higher normal loads, 20 N, both materials presented similar values of wear rates. For lower normal loads, the worn surfaces of the composite and the Al-Si alloy showed that delamination wear was the main mechanism of material removal. However, with load increase, a higher fraction of hard intermetallic particles, previously removed by delamination, introduced a strong abrasive component into the wear track, which led to higher wear rates.

2Investigation of Al26.5Cu25Fe12.5Quasicrystalline Phase Formation by Rapid Solidification Followed by Mechanical Milling (Dept.P)

The formation of the quasicrystalline phase Al62.5 Cu25FC12.5, by twin rolls rapid solidification technique has been investigated. The obtained phases are cauterized by XRD, Differential Thermal Analysis and electrical resistivity measurements. The effect of milling on the sample produced by rapid solidification is also examined. A quenched sample, a quasicrystalline (i-phase) is present in a relatively high volume fraction, in addition to two other phases that are most likely Al2Cu to be phase and Al7Cu2Fe phase (𝟂-phase). The milled samples does not give a single quasicrystalline phase, but the milling tends to stabilize the pre- existed i-phase.

Ultrafast synthesis of the nanostructured Al59Cu25.5Fe12.5B3 quasicrystalline and crystalline phases by high-energy ball milling: Microhardness, electrical resistivity, and solar cell absorptance studies

In this study, the Al59Cu25.5Fe12.5B3 nanoquasicrystalline alloy and related crystalline phases were synthesized through mechanical alloying using a high-energy ball milling and consolidated by a cold isostatic pressing apparatus. This paper focuses on the synthesis, structural and microstructural evolutions, thermal stability, microhardness, and electrical and optical properties of the Al59Cu25.5Fe12.5B3 nanoquasicrystalline alloy for solar selective absorber usages. The structural evolutions of the mechanically alloyed and heat-treated AlCuFeB powders were investigated by X-ray diffractometry. Accordingly, the effect of milling time and heat treatment on the formation of quasicrystalline and related crystalline phases were studied in the AlCuFeB alloy system. The microstructure, morphology, and chemical microanalysis of the un-milled and as-milled powders were examined by field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. The composition of the as-milled AlCuFeB powders was estimated employing inductively coupled plasma-atomic emission spectroscopy. The thermal stability of the AlCuFeB powders was recorded by differential thermal analysis, and the weight gain of the particles during annealing was investigated through thermogravimetric analysis. The nanostructured Al59Cu25.5Fe12.5B3 stable quasicrystalline phase and crystalline Al(Cu,Fe) solid-solution were synthesized by the ultrafast milling procedure in 1 h. The rationale behind using the term ultrafast synthesis is to synthesize the QC i-phase only by the high-energy ball milling procedure in short-term ball milling without subsequent annealing treatment. However, the single quasicrystalline phase could not be obtained even after the annealing treatment. The quasicrystalline size was calculated by the Williamson–Hall method and optimized by the Rietveld refinement procedure, and it was found that the size is varied between 53 and 61 nm. Furthermore, the particle size distribution of the as-milled AlCuFeB powders was measured using laser static light scattering, which ranges from 0.1 to 50 μm. The microhardness of the consolidated as-milled and heat-treated samples was estimated utilizing the Vickers microhardness indenter. At the same time, their electrical resistivity was assessed by the four-point probe method at room temperature. The spectral analyses of absorption on the consolidated as-milled samples were carried out in the ultraviolet, visible, and near-infrared regions. It was found that the presence of the quasicrystalline phase in the AlCuFeB alloy prominently improves the microhardness, electrical resistivity, and particularly sunlight absorptance.

Effect of milling time on XRD phases and microstructure of a novel Al67Cu20Fe10B3 quasicrystalline alloy

The quasicrystalline materials represent a new materials group with definite crystallite structural characteristics, in which the AlCuFe(B) quasicrystalline alloys have been widely studied owing to its various technological advantages such as easily accessible in nature, thermal stability, affordability as well as not having toxic constituent elements. Although these materials can be achieved by different procedures, the synthesis of more extensive amounts of AlCuFeB quasicrystalline single-phase powders is more complicated. In this study, the Al67Cu20Fe10B3 quasicrystalline alloys were synthesized through the mechanical alloying process and afterward consolidated to the bulk specimens by cold isostatic pressing (CIP) technique. The structural and microstructural evolutions, as well as the morphology of as-milled powders and phase transformations, were studied during the ball milling process using field-emission scanning electron microscopy (FESEM) and x-ray diffractometry (XRD), while the thermal behavior was investigated using differential thermal analysis (DTA). The most fascinated result revealed that the stable AlCuFeB single quasicrystalline phase could be directly synthesized in short milling times (around ∼4 h) by a high-energy planetary ball milling. It was appreciated that the icosahedral phase is stable up to 300 °C, which is misplaced stability at superior temperatures and transforms into crystalline phases. The microhardness of consolidated ball-milled powders at various milling times was determined and it was figured out that the icosahedral phase has an extreme microhardness as much as 10.73 GPa.

