bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling Creep Controlled by the Glide of Jogged Screw Dislocations in TiAl and Ti-Based Alloys
Authors: Karthikeyan S. , Moon J.H. , Viswanathan G.B. , Mills Michael J.
Published: March 2009

Crept microstructures in g-TiAl based alloys reveal a preponderance of 1/2[110]-type jogged-screw dislocations, suggesting that the rate of creep deformation is controlled by the glide of such dislocations. A creep model based on these microstructural observations has been recently developed. This leads to an excellent prediction of creep rates and stress exponents. In this paper,
the framework of this model including the verification and validation of the functional dependencies of various microstructural model parameters is reviewed. It has also been observed that creep phenomenology is extremely sensitive to microstructure – fully lamellar g-based alloys exhibit lower creep rates and higher stress exponents even though the deformation microstructure is similar
to that in equiaxed alloys. The modifications made to the model that account for the constrained nature of deformation in lamellar alloys are discussed. The applicability of the model is explored in materials systems, including a-Ti and a+b Ti alloys where similar creep exponents and deformation structures have been observed. Finally, the relevance, applicability and shortcomings of the model are critically analyzed.
Recent Advances in Point Defect Studies Driven by Density Functional Theory
Authors: Legris Alexandre
Published: March 2009

We highlight some of the most salient recent advances in point defects studies obtained from atomic-scale simulations performed in the framework of the density functional theory. The refinement of the theory, combined with its efficient numerical implementations and the (until now) everlasting growth of computer power allowed the transition from qualitative (in the beginning of the 90’) to quantitative results. Some of the longstanding controversies in the field have been tackled, and as far as aluminum is concerned, it has been shown that the curvature in the Arrheniusplot is due to anharmonic effects rather than to a two-defect diffusion mechanism. The anomalous diffusion in the b (bcc) phase of the group-IV elements has been related to the strong structural relaxation around vacancies, which significantly reduces their formation energy. Self-interstitials have been studied in materials of technological interest, their structure and mobility have been
analyzed allowing a better interpretation of experimental results and an improved understanding of processes occurring under irradiation. Dilute interstitial solid solutions have been investigated. The strong binding between C and vacancies in bcc Fe may partially explain the observed influence of low amounts of C on Fe self-diffusion; the attraction of H to stacking faults in a Zr should favor planar dislocations glide. Intermetallics involving Fe (Fe-Al, Fe-Co) behave like highly correlated systems requiring methodological improvements of the DFT for a quantitative description. However, valuable trends concerning the structural point defects (those that allow nonstoichiometric compositions at low temperature) as well as the temperature dependence of point defects concentrations have been obtained.
Diffusion Process Simulations - An Overview of Different Approaches
Authors: Strandlund Henrik , Larsson Henrik
Published: March 2009

Some different approaches to diffusion process simulations are briefly presented. Their varying areas of applicability are discussed. Example simulations using the phase-field method, the DICTRA software, and random-walk based approaches are presented.
Long-Term, Cyclic Oxidation Behaviour of Alumina- and Chromia-Forming Alloys
Authors: Bachorczyk Nagy Renata , Fordham Richard J.
Published: March 2009

The oxidation resistance behaviour of a number of surface-treated FeCrAl commercial alloys and some model alloys of well-defined composition, incorporating a range of reactive elements in trace amounts, has been studied under thermal cyclic conditions in air with and without additions of water vapour. Additions of reactive elements such as Zr, La, Y, Hf modify the oxidation resistance behaviour of FeCrAl-alloys by improving the scale adherence and consequently may extend the lifetime of FeCrAl steels. The presence of the water vapour can affect oxidation in a number of different ways. Our results may indicate that high content of water vapour can cause the lives of such alloys to be decreased. This work forms part of a larger
European-funded project to evaluate physical properties, microstructural features,
oxidation/corrosion resistance and lifetime improvement. The correlation between alloy parameters and lifetime; as well as the modeling of oxide scale behaviour as function of cycling conditions is also studied.
Chemical and Physical Interactions of Si-Rich Steel Substrates during Hot Dipping Experiments in a Molten Al-(25 wt%)Si Alloy
Authors: Barros José , Ros-Yáñez Tanya , Houbaert Yvan
Published: March 2009

The chemical and physical interaction between Fe-Si alloys in the range 0-3.8 Si wt% and a molten Al-(Si 25wt%) alloy at 800 °C has been studied for different reaction times (from 0.1 to 200s) by hot dipping tests. Several intermetallic phases have been identified, Fe2Al5, τ1-Al3Fe3Si2, τ2-Al12Fe6Si5, τ3- Al2FeSi and τ4- Al3FeSi2, which already were reported in the literature dealing with the interaction between iron and molten Al-Si alloys. In addition an ordered phase Fe3Si (D03) appears in contact with the Fe-Si substrate. Diffusion reaction and solidification phenomena appear to be involved in the developing of the coating. The growth kinetic has been studied and diffusion appears as the step controlling the intermetallic compounds growth. Special attention was paid to the effect of the microstructure of the dipped sheet on the interaction with the molten alloy. The
higher deformed structures react faster; this effect can be explained by the faster diffusion through high diffusivity paths like grain boundaries and dislocations.
Mechanisms of Diffusion and Dissociation of E-Centers in Silicon
Authors: Ganchenkova Mariya G. , Borodin V.A. , Nieminen Risto M.
Published: March 2009

