Range Of Alloy Compositions Research Articles

Retained Free Energy with Enhanced Nucleation during Electrostatic Levitation of Undercooled Fe-Co Alloys

Double recalescence in many ferrous alloy systems involves rapid solidification of metastable ferrite from the undercooled melt with subsequent transformation to stable austenite. Containerless processing is used to monitor the process using pyrometry and high-speed cinematography such that delay behavior can be predicted based on the application of the retained damage model (RDM). When comparing Fe-Cr-Ni alloys to Fe-Co alloys, the cluster attachment rate is enhanced while free energy retention is reduced. These trends are tied to specific alloy properties. A retained free energy criterion is proposed based on the ratio of thermophysical properties used to define the transformation driving force such that the thermodynamic limit for energy retention may be predicted. Surprisingly, at long delay times, healing occurs such that much of the retained free energy is not available to enhance the transition from metastable to stable phases. At delay times less than one second, no healing is observed and the RDM correctly predicts transformation delay behavior over a wide range of alloy compositions.

Automated assessment of a kinetic database for fcc Co–Cr–Fe–Mn–Ni high entropy alloys

The development of accurate kinetic databases by parametrizing the composition and temperature dependence of elemental atomic mobilities, is essential for correct multicomponent calculations and simulations. In this work the automated assessment procedure for the establishment of CALPHAD-type kinetic databases is proposed, including the storage of raw data and assessment results, automatic weighting of data, parameter selection and automated reassessments. This allows the establishment of reproducible up-to-date databases. The proposed software, written in python, is applied to the assessment of a kinetic database for the fcc Co–Cr–Fe–Mn–Ni high entropy alloy using only tracer diffusion data for a sharp separation of thermodynamic and kinetic data. The established database is valid for the whole composition range of the five-component high entropy alloy.

Elastic dipole tensors and relaxation volumes of point defects in concentrated random magnetic Fe-Cr alloys

Point defects in body-centred cubic Fe, Cr and concentrated random magnetic Fe-Cr are investigated using density functional theory and theory of elasticity. The volume of a substitutional Cr atom in ferromagnetic bcc Fe is approximately 18% larger than the volume of a host Fe atom, whereas the volume of a substitutional Fe atom in antiferromagnetic bcc Cr is 5% smaller than the volume of a host Cr atom. In an alloy, elastic dipole P and relaxation volume Ω tensors of vacancies and self-interstitial atom (SIA) defects exhibit large fluctuations, with vacancies having negative and SIA large positive relaxation volumes. Dipole tensors of vacancies are nearly isotropic across the entire alloy composition range, with diagonal elements Pii decreasing as a function of Cr content. Fe-Fe and Fe-Cr SIA dumbbells are more anisotropic than Cr-Cr dumbbells. We find that fluctuations of elastic dipole tensors of SIA defects are primarily associated with the variable crystallographic orientations of the dumbbells. Statistical properties of tensors P and Ω are analysed using their principal invariants, suggesting that point defects differ significantly in alloys containing below and above 10% at. Cr. The von Mises stresses caused by dumbbells are notably larger than those caused by vacancies. The relaxation volume of a vacancy depends sensitively on whether it occupies a Fe or a Cr lattice site. A correlation between elastic relaxation volumes and magnetic moments of defects found in this study suggests that magnetism is a significant factor influencing elastic fields of defects in Fe-Cr alloys.

Fang–Howard wave function modelling of electron mobility in AlInGaN/AlN/InGaN/GaN double heterostructures* *Project supported by the Xi’an Science and Technology Program, China (Grant No. 2019217814GXRC014CG015-GXYD14.3) and the Open Project of Key Laboratory of Wide Band-gap Semiconductor Materials, Ministry of Education, China (Grant No. Kdxkf2019-01).