Quasicrystal nucleation and \u2124 module twin growth in an intermetallic glass-forming system

While quasicrystals possess long-range orientational order they lack translation periodicity. Considerable advancements in the elucidation of their structures and formative principles contrast with comparatively uncharted interrelations, as studies bridging the spatial scales from atoms to the macroscale are scarce. Here, we report on the homogeneous nucleation of a single quasicrystalline seed from the undercooled melt of glass-forming NiZr and its continuous growth into a tenfold twinned dendritic microstructure. Observing a series of crystallization events on electrostatically levitated NiZr confirms homogeneous nucleation. Mapping the microstructure with electron backscatter diffraction suggests a unique, distortion-free structure merging a common structure type of binary alloys with a spiral growth mechanism resembling phyllotaxis. A general geometric description, relating all atomic loci, observed by atomic resolution electron microscopy, to a pentagonal {Bbb Z} module, explains how the seed’s decagonal long-range orientational order is conserved throughout the symmetry breaking steps of twinning and dendritic growth.

Partially-devitrified icosahedral quasicrystalline phase in Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 amorphous alloys with near equi-atomic compositions

Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 alloys were investigated for their possibility to be formed into a high-entropy alloy (HEA) with a quasicrystalline (QC) structure that contains an icosahedral- (I-) phase. The melt-spun alloys quenched at a circumference speed of 39 m/s were formed into an amorphous single phase. The amorphous alloys annealed up to a temperature between the first and second crystallization temperatures exhibited mixed phases of I- and remaining amorphous phases. Observation of the Zr30Hf30Ni15Cu10Ti15 amorphous alloy heated up to 745 K with transmission electron microscope revealed the presence of precipitates with diameters ranging 10–20 nm. Nano-beam diffraction demonstrated that the precipitates were identified to be the I-phase with the five-, three- and two-fold symmetries. The Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 alloys were not formed into a single quasicrystalline phase as HEAs, but the discussions of the current and early experimental data led to provide the way to approach high-entropy quasicrystalline alloys (HE-QCs).

Towards the growth of single quasicrystalline grains in Al-Cu-(Fe, Cr) alloys after mechanical alloying and subsequent high temperature heating

Coarse grains growth in Al65Cu23Fe12 and Al73Cu11Cr16 mechanically alloyed powders was studied. Heating up to 950 °C and further rapid cooling produces a range of single quasicrystalline grains having different sizes, shapes and the degree of perfection. In the Al-Cu-Fe system both secondary recrystallization in the solid state and crystallization from liquid state were found. Contrary to the mechanism of nucleation in the liquid state and further growth of nuclei we demonstrate another mechanism – the ready nuclei which survived after the short heating are incorporating the molten material, which results in the formation of perfectly shaped single grains. In the Al-Cu-Cr system only secondary recrystallization in the solid state and no crystallization from liquid state were found.

Numerical methods for crack loading analyses in quasicrystals

AbstractSince the first discovery of quasicrystals in a man made Al‐Mn alloy about thirty years ago, people made great effort to investigate this kind of outstanding material. The materials scientists are constantly trying to produce stable quasicrystalline particles or even a complete single quasicrystalline specimen. On the other hand, the fracture behaviour of quasicrystals is started to be investigated because the coupling effect between phonon and phason fields can rebuild the conventional fracture criteria. This work develops a numerical tool for simulating in‐plane problems of 1D QC and extends the fracture quantities i.e. stress intensity factors (SIF) and strain energy release rate to phason fields. Finally, numerical results are given to reveal what difference the phason field can bring into conventional fracture quantities. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Heat Treatment on Phase Composition and Microstructure of Al-Cu-Fe Alloys with Quasicrystalline Phases

The microstructure and phase composition of alloys Al-Cu-Fe in as-cast state and after heat treatment at different temperatures were investigated. The presence of a quasicrystalline phase Al65Cu20Fe15 which coexists with crystalline phases in as-cast condition is found. The formation of single quasicrystalline phase composition in Al - 40 wt.% Cu - 17 wt.% Fe alloy after annealing at 800 °C for 100 hours is established. After heat treatment, i.e. closer to equilibrium conditions, the quasicrystalline phase Al65Cu20Fe15 is transformed into quasicrystalline phase Al13Cu4Fe3 with more complicated lattice.