In this paper we discuss possible mechanisms of PV annealing in Si. Our approach includes a combination of density functional theory and lattice kinetic Monte-Carlo (LKMC) simulations. The density functional theory is used to find the binding energies and jump barriers for P-V pair at different separations (from one to three interatomic bonds between complex constituents) and in different charge states. The mobility of the complex is simulated by LKMC with event probabilities calculated based on the energies from ab-initio calculations. .
Auger Electron Spectroscopical Investigation of Interfacial Segregation in the Cu-Bi System
Authors: López Gabriel A. , Mittemeijer Eric Jan
Published: March 2009

A systematic investigation of the segregation of Bi at both free surfaces and grain
boundaries in Cu, under identical conditions, is reported. The problem of Bi evaporation upon Bi segregation at free surfaces was overcome using a special method for sample preparation. Cu bicrystals containing deliberately made internal cavities at the grain boundary were doped with Bi, annealed at temperatures between 1073 and 1223 K, and broken along the grain boundary in an ultrahigh
vacuum chamber for Auger electron spectroscopy. For the first time, the equilibrium surface segregation of Bi in Cu has been measured. The segregation at the free surface was found to be stronger than the segregation at the grain boundary.
Characterization of TiAlSi Coating Deposited by Arc-PVD Method on TiAlCrNb Intermetallic Base Alloy
Authors: Moskal G. , Góral M. , Swadźba Lucjan , Mendala B. , Jarczyk G.
Published: March 2009

Results of microstructural investigations of aluminide coatings modified by Si are
presented in this work. Protective coating (TiAlSi type) was deposited by Arc-PVD. Thickness of the outside layer of deposited coating was 35µm and it contained TiAl3 phase modified by Si as a main component. The second layer was found as a transition area between the TiAl3 outside layer and the surface of TiAlCrNb substrate. Thickness of the inside sublayer was 5 µm. The diffusion treatment caused the progress of coating homogenisation from the point of view of phase and
chemical composition. It was found that the coating consisted of the dominant TiAl3 phase and Ti5Si3 in thick outer sublayer and only TiAl2 phase in transition thin sublayer. Below the transition area, on the surface of TiAlCrNb substrate alloy, the layer of g−TiAl was found. The amount of silicides was increased in comparison with the coating only after the Arc-PVD process and the area of its presence had been removed in the outside direction of the coating.
Refinement in the Mathematical and Numerical Treatment of the Internal Oxidation of Alloys
Authors: Miszuris Wiktor , Öchsner Andreas
Published: March 2009

When oxygen dissolves from atmosphere and diffuses into an alloy during oxidation, the less noble alloy components may react to form oxide particles within the metal. This process is termed internal oxidation. Classical approaches to describe this phenomenon were derived under many strong simplifications such as constant diffusion coefficients, certain boundary conditions and semi-infinite sample. The presented general approach is based on the finite difference solution of the general diffusion equations coupled through the stoichiometry of reaction between oxygen and the considered element. The main enhancement is the consideration of concentration dependent diffusion coefficients, concentration dependent source terms and arbitrary time-dependent boundary conditions formulated as a concentration, a flux or mixed conditions. Furthermore, finite dimension of the specimen is incorporated. This general treatment also allows for the incorporation of the energy balance.
Monte Carlo Simulation of Diffusion with Uniform Sinks and Sources for Vacancies
Authors: Ženíšek Jaroslav , Svoboda Jiří , Fischer Franz Dieter
Published: March 2009

A new concept of generation and annihilation of vacancies at uniform sinks and sources for vacancies is incorporated into the standard Monte Carlo model for vacancy mediated diffusion. This model enables to treat the vacancy wind as well as the deformation of the specimen and the shift of the Kirkendall plane. The Monte Carlo model is used for the testing of the recent phenomenological theories of diffusion by Darken, Manning and Moleko. The agreement with the self-consistent Moleko theory is excellent. On the other hand the agreement with the classical
Darken theory used very often for the explanation of the Kirkendall effect is rather poor.
Ultraslow Diffusion in Polycrystalline h-LiTiS2 Studied by 7Li Spin-Alignment Echo NMR Spectroscopy
Authors: Wilkening Martin , Heitjans Paul
Published: March 2009

Multiple-time spin-alignment echo (SAE) NMR spectroscopy of spin- 3 2 nuclei is used to study ultraslow diffusion in the hexagonal layered Li ion conductor LixTiS2 (x 1). Two-time correlation functions were monitored by recording (Jeener-Broekaert) echo amplitudes for constant evolution and variable mixing times. Echo decay rates t
The Effective Interdiffusion Coefficients in Experimental Investigations of Interdiffusion in Ternary Systems
Authors: Ugaste Ü.
Published: March 2009

The application of the effective interdiffusion coefficients for describing the
interdiffusion process in ternary systems is discussed. It is shown that the relative values of effective interdiffusion coefficients, which are directly related to the diffusion path developed in a given diffusion couple, are responsible for deviation of the diffusion paths from linearity. The relationship between effective interdiffusion coefficients and partial (intrinsic) coefficients in ternary systems is analysed. It is shown that Boltzmann’s solution for diffusion equation with variable diffusion coefficient by means of relatively easy calculation procedure gives reliable results
for the calculation concentration distributions in a ternary diffusion couple.
Study of Fe3Al-Based Alloys by Internal Friction and 59Fe Radiotracer Diffusion Measurements
Authors: Pavlova Tatiana S. , Golovina S.B. , Divinski Sergiy V. , Golovin Igor S.
Published: March 2009

