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## Order-disorder transformation in the Ni-4.49 at.% Al alloy

Adorno, A. T.; Garlipp, W.; Cilense, M.; Silva, RAG
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 55-59
Português
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The order-disorder transformation in the Ni-4.49 at.% Al alloy was studied using electrical resistivity measurements, microhardness measurements, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The results confirmed the ordering behavior expected for Ni-Al dilute alloys and the suggested relation between resistivity changes and microhardness changes with antiferromagnetic spin ordering. The higher value obtained for the activation energy of vacancy migration was associated with a decrease in the Al concentration gradient near solute-depleted regions. (c) 2005 Elsevier B.V. All rights reserved.

## Microestrutura de solidificação e resistencias mecanicas e a corrosão de ligas Pb-Sn diluidas; Solidification microstructures and mechanical and corrosion resistances of dilute Pb-Sn alloys

Leandro Cesar de Lorena Peixoto
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
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## Theoretical - Experimental Analysis of Cellular and Primary Dendritic Spacings during Unidirectional Solidification of Sn-Pb Alloys

Rocha,Otávio F.L. da; Siqueira,Cláudio A.; Garcia,Amauri
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
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Structural parameters as grain size, dendritic and cellular spacings, segregated products, porosity and other phases are strongly influenced by the thermal behavior of the metal/mold system during solidification, imposing a close correlation between this and the resulting microstructure. Several unidirectional solidification studies with the objective of characterizing cellular and dendritic spacings have been developed in large scale involving solidification in steady-state heat flow. The main objective of this work is to determine the thermal solidification parameters during the cellular/dendritic transition as well as to compare theoretical models that predict cellular and primary dendritic spacings with experimental results for solidification situations in unsteady-state heat flow. Experiments were carried out in a water cooled unidirectional solidification apparatus and dilute alloys of the Sn-Pb system were used (Sn 1.5wt%Pb, Sn 2.5wt%Pb and Sn 5wt%Pb). The upper limit of the Hunt-Lu cellular growth model closely matched the experimental spacings. The lower limit calculated with the Hunt-Lu dendritic model best generated the experimental results. The cellular/dendritic transition was observed to occur for the Sn 2.5wt%Pb alloy over a range of analytical cooling rates from 0.28 K/s to 1.8 K/s.

## Numerical simulation of solute trapping phenomena using phase-field solidification model for dilute binary alloys

Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
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Numerical simulation of solute trapping during solidification, using two phase-field model for dilute binary alloys developed by Kim et al. [Phys. Rev. E, 60, 7186 (1999)] and Ramirez et al. [Phys. Rev. E, 69, 05167 (2004)] is presented here. The simulations on dilute Cu-Ni alloy are in good agreement with one dimensional analytic solution of sharp interface model. Simulation conducted under small solidification velocity using solid-liquid interface thickness (2λ) of 8 nanometers reproduced the solute (Cu) equilibrium partition coefficient. The spurious numerical solute trapping in solid phase, due to the interface thickness was negligible. A parameter used in analytical solute trapping model was determined by isothermal phase-field simulation of Ni-Cu alloy. Its application to Si-As and Si-Bi alloys reproduced results that agree reasonably well with experimental data. A comparison between the three models of solute trapping (Aziz, Sobolev and Galenko [Phys. Rev. E, 76, 031606 (2007)]) was performed. It resulted in large differences in predicting the solidification velocity for partition-less solidification, indicating the necessity for new and more acute experimental data.

## The effect of adding boron in solidification microstructure of dilute iron-carbon alloy as assessed by phase-field modeling

Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
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Alloying element like boron, even in small addition, is well known to improve hardenability of steels. Its application can improve mechanical properties of steels and reduce alloying costs. Despite these benefits is not easy to cast boron steels, mainly in dynamical solidification process like continuous casting, due to their crack susceptibility1,2. The strategy of using Phase-Field simulation of the solidification process is based on its proved capacity of predicting realistic microstructure that emerge during solidification under conditions even far from equilibrium3-5. Base on this, some comparative simulations were performed using a three component dilute alloy in a two dimensional domain under unconstrained (isothermal) and constrained (directional) solidification. Simulation results suggested two fragile mechanisms: one related to a deep dendritic primary arms space and other due to the remelting of this region at low temperature. Both resulted mainly from the high boron segregation in interdendritic regions.

## Note on the Superconducting Dilute Alloy with Paramagnetic Impurities. I: Basic Formulation and Some Application

Kawamura, Kiyoshi
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica Formato: text/html
Português
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Superconducting dilute alloys with paramagnetic impurities are considered with the method of thermal Green functions. The self-energy part of electron Green functions are expressed in terms of Green functions of spin operators. The formulation established in this paper is so useful that we can deal with spin operators dynamically. As an example, the effect of localized spins on the jump of the specific heat at the transition point and the order parameter at 0° K, as well as the known expression for the decrease of transition point are derived to the order of J3.

