Diffusion In Intermetallic Compounds Research Articles

Atomic defects and diffusion in intermetallic compounds with D03 structure: an ab-initio study

Article Atomic defects and diffusion in intermetallic compounds with D03 structure: an ab-initio study was published on October 1, 2004 in the journal International Journal of Materials Research (volume 95, issue 10).

Diffusion in intermetallic compounds: the ordered Cu3Au rule, its history

Diffusion in intermetallic compounds: the ordered Cu₃Au rule, its history

Modified embedded-atom method potential for cadmium

The second nearest-neighbor modified embedded atom method (2NN MEAM) is a semi-empirical simulation technique designed to calculate materials properties of metallic and covalent solids. It is a strong candidate for calculation of site occupation, defect association, and diffusion mechanisms in intermetallic compounds, which would provide a tool for interpreting experimental results and for predicting new, interesting measurements to perform. Potentials for 39 elements can be found in the literature, but cadmium, an important element for perturbed angular correlation spectroscopy (PAC), is absent. The purpose of this work was to develop a 2NN-MEAM potential for cadmium. Empirical parameters were determined through optimization of the potential’s ability to reproduce known physical properties of pure cadmium including cohesive energy, lattice parameters, elastic constants, structural enthalpy differences, surface enthalpy, vacancy formation energy, thermal expansion, and specific heat. Prospects for using this new potential with 2NN MEAM potentials for other elements to help interpret previous PAC studies of cadmium diffusion in intermetallic compounds will be discussed.

Site occupation of indium and jump frequencies of cadmium in FeGa 3

Perturbed angular correlation (PAC) measurements using the In-111 probe were carried out on FeGa3 as part of a broader investigation of indium site occupation and cadmium diffusion in intermetallic compounds. One PAC signal was observed with hyperfine parameters w1 = 513.8(1) Mrad/s and eta = 0.939(2) at room temperature. By comparison with quadrupole frequencies observed in PAC measurements on isostructural RuIn3, it was determined that indium occupies only the 8j site in the FeGa3 structure, denoted Ga(2) below because two out of the three Ga sites have this point symmetry. PAC spectra at elevated temperature exhibited damping characteristic of electric field gradients (EFGs) that fluctuate as Cd probes jump among Ga(2) sites within the lifetime of the excited PAC level. A stochastic model for the EFG fluctuations based on four conceivable, single-step jump-pathways connecting one Ga(2) site to neighboring Ga(2) sites was developed and used to fit PAC spectra. The four pathways lead to two observable EFG reorientation rates, and these reorientation rates were found to be strongly dependent on EFG orientation. Calculations using density functional theory were used to reduce the number of unknowns in the model with respect to EFG orientation. This made it possible to determine with reasonable precision the total jump rate of Cd among Ga(2) sites that correspond to a change in mirror plane orientation of site-symmetry. This total jump rate was found to be thermally activated with an activation enthalpy of 1.8(1) eV.

Application of random walk concept to the cyclic diffusion mechanisms for self-diffusion in intermetallic compounds

Huntington–Elcock–McCombie (HEM) mechanism involving six consecutive and correlated jumps, a triple-defect mechanism (TDM) involving three correlated jumps and an anti-structure bridge (ASB) mechanism invoking the migration of an anti-structure atom are the three mechanisms currently in vogue to explain the self- and solute diffusion in intermetallic compounds. Among them, HEM and TDM are cyclic in nature. The HEM and TDM constitute the theme of the present article. The concept of random walk is applied to them and appropriate expressions for the diffusion coefficient are derived. These equations are then employed to estimate activation energies for self-diffusion via HEM and TDM processes and compared with the available experimental data on activation energy for self-diffusion in intermetallic compounds. The resulting activation energies do not favour HEM and TDM for the self-diffusion in intermetallic compounds. A comparison of the sum of experimentally determined activation energies for vacancy formation and migration with the activation energies for self-diffusion determined from radioactive tracer method favours the conventional monovacancy-mediated process for self-diffusion in intermetallic compounds.

Diffusion in Intermetallic Compounds and Fabrication of Hollow Nanoparticles through Kirkendall Effect

. In intermetallic compounds, random vacancy motion is not possible as it would disrupt the equilibrium ordered arrangement of atoms on lattice sites. In view of this limitation, various atomistic models have been proposed, which allow atom-vacancy exchanges to take place without concomitant long range disordering. For a L12 -type A3B structure, the major element A diffuses faster than the minor element B. The trend is attributed to the different diffusing paths; A atoms can diffuse through site exchanges with a neighbouring vacancy on its own sublattice, while the jump of a B atom to a neighbouring site always creates wrong bonds. For L10-type structures such as γ-TiAl, significant diffusion anisotropy is observed; Ti atoms diffuse on the Ti sublattice, while Al atoms also diffuse on the Ti sublattice. The formation of hollow metal oxide nanoparticles through the oxidation process has been studied by transmission electron microscopy for Cu, Zn, Al, Pb and Ni. The hollow structure is obtained as a result of vacancy aggregation, resulting from the rapid outward diffusion of metal ions through the oxide layer during the oxidation process. This suggests the occurrence of two different diffusion processes in the formation of hollow oxides.