Anelastic effects caused by carbon and vacancy diffusion in Fe3Al based alloys with and without strong carbide forming elements (Ti and Nb) are investigated by internal friction measurements. The decrease of the Snoek peak in Fe–26Al–2Ti and Fe–26Al–0.3Nb alloys with respect to the Fe–26Al alloy is related to a decrease in the amount of interstitially dissolved carbon (C). The so-called X peak, which is observed in the Fe–26Al alloy, also almost disappears after alloying. In order to elucidate the vacancy contribution to the origin of the X peak radiotracer measurements of 59Fe diffusion were performed. The results indicate that the change in the interstitially dissolved C concentration is the main reason of the observed changes in the X peak, although a certain influence of Ti and Nb alloying on the total vacancy concentration may be deduced from the diffusion study.
Surface Chemical Reactions in Processes of Diffusion Mass Transfer
Authors: Prytula A. , Fedirko V. , Pohreliuk Y.M. , Matychak Ya.
Published: March 2009

The phenomenological theory for describing high-temperature interaction between metal and diluted gaseous medium has been developed. The theory is based on the assumption of duplex contact layer existence in the vicinity of interface (with relative thickness 2 d), where chemical reactions and processes of gas component migration occur. The non-stationary conditions of mass transfer at the
interface are described involving effective average parameters. These conditions allow considering a wide spectrum of boundary diffusion phenomena (in a short and prolonged time ranges), in order to describe the kinetics of accumulation of diffusing component close to the interface. The description of the kinetic of gaseous saturation of metal (nitriding and borating) in the diluted medium becomes a
partial proof of the suggested models. In order to approach the diffusion phenomena, boundary conditions, which contain, besides the coordinate derivative of concentration function, also the time derivative, were suggested. The derived equations describe the time dependence of change of surface concentration of gaseous component, the kinetics of its accumulation owing to chemical reaction, the specimen mass change owing to both, the diffusive addition dissolution in metal and its chemical interaction. The role of temperature is also discussed.
First Study of Iron Self-Diffusion in Fe2O3 Single Crystals by SIMS
Authors: Sabioni Antônio Claret Soares , Daniel Antônio Márcio J.M. , Macedo W.A.A. , Martins M.D. , Huntz Anne Marie , Jomard François , Persiano A.I.C.
Published: March 2009

Iron bulk self-diffusion coefficients were measured in Fe2O3 single crystals using an original methodology based on the utilization of 57Fe stable isotope as iron tracer and depth profiling by secondary ion mass spectrometry (SIMS). The iron self-diffusion coefficients measured along c-axis direction, between 900 and 1100o C, in oxygen atmosphere, can be described by the following Arrhenius relationship: D(cm2/s)= 5.2x106 exp [-510 (kJ/mol)/RT], and are similar to reliable data available in the literature, obtained by means of radioactive techniques.
Jump Frequency of Cd Tracer Atoms in β-Mn
Authors: Zacate Matthew O. , Collins Gary Scott
Published: March 2009

The jump frequency of Cd tracer atoms in pure and Al-doped b-Mn was determined
from measurements of quadrupole relaxation using the method of perturbed angular correlation of gamma rays. The jump frequency of Cd in b-Mn containing about 4.5 at.% Al had an activation enthalpy of 0.67(3) eV. In pure b-Mn at 950 K, the jump frequency was a factor about 8 larger than the value of 9.2 MHz in the alloy. Information was also obtained about the sluggish kinetics of the a-Mn to b-Mn polymorphic transformation.
Ru Self-Diffusion and Ru Diffusion in Al
Authors: Dyment Fanny , Balart Silvia , Lugo Constanza , Pérez Rodolfo A. , Di Lalla Nicolás , Iribarren Manuel J.
Published: March 2009

The self-diffusion of Ru in the temperature range of (1267-1373) K and the Ru diffusion in pure aluminum in the temperature range of (632-873) K is reported. Difficulties were encountered when working with Ru as matrix (its brittleness at room temperature impeded a good sectioning) and they are the reason why only the order of magnitude of the self-diffusion in the small range of temperature
studied is given. For Ru diffusion in aluminum, two experimental techniques were used: the conventional serial sectioning with use of a radiotracer, 103Ru, for the highest temperatures and Heavy Ions Rutherford Backscattering Spectrometry (HIRBS) for the lowest ones. The diffusion parameters are: Q = 199.4 kJ/mol and D0 = 4.1x10-2 m2/s. A comparison is made with Ru diffusion behavior in copper and silver.
Phase Transformation and Densification of Nanostructured Alumina. Effect of Seeding and Doping
Authors: Legros Corinne , Carry Claude , Lartigue-Korinek Sylvie , Bowen Paul
Published: March 2009

By following the densification kinetics of nanocrystalline g alumina and corresponding
microstructural evolution we showed that the diffusive transformation gamma-alpha involves several processes such as nucleation of alpha phase, rearrangement of gamma crystallite at alpha seed and grain surfaces, formation of porous alpha alumina monocrystalline colonies. Results concerning the effects of seeding and doping elements on the transformation-densification behaviour of the same g-alumina raw powder batch are also presented. Doping elements seem to have no influence on nucleation rate but could modify the redistribution rate of the ions during the transformation by short range diffusion of doping elements.
Thermal Stability of NiAl-Base Coatings for High Temperature Application
Authors: Filipek Robert , Danielewski Marek , Tyliszczak E. , Pawełkiewicz M. , Datta S.
Published: March 2009