## Nonequilibrium Partitioning During Rapid Solidification of Si-As Alloys

Aziz, Michael; Thompson, M. O.; Brunco, David P.; Kittl, Jorge A.
Português
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The velocity dependence of the partition coefficient was measured for rapid solidification of polycrystalline Si-4.5 at% As and Si-9 at% As alloys induced by pulsed laser melting. The results constitute the first test of partitioning models both for the high velocity regime and for non-dilute alloys. The continuous growth model (CGM) of Aziz and Kaplan fits the data well, but with an unusually low diffusive speed of 0.46 m/s. The data show negligible dependence of partitioning on concentration, also consistent with the CGM. The predictions of the Hillert-Sundman model are inconsistent with partitioning results. Using the aperiodic stepwise growth model (ASGM) of Goldman and Aziz, an average over crystallographic orientations with parameters from independent single-crystal experiments is shown to be reasonably consistent with these polycrystalline partitioning results. The results, combined with others, indicate that the CGM without solute drag and its extension to lateral ledge motion, the ASGM, are the only models that fit the data for both solute partioning and kinetic undercooling interface response functions. No current solute drag models can match both partitioning and undercooling measurements.; Engineering and Applied Sciences

## The effect of adding boron in solidification microstructure of dilute iron-carbon alloy as assessed by phase-field modeling

Furtado, Henrique Silva; Bernardes, Am?rico Trist?o; Machado, Romuel Figueiredo; Silva, Carlos Ant?nio da
Português
Relevância na Pesquisa
48.0415%
Alloying element like boron, even in small addition, is well known to improve hardenability of steels. Its application can improve mechanical properties of steels and reduce alloying costs. Despite these benefits is not easy to cast boron steels, mainly in dynamical solidification process like continuous casting, due to their crack susceptibility 1,2 . The strategy of using Phase-Field simulation of the solidification process is based on its proved capacity of predicting realistic microstructure that emerge during solidification under conditions even far from equilibrium 3-5 . Base on this, some comparative simulations were performed using a three component dilute alloy in a two dimensional domain under unconstrained (isothermal) and constrained (directional) solidification. Simulation results suggested two fragile mechanisms: one related to a deep dendritic primary arms space and other due to the remelting of this region at low temperature. Both resulted mainly from the high boron segregation in interdendritic regions.

## Numerical simulation of solute trapping phenomena using phase-field solidification model for dilute binary alloys

Furtado, Henrique Silva; Bernardes, Am?rico Trist?o; Machado, Romuel Figueiredo; Silva, Carlos Ant?nio da
Português
Relevância na Pesquisa
48.664785%
Numerical simulation of solute trapping phenomena using phase-field solidification model for dilute binary alloys Numerical simulation of solute trapping during solidification, using two phase-field model for dilute binary alloys developed by Kim et al. [Phys. Rev. E, 60, 7186 (1999)] and Ramirez et al. [Phys. Rev. E, 69, 05167 (2004)] is presented here. The simulations on dilute Cu-Ni alloy are in good agreement with one dimensional analytic solution of sharp interface model. Simulation conducted under small solidification velocity using solid liquid interface thickness (2?) of 8 nanometers reproduced the solute (Cu) equilibrium partition coefficient. The spurious numerical solute trapping in solid phase, due to the interface thickness was negligible. A parameter used in analytical solute trapping model was determined by isothermal phase-field simulation of Ni-Cu alloy. Its application to Si-As and Si-Bi alloys reproduced results that agree reasonably well with experimental data. A comparison between the three models of solute trapping (Aziz, Sobolev and Galenko [Phys. Rev. E, 76, 031606 (2007)]) was performed. It resulted in large differences in predicting the solidification velocity for partition-less solidification...

