Quasi-binary Alloys Research Articles

STRUCTURE AND PROPERTIES OF REFRACTORY BIMONOCRYSTAL MICROCOMPOSITES

The features of high-gradient crystallization of refractory quasi-binary alloys have been studied. The processes of phase nucleation and their joint influence on the evolution of the formation of spatially ordered microstructures are considered. The possibility of regulating the volumetric ratio of phases by crystallization of alloys of noneutectic composition has been revealed. The results of expanding the area of compositional growth and the possibility of creating a regular quasi-eutectic microstructure without primary carbides are explained. The mechanism of post-crystallization heat treatment has been determined, leading to the purification of the matrix from interstitial impurities and embrittling carbides, the creation of perfect bi-monocrystalline materials that are thermally stable up to pre-melting temperatures with a high level of ductility and heat resistance.

Comprehensive Analysis of Microstructure and Hot Deformation Behavior of Al-Cu-Y-Mg-Cr-Zr-Ti-Fe-Si Alloy

Low sensitivity to hot cracking is very important not only for casting but also for ingots of wrought alloys. Doping of Al-Cu-(Mg) alloys by eutectic forming elements provides an increasing resistance to hot cracking susceptibility, but it also leads to a decrease in plasticity. The quasi-binary alloys based on an Al-Cu-REM system with an atomic ratio of Cu/REM = 4 have a high solidus temperature, narrow solidification range and fine microstructure. The detailed investigation of microstructure, precipitation and hot deformation behavior, and mechanical properties of novel Al-Cu-Y-Mg-Cr-Zr-Ti-Fe-Si alloy was performed in this study. The fine Al8Cu4Y, needle-shaped Al11Cu2Y2Si2, compact primary (Al,Ti)84Cu6.4Y4.3Cr5.3 and Q (Al8Cu2Mg8Si6) phases were identified in the as-cast microstructure. Near-spherical coarse Al3(Zr,Y) and fine Al45Cr7 precipitates with a size of 60 nm and 10 nm were formed after 3 h of solution treatment at 580 °C. S′(Al2CuMg) precipitates with an average diameter of 140 nm, thickness of 6 nm and calculated volume fraction of 0.033 strengthened 36 HV during aging at 210 °C for 3 h. Three-dimensional hot processing maps demonstrated an excellent and stable deformation behavior at 440–540 °C and strain rates of 0.01–10 s−1. The rolled sheets had a good combination of yield strength (313 MPa) and plasticity (10.8%) in the recrystallized at 580 °C, with water quenched and aged at 210 °C for a 3 h state. The main calculated effect in the yield strength was contributed by Al45Cr7 precipitates.

Compositional and Structural Disorder in Two-Dimensional AIIIBVI Materials

Two-dimensional (2D) van der Waals (vdW) AIIIBVI semiconductor materials, such as InSe and GaSe, are of considerable interest due to their potential use in various microelectronics applications. The range of properties of materials of this class can be extended further through the use of quasi-binary alloys of the InSe(Te)-GaSe(Te) type. In this work, we study the effect of compositional and structural disorder in 2D In(Ga)Se(Te) on the band structure and electronic properties using first principles modeling. The results for In(Ga)Se demonstrate a noticeable decrease in the band gap for structures with a random distribution of indium and gallium cations, while for In(Ga)Te with a random cation distribution, metallization occurs. Changes in the compositional arrangement of chalcogens (there can be either the same or different atoms on each side of the vdW gap) lead to pronounced changes in the band gap, but no significant changes in topology are observed. In addition, a significant effect of the distance between the layers on the band gap under compression along the c axis was found for both alloys under study. An important point of our study is that van der Waals gap engineering is a very powerful tool to control the properties of 2D materials and its alloys.