Aluminide diffusion coatings act as a remedy against the aggressive environments in which modern aero-gas turbines operate. Platinum addition to basic aluminide coatings significantly improves the oxidation resistance of these coatings. The increase in operating temperatures of industrial energy systems and gas turbines, has led to the extensive use of coatings capable of providing improved service life. Interdiffusion plays a critical role in understanding the integrity of such coatings. The Danielewski-Holly model of interdiffusion which allows for the description of a wide range of processes (including processes stimulated by reactions at interfaces) is employed for studying of interdiffusion in the Pt-modified β-NiAl coatings. Using the inverse method the intrinsic diffusivities of Ni, Al and Pt were calculated. Such obtained diffusivities were subsequently used for modelling of thermal stability of Pt-modified aluminide coatings in air and in argon atmosphere.
Diffusion of Boron in Silicon and Silicon-Germanium in the Presence of Carbon
Authors: Karunaratne Mudith S.A. , Bonar Janet M. , Zhang Jing , Ashburn Peter , Willoughby Arthur F.W.
Published: March 2009

Boron diffusion in Si and strained SiGe with and without C was studied. Using gassource molecular beam epitaxy (MBE), B containing epitaxial layers of: (i) Si, (ii) Si containing 0.1% C, (iii) SiGe with 11% Ge and (iv) SiGe with 11% Ge and with a 0.1% C, were grown on substrates. These samples were then rapid thermal annealed (RTA) at 940, 1000 and 1050°C in an O2 ambient. Self-interstitial-, vacancy- and non-injection conditions were achieved by annealing
bare, Si3N4- and Si3N4+SiO2-coated surfaces, respectively. Concentration profiles of B, Ge and C were obtained using Secondary-Ion Mass Spectrometry (SIMS). Diffusion coefficients of B in each type of matrix were extracted by computer simulation. We find that B diffusivity is reduced by both Ge and C. The suppression due to C is much larger. In all materials, a substantial enhancement of B diffusion was observed due to self-interstitial injection compared to non-injection conditions. These results indicate that B diffusion in all four types of layers is mediated primarily by interstitialcy type defects.
Structural Defect Formation in Inorganic Sol-Gel Derived Oxides
Authors: Frolova Elena V. , Ivanoskaya Mariya I.
Published: March 2009

The advantages and uniqueness of the Inorganic modification of the Sol-Gel method have already been described. Homogeneous nano-composites as well as some exotic glasses, complex-metal-oxides systems with little glass-forming ability, can be produced by this method. Thus, the obtained materials are characterized by a complex structure that leads to the wide variety of physical and chemical properties. Zirconia-containing materials are of utmost interest because of the mechanical toughness and chemical resistance provided by the presence of ZrO2. In the present work, we report on unusual structural peculiarities of the Zr-O, two types of Zr-Ge-O systems (with Zr>Ge and Zr<Ge molar ratios) and Zr-Ce-Al-O glassy samples, successfully prepared by inorganic modification of the Sol-Gel technique. We tried to elucidate the cause of a self-reduction process in those oxides systems under thermal treatment in air and the way in which structural imperfections impact upon some properties of the materials obtained.
Size Effect on the Electronic Properties of Doped and Undoped Ceria
Authors: Zhou X.-D. , Huebner W. , Anderson H.U.
Published: March 2009

The roles of grain size and chemical composition on the electronic conductivity (σ) of CeO2 are reported. In undoped high purity (99.995%) CeO2, σ increases with decreasing grain size, indicating generation of low oxidation state Ce species, Ce3+ ions, which act as the electrons. In low purity undoped CeO2, the chemical impurities act as both the acceptor dopants, as well as the components (such as Si) to form amorphous phase in the grain boundaries. In low purity (99.5%) undoped CeO2, size effects are, therefore, influenced by the presence of acceptor dopants and/or blocking grain boundary phases. In low purity undoped CeO2, the grain boundary contribution to the overall resistance decreases with increasing grain size due to dilution effects of the amorphous grain boundary phases. The intentional addition of acceptors (10%) will pin oxygen vacancies over a wide range of oxygen activity. Size effects in acceptor doped CeO2 are mainly related to the presence of grain boundary phases. In Ce0.90Gd0.10O1.95, the grain boundary contribution to total resistance increases with decreasing size, which is due to trapping of oxygen ions.
The Size Distribution of Defect Clusters in n-Si (FZ, Cz), Irradiated by Fast Neutrons
Authors: Dolgolenko A.P. , Gaidar G.P.
Published: March 2009

The dependence of concentration of defects on doping level for average cluster in n-Si was calculated. It was shown that in the framework of the Gossick's model the concentration of defects for the average cluster is in inverse proportion to the square of a cluster radius. One obtains the size distribution of defect clusters created by fast neutrons of WWR-M reactor, by the transformation of energy spectrum of the primary knock-on atom in n-Si (FZ, Cz). Threshold energy of defect clusters formation 4.7 keV by comparing n-Si crystals irradiated by deuterons and fast-pile neutrons was calculated.
Oxygen Enrichment of Silicon Wafer by Ion Implantation Method and Fabrication of Surface Barrier Detectors
Authors: Chaudhuri S.K. , Rajesh P.V. , Ghugre S.S. , Das D.
Published: March 2009

