Function Of Alloy Composition Research Articles

Electroluminescence from Ge1−ySny diodes with degenerate pn junctions

The light emission properties of GeSn pn diodes were investigated as a function of alloy composition and doping levels. Very sharp interfaces between contiguous ultra-highly doped p- and n-layers were obtained using in situ doping with B2H6 and P(SiH3)3 in a chemical vapor deposition environment, yielding nearly ideal model systems for systematic studies. Changes in the doping levels and layer Sn concentrations are shown to greatly affect the electroluminescence spectra. This sensitivity should make it possible to optimize the emission efficiency for these structures in the interesting quasi-direct regime, for which direct gap luminescence is observed due to the proximity of the conduction band quasi-Fermi level to the minimum of the conduction band at the center of the Brillouin zone. Such structures represent the basic building block of Ge-based electrically pumped lasers.

Radiation tolerance of neutron-irradiated model Fe–Cr–Al alloys

The Fe–Cr–Al alloy system has the potential to form an important class of enhanced accident-tolerant cladding materials in the nuclear power industry owing to the alloy system's higher oxidation resistance in high-temperature steam environments compared with traditional zirconium-based alloys. However, radiation tolerance of Fe–Cr–Al alloys has not been fully established. In this study, a series of Fe–Cr–Al alloys with 10–18 wt % Cr and 2.9–4.9 wt % Al were neutron irradiated at 382 °C to 1.8 dpa to investigate the irradiation-induced microstructural and mechanical property evolution as a function of alloy composition. Dislocation loops with Burgers vector of a/2〈111〉 and a〈100〉 were detected and quantified. Results indicate precipitation of Cr-rich α′ is primarily dependent on the bulk chromium composition. Mechanical testing of sub-size-irradiated tensile specimens indicates the hardening response seen after irradiation is dependent on the bulk chromium composition. A structure–property relationship was developed; it indicated that the change in yield strength after irradiation is caused by the formation of these radiation-induced defects and is dominated by the large number density of Cr-rich α′ precipitates at sufficiently high chromium contents after irradiation.

The influence of the substitution of Se for Sn on the thermal, optical and dispersion properties of Ge14Se86−xSnx thin films

Bulk glasses of Ge14Se86−xSnx (x=0, 6, 10 and 22) were prepared by melt-quench technique. Glass transition temperature (Tg) and thermal stability of the bulk samples were found to decrease with Sn content. Thin films of Ge14Se86−xSnx were deposited onto chemically cleaned glass substrates by thermal evaporation. X-ray diffraction (XRD) patterns of the as-prepared films confirmed its amorphous nature except for the film with x=22at% which is polycrystalline. These results have been supported by scanning electron microscopy (SEM) and atomic force microscope (AFM) investigations. Transmittance and reflectance spectra of the as-prepared films were measured at normal incidence in the wavelength range of 350–2500nm. Refractive index and the film thickness were determined from optical transmittance data using Swanepoel’s envelope method. It was found that the refractive index dispersion data obeys the single oscillator Wemple and DiDomenico model from which the dispersion parameters were determined as a function of alloy composition. Analysis of the spectral behavior of the absorption coefficient revealed an allowed indirect optical band gap in the investigated films. The optical band gap was found to decrease along with a corresponding increase in the refractive index with the incorporation of Sn. These results have been discussed on bases of the chemical bond approach, electronegativity difference of the atoms, cohesive energy and heat of atomization.

Correlation of Electronic Structure with Catalytic Activity: H2–D2Exchange across CuxPd1–xComposition Space

The relationship between alloy catalyst activity and valence band electronic structure has been investigated experimentally across a broad, continuous span of CuxPd1–x composition space. CuxPd1–x composition spread alloy films (CSAFs) were used as catalyst libraries with a 100 channel microreactor to measure the H2–D2 exchange kinetics over a temperature range of 333–593 K at 100 discrete CuxPd1–x compositions spanning the range x = 0.30–0.97. The H2–D2 exchange activity exhibits a monotonic decrease over the composition range x = 0.30–0.97. A steady state, microkinetic model was used to estimate the energy barriers to dissociative H2 adsorption, ΔEads‡, and recombinative H2 desorption, ΔEdes‡, as functions of alloy composition, x. Their values fall in the ranges ΔEads‡(x) = 0.15 to 0.45 eV and ΔEdes‡(x) = 0.55–0.65 eV. Spatially resolved UV photoemission spectra were obtained from the CuxPd1–x CSAF and used to estimate the average energy of the filled states of the valence band as a function of alloy com...