The Creation of Complex Multi-Component Models of Mössbauer Spectra Based on the Example of a Study of Hyperfine Interactions in Quasi-Binary Alloys with the Laves Phase Structure

In this paper, we describe a method for creating new custom models of partial Mössbauer spectra based on the existing ones built into the SpectrRelax program without changing the program itself by writing code fragments in the built-in Lua programming language. The extension of the capabilities of the SpectrRelax program is demonstrated using the example of studying hyperfine interactions of 57Fe nuclei in quasibinary Tb(Fe0.8Al0.2)2 and Ho(Fe0.8Mn0.2)2 alloys with the C15 Laves phase structure. A model for processing the spectra, which simultaneously takes the composite and magnetic nonequivalence of the positions of Fe atoms in these alloys, has been created and used, which makes it possible to obtain new data about the orientation of the axis of the easiest magnetization, the anisotropy of the hyperfine magnetic field, and the effect of substitution of Al and Mn atoms for Fe atoms on hyperfine parameters of Mössbauer spectra.

The Creation of Complex Multi-Component Models of Mössbauer Spectra Based on the Example of a Study of Hyperfine Interactions in Quasi-Binary Alloys with the Laves Phase Structure

In this paper, we describe a method for creating new custom models of partial Mössbauer spectrabased on the existing ones built into the SpectrRelax program without changing the program itself by writing code fragments in the built-in Lua programming language. The extension of the capabilities of the SpectrRelaxprogram is demonstrated using the example of studying hyperfine interactions of 57Fe nuclei in quasibinary Tb(Fe0.8Al0.2)2 and Ho(Fe0.8Mn0.2)2 alloys with the C15 Laves phase structure. A model for processingthe spectra, which simultaneously takes the composite and magnetic nonequivalence of the positions of Fe atoms in these alloys, has been created and used, which makes it possible to obtain new data about the orientationof the axis of the easiest magnetization, the anisotropy of the hyperfine magnetic field, and the effect of substitution of Al and Mn atoms for Fe atoms on hyperfine parameters of Mössbauer spectra.

Effect of Cr on the Microstructure and Mechanical Properties of the Al-Cu-Y-Zr Alloy

The present investigation aimed at the determination of Cr addition on microstructure, phase composition, and mechanical properties of the Al-Cu-Y-Zr alloy. Quasi-binary alloys of the ternary Al-Cu-Y system with atomic rotation of Cu/Y = 4/1 have a narrow solidification range with high solidus temperature. The addition of 0.3% Cr in the Al-5.1Cu-1.7Y-0.3Zr alloy provides a formation of a novel quaternary Al81–85Cu7–10Y3–4Cr5 phase. L12-Al3(Zr,Y) phase spherical particles with a diameter of 50 nm were nucleated during solution treatment at 600 °C. Al7Cr precipitates were not found in the microstructure. The main strengthening effect of 32.4 MPa and 29.1 MPa was achieved from L12 and θ’(Al2Cu) precipitates, respectively, in accordance with the calculation. The calculated hardness of 61.5HV based on the calculated σy is consistent with the experimental value of hardness. Al3Zr and Al7Cr phases should be in equilibrium with (Al) in accordance with the calculated polythermal section. However, transmission electron microscopy investigation demonstrates the Al3(Zr,Y) precipitates only. As a result, the dissolved Cr atom provides a slightly higher hardness in the rolled and annealed AlCuYZrCr alloy. A suitable combination of strength and ductility was observed both after rolling and after rolling with subsequent annealing at 150 °C for 3 h—the alloy exhibited a yield strength of 308–315 MPa, an ultimate tensile strength of 323–335 MPa, and an elongation to failure of 2.0–3.3%.

Mapping structural heterogeneity at the nanoscale with scanning nano-structure electron microscopy (SNEM)