Silicon surface barrier (SSB) detectors have been fabricated with oxygen enriched, high-resistivity, detector grade, n-type FZ silicon. Oxygen enrichment of the wafer was done by high-energy (140 MeV) oxygen ion implantation. Annealing of the irradiated silicon wafer was done to minimize the irradiation-induced defect concentration. Positron annihilation lifetime studies were used to select the annealing temperature. A comparative study was carried out among various SSB detectors made from as-grown, as-irradiated and annealed silicon wafers. Detector made from the annealed wafer worked satisfactorily and its performance was comparable with that of a detector made from as-grown crystal.
Adolf Fick and Diffusion Equations
Authors: Philibert Jean
Published: March 2009

After some biographical notes, Fick’s 1855 seminal paper is analysed and the contributions of Stefan and Roberts-Austen are briefly mentioned.
Diffusion under Large Driving Forces
Authors: Beke Dezső L. , Erdélyi Z.
Published: March 2009

In the diffusion literature the classical Nernst-Einstein equation is used to describe the effect of driving forces. This implies that the diffusive flux is proportional to the driving force. However, this linear law will not be valid if the driving force is very large. Attempts in the literature for the derivation of an “improved relation” till now were restricted to the cases when the diffusion coefficient was independent of the composition. On the other hand, it is also known that even if no driving forces (other than related to the chemical driving force) are present then deviations from the Fick I law are expected on nanoscale. In this lecture attempts will be made to find a general description for the above problems, i.e. when the driving forces and the diffusion asymmetry (the composition dependence of the diffusion coefficient) are large.
Effect of a Third Element on the Stability of NiSi Thin Films on Si
Authors: Mangelinck Dominique
Published: March 2009

The effect of Pt and Ge on the stability of NiSi films has been examined. The addition of a small amount of Pt (5 at%) in the Ni film increases the disilicide nucleation temperature to 900oC leading to a better stability of NiSi at high temperatures. For Ni films on Si1-xGex with x=0.29 and 0.58, no NiSi2 was found after annealing at 850°C. The increase in thermal stability of NiSi has been explained in terms of nucleation concept. Calculated ternary phase diagrams allow to understand the effect of the third element (Pt or Ge) on the driving force for nucleation. The
redistribution of this element can also be explained with the ternary phase diagrams.
Shape of Moving Grain Boundary and its Influence on Grain Boundary Motion in Zinc
Authors: Sursaeva Vera G. , Straumal Boris B.
Published: March 2009

The migration of individual special [ ] 0 1 10 tilt grain boundary (GB) with Σ =15 and misorientation angle 29° in Zn bicrystal have been investigated. The stationary shape of migrating GB has been studied and the migration rate has been measured by optical microscopy in situ between 558 and 683 K using polarized light. In certain experimental runs the migrating GB is faceted and moves thermally activated. Its kinetics follows the Arrhenius type dependence despite the fact that shape of moving GB depends on temperature. After detachment from impurity cloud the [ ] 0 1 10 tilt GB migrates activationless in the temperature interval 618÷683 K. The detachment temperature is 618 K. The non-physically high value of the apparent migration activation enthalpy can appear due to the change of GB shape from faceted to smooth and back.
On the Kinetic Mechanism of Ga Penetration in Al Bicrystals under Small Residual Stress
Authors: Glickman Evgeny E.
Published: March 2009

Thermodynamic conditions for spontaneous grain boundary wetting (GBW) and stress driven liquid metal embrittlement (LME) are related to each other. Kinetic mechanism responsible for fast GB penetration (GBP) under small stress is described. Dissolution–condensation mechanism of LME and linear fracture mechanics for calculation of crack profile are applied to the classical system “Al-liquid Ga”. The results tend to support the idea that the recently observed fast linear penetration of Ga along 150° tilt <110> GB of Al should be considered as propagation of LME crack under small residual stress rather than as spontaneous GBW. With the residual tensile stress σ≈ 0.5MPa acting normal to the GB plane, all major findings reported for this model system are explained in semi quantitative way assuming that GB spreading coefficient is extremely small by its absolute value, i.e. that the system is near the threshold of spontaneous GBW.
Surface Spreading and Penetration of Liquid and Solid Ga in Thin Polycrystalline Ag Films
Authors: Glickman Evgeny E. , Levenshtein M. , Budic L. , Eliaz N.
Published: March 2009

Spreading of liquid and solid Ga over the surface of thin polycrystalline Ag film is accompanied by fast penetration of Ga through the film. The penetration process between +60°C and –10°C has likely a common mechanism with the spreading. The activation energies of the process responsible for spreading/penetration are EL = 0.3±0.05 eV and ES = 0.5±0.1 eV for liquid and solid Ga, respectively. The common mechanism is attributed to grain boundary (GB) grooving with diffusion of Ag out of the groove either via liquid Ga or along GBs in solid Ga. A possible formation of intermetallic compound between Ag and Ga is considered as the secondary process, which does not control the kinetics. The model reproduces the spreading/penetration rates that are observed, and gives reasonable estimates of the experimental activation energies ES and EL.
Liquid Ga Penetration along Al Grain Boundaries: Effect of External Stress and Ga Undercooling
Authors: Kozlova Olga , Rodin Alexey
Published: March 2009