To study the electron transport properties in InGaN channel-based heterostructures, a revised Fang-Howard wave function is proposed by combining the effect of GaN back barrier. Various scattering mechanisms, such as dislocation impurity (DIS) scattering, polar optical phonon (POP) scattering, piezoelectric field (PE) scattering, interface roughness (IFR) scattering, deformation potential (DP) scattering, alloy disorder (ADO) scattering from InGaN channel layer, and temperature-dependent energy bandgaps are considered in the calculation model. A contrast of AlInGaN/AlN/InGaN/GaN double heterostructure (DH) to the theoretical AlInGaN/AlN/InGaN single heterostructure (SH) is made and analyzed with a full range of barrier alloy composition. The effect of channel alloy composition on InGaN channel-based DH with technologically important Al(In,Ga)N barrier is estimated and optimal indium mole fraction is 0.04 for higher mobility in DH with Al0.4In0.07Ga0.53N barrier. Finally, the temperature-dependent two-dimensional electron gas (2DEG) density and mobility in InGaN channel-based DH with Al0.83In0.13Ga0.04N and Al0.4In0.07Ga0.53N barrier are investigated. Our results are expected to conduce to the practical application of InGaN channel-based heterostructures.

Aluminium nanoparticles alloyed with other earth-abundant plasmonic metals for light trapping in thin-film a-Si solar cells

Plasmonic nanoparticles have been used for a variety of applications, including light trapping in thin film solar cells. Due to costs associated with the most commonly studied plasmonic metals (Au and Ag), other metals such as Al, In, Mg and Ni have recently emerged as alternative, earth-abundant plasmonic metals. Though the plasmonic properties of these metals have been studied individually (particularly Al) there have been few reports on the plasmonic properties of alloys of earth-abundant plasmonic metals. This is of interest because alloying could offer a degree of plasmonic tunability, improved corrosion resistance and drive down costs. In this report we study the light trapping ability of Al–Cu, Al–Au, Al–Ni, Al–In and Al–Mg alloys in an amorphous silicon solar cell. We use a combination of Mie Theory, Transfer Matrix Modelling and Effective Medium Theory to develop a simple numerical solution to this problem, and benchmark it against known theoretical results. Al–In and Al–Mg alloy nanoparticles emerge as the most suitable (of the candidates studied) for this application. Al (75%) In (25%) (by volume fraction) nanoparticles of radius 15 nm are shown to improve the absorption of amorphous silicon by 18%. We provide maps of the plasmonic behaviour of alloy nanoparticles for a range of radii (1-100 nm) and alloy compositions, enabling materials design. Therefore, we hope that this report will spur further interest into the utility of Al-alloy nanoparticles for plasmonic applications.

A Universal Model for DX‐Center Binding Energy in Cubic III–V Compounds

Based on the approach suggested by Chadi and Chang, a simple analytical model is suggested for estimating binding energies of DX‐centers in n‐type zinc‐blende semiconductor alloys with direct–indirect bandgap transition. Comparison of the model predictions with numerous experiments shows the only adjustable model parameter to be independent of either kind of n‐type impurity or particular alloy. Though the nature of such a universality is not completely clear, the model can be helpful for practical estimations and modeling/simulation of semiconductor devices utilizing the ternary and quaternary compounds. Application of the model to wide‐bandgap zinc‐blende semiconductors reveals a general trend of decreasing DX‐center binding energy with the bandgap, resulting in narrowing the composition range of alloys where DX‐center formation dominates over that of conventional shallow donors. Considering DX‐centers with multiple‐charge impurity statistics enables accurate calculation of free electron concentration and concentration of ionized impurities in the space‐charge regions.

Optical gain and threshold current density for mid-infrared GaSbBi/GaSb quantum-well laser structure

This work is focused on band structure engineering and optical proprieties of GaSbBi/GaSb type I quantum well mid-infrared laser structure on GaSb substrate. Wherefore, the band alignment is tailored and optoelectronic properties are investigated for the proposed structure based on GaSb1−xBix/GaSb hetero-interfaces in the range of alloy compositions between 0≤x≤0.14. The electron and holes effective masses are deduced from the expressions extracted from the k.p model. The laser structure is designed to function at 2.7 μm at room temperature (RT), the addition of bismuth into the GaSb active region improve a preferment optical gain and the threshold current density (Jth) including computation of radiative, non radiative and Auger recombination. For typical carrier injection 5×1018cm-3at 300 k peak gain value of the order of 2000 cm−1 are reached and a modal gain equal to 96 cm−1 can be attained. A Jth around1.2 kA/cm2 is expected through moderate optical losses.

