Stability Of Quasicrystalline Phase Research Articles

Characterization in the icosahedral phase of the system Al63Cu25Fe12

The present work aimed to characterize the microstructure of the icosahedral phase (ɸ-quasicrystalline phase) of the system with stoichiometric composition of the quasicrystal Al63Cu25Fe12. The ternary alloy with nominal composition of Al63Cu25Fe12 was processed by Mechanical Alloying (MA) as a viable solid state processing method for producing various metastable and stable quasicrystalline phases. The structural characterization of the obtained samples was performed by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), while the elemental composition of the chemical elements Al, Fe and Cu were determined by the technique of X-ray spectroscopy by dispersive energy (EDS). According to the results of XRD, the diffraction patterns of Al63Cu25Fe12 showed the presence of β-Al (Fe, Cu) and λ-Al13Fe4 phases coexist with the thermodynamic ɸ-phase quasicrystalline. Finally, elemental analysis indicates that during alloy synthesis there is little variation of the ideal composition. The results indicate that alloys with high percentage of icosahedral phase can be obtained by casting in the air.

An uncomplicated method for growing nano-quasicrystalline structures in the AlCuFeB quaternary alloy system: A short-time milling

Quasicrystals have been comprehensively studied since their discovery in 1984 by Daniel Shechtman to dissolve their complex structures concerning their physical properties [1–5]. The quasi-periodic well-ordered atomic structures made QCs as a novel type of solids differing from the crystalline or amorphous materials [5–7]. The QC alloys have non-crystallographic rotational symmetries, such as five-fold, eight-fold, and even ten-fold rotational axes that are prohibited in ordinary periodic crystals [5–7]. The QC alloys have been recently considered for several applications owing to a series of the unusual combination of exclusive physicomechanical properties for metallic-based alloys [5–7]. Accordingly, the properties of these alloys can be pointed out to their high strength, elevated hardness, desirable corrosion and wear resistance, minute adhesion, low values of thermal and electrical conductivity, and superior optical properties [5–7].•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. Accordingly, there are various advanced techniques for synthesizing the nanostructured quasicrystals, such as laser ablation, sol-gel, electros pining, mechanical alloying, and hydrothermal methods.•The structural and microstructural evolutions of the mechanically alloyed AlCuFeB powders were investigated by X-ray diffractometry and field-emission scanning electron microscopy. The thermal stability of the AlCuFeB powders was recorded by differential thermal analysis.•The nanostructured Al59Cu25.5Fe12.5B3 stable quasicrystalline phase was synthesized by short-time milling procedure in 1 h. It was found that the presence of the quasicrystalline phase in the AlCuFeB alloy prominently improves the microhardness, electrical resistivity, and sunlight absorptance.

ICOSAHEDRAL PHASE OF Al65Cu25Fe15

The present work aimed to characterize the microstructure of the icosahedral phase (quasicrystalline phase-ϕ) of the system with stoichiometric composition of the quasicrystal Al65Cu25Fe15 . The ternary alloy with nominal composition of Al63Cu25Fe12 was processed by mechanical alloying (MA) as a viable solid state processing method for producing various metastable and stable quasicrystalline phases. The structural characterization of the obtained samples was performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the elemental composition was determined by dispersive energy spectroscopy (DES). The diffraction patterns of Al65Cu25Fe15 showed the presence of ω-Al7Cu2Fe , β-Al(Fe, Cu) and λ-Al13Fe4 phases that coexist with the thermodynamic quasicrystalline phase-ϕ. Finally, elemental analysis indicates that during alloy synthesis there is little variation of the ideal composition. The results indicate that alloys with high percentage of icosahedral phase can be obtained by casting in the air.

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.