The effects of compressive stress and undercooling of Ga to liquid gallium penetration along grain boundaries (GBs) of aluminum were investigated. It was shown that the penetration rate does not change with the temperature if gallium is in liquid state. The effect of compressive stress applied to Al samples was demonstrated. The time to wetting of all aluminum GBs increased several orders of magnitude if the compressive stress was between 0.1 and 6 MPa. It was proved that solid-liquid transformation does not take place during penetration process.
Kirkendall Effect: Dramatic History of Discovery and Developments
Authors: Paritskaya Lyudmila N.
Published: March 2009

The importance and generality of Kirkendall discovery, which opened new area in diffusion science, have been discussed. The developments of Kirkendall’s idea for sub-surface (SS) and grain boundary (GB) interdiffusion have been considered and applied for the advanced structural materials, such as thin films and nano-composites. The kinetics and mechanisms of SS and GB Kirkendall effects have been analyzed theoretically and studied experimentally.
On the Physics of the Anomalous Characteristics of Fickian Diffusion of Fe and Other Transition-Element Impurities in Crystalline Al at Elevated Temperatures
Authors: Nechaev Yuriy S.
Published: March 2009

As the critical constructive analysis, with using the thermodynamic and crystal-chemical
approaches, of the related experimental data is shown, the anomalous (with respect to the Al selfdiffusion
characteristics (DAl - the self-diffusion coefficient, D0Al - the entropy (frequency) factor of
the self-diffusion coefficient, QAl – the self-diffusion activation energy (enthalpy)) quantities of D*,
D0*, Q* of the transition impurity Fickian diffusion in Al in many cases can be of the apparent
character (related to the known Oriani model), whereas the normal quantities of D, D0, Q (i.e., close
to DAl, D0Al, QAl), and the anomalously low quantities of D⊥, Q⊥, D0⊥ can be as the true
characteristics of the impurity Fickian diffusion in the normal Al lattice (bulk) and in the
compound-like nanosegregation (CLNS) structures at dislocations, respectively.
On the Physics of Enhanced Fickian Diffusion and Structural-Phase Changes in Intensively Deforming Metallic Materials
Authors: Nechaev Yuriy S.
Published: March 2009

Urgent open questions and their solution ways are considered of the thermodynamic stimuli and mechanisms of the enhanced Fickian diffusion mass-transport providing the unusual structuralphase transformations in metallic materials undergoing the intensive cold deformation, those can not be described in the framework of the conventional phase diagrams.
Grain Boundary Defects Induced Switching in Zn- Bi- Mo Ceramic
Authors: El-Hofy M.
Published: March 2009

Three Zinc Molybdenum ceramic samples doped Bi have been prepared according to the chemical formula (1-x) ZnO – 0.2MoO3 – xBi2O3, where (x = 0.2, 0.5, 1.0) mol %. The samples were studied at room temperature through X-ray Diffraction analysis, SEM, EDAX, I-V characteristics and C-V measurements. The results decleared the presences of two phases; ZnO as a major phase beside Bi2MoO6 as a minor phase. At lower Bi additions; Bi and Mo ions are highly segregated at the grain boundaries, while at higher additions more homogenous distribution for these ions inside the grain is observed. Some pores are observed around the batches of the minor phase and at the grain boundaries. The grain size is enlarged with increasing Bi addition; while the number and size of the pores are decrease. Creation of the pores is attributed to oxygen liberation from the surface of the sample during sintering. Formation of Schottky barrier is indicated via I-V and C-V measurements and attributed to Zn vacancies at the grain boundary. Interface potential barrier, donor density, interface state density and barrier width are decrease with increasing Bi addition. I-V characteristics revealed voltage switching. The switching voltage E0 decreases with increasing Bi addition and it is reproducible even after several on-off cycles.
Six-Jump-Cycle Mechanism for Collective Correlations in Nonstoichiometric Intermetallic Compounds
Authors: Gosain K.L. , Chaturvedi D.K. , Belova Irina V. , Murch Graeme E.
Published: March 2009

The six-jump-cycle (6JC) mechanism is used to derive expressions for collective correlation factors in a nonstoichiometric binary intermetallic compound AB. The 6JC is used as a fundamental unit for the cycle involving a perfectly ordered configuration and a two-jumpcycle (2JC) as a fundamental unit for the cycle involving existing antistructural atoms. The jump frequency for the 6JC is calculated in terms of a four-frequency-model using the mean first passage concept of Arita et al., while the jump frequency for the 2JC is taken to be the harmonic mean of the individual jump frequencies. The expressions for phenomenological transport coefficients are obtained through the linear response approximation using the kinetic equation approach. The results for collective correlation factors are compared with Monte Carlo simulation and are found to be in reasonably good agreement when the ratio of jump frequencies of regular site and antistructural atoms is of the order of 10-1.
Phase Transitions in Mixed Jahn–Teller Systems with Competitive Interactions
Authors: Fishman Anatoly Yakovlevich , Ivanov M.A. , Tkachev Nickolai , Shunyaev K. Y. , Zinigrad Michael
Published: March 2009

Phase diagrams of mixed crystal systems exhibiting the cooperative Jahn–Teller effect
are investigated. The competition of Jahn–Teller interaction with a) the preference energy of cation
distribution over nonequivalent sublattices or b) stabilization energy of 3d-ion valence
configuration is considered. The developed model enables to explain the nature of equilibrium and
metastable states, the variety of phase diagrams and its special features in crystals with the
competing interactions.
Effect of Solidification Rate and Composition on Segregation in Al-Li-Cu-Zr Alloys
Authors: Ahmadi Shahram , Shokuhfar Ali , Hadavi S.M.M. , Rezaei Arash , Azimi H.
Published: March 2009