High-throughput ion irradiation of additively manufactured compositionally complex alloys

Several advanced nuclear reactor designs promise efficiency and safety improvements over the current reactor fleet but are limited by the current set of ASME code-qualified materials. Novel alloys including high-entropy alloys (HEAs), and more broadly compositionally complex alloys (CCAs), have shown promising irradiation-tolerance. However, the vast range of alloy compositions adds to an already time-consuming alloy development process. In this study, to accelerate the development of novel alloys for nuclear applications, a high-throughput (HTP) methodology has been employed. Additive manufacturing has been used to produce a compositional array of unary, binary, ternary, and quaternary alloys, including several CCAs, which span the Cr-Fe-Mn-Ni composition space. The compositional array was homogenized at 1000°C for 24 hours and each sample was irradiated using 4-MeV Ni2+ ions at room temperature to a peak damage of 50 dpa, as estimated using SRIM, at the University of Wisconsin Ion Beam Laboratory. A custom XY stage was built to accommodate the large compositional array and half of each sample was masked during irradiation enabling both the irradiated and unirradiated properties of each alloy to be characterized side-by-side. Each alloy was characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and nanoindentation. CALPHAD simulations spanning the entire Cr-Fe-Mn-Ni composition space at 1000°C were performed to compare predicted equilibrium phases with phases identified experimentally from the unirradiated regions of each alloy. Nanoindentation measurements indicate radiation-induced hardening ranging from ~1-1.5 GPa in each of Cr-Fe-Mn-Ni CCAs, which is relatively insensitive to modest changes in alloy composition and comparable to hardening observed in neutron irradiated Cr-Fe-Mn-Ni CCAs in the literature. Overall, a substantial time savings was realized by employing HTP synthesis, irradiation, and characterization in this study compared to conventional techniques, the implications of which are discussed.

High-Throughput Characterization of Composition and Performance of Titanium Alloys Based on Nanoindentation Technology and EPMA

Traditional high-throughput experiments increase the test efficiency by designing component gradient tests and other methods. This article intends to improve the traditional high-throughput experiments and proposes an experimental scheme combining nanoindentation technology and electron probe microanalysis (EPMA). Based on a new Ti-Mo-Al-Zr-Cr-Sn alloy, micro-region composition and corresponding performance at multiple indentations are directly characterized, including a series of different alloy compositions composed of 8 elements such as Mo, Al and the corresponding hardness (H) and elastic modulus (E). Then the principal analysis method in statistics, the theory of molybdenum equivalent and aluminum equivalent are used to process the obtained data, and a series of atlases such as "E-H-component characteristic parameters" and "E-H-alloy equivalents" are constructed, which has achieved high-throughput characterization of the relationship between composition and performance of titanium alloy. Related work can not only quickly determine the alloy composition range corresponding to high E and high H values, but also provide guidance for further optimization of titanium alloy composition design.

Influence of the Composition on the Environmental Impact of a Casting Magnesium Alloy

The influence of the composition of magnesium alloys on their environmental impact was analyzed. In order to perform a more accurate environmental impact calculation, life cycle assessment (LCA) with the ReCiPe 2016 Endpoint and IPCC 2013 GWP (100 y) methodology was used, taking the EcoInvent AZ91 magnesium alloy dataset as reference. This dataset has been updated with the material composition range of several alloys included in the European standard EN 1753:2019. The balanced, maximum, and minimum environmental impact values were obtained. In general, the overall impact of the studied magnesium alloys varied from 3.046 Pt/kg to 4.853 Pt/kg and from 43.439 kg CO2 eq./kg to 55.427 kg CO2 eq./kg, depending on the composition. In the analysis of maximum and minimum environmental impacts, the alloy that had the highest uncertainty was 3.5251, with a range of ±7.20%. The element that contributed the most to increase its impact was silver. The AZ91 alloy, provided by the EcoInvent dataset, had a lower environmental impact than all the magnesium alloys studied in this work. The content of critical raw materials (CRMs) was also assessed, showing a high content in CRMs, between 89.72% and 98.22%.