Microstructure and Mechanical Properties of Al-12.6%Si Composite Reinforced by Al<sub>63</sub>Cu<sub>25</sub>Fe<sub>12</sub>Quasicrystal

In this paper, Al-12.6%Si/Al63Cu25Fe12 composites were fabricated by method of casting. The microstructure and chemical composition of Al63Cu25Fe12 quasicrystal alloy and Al-12.6%Si alloy reinforced by the quasicrystal were studied, and the mechanical properties of Al-12.6%Si composite were also measured. The results show that almost single quasicrystalline phases exist in the samples which are cast with the 1300°C melt. Quickly enough cooling rate and appropriate melt temperature are necessary for the formation of the quasicrystalline phase. In addition, Al-12.6%Si composite has optimal mechanical properties when the amount of Al63Cu25Fe12 quasicrystal is 3 wt%.

Growth morphology of single-crystal grains obtained by directional crystallisation of an Al–Cu–Fe alloy

Quasicrystalline as well as crystalline faceted single grains of four phases were obtained during directional crystallisation of an Al–Cu–Fe alloy by the Bridgman technique. The monoclinic λ phase, Al13(Cu, Fe)4, dominating at high temperatures formed single-crystal lamellae 0.5 mm to 1 mm thick. A second type of attractive morphological form exhibiting flux dissolution terraces was observed on spherical single crystals of β phase Al(Fe, Cu). Rectangular, hexagonal and octagonal shaped dissolution terraces were revealed at the positions of two-, three- and four-fold symmetry axes, respectively. A single quasicrystalline ψ phase, Al6Cu2Fe, exhibited icosahedral symmetry with growth forms of a dodecahedron with pentagonal facets. The flux dissolution of the β phase apparently plays an essential role in a peritectic reaction leading to quasicrystalline ψ phase formation. Polygonal single grains of ω phase Al7Cu2Fe exhibiting tetragonal symmetry formed the fourth type of thermodynamically stable growth forms. Single grains of the ω phase crystallised in the form of pellets with an octagonal cross-section. The growth morphology of the stable phases was investigated by scanning electron microscopy. The chemical composition of the growth forms described was confirmed by X-ray microanalysis using a scanning electron microscope, whereas the phase composition was determined using electron selected area diffraction and X-ray powder diffraction.

Characterization of the icosahedral quasicrystalline phase in rapidly solidified Al–Cu–Fe alloys

Abstract The present research aimed to characterize the microstructure of icosahedral quasicrystalline phase (i-phase) in different chemical compositions of Al–Cu–Fe alloys. The ternary alloys with the nominal compositions of Al70Cu20Fe10, Al65Cu20Fe15 and Al63Cu25Fe12 (at%) were rapidly solidified by melt-spinning technique. The melt-spun ribbons were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). According to the XRD results, diffraction patterns of Al70Cu20Fe10 alloy showed the presence of the i-phase together with tetragonal θ-Al2Cu phase. However, XRD pattern of the melt-spun Al63Cu25Fe12 alloy showed the formation of i-phase together with a small amount of β-phase. The single quasicrystalline phase was observed only in the rapidly solidified Al65Cu20Fe15 alloy. The SEM examinations showed that the melt-spun Al70Cu20Fe10 and Al63Cu25Fe12 alloys composed of i-phase with an average grain size of 1–5 μm. However, for the Al65Cu20Fe15 alloy, the quasicrystalline particles in the star-shape dendritic formations were observed. The melting point of i-phase was determined as 890 °C by DTA examinations.