Effects of chemical ordering and composition on the magnetic properties of disordered FeAl alloys

Recent studies have shown that FeAl alloys are promising candidate for magnetically patterned media owing to their disorder induced magnetism property at room temperature. In this paper, we have studied the effect of chemical ordering on the magnetic properties of FeAl alloys. At first we have calculated the magnetic exchange interactions in disordered FexAl1-x (50⩽x⩽65) alloys from first-principles theories. With these exchange interaction parameters, we carried out Monte-Carlo simulations with the resulting Ising Hamiltonian, onto which the alloy system was mapped and obtained the x-T phase diagram of the system. We have studied the effect of chemical ordering from a body-centered cubic (A2 phase) to an ordered cubic B2 phase in FeAl on the paramagnetic to ferromagnetic transition as a function of alloy composition and ordering fraction. We have also studied the behavior of hysteresis loop and coercive field as a function of alloy composition, temperature and ordering fraction.

Phase stability of ternary fcc and bcc Fe-Cr-Ni alloys

The phase stability of fcc and bcc magnetic binary Fe-Cr, Fe-Ni, Cr-Ni alloys and ternary Fe-Cr-Ni alloys is investigated using a combination of density functional theory (DFT), Cluster Expansion (CE) and Magnetic Cluster Expansion (MCE). Energies, magnetic moments, and volumes of more than 500 alloy structures are evaluated using DFT, and the most stable magnetic configurations are compared with experimental data. Deviations from the Vegard law in fcc Fe-Cr-Ni alloys, associated with non-linear variation of atomic magnetic moments as functions of alloy composition, are observed. Accuracy of the CE model is assessed against the DFT data, where for ternary alloys the cross-validation error is smaller than 12 meV/atom. A set of cluster interaction parameters is defined for each alloy, where it is used for predicting new ordered alloy structures. Fcc Fe2CrNi phase with Cu2NiZn-like structure is predicted as the global ground state with the lowest chemical ordering temperature of 650K. DFT-based Monte Carlo (MC) simulations are used for assessing finite temperature fcc-bcc phase stability and order-disorder transitions in Fe-Cr-Ni alloys. Enthalpies of formation of ternary alloys calculated from MC simulations at 1600K combined with magnetic correction derived from MCE are in excellent agreement with experimental values measured at 1565K. Chemical order is analysed, as a function of temperature and composition, in terms of the Warren-Cowley short-range order (SRO) parameters and effective chemical pairwise interactions.

Determinations of enthalpy and partial molar enthalpy in the alloys Bi–Cd–Ga–In–Zn, Bi–Cd–Ga–Zn and Au–Cu–Sn

In the present study, the relations of thermodynamic associated with Chou's general solution model (GSM), the models of Muggianu and Toop have been used in order to calculate the mixing enthalpy and partial molar mixing enthalpy of mixing of Bi–Cd–Ga–In–Zn, Bi–Cd–Ga–Zn with equimolar section at a temperature of 730 K and Au–Cu–Sn with the section xAu/xCu = 1/1 on the entire molar fraction range as a function of alloy composition at a temperature of 900 K. Some negativities are reported in the selected alloys mentioned above, particularly at high temperatures for the human health as well as difficulties in experimental measurement and high costs. Moreover, aim of us is to close the current article gap seen in the literature. In order to close the current gap seen in the literature, the article on the thermodynamic properties of the Bi–Cd–Ga–In–Zn alloys are presented in this study.

Studies of compositional dependent Cu2Zn(GexSn1−x)S4 thin films prepared by sulfurizing sputtered metallic precursors

Ge-substituted Cu2ZnSnS4 (CZTS) thin films are promising for solar cell manufacturing, especially for graded-band-gap solar cells and multi-junction solar cells. However, there is no systematic research on the change of structural properties of Cu2Zn(GexSn1−x)S4 (CZTGS) as the function of alloy composition x. In this work, polycrystalline CZTGS thin films were prepared by sulfurizing sputtered Zn/Cu/Ge/Sn metallic precursor stacks. Energy-dispersive X-ray spectroscopy(EDS) line scans conducted in a transmission electron microscopy (TEM) system shows uniform element distribution (except of some ZnS segregation) throughout the synthesized films. The analysis of X-ray diffraction (XRD) and Raman spectroscopy confirms that Cu2ZnGeS4 is successfully obtained by sulfurizing metallic stacks at 580°C for 2h. The lattice constants a and c of CZTGS as derived from XRD patterns follow the Vegard’s rule that lattice constants vary linearly with Ge content (x). Raman spectra shows an A1 mode shift towards high frequency when Sn is gradually replaced by Ge. Chemical composition study indicates the increase in x value leads to higher (Ge+Sn) element loss during the sulfurization process, which can be explained by the high vapour pressure of Ge sulfides. By alloying with Ge, the grain size of CZTS is enlarged which also leads to a rough surface.