THE ICOSAHEDRAL PHASE OF Al63Cu25Fe12 SYSTEM

The present work aimed to characterize the microstructure of the icosahedral phase (quasicrystalline phase-ϕ) of the system with stoichiometric composition of the quasicrystal Al63Cu25Fe12. The ternary alloy with nominal composition of Al63Cu25Fe12 was processed by mechanical alloying (MA) as a viable solid state processing method for producing various metastable and stable quasicrystalline phases. The structural characterization of the obtained samples was performed by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), while the elemental composition of the chemical elements Al, Fe and Cu were determined by X-ray spectroscopy technique of dispersive energy (EDS). According to the results of XRD, the diffraction patterns of Al63Cu25Fe12 showed the presence of β-Al(Fe, Cu) and λ-Al13Fe4 phases coexist with the thermodynamic ϕ-phase quasicrystalline. Finally, elemental analysis indicates that during alloy synthesis there is little variation of the ideal composition. The results indicate that alloys with high percentage of icosahedral phase can be obtained by casting in the air.

Characterization in the Icosahedral Phase of Al63Cu25Fe12 System

The present work aimed to characterize the microstructure of the icosahedral phase (quasicrystalline phase-ϕ) of the system with stoichiometric composition of the quasicrystal Al 63 Cu 25 Fe 12 . The ternary alloy with nominal composition of Al 63 Cu 25 Fe 12 was processed by mechanical alloying (MA) as a viable solid state processing method for producing various metastable and stable quasicrystalline phases. The structural characterization of the obtained samples was performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the elemental composition was determined by dispersive energy spectroscopy (DES). The diffraction patterns of Al 63 Cu 25 Fe 12 showed the presence of quasicrystalline phase-ϕ, ω-Al 7 Cu 2 Fe, β-Al(Fe, Cu) and λ-Al 13 Fe 4 phases that coexist with the thermodynamic quasicrystalline phase-ϕ. In icosahedral phase oxidation of aluminum forms a dense layer on the passivating outer most surface of the quasicrystal which causes depletion in both copper and iron. It was observed not only the presence of alumina, γ-Al 2 O 3 , but also the formation of hematite and copper oxide in the dense layer. Finally, elemental analysis indicates that during alloy synthesis there is little variation of the ideal composition. The results indicate that alloys with high percentage of icosahedral phase can be obtained by casting in the air. DOI: http://dx.doi.org/10.17807/orbital.v11i3.1381

Quasicrystalline Phase Formation of the Al67Cu26Fe15 Alloy

O presente trabalho teve como objetivo caracterizar a microestrutura da fase icosaedral (f-fase quasicristalina) do sistema com composição estequiométrica do quasicristal Al67Cu26Fe15. A liga ternária com composição nominal de Al67Cu26Fe15 foi processada por Moagem Mecânica de Alta Energia, como um método viável de processamento no estado sólido para a produção de várias fases quasicristalinas metaestáveis e estáveis. A caracterização estrutural das amostras obtidas foi realizada por difração de raios-X (DRX) e Microscopia Eletrônica de Varredura (MEV), enquanto a composição elementar dos elementos químicos Al, Fe e Cu foram determinados pela técnica de Espectroscopia de raios X por energia dispersiva (EDS). Na superfície da liga quasicristalina, podemos observar no SEM a presença da alumina g-Al2O3, que contribui para as propriedades texturais de suporte catalítico deviso a sua atividade catalítica, visando maior desempenho em reações de oxidação do metanol. De acordo com os resultados de XRD, os padrões de difração da liga Al67Cu26Fe15 mostraram a presença das fases w-Al7Cu2Fe, b-Al(Fe;Cu) e l-Al13Fe4 coexistem com a f-fase quasicristalina em regime termodinâmico. Finalmente, a análise elementar indica que durante a síntese da liga existe pequena variação da composição ideal. Os resultados indicam que ligas com alto percentual de fase icosaedral podem ser obtidas por fundição ao ar.