Formation of a single quasicrystalline phase in an Al55Cu25.5Fe12.5Be7 alloy

An alloy with a single quasicrystalline icosahedral phase (I phase) can be produced by partial replacement of Al with Be (7at.%) in an Al62Cu25.5Fe12.5. alloy. The I phase nucleates first and then grows in a dendritic manner and the remaining liquid solidifies into the metastable t phase at a later stage of solidification during conventional casting with a Cu mould. With a lower cooling rate (crucible cooling), the liquid melt solidifies into an almost single I phase without heat treatment. The present study shows that the addition of Be stabilizes the I phase and expands the I-phase region. The Al55Cu25.5Fe12.5Be7I phase exhibits a highly ordered F-type structure like the Al-Cu-Fe I phase, and the intensities of the superlattice peaks in the electron or X-ray diffraction patterns do not vary on the addition of Be.

On the crystalline-amorphous supermolecular structure of poly(4-methyl-1-pentene) films cast from solution: experimental evidences and theoretical remarks

We regard the formation of crystalline-amorphous structure of polymeric films cast from solution. We pay a special attention to its formation on a level of single quasicrystalline domain, and try to embark on the problem, when a possibly large group of such domains has to be considered. In the former, one is nearly enforced to make use of a modification of the stochastic diffusion-limited aggregation model, first introduced by Witten and Sander. In the latter, certain diffusion-type (Potts-like) models, invented for polycrystalline microstructure formation, could be adopted. When considering the problem on the first level mentioned, one may notice an apparent agreement between experiment and theory, whereas on the second level, some conceptual similarity seems to be attractive.

超微細結晶粒材料の作成と物性 非周期構造をもつナノ粒子分散Ａｌ‐Ｍ（Ｍ＝Ｃｒ，Ｖ，Ｔｉ）系合金の作製と機械的性質

We examined the structure in rapidly solidified Al-M (M=Mo, V, Cr, Mn, Fe, Co, Ni) binary alloys and noticed that a quasicrystalline phase is formed in the M=V, Cr and Mn alloys. The fcc-Al plus quasicrystalline structure was formed in the range of 4 to 16 at%Cr or 6 to 23 at%Mn, and having almost single quasicrystalline phase in the vicinity of 14.0 at%V, 15.4 at%Cr or 22.5 at%Mn. The Vickers hardness values of the Al86V14, Al84.6Cr15.4 and Al77.5Mn22.5 alloys with having almost single quasicrystalline phase were 735, 1010 and 710, respectively and the grain size of the quasicrystalline phase was 200, 450 and 650 nm, respectively. The addition of Ce in the Al-Cr binary alloys was effective for the extension of the solute concentration range of quasicrystalline phase to a lower solute concentration range. The particle size and volume fraction of the quasicrystalline phase in the A194Cr5Ce1 alloy were about 200 nm and 70 %, respectively and the tensile fracture strength (σf) was 650 MPa. The σf increased to 1080 MPa for the Al95Cr3Ce1Co1 alloy in which the particle size and volume fraction were about 50 nm and 70 %, respectively. The σf of the Al94V4Fe2 alloy was 1390 MPa and the particle size and volume fraction were about 13 nm and 50 %, respectively. Similarly, the of of the Al93Ti4Fe3 alloy was 1320 MPa and the particle size and volume fraction were about 12 nm and 30 %, respectively. In aluminum alloys containing nanoscale quasicrystalline and amorphous particles, the 0.2 % proof stress (σ0.2) increased with decreasing particle size up to about 25 nm. When the particle size decreased further to was less than about 25 nm, the σ0.2 decreased with decreasing particle size. The transition from Hall-Petch relation to inverse Hall-Petch relation was recognized to occur in the vicinity of 25 nm.

Neutron Scattering Study Of Antiferromagnetic Correlations In The Zn-Mg-Ho Icosahedral Quasicrystal

AbstractMagnetism in the Zn-Mg-Ho icosahedral quasicrystal has been studied by neutron scattering. Powder samples of the icosahedral and related crystalline phases were reexamined to clarify the origin of the previously-reported long-range magnetic order [Charrier et al., Phys. Rev. Lett. 78 (1997) 4637]. The long range order was found to originate from the related crystalline phase, which is a contaminant in the previously-used samples. Whereas for high-quality icosahedral phase, we could detect only magnetic diffuse scattering. This apparently shows the absence of the long range order in the icosahedral phase. The diffuse scattering was studied in detail by using a single quasicrystalline sample. It was found that the diffuse scattering appears as satellites from intense nuclear Bragg reflections. This indicates that corresponding spin correlations can be regarded as developed between spins on the six-dimensional virtual hypercubic lattice. A magnetic modulation vector for the correlations is proposed.