Ab Initio Study of Stability, Local Order, and Phase Diagram For a Series of bcc-based Transition Metal Alloys

A parameter-free electronic structure approach is applied to the study of stability and chemical order in the 15 substitutional body-centered cubic (bcc)-based alloys made of the six transition metals of groups 5 (V, Nb, Ta) and 6 (Cr, Mo, W) of the periodic table. The method is based on a Green’s function description of the electronic structure of the random alloys. Configurational order is treated within the generalized perturbation method, and temperature effects are examined with a generalized mean-field approach. In contrast to the results summarized in the assessed phase diagrams, stability and ordering trends are predicted in a broad range of alloy composition for at least seven alloys, and explanation is found in their electronic structure properties. Short-range order results, thermodynamics analysis, and bcc-based phase diagrams are also presented.

Catalytic activity of electrodeposited ternary Co–Ni–Rh thin films for water splitting process

The influence of the deposition parameters on the composition and structure of Co–Ni–Rh ternary alloys was studied. The catalytic activity of the coatings for the hydrogen evolution process was investigated in 6 M KOH electrolyte. The thin films were deposited from baths containing a mixture of Co2+, Ni2+, and Rh3+ chloride complexes. A wide range of alloy compositions were achieved by applying different deposition potentials from −0.5 to – 0.9 V vs SCE. The obtained coatings were examined by energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) techniques. The surface morphology and chemical composition were also characterized with scanning electron microscopy (SEM) combined with EDX. The hydrogen evolution activity of some selected electrodes were examined in 6 M KOH using current-potential curve and electrochemical impedance spectroscopy (EIS) techniques. The SEM results showed that the surface morphology of the electrodes can be tailored by modification of the deposition potential. The higher exchange current densities were observed in catalytic measurements for the ternary alloys, which confirms their better catalytic activity in the water-splitting process.

Tuning carrier localization in In-rich InGaN alloys: Correlations between growth kinetics and optical properties

Alloy clustering and consequent carrier localization in InGaN alloys are important aspects with large effect in materials’ optoelectronic properties and related device operation. Their importance is even higher for alloy compositions close to midrange where alloy compositional fluctuations get stronger. Such fluctuations are considered a result of thermodynamic immiscibility and indium segregation to structural defects. However, their dependence on the epitaxial growth process is unknown. Here, we examined the dependence of the degree of resulting carrier localization on growth surface kinetics in InGaN alloys developed by plasma-assisted molecular beam epitaxy. We deposited a large number of alloy thin films, heteroepitaxially on GaN(0001), under different growth temperatures and metallic surface coverage during growth but with similar compositions (∼40%), thicknesses, and growth rates. Their structure was examined by x-ray diffraction. Carrier localization phenomena were investigated employing temperature dependent photoluminescence, while spectroscopic ellipsometry was applied to determine the films’ complex dielectric function. A strong correlation of compositional uniformity and decreased carrier localization with growth conditions that reduce adatoms surface mobility and enhance “out-of-equilibrium” epitaxy character was revealed. This correlation was largely independent of the effects on films' structural properties. Thus, the importance of epitaxial surface kinetic effects on alloy clustering and localization is highlighted. These results are expected to be applicable to the entire alloy composition range and could pave the way for on demand optimal tuning of their optoelectronic properties depending on application requirements.

Effect of bismuth–tin composition on bonding strength of zinc particle–mixed copper nanoparticle/bismuth–tin solder hybrid joint