Microstructure characterization of Al–Cr–Fe quasicrystals sintered using spark plasma sintering

In this study, Al–Cr–Fe powders were consolidated using spark plasma sintering at different temperatures (650°C, 700°C, 750°C and 800°C). The sintered samples were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The porosity of the pellets is very sensitive to the sintering temperature: it reduces sharply from around 29.3% to around 3.1% when the sintering temperature increases from 650°C to 700°C probably due to the softening of quasicrystals at elevated temperatures. Metastable icosahedral Al–Cr–Fe transforms to stable decagonal Al–Cr–Fe in sintering process. Stable icosahedral Al–Cr–Fe forms in the samples sintered at 700°C, 750°C and 800°C. Both stable quasicrystalline phases form through the nucleation and growth process in the sintering process. Selected area electron diffraction (SAED) analysis shows that the icosahedral phase and the decagonal phase formed in the sintering process have a quasilattice constant of about 0.45nm and 1.2nm, respectively.

Effect of Mo on stability of quasicrystalline phase in Al–Mn–Fe alloy

Microstructure evolution in rapidly solidified Al91Mn6Fe2Mo1 ribbons after annealing was investigated using X-ray diffraction, scanning electron microscopy and analytical transmission electron microscopy including in situ heating experiment in TEM. As spun ribbons consisted of icosahedral quasicrystalline particles enriched in Fe, Mn and Mo embedded in an aluminium matrix. A small amount of quasicrystals containing Fe and Mn which coexisted with the Al3(Fe, Mn) phase was also observed between the aluminium grains. Further annealing experiments and subsequent analysis of microstructure changes in the sample showed that the quasicrystalline particles underwent a transformation into stable crystalline phases at temperatures which depended on their composition. It was observed that quasicrystals enriched in Mn and Fe transformed at much lower temperatures than primary quasicrystals with Mo content. It was noticed that two different crystalline phases formed in dependence on the temperature of annealing. The Al6(Mn, Fe) phase appeared first at the quasicrystal/matrix interface. At higher temperature, the Al12(Mn, Mo) phase formed due to reaction of the Al6(Mn, Fe) phase with the aluminium matrix. Microstructural and DSC investigations showed that addition of molybdenum improved thermal stability of the quasicrystals in Al–Mn–Fe system.

Study of melt-grown quasicrystalline samples in the Cd-Yb and Al-Cu-Fe systems

The regimes of preparation of bulk samples of the quasicrystalline phase in the Cd-Yb and Al-Cu-Fe systems have been investigated. A thermodynamically stable quasicrystalline phase Cd5.7Yb and its approximant Cd6Yb with a high degree of texture along the cooling axis have been obtained. X-ray diffraction analysis made it possible to reveal changes in the structure and phase composition of bulk samples with variation in the melting temperature and annealing for different methods of sample preparation. It is shown that the presence of a temperature gradient along the furnace axis significantly affects the volume of the quasicrystalline phase. It is established that, with a decrease in the volume of the quasicrystalline phase mixed with the crystalline phase, the character of the temperature dependence of resistivity changes from the semiconductor type to the metallic type and the microhardness decreases according to a linear law.

The conditions of formation and stability of quasi-crystalline phases in aluminum-manganese alloys

The conditions of formation, stability, and thermodynamic properties of the icosahedral and decagonal quasi-crystalline phases in the Al-Mn system were studied experimentally. The thermodynamic properties of equilibrium crystalline Al-Mn compositions over the composition and temperature ranges 0–26 at % Mn and 628–1193 K, respectively, and of melts over wide temperature and composition ranges (1043–1670 K and 0–50.1 at % Mn) were determined. Measurements were made by the integral variant of the effusion method under the conditions of an ultrahigh oilless vacuum and Knudsen mass spectrometry. An original technique based on the initiation and study of equilibria in reactions of the alloys with special admixtures of sodium or magnesium fluorides with the formation of volatile products was used to extend the interval of measurements to low temperatures. Complete, reliable, and consistent data on the thermodynamic properties of icosahedral and decagonal quasi-crystalline and crystalline phases based on aluminum and Al-Mn melts were obtained for the first time. Al-Mn melts were shown to contain associates of three types, AlMn, Al2Mn, and Al5Mn. The contributions of covalent interactions to the Gibbs energy and enthalpy of mixing was found to be by far predominant. The thermodynamic properties of alloys of the same chemical composition in the quasi-crystalline and equilibrium crystalline states were compared. The decagonal phase was found to be more stable than icosahedral quasi-crystals. The difference of the Gibbs energies of quasi-crystals of the two types and crystalline compositions increased as the temperature lowered. Arguments in favor of the entropy nature of the stabilization of quasi-crystals were obtained. These phases, like metallic glasses, are only an intermediate state between liquids and crystals and cannot be ground stable alloy states. The conditions of obtaining quasi-crystalline phases from melts were found to be controlled by the appearance of a substantial fraction of icosahedral short-range order in liquids in the region of compositions where associates of a certain kind (Al5Mn) were formed in substantial amounts, x(Al5Mn) ≥ 0.11.