In the present study, solidification and segregation of Al-Li-Cu-Zr alloys have been
investigated. Results show that shape of ingots and amount of lithium can change solidification
essence. Increasing solidification rate, not only eliminates grain-refining effect of zirconium but
also causes coarse segregation of copper in grain boundaries (negative segregation). Increasing
amount of lithium in Al-Cu-Li-Zr alloys can change the solubility of other alloying elements (Cu,
Zr) and increase solidification range and microsegregation of copper in structure.
High Temperature Oxidation of Ultra-Low-Carbon Steel
Authors: Suarez Lucia , Coto R. , Vanden Eynde X. , Lamberigts M. , Houbaert Yvan
Published: March 2009

An oxide scale layer always forms at the strip surface during the hot rolling process. Its
properties have a large impact on surface quality. The most important features of the oxide layer are
its thickness, composition, structure, adherence and coherence. Temperature, time and gas
atmosphere determine the growth of oxide layers. In this paper, the high temperature oxidation
properties of ultra low carbon steels are discussed in terms of oxide growth mechanism, kinetics and
phase morphology. The oxidation kinetics of ultra-low carbon steel (ULC) in air, its scale structure
and composition were investigated over the temperature range 923-1473K. Oxidation experiments
were performed either under controlled atmosphere or in air, to analyse the oxidation process during
strip production. A first series of experiments was carried out in an electric furnace at temperatures
ranging from 923 to 1473K, for times between 16 and 7200s. A second series was carried out in a
device especially designed to control the atmosphere. After heating under pure nitrogen, the samples
were oxidised in air at temperatures between 923-1323K for various oxidation times. Thus treated
specimens were characterised by metallography and their scale thickness was measured under the
optical microscope. Scale morphology was studied and scale composition confirmed by EDS
(Energy Dispersive Spectroscopy) and EBSD (Electron Backscattered Diffraction) analysis. Results
show that scale growth under controlled atmosphere is significantly faster than under non controlled
conditions, additionally the adherence of the scale formed in the laboratory device was significantly
better than the other one. It is clear that scale thickness and constitution depend strongly on the
oxidation potential of atmosphere. Computed parabolic activation energies (Ea) values are in good
agreement with those found in the literature.
Effect of Homogenization Process on Hot Rolling of Aluminum-Lithium Alloys
Authors: Shokuhfar Ali , Rezaei Arash , Hadavi S.M.M. , Ahmadi Shahram , Azimi H.
Published: March 2009

Aluminum-Lithium alloys are attractive choices for weight saving of aerospace
structures. By addition of Lithium to Aluminum alloys, the mechanical and physical properties are
improved, density decreases up to 10% and module of elasticity increases up to 15%. As-cast Al-Li
ingots include some continues brittle phases in grain boundaries that decrease formability by crack
initiation during hot rolling. In the present work, influence of homogenization on hot rolling of Al-
Li alloys was studied. Homogenization temperature determined based on DTA test and
homogeneity properties were characterized by microstructures observation. One specimen was cast
in conventional method and the other was cast by direct casting (DC) method. Homogenization was
performed at four different times: 10, 24, 50 and 100 hours at 500°C also no cracking has been
observed in both ingots in 100 hr and 24 hr at 500°C respectively due to eliminate the brittle phases.
Moisture Effective Diffusivity in Porous Media with Different Physical Properties
Authors: M.N.N. Miranda , Silva M.A.
Published: March 2009

In the drying of porous media, the mass transport occurs in the pores as well as on the
surface of the solid. The mechanisms involved can take place simultaneously, influenced by the
predominant one and can change depending on the moisture content. In this work, the moisture
effective diffusivity was estimated in solids with distinct structural properties in order to verify the
predominant mechanisms according to the moisture content, analyzing the influence of the physical
properties. The materials studied were NaY Zeolite, Kaolin, Silica and Alumina. The results of
diffusion coefficient present a minimum at low moisture content that can be related to pore size.
Drying Kinetics of Grape Stalk
Authors: García-Pérez J.V. , Blasco M. , Cárcel J.A. , Clemente G. , Mulet A.
Published: March 2009

Grape stalk may be considered as an agro-food byproduct of the wine industry, being
considered as a potential source of antioxidant compounds. Actually, before the extraction of
antioxidants a previous stage of drying would be necessary. Stalks obtained from a red wine
processing (Vitis vinifera var. Bobal) were characterized as a cylinder net with different size ending
in spheres. The average diameters and mass fractions of the individual parts of the stalk were
measured: spheres (4.4±0.7 mm and 0.352 mass fraction), large cylinders (3.3±0.6 mm and 0.204
mass fraction), intermediate cylinders (2.1±0.4 mm and 0.294 mass fraction) and small cylinders
(1.1±0.3 mm and 0.150 mass fraction). Drying kinetics of each one of the parts of the stalk were
carried out at 40 °C and 2 m/s using an initial mass load of 30 g. Furthermore, drying experiments of
the whole stalk were conducted at the same experimental conditions. Different diffusion models
were considered to predict the drying kinetics for each one of the individual parts of the stalk
according to the geometry considered. A diffusion model for the whole stalk was developed by
adding the individual diffusion models weighed by the corresponding mass fractions. The diffusion
models considered fitted properly the drying kinetics of the individual parts considered on the stalk.
The figures of the effective moisture diffusivity identified for the different kinds of cylinders were
close (1.07-1.78 10-11 m2/s), however, the spheres showed a different behavior characterized by a
significantly higher figure of effective moisture diffusivity (3.92 10-8 m2/s). Finally, the usefulness
of the model considered to describe the drying kinetics of the whole stalks was shown.
Diffusion of Critical Elements in Steel during Thermal Treatments in a Diamond Chemical Vapour Deposition Atmosphere
Authors: Neto V.F. , Vaz Raquel , Shokuhfar T. , Ghumman C.A.A. , Teodoro Orlando M.N.D. , Ali N. , Oliveira Monica S.A. , Grácio J.
Published: March 2009