In this study, the effect of Bi–Sn composition on the bonding strength of Zn-mixed hybrid joints composed of SiC/Cu and SiC/direct bonded copper (DBC) was examined. For both joints, the bonding strength exhibited a similar dependence on Bi–Sn composition, and the maximum strength obtained for the average Bi fraction in the Bi–Sn alloy particles was 38.2 wt%. This composition is more Sn-rich than the eutectic composition of the Bi–Sn alloy. The bonding strength of the SiC/Cu joints was lower than that of the SiC/DBC joints throughout the entire Bi–Sn alloy composition range. The degree of Bi segregation at the interfacial region decreased with a decreasing Bi fraction in the Bi–Sn particles and was correlated with the bonding strength for the Bi fraction below 38.2 wt%. Defects such as voids and cracks were also observed in the bonding layer, which were likely a result of the difference in the bonding strengths between the SiC/Cu and SiC/DBC joints. Furthermore, delamination of the bonding layer at the interface was observed in the joint that had Sn particles as the starting material. These results indicate that Zn mixing in the hybrid joint enables the reduction of the Bi fraction of the Bi–Sn alloy, leading to improved bonding strength.

The Thermoelectric Properties of n-Type Bismuth Telluride: Bismuth Selenide Alloys Bi2Te3-x Se x.

Alloying bismuth telluride with antimony telluride and bismuth selenide for p- and n-type materials, respectively, improves the thermoelectric quality factor for use in room temperature modules. As the electronic and thermal transports can vary substantially, the alloy composition is a key engineering parameter. The n-type Bi2Te3-xSex alloy lags its p-type counterpart in thermoelectric performance and does not lend itself as readily to simple transport modeling which complicates engineering. Combining literature data with recent results across the entire alloy composition range, the complex electronic structure dynamics and trends in lattice thermal conductivity are explored. Spin-orbit interaction plays a critical role in determining the position and degeneracy of the various conduction band minima. This behavior is incorporated into a two-band effective mass model to estimate the transport parameters in each band. An alloy scattering model is utilized to demonstrate how phonon scattering behaves differently on either side of the intermediate ordered compound Bi2Te2Se due to chalcogen site occupancy preference. The parametrization of the electronic and thermal transports presented can be used in future optimization efforts.

The reactivity, selectivity and structure of 2-butanol on clean and oxygen-covered Au/Pd(100) alloys

The surface chemistry of 2-butanol is studied on clean and oxygen-saturated Au/Pd(100) alloys using a combination of temperature-programmed desorption (TPD) and reflection-absorption infrared spectroscopy (RAIRS) as a function of alloy composition. The alloys are synthesized by evaporating gold on a Pd(100) substrate and heating to various temperatures to obtain a range of alloy compositions. It is found that 2-butanol initially forms 2-butoxide species both on clean and oxygen-saturated Au/Pd(100) alloys and can react either to reform 2-butanol or undergo a β-hydride elimination reaction to form 2-butanone. No 2-butanone is formed on alloys with palladium coverages below ~0.5 ML, and the 2-butanone yield increases linearly with palladium coverage at high coverages as the proportion of Pd‒Pd bridge sites on the alloy increases. Some ethylene is formed on alloys with palladium coverages between ~0.4 and 0.6 ML. Saturating the gold-palladium alloy with oxygen for palladium coverages above ~0.5 ML, where oxygen can dissociatively adsorb on the surface at pressures attainable in ultrahigh vacuum, increases the selectivity to 2-butanone formation to 100% for palladium coverages above ~0.75 ML, when Pd‒Pd bridge sites are present, while the selectivity decreases for palladium coverages of ~0.6 ML, when both isolated and bridge sites are present. This indicates that alloy catalysts containing just bridge sites at gold coverages below ~0.35 ML should be the most selective, while still being able to dissociatively adsorb oxygen

Design of Nb-based multi-phase alloy membranes for high hydrogen permeability and suppressed hydrogen embrittlement

