Function Of Alloy Composition Research Articles

A microscopic bonding model for the compositional dependence of the first sharp diffraction peak (FSDP) in GexSe1‐xalloys

AbstractThis article analyzes results from two papers that have studied the first sharp diffraction peak, FSDP, in GexSe1‐x alloys as a function of the alloy composition, x. The research reported in one of these papers obtained the FSDP in eighteen closely spaced compositions for x between 0.15 and 0.4, and included the intermediate phase, IP, regime between x = ∼0.2 and ∼0.25. S(Q) structure factor plots from diffraction measurements were characterized empirically in terms with several different fitting functions. These second paper used Monte‐Carlo methods for a smaller set of compositions. In this paper, the positions and widths of the FSDP's peaks as a function of alloy composition are correlated with changes in the atomic bonding from Se‐rich to Ge‐rich regimes. Additionally this paper identifies medium range order, MRO, length scales for chemical bonding self‐organizations within the IP regime that are important for promoting macroscopic strain reduction. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Passivation of Aluminum–Molybdenum Alloys in Hydrochloric Acid

The electrochemical properties of the system Al–Mo alloy∣anodic oxide film∣1.0 M HCl solution were investigated as a function of alloy composition and applied potential in 1.0 M HCl. Voltammetry measurements have revealed that the alloy systems with behave almost like pure Mo. The alloy systems with showed the potential regions of primary and secondary passivities in which the structural and protective properties of the anodic oxide films were studied using electrochemical impedance spectroscopy. Orazem’s graphical methods and Mott–Schottky analysis were used to extract the values of parameters of the constant-phase element, interfacial capacitance, ohmic resistance, type of conductivity, and concentration of charge carriers in the semiconducting oxide film, which are all from the high frequency impedance data. The pseudoinductive behavior observed at low frequencies in the potential range of the secondary passivity was discussed in terms of the surface-charge approach based on the chemistry of the point defect model.

Composition-Dependent Crystal Structure and Magnetism in Nanocrystalline Co-Rich Alloy

We report the magnetism of a ferromagnetic two phase mixture system by investigating the microstructural evolution and relevant property changes as a function of alloy composition in CoFeSiB film. The crystal structure evolved from an amorphous to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hcp</i> Co nanocrystal embedded two-phase mixture when Co concentration exceeded the critical amount (~75 at.%) confirmed through TEM and XRD. Very low coercivity value was observed in the amorphous samples. The soft magnetic properties are due to the fact that the magnetic moments of Co-rich phase are exchange-coupled via the amorphous matrix, as a consequence the magnetic anisotropies are averaged out in the amorphous system. Meanwhile, beyond 75 at.% of Co, an abrupt increase in coercivity was observed in the nanocrystalline samples where highly anisotropic Co nanocrystals were precipitated. The hard magnetic properties resulted from the magnetic decoupling (breaking of the nanocrystal-amorphous matrix-nanocrystal coupling chain) because the exchange forces are not able to overcome the magnetocrystaline anisotropy. We also found that antiferromagnetic exchange coupling existed at the nanocrystal-amorphous matrix interfaces.

T(z) diagram and magnetic behavior of the Zn1−zMnzIn2Te4 alloy system

Abstract Measurements of X-ray diffraction, differential thermal analysis (DTA) and of magnetic susceptibility χ, in the temperature range from 2 to 300 K, were carried out on polycrystalline samples of the Zn1−zMnzIn2Te4 alloy system. The X-ray diffraction patterns were used to check the equilibrium conditions and to estimate crystalline parameter values. The DTA transition temperature values were plotted as a function of alloy composition z. The 1/χ vs T curves indicated that samples in the α1 I 4 ¯ range (0 I 4 ¯ 2 m range (0.4

Thermal behavior and melt fragility number of Cu100-x Zrx glassy alloys in terms of crystallization and viscous flow

Six Cu100-xZrx amorphous alloys (x in the range 35.7 - 60 at. percent) were prepared via chill block melt spinning (CBMS) method under low pressure Helium atmosphere. Their crystallization and viscous flow behavior was studied with the aid of Perkin Elmer DSC 2C and Perkin Elmer TMS 2 devices, respectively. The viscous flow temperature dependencies at a heating rate of 20 K min-1 were interpreted on the basis of the f ree volume model. The DSC and TMS data were used to determine the fragility number m of Angell in three different ways as a function of alloy composition. It has been shown that the fragility number goes over a maximum and has a minimum at x very near to the alloy composition Cu64Zr36 in good agreement with the results of Donghua Xu et al. and Wang D et al. The experimental techniques and model interpretation used provide a tool for understanding the glass forming ability (GFA) and relaxation phenomena in metallic glasses.