In this study, it will be investigated the diffusion of critical elements, namely, carbon (C)
and iron (Fe), into a steel substrate (Impax Supreme) during the diamond chemical vapour
deposition (CVD) process. The substrate temperature was varied from 700 to 850°C by plasma
power manipulations to enable the correlation of substrate temperature with diffusion length and
depth of the above mentioned critical elements into steel during film growth conditions. Methane
concentration is also a parameter which has been considered during the parametric analysis. The
crystalline compounds formed during the diamond growth process are studied using XRD analysis.
In addition, SIMS technique is used with depth profiling to monitor the diffusion of elements during
the process. The results obtained enabled to improve traditional understanding about the
mechanisms relating to diamond deposition on steel substrates using CVD processes.
Reactive Diffusion in Cu-Nb-Sn Internal Tin Superconducting Wires for the ITER Project
Authors: Pong I. , Hopkins Simon C. , Fu Xiao Wei , Glowacki Bartek A. , Elliott James , Baldini Alberto
Published: March 2009

The reactive diffusion and phase formation sequences in two types of ‘internal tin’
superconducting wires designed for the ITER project, which investigates the production of
electricity by means of nuclear fusion, have been studied during heat treatments both in situ, using
electrical resistometry [1] and ex situ, using optical and scanning electron microscopy, energy
dispersive X-ray spectrometry (EDS) and X-ray Micro-Tomography (XMT).
XMT reveals long pores in the longitudinal direction which may result in tin deficiency thereat and
hence local off-stoichiometric Nb3Sn. Microscopy suggests there are incomplete conversion of
elemental tin to copper-tin intermetallics before ramping above the tin melting temperature, nonuniform
distribution of tin before formation of Nb3Sn, and filament movement and bridging,
stacking cracks and unreacted niobium at the end of the heat treatment. FEGSEM shows a fine
microstructure which nevertheless could still be improved.
Effect of Deformation, Annealing and Doping with Zr on Nb Filaments Nanocrystalline Structure in High-Strength In Situ Cu-Nb Composites
Authors: Popova E.N. , Popov Vladimir V. , Romanov E.P. , Hlebova N.E. , Pantsyrny V.I. , Shikov A.K.
Published: March 2009

The structure and properties of in situ Cu-Nb composites have been studied by the
methods of TEM and SEM, X-ray analysis and mechanical testing. The evolution of Nb filaments
structure at drawing and the effect of annealing and doping with Zr on the composites structure and
texture have been investigated. Sharp fibre texture with <110>Nb develops in the ribbon-shaped Nb
filaments, while the Cu matrix possesses a two-component fibre texture, <111>Cu and <100>Cu,
appreciably affected by annealing. Annealing results in softening due to Nb filaments coagulation.
In Zr doped composites two types of ZrO2 particles are observed, dispersed and coarse ones. The
former result in the dispersion strengthening, while the latter may cause embrittlement.
Hydrogen Diffusion in Austenitic Stainless Steels
Authors: Chen Yun , Santos Diogo M.F. , Sequeira César A.C.
Published: March 2009

The electrochemical permeation technique was used to evaluate the hydrogen diffusion,
and analyse its interdependent solubility and trapping behaviour in 9 austenitic stainless steels. The
hydrogen diffusion of all alloys obeyed Arrhenius relationships in the temperature range between
25 °C to 100 °C. The apparent diffusion coefficients were determined and the relevant activation
energies were estimated. It was observed that Ni, Mo, Mn and N, among other alloying elements,
clearly effect the hydrogen diffusion.
Chronopotentiometric Study of the Electrooxidation of Borohydride Anion in Alkaline Medium
Authors: Santos Diogo M.F. , Sequeira César A.C.
Published: March 2009

Borohydrides present interesting options for electrochemical power generation acting
either as hydrogen sources or anodic fuels for direct borohydride fuel cells and batteries. Though
there have been several papers concerning electrochemical determination of relevant
thermodynamic and kinetic parameters to the borohydride system, a number of its basic aspects
have not been yet systematically studied. In this paper we report chronopotentiometric studies of the
electrooxidation of sodium borohydride at a gold sphere electrode in 2M NaOH solutions, at
temperatures ranging from 25 to 55 °C. Gold displayed a rather good BH4
- oxidation activity, and
the overall oxidation process was shown to be irreversible involving a number of electrons very
close to the theoretically expected value of 8. The results suggested that the rate-determining step is
an irreversible, diffusion controlled, one-electron oxidation step, for which the transfer coefficients
were calculated.