Nb-Hf-Co alloys, consisting of a multi-phase microstructure with primary BCC-(Nb, Hf) and eutectic {BCC-(Nb, Hf) + HfCo} phases, are a potential alloys for hydrogen separation and purification. However, the compositional window, comprising of the above phases, has not yet been established because of lack of important information concerning the phase diagrams. To address this need, this study first calculated the phase diagram and related phase equilibria information of this class of alloys, by using the CALPHAD approach, and established a new compositional window suitable for hydrogen permeation. The alloys in this window exhibit very high hydrogen permeability. In particular, Nb45Hf27.5Co27.5 exhibits the highest permeability of 5.32 × 10−8 mol H2 m−1s−1Pa−0.5 at 673 K, which is the best among all the Nb-based multi-phase alloys. Secondly, the boundary for ductile to brittle transition-hydrogen concentration (DBTC) of the Nb-HfCo multi-phase alloy was determined for the first time and found to occur at around 0.72–0.82 H/M, which reveals the fundamental reasons for brittle failure occurring during hydrogen permeation. From the point of DBTC, a new design concept for Nb-based hydrogen permeable membranes is proposed and the factors affecting their brittle failure are analysed. Thirdly, to verify the feasibility of the above concept, Nb45Hf27.5-xTixCo27.5 (x = 0 … 10) alloys were designed and comprehensively studied. It is demonstrated that Nb45Hf20Ti7.5Co27.5 alloy exhibits excellent hydrogen permeability with enhanced hydrogen embrittlement under appropriate permeation conditions. The significance of the study is that the best composition range for hydrogen-permeable Nb-HfCo alloys is explored, and some novel hydrogen-permeable alloys can be easily developed by analysing their absorption pressure-composition isotherms in combination with the newly explored DBTC.

Rapid heating blow molding of metallic glasses by infrared heating

Rapid heating blow molding is introduced as a thermoplastic molding process for bulk metallic glasses. Infrared heating allows the selective and quick heating of an object with precise control, providing the opportunity to achieve much lower viscosities than in conventional blow molding. These low viscosities enable short processing times, high strain rates, large strains, and good surface finishes even under a forming pressure as low as 105 ​Pa. This technology permits the blow molding of glassy metal sheets with a wide range of alloy compositions.

Ultrasonic Processing for Structure Refinement: An Overview of Mechanisms and Application of the Interdependence Theory.

Research on ultrasonic treatment (UST) of aluminium, magnesium and zinc undertaken by the authors and their collaborators was stimulated by renewed interest internationally in this technology and the establishment of the ExoMet program of which The University of Queensland (UQ) was a partner. The direction for our research was driven by a desire to understand the UST parameters that need to be controlled to achieve a fine equiaxed grain structure throughout a casting. Previous work highlighted that increasing the growth restriction factor Q can lead to significant refinement when UST is applied. We extended this approach to using the Interdependence model as a framework for identifying some of the factors (e.g., solute and temperature gradient) that could be optimised in order to achieve the best refinement from UST for a range of alloy compositions. This work confirmed established knowledge on the benefits of both liquid-only treatment and the additional refinement when UST is applied during the nucleation stage of solidification. The importance of acoustic streaming, treatment time and settling of grains were revealed as critical factors in achieving a fully equiaxed structure. The Interdependence model also explained the limit to refinement obtained when nanoparticle composites are treated. This overview presents the key results and mechanisms arising from our research and considers directions for future research.

Precipitation and hardening in irradiated low alloy steels with a wide range of Ni and Mn compositions

Mn-Ni-Si intermetallic precipitates (MNSPs) that are observed in some Fe-based alloys following thermal aging and irradiation are of considerable scientific and technical interest. For example, large volume fractions (f) of MNSPs form in reactor pressure vessel low alloy steels irradiated to high fluence, resulting in severe hardening induced embrittlement. Nine compositionally-tailored small heats of low Cu RPV-type steels, with an unusually wide range of dissolved Mn (0.06–1.34 at.%) and Ni (0.19–3.50 at.%) contents, were irradiated at ≈ 290 °C to ≈ 1.4 × 1020 n/cm2 at an accelerated test reactor flux of ≈3.6 × 1012 n/cm2-s (E > 1 MeV). Atom probe tomography shows Mn-Ni interactions play the dominant role in determining the MNSP f, which correlates well with irradiation hardening. The wide range of alloy compositions results in corresponding variations in precipitates chemistries that are reasonably similar to various phases in the Mn-Ni-Si projection of the Fe based quaternary. Notably, f scales with ≈ Ni1.6Mn0.8. Thus f is modest even in advanced high 3.5 at.% Ni steels at very low Mn (Mn starvation); in this case Ni-silicide phase type compositions are observed.