Here we explore the use of scanning electron diffraction (also known as 4D-STEM) coupled with electron atomic pair distribution function analysis (ePDF) to understand the local order (structure and chemistry) as a function of position in a complex multicomponent system, a hot rolled, Ni-encapsulated, Zr65Cu17.5Ni10Al7.5 bulk metallic glass (BMG), with a spatial resolution of 3 nm. We show that it is possible to gain insight into the chemistry and chemical clustering/ordering tendency in different regions of the sample, including in the vicinity of nano-scale crystallites that are identified from virtual dark field images and in heavily deformed regions at the edge of the BMG. In addition to simpler analysis, unsupervised machine learning was used to extract partial PDFs from the material, modeled as a quasi-binary alloy, and map them in space. These maps allowed key insights not only into the local average composition, as validated by EELS, but also a unique insight into chemical short-range ordering tendencies in different regions of the sample during formation. The experiments are straightforward and rapid and, unlike spectroscopic measurements, don’t require energy filters on the instrument. We spatially map different quantities of interest (QoI’s), defined as scalars that can be computed directly from positions and widths of ePDF peaks or parameters refined from fits to the patterns. We developed a flexible and rapid data reduction and analysis software framework that allows experimenters to rapidly explore images of the sample on the basis of different QoI’s. The power and flexibility of this approach are explored and described in detail. Because of the fact that we are getting spatially resolved images of the nanoscale structure obtained from ePDFs we call this approach scanning nano-structure electron microscopy (SNEM), and we believe that it will be powerful and useful extension of current 4D-STEM methods.

Structure and properties of AL–Cu–Yb alloy with iron and silicon impurities

The effect of iron and silicon impurities on the phase composition and properties of the Al–4.3Cu–2.2Yb quasi-binary alloy was determined. In addition to the aluminum solid solution and dispersed eutectic ((Al) + Al8Cu4Yb) containing about 1 % of dissolved iron, Al3 Yb/(Al,Cu)17Yb2 and Al80Yb5Cu6 Si8 phases were identified in the cast alloy microstructure (the latter was not found in an alloy of a similar composition but without impurities). After homogenization annealing at t = 590 °C for 3 h, the structure is represented by compact fragmented and coagulated intermetallic compounds 1–2 μm in size, and a solid solution (Al) with a maximum copper content of 2.1 %. The hardness of deformed sheets significantly decreases after 30 min of annealing, and then changes slightly in the following 5.5 h of annealing at t = 150÷210 °C. After annealing at 180 °C (τ = 3 h), a substructure with a subgrain size of 200–400 nm is formed in the alloy structure. Rolled sheet softening occurs due to recovery and polygonization processes after annealing at temperatures up to 250 °C, and due to recrystallization after annealing at temperature above 300 °C. After annealing at 300 °C (τ = 1 h), the recrystallized grain size is 7 μm. The grain increases to 16 μm after annealing at t = 550 °C (τ = 1 h). The alloy under study has a high level of mechanical properties (conditional yield limit is 205–273 MPa, tensile strength is 215–302 MPa, relative elongation is 2.3–5.6 %) in the annealed state after rolling. Iron and silicon impurities do not lead to the formation of coarse lamellar intermetallic phases and do not reduce the ductility of the investigated alloy.

The influence of surface corrosion on microstructure and hydrogen permeability of Nb-Hf-Co dual-phase alloys

Nb-HfCo quasi-binary alloys are prospective hydrogen separation membrane materials due to their price advantage and excellent hydrogen permeation performance. However, a small amount of acidic gas (e.g. CO2 and H2S) is often mixed in the feed gas, which corrodes the surface of the alloy membrane in the process of their application. Up to now, the corrosion behaviours and the corresponding influencing factors have not been studied yet, and the relationship between the microstructure and corrosion resistance has yet to be established. To this end, NbxHf(100−x)/2Co(100−x)/2 (x = 40.60) dual-phase alloys were prepared by arc melting and then corroded using an electrochemical workstation, and their microstructure, corrosion resistance and hydrogen permeability before and after corrosion were systematically studied. The results show that an oxide layer (Nb2O5, HfO2, CoO) is formed around the alloy surface after corrosion, and the order of corrosion resistance of these alloys is as follows: Nb60Hf20Co20 < Nb40Hf30Co30 < Nb50Hf25Co25 < Nb45Hf27.5Co27.5. The Nb45Hf27.5Co27.5 alloy, with the strongest corrosion resistance, exhibits a high hydrogen permeability of 6.70 × 10−8 mol H2 m−1 s−1 Pa−1/2 at 673 K after corrosion, which is the highest value reported in this alloy system up to now. In addition, the hydrogen permeation mechanism for Nb-based alloy membranes in a corrosive environment, is proposed for the first time. The present work demonstrates that Nb45Hf27.5Co27.5 alloy is an attractive candidate for hydrogen separation in an acidic corrosive environment.