Deformation behavior of laser welds in high temperature oxidation resistant Fe–Cr–Al alloys for fuel cladding applications

Ferritic-structured Fe–Cr–Al alloys are being developed and show promise as oxidation resistant accident tolerant light water reactor fuel cladding. This study focuses on investigating the weldability and post-weld mechanical behavior of three model alloys in a range of Fe–(13–17.5)Cr–(3–4.4)Al (wt.%) with a minor addition of yttrium using modern laser-welding techniques. A detailed study on the mechanical performance of bead-on-plate welds using sub-sized, flat dog-bone tensile specimens and digital image correlation (DIC) has been carried out to determine the performance of welds as a function of alloy composition. Results indicated a reduction in the yield strength within the fusion zone compared to the base metal. Yield strength reduction was found to be primarily constrained to the fusion zone due to grain coarsening with a less severe reduction in the heat affected zone. For all proposed alloys, laser welding resulted in a defect free weld devoid of cracking or inclusions.

Dispersion and optical properties of thermally deposited Se91 − xTe9Px (x = 0, 10) films

Se91Te9 and Se81Te9P10 bulk glasses have been prepared by melt-quench technique. The amorphous nature of the as-prepared alloys is confirmed by using X-ray diffraction patterns. Thin films of Se91Te9 and Se81Te9P10 are prepared on chemically cleaned glass substrates by thermal evaporation under vacuum. Differential scanning calorimetery revealed a higher glass transition temperature for Se91Te9 in comparison to Se81Te9P10 bulk glasses. Transmission spectra of the as-prepared films are measured at normal incidence in the wavelength range of 300–2500nm. Refractive index and the film thickness were determined from optical transmittance data using Swanepoel envelope method. It was found that the refractive index dispersion data obeys the single oscillator Wemple and DiDomenico model from which the dispersion parameters were determined. The single oscillator energy, the dispersion energy, the high frequency dielectric constant and the ratio of free charge carrier concentration to the effective mass are then estimated as a function of alloy composition. Analysis of the spectral behavior of the absorption coefficient revealed an allowed indirect optical band gap in this alloy system. With phosphorus incorporation, the optical band gap is found to decrease along with a subsequent increase in the refractive index. The ensemble of these results is interpreted in terms of the chemical bond approach, electronegativity difference of the atoms, cohesive energy and overall mean bond energy.

Nickel Alloy Catalysts for the Anode of a High Temperature PEM Direct Propane Fuel Cell

High temperature polymer electrode membrane fuel cells that use hydrocarbon as the fuel have many theoretical advantages over those that use hydrogen. For example, nonprecious metal catalysts can replace platinum. In this work, two of the four propane fuel cell reactions, propane dehydrogenation and water dissociation, were examined using nickel alloy catalysts. The adsorption energies of both propane and water decreased as the Fe content of Ni/Fe alloys increased. In contrast, they both increased as the Cu content of Ni/Cu alloys increased. The activation energy for the dehydrogenation of propane (a nonpolar molecule) changed very little, even though the adsorption energy changed substantially as a function of alloy composition. In contrast, the activation energy for dissociation of water (a molecule that can be polarized) decreased markedly as the energy of adsorption decreased. The different relationship between activation energy and adsorption energy for propane dehydrogenation and water dissociation alloys was attributed to propane being a nonpolar molecule and water being a molecule that can be polarized.

Composition-controlled synthesis of carbon-supported Pt-Co alloy nanoparticles and the origin of their ORR activity enhancement.

The ability to precisely tune the chemical compositions and electronic structures of nanoalloy catalysts is essential to achieve the goals of high activity and selectivity for the oxygen reduction reaction (ORR) on the catalysts by design. In this work, we synthesized carbon-supported Pt-Co alloy nanoparticles with controlled bimetallic compositions (Pt/Co atomic ratio = 81 : 19, 76 : 24, 59 : 41, 48 : 52, 40 : 60 and 26 : 74) by regulating solution pH and the amount of Pt and Co precursor salts to elucidate the effect of catalyst composition on ORR activity. The obtained Pt-Co alloy nanoparticles have face-centred cubic (fcc) structures and are well-dispersed on the surface of the carbon support with a narrow particle size distribution (2-4 nm diameters). The electrocatalysis experiments in alkaline solution reveal a strong correlation between ORR activity and the alloy composition of the catalysts. Interestingly, the mass-specific activities of the catalysts manifest a typical double-volcano plot as a function of alloy composition. In this Pt-Co alloy series, the catalyst with a Pt : Co atomic ratio of 76 : 24 exhibits the best ORR performance, which is remarkably higher than that of the commercial Pt/C (E-TEK). X-ray photoelectron spectroscopy (XPS) measurements demonstrate that the electronic structures of these catalysts can be tuned by controlling their alloy compositions, which are highly correlated with the trends in ORR activity. The origin of the enhancement in ORR activity may be strongly related to the unique chemical surface structures of the catalysts.

