bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Austenite Grain Size on the Growth of Different Ferrite Morphologies in a Nb-Microalloyed Steel
Authors: Esmailian Mohamad
Published: September 2009

The effect of austenite grain size on the austenite to ferrite transformation temperature and different ferrite morphologies and growth behaviour in one Nb-microalloyed (HSLA) steel has been investigated. Three different austenite grain sizes were selected and cooled for obtaining austenite to ferrite and growth behaviour of ferrite.
Moreover, samples with specific austenite grain size have been quenched, partially, for investigation of the microstructural evolution.
The optical microscopy observation suggested that the nucleation site of ferrite is on edge and inside of austenite grains in Nb- microalloyed steels.
Micrographs of different ferrite morphologies show that at high temperatures, where diffusion rates are higher, grain boundary ferrite nucleates both at the edge and corner of austenite grains and grows into both austenite grains. As the temperature is lowered and the driving force for ferrite formation increases, intragranular sites inside the austenite grains become operative as nucleation sites and suppress the grain boundary ferrite growth. With more undercooling,intragranular ferrites are seen to nucleate and grow more extensively , indicating the beginning of displacive transformation.
Furthermore, growth rate of intragranular ferrite shows that by increasing of austenite grain size, the growth rate of intragranular ferrite increases extensively and growth rate of grain boundary ferrite decreases.
The growth kinetics of grain boundary ferrite shows that this transformation is controlled by the diffusion of carbon in the austenite ahead of the interface.
Surface Alloying of AISI H13 Steel during Electrical Discharge Machining (EDM)
Authors: Rodriguez Gloria P. , Simao Jorge , Herranz Gemma
Published: September 2009

Electrical discharge machining (EDM) is one of the most widely used non-conventional machining processes for the production of moulds/dies, cutting tools and aero-engine parts, such as turbine/compressor blades. The paper details experimental research on the surface alloying/modification of chromium martensitic hot-work tool steel components (AISI H13, 55HRC) during EDM die-sinking operations using powder metallurgy (PM) tool electrodes, as a means of achieving enhanced workpiece wear resistance without resorting to a subsequent coating operation. Tool electrode performance of partially sintered WC/Co electrodes operating in a common hydrocarbon oil dielectric was assessed and subsequently compared with that of conventional electrode materials, such as Cu and Graphite. Surface/subsurface observations by optical and scanning electron microscopy (SEM) showed a recast solidified layer of ~ 8 µm when using WC/Co electrodes. Performed XRD and SEM-EDX analysis indicated that WC and Co contained in the PM tool electrodes, together with C decomposed from the hydrocarbon oil during sparking, were transferred and alloyed to the steel substrate surfaces. EDM surface alloyed layers were hardened over 1200 HK0.025. This hardening is related both to the formation of tungsten carbides with different stoichiometries and to the non-equilibrium microstructure evolution. Thickness of the hardened zone was shown to be dependent on EDM operating parameters, in particular peak-current (A) and pulse on-time (s).
Thermal Stability and Creep Behaviour of MgNiYCe-Rich Mischmetal Alloys Processed by a Powder Metallurgy Route
Authors: Pérez P. , Milicka K. , Badía Jose Maria , Garcés G. , Antoranz J.M. , González S. , Dobes F. , Adeva P.
Published: September 2009

The thermal stability and creep behaviour of MgNi2Y1CeMM1 and MgNi3Y1.5CeMM1.5 alloys have been investigated at 523 and 623 K. Both alloys were processed by a powder metallurgy route involving rapid solidification of powders, cold isostatic pressing and extrusion at 673 K. The microstructure of both alloys was studied in the as-extrusion condition and after thermal treatments at 523 and 623 K up to 500 h. Mechanical characterization was carried out by hardness measurements in samples annealed at 523 and 623 K and stepwise stress compressive creep tests at these temperatures.
Results have shown long-term stability of the microstructure after annealing at 523 K in both alloys and hardness values remained constant along all treatment. After treatment at 623 K, however, the microstructure of both alloys remained relatively stable and a decrease in hardness was noticed after 6 h. Creep behaviour of both alloys was very similar. The stress dependences of the creep rate can be well described by modified Garofalo sinh relationship. Activation energies for creep, practically twice of the activation enthalpy of lattice diffusion for pure magnesium (135 kJ mol-1), have been obtained. Therefore, no direct evidence of the controlling role of diffusion processes can be obtained from these experiments.
A Methodology to Deduce the Microstructural Spatial Deformation of Polycrystalline Structures: Application to the Alloy 600
Authors: Clair Aurélie , Foucault Marc , Salazar J. Marcos , Vignal Vincent , Finot Eric , Markey Laurent
Published: September 2009