Effect of External Impacts on the Structure and Martensitic Transformation of Rapidly Quenched TiNiCu Alloys

TiNi-TiCu quasibinary system alloys with a high Cu content produced by rapid quenching from liquid state in the form of thin amorphous ribbons exhibit pronounced shape memory effect after crystallization and are promising materials for miniaturized and fast operating devices. There is currently no complete clarity of the mechanisms of structure formation during crystallization from the amorphous state that determine the structure-sensitive properties of these alloys. This work deals with the effect of the initial amorphous state structure and crystallization method of the alloys on their structure and phase transformations. To this end the alloy containing 30 at.% Cu was subjected to thermal and mechanical impact in the amorphous state and crystallized using isothermal or electropulse treatment. We show that after all types of treatment in the amorphous state the structure of the alloy remains almost completely amorphous but the characteristic temperatures and enthalpy of crystallization become slightly lower. Isothermal crystallization of alloy specimens produces a submicrocrystalline structure with an average grain size in the 0.4–1.0 μm range whereas electropulse crystallization generates a bimorphic structure consisting of large 4–6 μm grains and 2–3 μm high columnar crystals in the vicinity of the surface. The grains have nanosized plate-like and subgrain structures. The largest grains are observed in thermally activated samples, meanwhile, mechanical impact in the amorphous state leads to the formation of equiaxed finer grains with a less defective subgrain structure and to the shift of the temperature range of the martensitic transformation toward lower temperatures.

Structure and functional properties of rapidly quenched TiNiCu alloys with high copper contents

Thin materials exhibiting the shape memory effect, with a narrow temperature hysteresis, are required to create miniature and high-speed devices. Quasi-binary intermetallic TiNi-TiCu alloys with high copper contents (more than 10 at %) demonstrate the reversible martensitic transformation with a small (4-6 K) hysteresis. Alloys of the TiNi–TiCu system with a copper content of 30–40 at.% were fabricated in an amorphous state by the planar flow casting technique at a melt cooling rate of 106 K/s in the form of ribbons 30–50 μm thick. The alloy samples were subjected to dynamic crystallization using a single electric current pulse with duration of 5 ms. X-ray diffraction studies revealed almost fully martensitic state of the alloys with B19 structure at room temperature. TEM examination showed their structure to contain typical B19-martensite plates with a mean size of 20–80 nm. At the same time, the alloys exhibit a one-stage phase martensitic transformation B2↔B19 in the temperature range of (55÷75)°C, as well as pronounced shape memory effect, whose properties are largely determined by the structural parameters of the alloys.

In situ mapping of chemical segregation using synchrotron x-ray imaging

Abstract

A comparative analysis of magnetic properties and microstructure of high coercivity Sm(CoCuFe)5 quasi-binary alloys in the framework of fractal geometry

The results of the micro- and nanostructures investigation of Sm(CoCuFe)5 alloys by means of scanning electron and atomic force microscopy are presented. It was shown that sequential high- and low-temperature heat treatments lead to the formation of a homogeneous microstructure with nanoscale compositional heterogeneities. Such a structure provides a coercive filed of up to 32 kOe. The coercivity and remanent magnetization of the samples in the temperature range from 300 to 700 K linearly decrease. The predominant coercivity mechanism in these materials is pinning on nanoscale inhomogeneities with an increased copper concentration. The fractal dimension of the surface of the Sm(CoCuFe)5 alloy metallographic specimen was determined at different stages of heat treatments. The comparative analysis of magnetic properties and microstructure in the framework of fractal geometry was carried out.