Dynamic recrystallisation and precipitation behaviour of high strength and highly conducting Cu–Ag–Zr-alloys

Dynamic recrystallisation of CuAgZr alloys within a composition range of (3–7)wt% Ag and (0.05–0.3)wt% Zr is studied as a function of alloy composition, temperature and strain. Dynamic recrystallisation was investigated using hot-compression and hot-rolling experiments at temperatures between 500°C and 850°C. For CuAgZr with 7wt% Ag and 0.05wt% Zr, an optimised hot-rolling temperature of 750°C was found and a mean grain size of 25μm was established at a true strain of 2.2. Similar grain size distributions were found for the extended range of alloy compositions while the active mechanism for dynamic recrystallisation changes from necklace towards a particle stimulated nucleation mechanism. This change is driven by the volume fraction of the ternary phase Cu4AgZr as these particles are identified to stimulate nucleation of dynamic recrystallisation in the samples with increased Zr content. The final tapes exhibit an outstanding combination of ultimate tensile strength of 1GPa and an electrical conductivity of 70%IACS at a true strain of 4.8 of cold work being applied.

Modelling high temperature oxidation behaviour of Ni–Cr–W–Mo alloys with Bayesian neural network

Abstract High temperature oxidation property of Ni–Cr–W–Mo alloys is modelled as a function of alloy composition. A database has been constructed from cyclic oxidation experiments performed between 1150 °C and 400 °C of 27 alloys having various contents of Cr, W, and Mo. The Bayesian neural network technique was used for the modelling of cyclic oxidation experiments. With a 3-17-1 neural network architecture, the model shows a precise prediction of oxidation property of Ni–Cr–W–Mo alloys ( R = 0.999). Automatic relevance determination (ARD) analysis reveals that the influence of alloying elements on the output is in the order of Cr, Mo, and W.

Prediction of Contact Fatigue Life of Alloy Cast Steel Rolls Using Back-Propagation Neural Network

In this study, an artificial neural network (ANN) was employed to predict the contact fatigue life of alloy cast steel rolls (ACSRs) as a function of alloy composition, heat treatment parameters, and contact stress by utilizing the back-propagation algorithm. The ANN was trained and tested using experimental data and a very good performance of the neural network was achieved. The well-trained neural network was then adopted to predict the contact fatigue life of chromium alloyed cast steel rolls with different alloy compositions and heat treatment processes. The prediction results showed that the maximum value of contact fatigue life was obtained with quenching at 960 °C, tempering at 520 °C, and under the contact stress of 2355 MPa. The optimal alloy composition was C-0.54, Si-0.66, Mn-0.67, Cr-4.74, Mo-0.46, V-0.13, Ni-0.34, and Fe-balance (wt.%). Some explanations of the predicted results from the metallurgical viewpoints are given. A convenient and powerful method of optimizing alloy composition and heat treatment parameters of ACSRs has been developed.

Optical and Scanning Electron Microscope Studies of Recycled (Secondary) Al-Si Cast Alloys

Production of primary Al- alloys belong to heavy source fouling of life environs. Care of environment in industry of aluminium connects with the decreasing consumptions resource as energy, materials, water and soil, with increase recycling and extension life of products. Recycled (secondary) aluminium alloys are made out of Al-scrap and workable Al-garbage by recycling. Applications of these alloys in recent years increase especially in automotive industry (dynamic exposed cast, engine parts, cylinder heads, pistons and so on). Controlling the microstructure of secondary aluminium cast alloy is very important, because these alloy containing more of additions elements, that forming various intermetallic phases in the structure. Improved mechanical properties of secondary alloys are strongly dependent upon the morphologies, type and distribution of the second phases, which are in turn a function of alloy composition and cooling rate. The presence of additional elements as Mg, Mn, Fe or Cu allows many complex intermetallic phases to form, which make characterization non-trivial. A combination of different analytical techniques (light microscopy, scanning electron microscopy (SEM) upon deep etching and energy dispersive X-ray analysis (EDX)) were therefore been used for the various phases identification.