## DISORDERED MAGNETISM IN DILUTE MAGNETIC ALLOYS STUDIED BY MUON SPIN RELAXATION (GLASS, FERROMAGNETISM)

GIST, GRANT ALAN
Português
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Muon spin relaxation ((mu)SR) has been used to study the magnetic ordering in PdMn and AgMn dilute alloys representing disordered ferromagnetism, reentrant ferromagnetism, and spin glass order. A theory of static linewidths for both transverse applied field and zero applied field (mu)SR is described for all types of spin order. The temperature dependence of the static linewidth in the spin glass and ferromagnetic phases is consistent with both a mean field theory of disordered magnetism and an inhomogeneous percolation model. Linewidths in paramagnetic AgMn privde the first direct observation of a conduction electron mediated RKKY component to the muon-local moment interaction. In PdMn, muons are excluded from occupying octahedral interstitial sites directly adjacent to Mn impurities. A theory relating muon spin-lattice relaxation to impurity spin correlation times in the paramagnetic and ordered phases is described. All types of magnetic ordering show a rapid slowing down of impurity spin fluctuations just above the ordering temperature. Muon spin-lattice relaxation in both the ferromagnetic and spin glass state is expected to be insensitive to both long wavelength spin waves and to higher frequency localized spin wave-like excitations. The observed spin glass state relaxation is consistent with a phenomenological theory of low-frequency barrier mode excitations.

## Morphological evidence for a pitting mechanism in dilute aluminum alloys

Perkins, Arthur Jeffery; Cummings, J. R.; Graham, Kenneth J. (Kenneth Judson)
Tipo: Relatório
Português
Relevância na Pesquisa
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In the course of an investigation of the seawater corrosion behavior of several dilute aluminum alloys, direct microscopic evidence of pitting phenomena was obtained. Observations, obtained by scanning electron microscopy after galvanic corrosion exposures, illustrate a pitting mechanism involving the extrusion of columns of corrosion product from pits by the action of hydrogen gas generated inside the pits. The macroscopic dissolution patterns of the various alloys and their respective microscopi dissolution morphologies are also described. The observations support the classical model for pitting of aluminum originally presented by Edeleanu and Evans. (Author)

## Correlação entre microestrutura de solidificação e resistências mecânica e à corrosão de ligas Pb-Ag e Pb-Bi; Correlation between solidification microstructure and mechanical and corrosion resistances of Pb-Ag and Pb-Bi alloys

Leandro Cesar de Lorena Peixoto
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Relevância na Pesquisa
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O presente trabalho pretende contribuir para o entendimento do desenvolvimento microestrutural e das propriedades de ligas diluídas dos sistemas Pb-Ag e Pb-Bi que apresentam importância para a indústria na fabricação de componentes de baterias automotivas e estacionárias. As amostras foram obtidas através de experimentos de solidificação unidirecional realizados em dispositivo no qual o calor é extraído somente pelo sistema de resfriamento a água, localizado na base do conjunto lingote/lingoteira (solidificação vertical ascendente). Taxas e velocidades de solidificação são determinadas a partir do registro de temperaturas a partir de termopares posicionados dentro da lingoteira em diferentes posições. As amostras foram utilizadas para analisar as influências das variáveis térmicas de solidificação e da concentração de soluto das ligas nas macro e microestruturas resultantes e na resistência mecânica. São determinados os limites de resistência à tração e escoamento e alongamentos específicos em função de espaçamento dendrítico e celular. A influência do arranjo microestrutural no comportamento eletroquímico é também avaliada por intermédio dos ensaios de espectroscopia de impedância eletroquímica...

## Studies of homogeneous precipitation in very dilute iron-coper alloys using kinetic Monte Carlo simulations and statistical theory of nucleation

Vaks, V. G.; Soisson, F.; Zhuravlev, I. A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Kinetics of homogeneous nucleation and growth of copper precipitates under electron irradiation of Fe_{1-x}Cu_x alloys at concentrations x from 0.06 at.% to 0.4 at.% and temperatures T from 290 to 450C is studied using the kinetic Monte Carlo (KMC) simulations and the statistical theory of nucleation (STN). The conventional assumption about the similarity of mechanisms of precipitation under electron irradiation and during thermal aging is adopted. The earlier-developed ab initio model of interactions in Fe-Cu alloys is used for both the KMC simulations and the STN calculations. Values of the nucleation barrier F_c and the prefactor J_0 in the Zeldovich-Volmer relation for the nucleation rate J are calculated for a number of concentrations and temperatures. For the dilute alloys with x less then 0.2%, the STN and the KMC results for the nucleation barrier F_c do virtually coincide with each other, which seems to confirm a high reliability of the STN for this problem. The STN calculations are also used to estimate the temperature dependencies of concentrations which correspond to the homogeneous or the heterogeneous precipitation limit and both dependencies are found to be rather sharp.; Comment: 21 page, 8 postscript figures, LaTeX

## Impurity correlations in dilute Kondo alloys

Barzykin, Victor; Affleck, Ian
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The single impurity Kondo model is often used to describe metals with dilute concentrations (n_i) of magnetic impurities. Here we examine how dilute the impurities must be for this to be valid by developing a virial expansion in impurity density. The O(n_i^2) term is determined from results on the 2-impurity Kondo problem by averaging over the RKKY coupling. The non-trivial fixed point of the 2-impurity problem could produce novel singularities in the heat capacity of dilute alloys at O(n_i^2).; Comment: 6 pages, no figures