Theoretical investigation of V2xFe2(1-x)Zr and ScxY1-xFe2 (0

Combining experimental XRD phase analysis and melting-annealing temperature with the high-through first-principles calculation, the structural stability, mechanical strength and electronic properties of V-Fe-Zr and Sc-Fe-Y quasi-binary alloys have been systematically investigated. The calculation of formation enthalpy and the free energy show that VxFe2(1-x)Zr alloy has a completely ordered solid solution at low temperature, while ScxY1-xFe2 alloy needs to be annealed at a high temperature up to 700°C to reach disordered fusion state. The bond energy model can accurately predict the total energy and bulk modulus of the target alloy structure at each substitution concentration, whose numerical differences per atom between the calculated results and predicted ones by bond energy model (BEM) are less than 1 meV and 0.2 GPa, respectively. The elastic modulus obtained by fitting within Birch-Murnaghan equation and calculating from elastic constants has good consistency.

Quasi-Binary Transition Metal Dichalcogenide Alloys: Thermodynamic Stability Prediction, Scalable Synthesis, and Application.

Transition metal dichalcogenide (TMDCs) alloys could have a wide range of physical and chemical properties, ranging from charge density waves to superconductivity and electrochemical activities. While many exciting behaviors of unary TMDCs have been demonstrated, the vast compositional space of TMDC alloys has remained largely unexplored due to the lack of understanding regarding their stability when accommodating different cations or chalcogens in a single-phase. Here, a theory-guided synthesis approach is reported to achieve unexplored quasi-binary TMDC alloys through computationally predicted stability maps. Equilibrium temperature-composition phase diagrams using first-principles calculations are generated to identify the stability of 25 quasi-binary TMDC alloys, including some involving non-isovalent cations and are verified experimentally through the synthesis of a subset of 12 predicted alloys using a scalable chemical vapor transport method. It is demonstrated that the synthesized alloys can be exfoliated into 2D structures, and some of them exhibit: i) outstanding thermal stability tested up to 1230 K, ii) exceptionally high electrochemical activity for the CO2 reduction reaction in a kinetically limited regime with near zero overpotential for CO formation, iii) excellent energy efficiency in a high rate Li-air battery, and iv) high break-down current density for interconnect applications. This framework can be extended to accelerate the discovery of other TMDC alloys for various applications.

Spin Fluctuations and Concentration Magnetic Transitions in Chiral Helical Ferromagnets Fe1 – xCoxSi

The fluctuation theory is applied to the study of concentration transformations in Fe1 – xCoxSi disordered quasi-binary chiral helical ferromagnetic alloys with the Dzyaloshinsky–Moriya interaction. The ground state is described on the basis of the LDA + U + SO approximations used in ab initio calculations, with additional allowance for concentration fluctuations associated with the difference in the potentials of the intraatomic Hubbard interaction at sites occupied by iron and cobalt atoms. The solutions of the obtained magnetic equations of state for the long- and short-range ordered phases with right and left magnetic chirality are considered. The concentration dependences of the parameters of the intermodal interaction and the area of compositions, in which the first-order magnetic phase transitions induced by thermal fluctuations are accompanied by the occurrence of spin helix fluctuations, are studied. It is shown that the transition with a change in the sign of magnetic chirality is accompanied by the appearance of a minimum on the concentration dependence of the mode–mode parameter and the emergence of quantum helical ferromagnetism with noticeable intensification of zero spin fluctuations.

Спиновые флуктуации и концентрационные магнитные переходы в киральных геликоидальных ферромагнетиках Fe-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-Si

The fluctuation theory is applied to the study of concentration transformations in chiral helicoidal ferromagnetic quasi-binary unordered Fe1-xCoxSi alloys with Dzyaloshinsky-Moriya interaction. The ground state is described on the basis of the LDA + U + SO approximations used in ab initio calculations with additional allowance for concentration fluctuations associated with the difference in the potentials of the intra-atomic Hubbard interaction at the sites occupied by iron and cobalt. Solutions of the obtained equations of the magnetic state for the phases of the long-range and short-range orders with the right and left magnetic chirality are considered. The concentration dependences of the parameters of the intermode interaction are investigated, and the regions of the compositions in which magnetic phase transitions of the first kind induced by thermal fluctuations take place, accompanied by the appearance of fluctuations of the spin helix. It is shown that the transition with a change of the sign of magnetic chirality is accompanied by the appearance of a minimum in the concentration dependence of the mode-mode parameter and the appearance of quantum helicoidal ferromagnetism with a noticeable increase in zero spin fluctuations.