Atomistic simulation of phonon and alloy limited hole mobility in Si1–xGex nanowires

Abstractmagnified imageThe role of alloy and phonon scattering is theoretically explored in 5 nm diameter SiGe nanowires at room temperature. Low‐field mobility calculations are performed by utilizing sp3d5ds*‐spin–orbit‐coupled tight binding model for electronic structure and Boltzmann transport formalism. Three different transport orientations 〈100〉, 〈110〉 and 〈111〉 are considered. Alloy scattering is found to play an important role in these Si1–xGex nanowires, leading to a characteristic ‘U’ shaped mobility curve as a function of alloy composition. It is concluded that to extract any advantage of higher Ge hole mobility by alloying, Ge% > 70% is needed. Furthermore, the 〈111〉 channel orientation exhibits the highest hole mobility while 〈100〉 has the lowest hole mobility for any given alloy composition. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Cu2Zn(Sn,Ge)Se4and Cu2Zn(Sn,Si)Se4alloys as photovoltaic materials: Structural and electronic properties

As alternatives to the mixed-anion Cu${}_{2}$ZnSn(S,Se)${}_{4}$ alloys, the mixed-cation Cu${}_{2}$Zn(Sn,Ge)Se${}_{4}$ and Cu${}_{2}$Zn(Sn,Si)Se${}_{4}$ alloys can also span a band gap range that fits the requirement of the solar cell light absorber. However, material properties of these alloys as functions of alloy composition $x$ are not well known. In this paper, using the first-principles calculations, we study the structural and electronic properties of these alloys. We find that (i) the Cu${}_{2}$Zn(Sn,Ge)Se${}_{4}$ alloys are highly miscible with low formation enthalpies, while the Cu${}_{2}$Zn(Sn,Si)Se${}_{4}$ alloys are less miscible; (ii) the band gap of Cu${}_{2}$Zn(Sn,Ge)Se${}_{4}$ increases almost linearly from 1.0 eV to 1.5 eV as the Ge composition $x$ increases from 0 to 1, whereas the band gap of Cu${}_{2}$Zn(Sn,Si)Se${}_{4}$ spans a larger range from 1.0 eV to 2.4 eV and shows a slightly larger bowing; and (iii) the calculated band offsets shows that the band gap increase of the alloys with the addition of Ge or Si results primarily from the conduction band upshift, whereas the valence band shift is less than 0.2 eV. Based on these results, we expect that the component-uniform and band-gap-tunable Cu${}_{2}$Zn(Sn,Ge)Se${}_{4}$ and Cu${}_{2}$Zn(Sn,Si)Se${}_{4}$ alloys can be synthesized and have an improved photovoltaic efficiency.

A novel prediction method of creep rupture life of 9–12% chromium ferritic steel based on abductive network

The creep rupture life of 9–12% chromium ferritic steel is predicted as a function of alloy composition, creep stress, and creep temperature. A database is made up from data in previous publications. A novel abductive network is constructed to predict creep rupture life. With a four-layer architecture, the network shows a precise prediction of creep rupture life of 9–12% chromium ferritic steel. Performance is examined and compared with backpropagation algorithm (BP) neural network. Results indicate that the proposed approach is more accurate than Larson–Miller parametric method and more efficient than that of BP neural network. Automatic relevance determination reveals that the influence of Cr and W on creep rupture life of 9–12% chromium ferritic steel are the greatest amongst the alloying elements.

Phase Stability of Iron Oxides on Palladium–Iron Alloy at Elevated Temperatures and Its Application to High Temperature Oxidation

Phase stability of iron-oxides as a function of alloy composition in Pd­Fe­O system has been examined by emf measurement with solid electrolyte of CaO-stabilized zirconia at the temperature ranging from 973 to 1123K. Phase boundary between the alloy and iron-oxide was determined with six alloys in which Fe-composition is ranging from 1 to 64at%. The boundary composition of wustite lies in between 34at% Fe and 54at% Fe and hematite was expected to be formed at the alloy composition less than 1at% Fe. Thickness of iron oxide was estimated from the amount of consumed Fe in the alloy, which is given by the difference of initial and final composition at the temperature and oxygen partial pressure. Estimated thickness of iron oxide was in good agreement of that obtained from high temperature oxidation of Pd­Fe alloy. Emf measurement gives useful information to obtain single-phase iron-oxide with the expected thickness on Pd­Fe alloy by high temperature oxidation. [doi:10.2320/matertrans.M2013122]