Thermally stable quasicrystalline phase in a superplastic Mg–Zn–Y–Zr alloy

A Mg-rich Mg–Zn–Y–Zr alloy sheet, which contains two different particles, icosahedral quasicrystalline phase (I-phase) and Zr-rich phase in the fine-grained α-Mg matrix, has been developed by thermomechanical processes. With an addition of zirconium in the ternary Mg–Zn–Y alloy, the I-phase/α-Mg eutectic temperature increases to 500 °C and the lattice constant of the I-phase slightly increases, leading to a more thermally stable eutectic structure. The fine-grained Mg–Zn–Y–Zr alloy shows large elongations to failure at the temperature above 400 °C, and no cavity is formed at the interface between the α-Mg and the I-phase during superplastic deformation.

Ductile titanium-based glassy alloy ingots

We report that ductile and strong amorphous titanium metallic alloys (∼ twice the strength of high-strength titanium alloys) have been discovered that are in the form of glassy ingots. It is found that the suppression of a competing stable quasicrystalline phase upon solidification is particularly important in forming the current glassy ingots. While there is significant technological potential for these titanium alloys, the present findings have important implications on the design of highly processable bulk metallic glasses.

Phase equilibrium in the vicinity of the Al–Ni–Ru decagonal phase

The Al-rich part of the Al–Ni–Ru phase diagram was re-investigated with respect to the existence of stable quasicrystalline phases. The thermodynamic stability of the ternary decagonal phase with a 1.6 nm periodicity was confirmed in a small compositional range around Al 73.1Ni 15.7Ru 11.2 and at temperatures below 1050 °C. The partial 900 °C isothermal section of Al–Ni–Ru is presented. Apart from the decagonal phase, two ternary crystalline compounds are stable at this temperature. The results are compared to those in Al–Ni–Fe.

THE SIGNIFICANCE OF VALENCE ELECTRON CONCENTRATION ON THE FORMATION MECHANISM OF SOME TERNARY ALUMINUM-BASED QUASICRYSTALS

In the present study we report on the formation mechanism of some binary Al-TM and ternary Al-Cu-TM (TM = transition metal) quasicrystals. We have found that the formation mechanism of quasicrystalline phases in the binary Al-TM system takes place at extremely high solidification rates, is linked to the location of the transition metal in the periodic table, depends upon the atomic radius ratio of the constituents, is composition sensitive, and as a result is strongly affected by the effective atomic radius ratio (a eff ). Applying empirical criteria on the formation of ternary Al-Cu-TM quasicrystals we were able to calculate the composition range at which the formation tendency and stability of quasicrystalline phases is enhanced. The method presented can be viewed as an empirical criterion to find new and high quality quasicrystalline materials and to optimize the quasicrystalline material composition. Furthermore, it was observed that the stabilization mechanism of the quasicrystalline Al-Cu-(Fe, Co, Ru, Rh, Os, Ir) phases takes place when the atomic ratio (TM+Cu)/Al ranges from 0.46 to 0.69 and for a eff values between 4.10 and 7.30. At the same valence electron concentration, metastable icosahedral Al-Cu-(Cr, Mn) phases are formed at relatively smaller atomic ratios (TM+Cu)/Al and having higher a eff values in comparison to those of the stable D- and I-phases.