Vacancy formation energy in CuNiCo equimolar alloy and CuNiCoFe high entropy alloy: ab initio based study

In this research, the interaction between the composing elements of CuNiCoFe high entropy alloy with vacancies was investigated employing EMTO-LSGF and EMTO-CPA codes based on DFT calculations. In this regard, for the equimolar CuNiCo and CuNiCoFe alloys with the face center cubic structure, variation of vacancy formation energy was calculated as a function of the number of the nearest neighbors of composing elements. The results reveal that copper atoms have the strongest interaction with vacancy among all elements in both CuNiCo and CuNiCoFe equimolar alloys. The mean local vacancy formation energy (<Ef>) was calculated based on its distribution function for both alloys. Since the differences between the interaction energy of Cu-vacancy and other metal-vacancies in these two equimolar alloys was significant, to calculate the distribution function of vacancy formation energy and its dependence to temperature, equimolar CuNiCo and CuNiCoFe were estimated by a quasi-binary alloy. In this quasi-binary alloy copper is one of the components and other elements could be other components. The results show that <Ef> of equimolar CuNiCoFe is 0.176 eV greater than that for CuNiCo equimolar alloy. The dependence of effective vacancy formation energy (E¯f) and renormalized vacancy formation energy (E˜f) to temperature is estimated using the single-site mean field approximations with energy parameters obtained in ab initio calculations. In these calculations, the alloy configurational entropy was used. The results indicate higher E¯f and E˜f values with increasing temperature from 400 to 2500K in both alloys. The values of E¯f and E˜f for CuNiCoFe are greater than those in CuNiCo within this range of temperature.

Determination of surface tension of liquid ternary Ni–Cu–Fe and sub-binary alloys

ABSTRACTExperimental data in the literature are almost limited to determine the thermophysical properties of multicomponent complex alloys, especially due to the inability of laboratories to achieve the desired ideal conditions, due to the difficulty of protection from oxidation at high temperatures and other contamination at high temperatures, due to time and cost in laboratory studies. Due to these reasons, the theoretical data obtained in this subject is of great importance. In this study, a series of geometric and physical models, such as Chou’s general solution model (GSM), Muggianu’s Model, Kohler’s Model, Toop’s Model, Hillert’s Model, Guggenheim’s Model, Butler’s Model, Egry’s Model and ideal solution model for quasi-binary alloy system for Section A: Ni0.4(1 – x)CuxFe0.6(1 – x). and Section B: (NixCu0.2Fe0.8 – x) are used to calculate the surface tension-composition and surface tension-temperature curves of the Cu-Fe-Ni ternary liquid system are plotted. The data for this process is evaluated by means of an extended Redlich-Kister-Muggianu polynomial fit to the experimental values of the surface tensions of the binary liquid alloy systems. The obtained results for these models are also compared with the available data in the literature and relatively good agreements are observed. In addition, the surface segregation having important key factor in determining surface tension of the liquid alloy Ni-Fe-Cu has also been investigated in this work.

Structure and phase transformations in copper-alloyed rapidly melt-quenched Ni50Ti32Hf18-based alloys with high-temperature shape memory effect

Methods of transmission and scanning electron microscopy, chemical microanalysis, electron diffraction, and X-ray diffraction have been used to carry out the comparative study of the structure and chemical and phase composition of thin ribbons of four quasi-binary alloys (Ni50Ti32Hf18, Ni45Ti32Hf18Cu5, Ni35Ti32Hf18Cu15, and Ni25Ti32Hf18Cu25) obtained in the amorphous state by rapid quenching from the melt by jet spinning. The critical temperatures of the devitrification and B2 ↔ B19′ martensitic transformation of the alloys have been determined based on the data of temperature dependences of the electrical resistivity. The specific features of the formation of the ultrafine-grained structure upon the devitrification and of the phase transformations have been studied depending on the heat-treatment regimes and chemical composition of the alloys (concentration of copper atoms).