## Magnetic Properties of Dilute Alloys: Equations for Magnetization and its Structural Fluctuations

Vakarchuk, I.; Tkachuk, V.; Kuliy, T.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The dilute Heisenberg ferromagnet is studied taking into account fluctuations of magnetization caused by disorder. A self-consistent system of equations for magnetization and its mean quadratic fluctuations is derived within the configurationally averaged two-time temperature Green's function method. This system of equations is analised at low concentration of non-magnetic impurities. Mean relative quadratic fluctuations of magnetization are revealed to be proportional to the square of concentration of impurities.; Comment: 16 pages, LaTex

## Kinetics of formation of twinned structures under L1_0 type orderings in alloys

Belashchenko, K. D.; Pankratov, I. R.; Samolyuk, G. D.; Vaks, V. G.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The earlier-developed master equation approach and kinetic cluster methods are applied to study kinetics of L1_0 type orderings in alloys, including the formation of twinned structures characteristic of cubic-tetragonal-type phase transitions. A microscopical model of interatomic deformational interactions is suggested which generalizes a similar model of Khachaturyan for dilute alloys to the physically interesting case of concentrated alloys. The model is used to simulate A1->L1_0 transformations after a quench of an alloy from the disordered A1 phase to the single-phase L1_0 state for a number of alloy models with different chemical interactions, temperatures, concentrations, and tetragonal distortions. We find a number of peculiar features in both transient microstructures and transformation kinetics, many of them agreeng well with experimental data. The simulations also demonstrate a phenomenon of an interaction-dependent alignment of antiphase boundaries in nearly-equilibrium twinned bands which seems to be observed in some experiments.; Comment: 20 pages, 11 figures (figures are better in PS than in PDF). Submitted to J. Phys.: Condens. Matter

## 12-band $\textbf{k}\cdot\textbf{p}$ model for dilute bismide alloys of (In)GaAs derived from supercell calculations

Broderick, Christopher A.; Usman, Muhammad; O'Reilly, Eoin P.
Tipo: Artigo de Revista Científica
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Incorporation of bismuth (Bi) in dilute quantities in (In)GaAs has been shown to lead to unique electronic properties that can in principle be exploited for the design of high efficiency telecomm lasers. This motivates the development of simple models of the electronic structure of these dilute bismide alloys, which can be used to evaluate their potential as a candidate material system for optical applications. Here, we begin by using detailed calculations based on an $sp^{3}s^{*}$ tight-binding model of (In)GaBi$_{x}$As$_{1-x}$ to verify the presence of a valence band-anticrossing interaction in these alloys. Based on the tight-binding model the derivation of a 12-band $\textbf{k}\cdot\textbf{p}$ Hamiltonian for dilute bismide alloys is outlined. We show that the band structure obtained from the 12-band model is in excellent agreement with full tight-binding supercell calculations. Finally, we apply the 12-band model to In$_{0.53}$Ga$_{0.47}$Bi$_{x}$As$_{1-x}$ and compare the calculated variation of the band gap and spin-orbit-splitting to a variety of spectroscopic measurements performed on a series of MBE-grown In$_{0.53}$Ga$_{0.47}$Bi$_{x}$As$_{1-x}$/InP layers.

## First principles study of helium, carbon and nitrogen in austenite, dilute austenitic iron alloys and nickel

Hepburn, D. J.; Ferguson, D.; Gardner, S.; Ackland, G. J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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An extensive set of first-principles density functional theory calculations have been performed to study the behaviour of He, C and N solutes in austenite, dilute Fe-Cr-Ni austenitic alloys and Ni in order to investigate their influence on the microstructural evolution of austenitic steel alloys under irradiation.; Comment: 29 pages, 19 figures

## Theory for the electromigration wind force in dilute alloys

Dekker, J. P.; Lodder, A.; van Ek, J.
Tipo: Artigo de Revista Científica
A multiple scattering formulation for the electromigration wind force on atoms in dilute alloys is developed. The theory describes electromigration via a vacancy mechanism. The method is used to calculate the wind valence for electromigration in various host metals having a close-packed lattice structure, namely aluminum, the noble metals copper, silver and gold and the $4d$ transition metals. The self-electromigration results for aluminum and the noble metals compare well with experimental data. For the $4d$ metals small wind valences are found, which make these metals attractive candidates for the experimental study of the direct valence.; Comment: 18 pages LaTeX, epsfig, 8 figures. to appear in Phys. Rev. B 56 of 15/11/1997