Diffusion in Intermetallic Compounds Studied Using Nuclear Quadrupole Relaxation

The jump frequency of Cd tracer atoms was measured as a function of temperature in seven rare-earth tri-indide intermetallic compounds having the L12, or Cu3Au, structure. The frequency, proportional to the diffusivity, was detected by relaxation of nuclear quadrupole interaction at Cd nuclei caused by reorientation of the electric field gradient in each diffusive jump. Measurements were made using perturbed angular correlation of gamma rays, sensitive to jump frequencies in the range 1-1000 MHz. Results are as follows. (1) Jump frequencies measured in LaIn3 and CeIn3 were observed to be 10-100 times greater at the more In-rich boundary composition than the less In-rich boundary composition, even though the phases appear as line compounds in phase diagrams. (2) Arrhenius plots of the jump frequency were fitted to activation enthalpies that increase from 0.535 to 1.80 eV across the series of phases LaIn3, CeIn3, PrIn3, and NdIn3.

Atomic defects and diffusion in intermetallic compounds with D03structure: an ab-initio study

Abstract The effective formation energies of vacancies and antistructure atoms in the D03 phase of FexAl1–x, FexSi1–x and NixSb1–x are calculated by means of the ab-initio electron theory and statistical mechanics. It is shown how the results of these calculations can be combined with available experimental data mainly from tracer diffusion studies, positron-annihilation experiments, quasielastic neutron scattering, and quasielastic Mossbauer studies to promote the understanding of the diffusion mechanisms in these materials.

Mechanical Damping by Hydrogen Diffusion in Intermetallic Compounds

In the present paper, it is shown by some experimental examples how a recently discoverd, new interstitial relaxation mechanism , based on log-range intercrystalline diffusion, affects the damping spectraof H-absorbing intermetallic compounds. Its potential to develop new materials with adjustable damping properties is discussed

Muon diffusion in intermetallic compounds of the MoSi2-typestructure

The localization and diffusion of positive muons are studied in three binarymetallic systems, Zr2Cu, Hf2Cu and Ti2Cu, presenting the MoSi2-type structure.Zero-field µSR measurements are interpreted as the muons being static in theTb/Ob interstitial site at low temperatures and, as the temperature isincreased, starting diffusing through the network of Tb sites around the Obsite, until they reach a state occupying simultaneously the four Tb sites.Long-range diffusion is observed above 300 K. Activation energies for thelower-temperature diffusion processes are obtained. The results areinterpreted in terms of the lattice structure characteristics.

Bulk and Grain Boundary Diffusion in Intermetallic Compounds of the Systems Ni-Al and Ti-Al

Bulk and Grain Boundary Diffusion in Intermetallic Compounds of the Systems Ni-Al and Ti-Al

The vacancy wind effect for chemical diffusion in intermetallic compounds

Abstract In this paper we examine the behaviour of the vacancy wind factors in the intrinsic diffusivities and the chemical or interdiffusivity in highly ordered stoichiometric AB intermetallic compounds. We show that the six-jump cycle gives quite different limits for these factors from those given by the well-known Manning expressions. Remarkably, there is non-trivial behaviour of these factors even when the vacancy flux is zero. The findings are all verified by computer simulations of a four-frequency model in the square planar lattice and an Ising model in the B2 structure. The consequences of the findings for the interpretation of experimental data are commented on.

The vacancy wind effect for chemical diffusion in intermetallic compounds

In this paper we examine the behaviour of the vacancy wind factors in the intrinsic diffusivities and the chemical or interdiffusivity in highly ordered stoichiometric AB intermetallic compounds. We show that the six-jump cycle gives quite different limits for these factors from those given by the well-known Manning expressions. Remarkably, there is non-trivial behaviour of these factors even when the vacancy flux is zero. The findings are all verified by computer simulations of a four-frequency model in the square planar lattice and an Ising model in the B2 structure. The consequences of the findings for the interpretation of experimental data are commented on.

Chemical diffusion by vacancy pairs in intermetallic compounds with the B2 structure

This paper is concerned with the implications of vacancy-pair mechanisms on chemical diffusion in intermetallic compounds with the B2 structure. The discussion specifically includes the so-called triple-defect mechanism. It is shown that the vacancy-pair mechanism cannot contribute to chemical diffusion in the intermetallic compound at the stoichiometric composition AB. Focusing on the triple-defect mechanism we extend it to non-stoichiometric compositions by including isolated antistructural atoms. By means of Monte Carlo simulation we show that the efficiency of the triple-defect mechanism in providing for chemical diffusion increases linearly with increasing antistructural atom composition but the efficiency remains relatively low unless the composition is highly non-stoichiometric.