Modeling medium carbon steels by using artificial neural networks

An artificial neural network (ANN) model has been developed for the analysis and simulation of the correlation between the mechanical properties and composition and heat treatment parameters of low alloy steels. The input parameters of the model consist of alloy compositions (C, Si, Mn, S, P, Ni, Cr, Mo, Ti, and Ni) and heat treatment parameters (cooling rate and tempering temperature). The outputs of the ANN model include property parameters namely: ultimate tensile strength, yield strength, percentage elongation, reduction in area and impact energy. The model can be used to calculate the properties of low alloy steels as a function of alloy composition and heat treatment variables. The individual and the combined influence of inputs on properties of medium carbon steels is simulated using the model. The current study achieved a good performance of the ANN model, and the results are in agreement with experimental knowledge. Explanation of the calculated results from the metallurgical point of view is attempted. The developed model can be used as a guide for further alloy development.

The adsorption and reaction of vinyl acetate on Au/Pd(1 1 1) alloy surfaces

The adsorption of vinyl acetate is studied on Au/Pd(1 1 1) alloys as a function of alloy composition using temperature-programmed desorption and reflection–adsorption infrared spectroscopy. Vinyl acetate adsorbs weakly on gold sites on the alloy with a heat of adsorption of ∼55 kJ/mol, which is independent of the size of the gold ensembles. In contrast, adsorption of vinyl acetate on palladium sites is strongly affected by alloying. Vinyl acetate desorbs from isolated palladium sites on the alloy with an activation energy of ∼70 kJ/mol, close to that found on pure Pd(1 1 1). As the palladium coverage, and the number of palladium dimers and larger ensembles in the alloy increases, the heat of adsorption of vinyl acetate increases attaining a maximum of ∼80 kJ/mol at a gold coverage in the alloy of ∼0.5. However, in spite of the larger heat of adsorption on the alloy than on pure Pd(1 1 1), vinyl acetate does not undergo significant thermal decomposition on this alloy surface. This is ascribed to the formation of more distorted vinyl acetate in which the acetate group is more remote from the surface due to the rehybridization of the vinyl group. As the gold coverage decreases to ∼0.35 and lower, thermal decomposition products are found similar to those on Pd(1 1 1).

An Investigation of Microstructure and Microhardness of Sn-Cu and Sn-Ag Solders as Functions of Alloy Composition and Cooling Rate

The microstructure and microhardness of Sn-xAg and Sn-xCu solders were investigated as functions of alloy composition and cooling rate. The Ag compositions examined varied from 0.5 wt.% to 3.5 wt.%, while Cu varied from 0.5 wt.% to 2.0 wt.%. Three cooling rates were employed during solidification: 0.02°C/s (furnace cooling), about 10°C/s (air cooling), and 100°C/s or higher (rapid solidification). Sn grain size and orientation were observed by cross-polarization light microscopy and electron-backscattering diffraction (EBSD) techniques. The microhardness was measured to correlate the mechanical properties with alloy compositions and cooling rates. From this study, it was found that both alloy composition and cooling rate can significantly affect the Sn grain size and hardness in Sn-rich solders. The critical factors that affect the microstructure–property relationships of Sn-rich solders are discussed, including grain size, crystal orientation, dendrite cells, twin boundaries, and intermetallic compounds (IMC).

A general model for the repassivation potential as a function of multiple aqueous species. 2. Effect of oxyanions on localized corrosion of Fe–Ni–Cr–Mo–W–N alloys

A recently developed model for predicting the repassivation potential has been applied to stainless steels and nickel-base alloys in aqueous environments containing chlorides and various inhibiting anions. The model accounts for the effects of solution chemistry and temperature on the repassivation of localized corrosion by considering competitive dissolution, adsorption, and oxide formation processes at the interface between the metal and the occluded site solution. An extensive database of repassivation potentials has been established for six alloys (UNS 31603, N06600, N06690, S31254, S32205, and UNS S41425) in contact with solutions that combine chlorides with hydroxides, molybdates, vanadates, sulfates, nitrates, and nitrites at various concentrations and temperatures. Also, repassivation potentials are reported for four alloys (UNS N08367, N08800, N06625, and N10276) in chloride solutions. The database has been used to establish the parameters of the model and verify its accuracy. The model quantitatively predicts the transition between concentrations at which localized corrosion is possible and those at which inhibition is expected. It is capable of predicting the repassivation potential over wide ranges of experimental conditions using parameters that can be generated from a limited number of experimental data. The parameters of the model have been generalized as a function of alloy composition, thus making it possible to predict the repassivation potential for alloys that have not been experimentally investigated.