Stable quasicrystalline phase in Al-Cu-Fe-Cr coating materials

Transmission electron microscopy (TEM) studies have been carried out on magnetron-sputtered coatings in the Al-rich region of the Al-Cu-Fe-Cr quasicrystalline phase field, focusing on the composition that exhibited the best tribological performance among a group of sputtered coatings. The size of the particles in the as-deposited coating is around 10 nm. The TEM experiments on annealed coatings (450 °C for 6 hours+400 °C for 7 hours) revealed that the material is composed of a decagonal quasicrystalline phase with a periodicity of 1.24 nm along the unique axis and a hexagonal crystalline phase, with a=2.48 nm and c=1.24 nm. These results show that a thermodynamically stable quasicrystalline phase exists in the Al-Cu-Fe-Cr alloy system, in addition to previously reported microcrystalline structures and orthorhombic and monoclinic approximants. The hexagonal phase is a crystalline approximant of the decagonal phase, structurally related to hexagonal crystalline phases previously reported in Al-Mn and Al-Cr-Ni quasicrystalline alloys.

Microstructure and phase decomposition of quasi-crystal Zn 60Mg 30Y 10 alloy

The microstructure and aging characteristics of a quasi-crystal Zn 60Mg 30Y 10 alloy were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Typical structures of the icosahedral quasi-crystalline phase were characterized by three symmetries: 5-fold, 3-fold and 2-fold, based on which a structure model of this complex quasi-crystalline phase was proposed. Fine-dispersed precipitates were found inside the relatively stable quasi-crystalline phase during aging. Decomposition of the crystalline phase (MgZn 2) was also investigated.

Formation of icosahedral quasicrystals in an annealed Zr65Al7.5Ni10Cu12.5Ag5 metallic glass

The formation and thermal stability of an icosahedral quasicrystalline phase in an annealed Zr65Al7.5Ni10Cu12.5Ag5 metallic glass have been investigated by X-ray diffraction and transmission electron microscopy analyses. It was found that the quasicrystalline phase can precipitate from the glassy state and the supercooled liquid of the alloy over a wide range of annealing temperatures. After optimizing the heat-treatment conditions, the volume fraction of the quasicrystalline phase in the alloy can reach as high as about 80%. Investigation of the thermal stability of the quasicrystalline phase demonstrates that it is very stable when the annealing temperature is below the glass transformation temperature T g of the alloy.

Ａｌ‐Ｌｉ‐Ｃｕ準結晶合金におけるＴＴＴ曲線

Quasicrystal has some interesting properties due to its quasiperiodisity, which include higher hardness, higher electrical resistivity, and so on. We know that Al5-Li3-Cu has stable quasicrystalline phase. So, we investigated the formation of Al-Li-Cu quasicrystalline phase at various temperatures by making TTT curve. In this way, we could obtain the fundamental knowledge about the self-organization of the phase. The reason for the stability of the phase is discussed in terms of the quasicrystal growth kinetics.

Classical Lattice-Gas Models of Quasicrystals

One of the fundamental problems of quasicrystals is to understand their occurrence in microscopic models of interacting particles. We review here recent attempts to construct stable quasicrystalline phases. In particular, we compare two recently constructed classical lattice-gas models with translation-invariant interactions and without periodic ground-state configurations. The models are based on nonperiodic tilings of the plane by square-like tiles. In the first model, all interactions can be minimized simultaneously. The second model is frustrated; its nonperiodic ground state can arise only by the minimization of the energy of competing interactions. We put forward some hypotheses concerning stabilities of nonperiodic ground states. In particular, we introduce two criteria, the so-called strict boundary conditions, and prove their equivalence to the zero-temperature stability of ground states against small perturbations of potentials of interacting particles. We discuss the relevance of these conditions for the low-temperature stability, i.e., for the existence of thermodynamically stable nonperiodic equilibrium states.