Defects and diffusion in intermetallic compounds

Defects and diffusion in intermetallic compounds

Hydrogen Diffusivity in a Fe 3Al-Based Alloy

Many studies of environmental embrittlement have revealed that the active element (Al in aluminides) in intermetallics reacts with moisture in air, resulting in the generation of atomic hydrogen, which penetrates into crack-tip region and causes brittle intergranular or cleavage fracture. In the mean time, the active element can be oxidized as a result of the reaction with water vapor, leading to the formation of an adherent surface oxide film, which makes it more difficult to investigate the hydrogen diffusion in intermetallic compounds. Presumably, this is the reason why the hydrogen diffusivity data for intermetallics are not yet available. Nishimura et al. have found that a Ni{sub 3}Al specimen with columnar grain structure, grown unidirectionally by a floating zone method, exhibited in excess of 50% elongation to fracture in air at room temperature, indicating no environmental embrittlement. A great deal of research has also shown that Fe{sub 3}Al and its related alloys have similar characteristics. The elongation of the incompletely recrystallized Fe{sub 3}Al with an elongated grain shape is 23% in dry oxygen and 12.2% in air, while that of the same material with a completely recrystallized equiaxed grain shape is only 17.5% in dry oxygen and 7.2% in air. Itmore » has been assumed that the effect of morphology of the microstructure on the sensitivity to environmental embrittlement in Fe{sub 3}Al-based alloy may be related to the different hydrogen diffusivity. The purpose of this study is to investigate the hydrogen diffusivity in a Fe{sub 3}Al-based alloy with different grain shapes or sizes.« less

Diffusion in Materials—History and Recent Developments

Diffusion is a process that is fundamental in the art and science of materials. The knowledge of diffusion behaviour, therefore, is essential for the production of materials or for their use in practical applications. In the first part of this paper, a brief review is given on the historical developments of the quantitative study of diffusion: the establishment of the diffusion law by A. Fick, the first quantitative measurement of solid-state diffusion (Au in Pb) by W. C. Roberts-Austen and the demonstration of the self-diffusion in Pb using a natural radioactive isotope by G. Hevesy. In the second part, the development and the present status of our understanding of several problems: correlation effects in diffusion, fast diffusion in metals and the mechanism of diffusion in intermetallic compounds will be reviewed.

Reactive diffusion in a prototype system: nickel-aluminum I: Non-constant diffusion coefficient

The formation of new solid phases by diffusion between two interacting elements is analyzed on the basis of observations made (by others) on the well characterized aluminum-nickel system. Variations of the diffusion coefficients with composition have dramatic effects on the growth of AlNi and Al 3Ni 2. These phases are split into relatively sharply defined regions of different compositions, but not, as one may think, into separate phases. The effects of internal stresses, due to changes in lattice parameters with composition, on the actual composition profile of a growing phase are analyzed in the light of considerations relating to parallel effects of stresses on diffusion in simple solid solutions. The similar results reported for aluminum-nickel reactions carried out at 1000°C and 220°C provide the motivation for a review of what is known about lattice and grain boundary diffusion in intermetallic compounds. The conclusions are presented in the form of rules and observations believed to be generally valid for all diffusive reactions in the solid state.

ChemInform Abstract: Diffusion in Intermetallic Compounds

ChemInformVolume 20, Issue 41 Reviews ChemInform Abstract: Diffusion in Intermetallic Compounds H. WEVER, H. WEVER Inst. Metallforsch., TU Berlin, D-1000 Berlin 12Search for more papers by this authorJ. + HUENECKE, J. + HUENECKE Inst. Metallforsch., TU Berlin, D-1000 Berlin 12Search for more papers by this authorG. FROHBERG, G. FROHBERG Inst. Metallforsch., TU Berlin, D-1000 Berlin 12Search for more papers by this author H. WEVER, H. WEVER Inst. Metallforsch., TU Berlin, D-1000 Berlin 12Search for more papers by this authorJ. + HUENECKE, J. + HUENECKE Inst. Metallforsch., TU Berlin, D-1000 Berlin 12Search for more papers by this authorG. FROHBERG, G. FROHBERG Inst. Metallforsch., TU Berlin, D-1000 Berlin 12Search for more papers by this author First published: October 10, 1989 https://doi.org/10.1002/chin.198941344Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue41October 10, 1989 RelatedInformation

金属間化合物における拡散

金属間化合物における拡散