The three-dimensional reconstruction of the dendritic structure at the solid-liquid interface of a Ni-based single crystal

Directional solidification of nickel-based single crystals requires control of the heat transfer, fluid flow, and phase transformations at the solid-liquid interface during withdrawal in the Bridgman process. While the morphological details of the dendritic structure at the solid-liquid interface influence defect formation processes, there is an incomplete understanding of this structure as a function of alloy composition and processing conditions. A three-dimensional serial sectioning and image reconstruction approach for characterization of the solidification front has been developed and structural characteristics of the dendritic structure are quantified.

Effects of Addition of Al, Ti and Ag on Glass-Forming Ability of Cu&lt;sub&gt;50&lt;/sub&gt;Zr&lt;sub&gt;50&lt;/sub&gt; Alloy

The thermal stability and crystalline phases precipitated from the as-cast rods of the Cu50Zr50-based alloys with addition of Al or simultaneous addition of Al/Ti or Al/Ag elements were investigated using DSC, DTA and XRD. The value of Tx, Trg and γ as a function of alloy composition shows a same trend, in which the Cu46Zr46Al8 alloy exhibits the largest value of Tx, Trg and γ. However, this trend is different from the variation of the dc with alloy composition, in which the Cu42Zr42Al8Ag8 alloy has the largest dc for glass formation. Trg′ based on Tg/Tm has a good correlation with the critical diameter for glass formation in this alloy system. It was found that the alloy with higher GFA has more complex precipitated crystalline phases from the as-cast rod with a diameter larger than the critical diameter for glass formation.

InGaN: An overview of the growth kinetics, physical properties and emission mechanisms

This article reviews the fundamental properties of InGaN materials. The growth kinetics associated with the growth parameters, such as growth temperatures, V/III ratios, and growth rates which influence the quality of the InGaN epilayers , are briefly described. An overview of the properties of the InGaN alloys, such as the optical, structural and electrical characteristics, is presented. The design and fabrication of novel optoelectronic device structures require an accurate knowledge of the band gap as a function of alloy composition; therefore, attention is paid to Vegard’s law and the bowing parameter; in addition, the major factors leading to the uncertainties of the bowing parameter of InGaN are addressed. Apart from that, the determination of indium composition by X-ray diffraction (XRD) using different assumptions and various equations are summarized. The erroneous measurements of the indium composition by using this technique are also described. Finally, different emission mechanisms of the strained InGaN quantum wells proposed by different groups of researchers are also discussed.

Bimodal Bond-Length Distributions in Cobalt-Doped CdSe, ZnSe, and Cd1-xZnxSe Quantum Dots

Electronic absorption spectroscopy has been used to study changes in Co2+ ligand-field parameters as a function of alloy composition in Co2+-doped Cd(1-x)Zn(x)Se nanocrystals. A shift in the energy of the 4T1(P) excited-state with alloy composition is observed. Analysis reveals that Co2+-Se2- bond lengths change relatively little as the host is varied continuously from CdSe to ZnSe, generating a large difference between microscopic and average cation-anion bond lengths in Co2+-doped CdSe nanocrystals but not in Co2+-doped ZnSe nanocrystals. The bimodal bond-length distributions observed here are shown to cause a diameter-dependent enthalpic destabilization of doped semiconductor nanocrystals.

Optimization of composition and processing parameters for alloy development: a statistical model-based approach

We describe the second step in a two-step approach for the development of new and improved alloys. The first step, proposed by Golodnikov et al [3], entails using experimental data to statistically model tensile yield strength and the 20th percentile of the impact toughness, as a function of alloy composition and processing variables. We demonstrate how the models can be used in the second step to search for combinations of the variables in small neighborhoods of the data space, that result in alloys having optimal levels of the properties modeled. The optimization is performed via the efficient frontier methodology. Such an approach, based on validated statistical models, can lead to a substantial reduction in the experimental effort and cost associated with alloy development. The procedure can also be used at various stages of the experimental program, to indicate what changes should be made in the composition and processing variables in order to shift the alloy development process toward the efficient frontier. Data from these more refined experiments can then be used to adjust the model and improve the second step, in an iterative search for superior alloys.

Dopant Diffusion in SiGeC Alloys

In this paper, we discuss the impact of germanium and carbon on the diffusion of common dopants in Si-based alloys. We review results of various diffusion experiments and discuss the basic physical mechanisms of the observed changes of diffusion coefficients as a function of alloy composition. Results of boron and phosphorus marker layer diffusion experiments are presented for binary Si1-xGex and Si1-yCy and ternary Si1-x-yGexCy alloys.

Magnetization dynamics of the ferrimagnet CoGd near the compensation of magnetization and angular momentum

Magnetization dynamics in alloys of ferrimagnetic CoGd have been studied in the vicinity of the magnetization and angular momentum compensation point as a function of alloy composition and temperature. In agreement with standard mean-field treatments of the dynamics of the total magnetization we observe an increase of the precessional frequency and the effective damping parameter near the angular momentum compensation point. We demonstrate the consistency of the magnetization dynamics extracted from frequency domain methods such as ferromagnetic resonance and time resolved laser pump-probe measurements.

Effect of Composition on the Photoelectrochemical Behavior of Anodic Oxides on Binary Aluminum Alloys

The photoelectrochemical behavior of anodic films on Al alloys, containing titanium, tantalum, and tungsten (valve metals), has been studied as a function of alloy composition and anodizing conditions. Photocurrent spectroscopy has been used to get information on bandgap and the flatband potential values of different mixed oxides. Both insulator-like and semiconducting behavior has been observed for anodic oxides grown on and alloys dependent on alloy initial composition. Optical bandgap values, , of different oxides are in accordance with predictions based on the correlation between and the difference of electronegativities of the oxide constituents, indicating potential for tailoring solid state properties of ternary oxides.

An Overview of Metal Dusting in Synthesis Gas Environments

This paper gives an overview of the different processes of metal dusting (MD) that operate on low and high alloyed iron and nickel base alloys exposed in CO+H2–containing environments with or without water vapour. MD of pure metals like iron and nickel occur with a solely carbon-induced corrosion mechanism. However, in high alloyed materials with strong oxide formers such as Cr and Al, a more complex MD-process takes place which involves both carbon and oxygen in close collaboration. The “alloyed” carbides, i.e normally Cr-containing carbides, formed in such materials are thermodynamically stable with respect to the carbon activity. However, in the reaction front of a MD-pit with non-protective spinel oxide, they destabilise and dissolve due to the influence of the low oxygen activity determined by CO-dissociation. Based on recent results in the field of MD a chart with tentative MD mechanisms is presented as a function of alloy composition and temperature.

Electronic and magnetic properties in Fe-based Fe 1− xNi x, Fe 1− xCo x, and Fe 1− xV x films on W(1 1 0)

We investigate the correlation between the change of magnetic properties and structural transition for Fe-based alloy (Fe 1− x Ni x , Fe 1− x Co x , and Fe 1− x V x ) films, which were grown on W(1 1 0) substrate. To clarify the correlation clearly among the electronic structure, magnetic properties, and structural transition as a function of alloy composition, we performed the spin-summed and resolved photoemission spectra (SSRPES) and low energy electron diffraction (LEED).

Effects of Pt on the elastic properties of B2 NiAl: A combined first-principles and experimental study

First-principles calculations were performed to investigate the effects of Pt addition on the elastic properties of B2 NiAl. By correlating single-crystal elastic constants with point defect concentrations in the context of the Wagner–Schottky model, a general equation is proposed to calculate elastic properties of ternary B2 NiAl–Pt alloys as a function of alloy composition, in which the defect formation parameters were obtained from first-principles supercell calculations. At constant Al content, the calculations showed that the addition of Pt to B2 NiAl will increase its bulk modulus B but decrease both its shear moduli C′ and C 44. Results from the model calculations were found to be in good agreement with experimental measurements on polycrystalline samples, as well as direct first-principles calculations on special quasirandom structures.