Studying the corrosion of the alloy 600, under water pressure, is of high importance to understand the ageing process of pressurized water reactors. Today, the impact of the oxide growth on the mechanical properties of nickel alloys is a challenge. The surface analysis and the quantification of the local deformation are key factors to deduce the surface damage of the substrate produced by corrosion.
Here, we introduce a new methodology to determine the deformation distribution of the alloy 600 by using polycrystalline samples. The method is based on nanopads disposed on the surface samples, which allow a mapping, at the microscopic scale, of the spatial deformation. We applied to the samples a tensile loading in the plastic domain from 0 to 4%. The obtained asymmetric deformations distribution reflects the polycrystallinity of the system.
Evolution of Precipitate Depleted Zones in Mg-Based Alloys Strengthened by Precipitation Hardening
Authors: Katsman A. , Gorny Anton , Shepelev D. , Bamberger Menachem
Published: September 2009

Extensive research work has been devoted to Mg-based alloys strengthened by precipitation hardening. Increasing the aging time leads to the appearance of zones depleted of precipitates near grain boundaries. The formation of precipitate depleted zones (PDZ's) is explained by near-grain boundary (NGB) coarsening. The evolution of PDZ's was considered on the basis of the model taking into account diffusional fluxes between adjacent precipitates. The set of equations was solved numerically by using a fourth-order Runge-Kutta method for different initial sizes of precipitates and densities of precipitate layers near grain boundaries. The dissolution of precipitates in the NGB-zones is initially provided by diffusion from them to large precipitates at the grain boundary, and then also by diffusion from these decreased precipitates to the larger precipitates at the outer border of the PDZ. As a result, the outer borders of the depleted zones are adjoined by bands of enlarged precipitates forming a PDZ "crust". Being a diffusion controlled process, the depleted zones are widened with temperature and aging time. Experimental investigation of PDZ evolution was conducted by SEM and TEM on Mg-Zn-Sn-alloys aged at different temperatures for different times. Comparison of the calculated results with experimental data allowed the evaluation of the model parameters and physical parameters of the system (diffusion coefficients and interface energy of the precipitated phases).
Influence of Interstitials Content on the Diffusion of Niobium in Alloy 718
Authors: Ter-Ovanessian Benoît , Berrest Cedric , Deleume Julien , Cloué Jean Marc , Andrieu Eric
Published: September 2009

Many studies have emphasized the beneficial effect of niobium on the physical metallurgy of Ni-Cr-Fe alloy 718. Among the different strengthening actions of niobium, such as solid solution hardening and carbide precipitation, the precipitation of niobium with nickel in a strengthening phase γ” (Ni3Nb) during the aging heat treatment has the largest influence on the mechanical properties of alloy 718. The improvement of the niobium distribution and diffusion in the Ni-matrix may allow a more homogenized repartition of γ” precipitates and seems then to be an effective way to upgrade the mechanical properties. As γ” precipitates decompose to the stable δ phase at very long aging times, the study of the effect of carbon, nitrogen and oxygen concentrations on precipitation and dissolution of the δ phase may give information on γ” precipitation and on niobium distribution. It is the purpose of the present work to examine the role that the alloy content of interstitial species plays with the niobium-rich δ phase evolution in alloy 718. Alloy 718 samples were heat treated under hydrogenated argon at 980°C for 0 to 96 hours in order to gradually curb the content of interstitial species by reaction with the reducing atmosphere. Chemical analyses realized by glow discharge mass spectrometry (GDMS) confirmed the reduction of the concentration of these species. Specimens were solution-treated for 1h at 1050°C in an inert atmosphere and furnace cooled. Some of the samples were then aged at 920°C for times ranging from 10 min to 1 hour. The precipitation was measured quantitatively in terms of volume fraction and the morphology of the precipitates was appreciated using scanning electron microscopy (SEM). The differences in the precipitation kinetics and in the microstructure evolution for each interstitial concentration are then discussed.
Investigation of Phase Transformation of Forged Steel Cold Rolls due to Heat Affecting and Prevent its Failure
Authors: Mottahedi Ali Akbar
Published: September 2009

In rolling Industries, cold rolls are chosen of low alloy steel heat treated to about 60 RC in 50 millimeter depth on surface. Troostite phase which happens in some cases in tempered martensite has lower fracture toughness, although its ductility is a little more. In rolling process, some technological problems seldom take place, and the roll might be locally heated accidentally. In cold rolling technology, this effect may cause a phase change in metallurgical structure on the surface of the cold work forged steel rolls, named Troostite. However, the rolls which subjected to this problem have no mechanical defect to be detected by NDT, but these kinds of affected rolls may be failed in working (rolling) by fracture, spalling or cracks. So Troostite is a harmful phase for rolls and causes lots of losses for rolling companies. The following paper is a practical industrial approach to show and follow thermal instability of roll surface and metallurgical change of the surface from sorbite to troostite by diffusion mechanism, due to any improper mill usage.
The Electrolytic Actuator-An Effect Dominated by Dissipative Currents
Authors: Temmen Hubert , Caracciolo Paola
Published: September 2009

For a conductive, elastic matter in thermodynamic equilibrium the LORENTZ force, which includes the COULOMB force for charged systems, is the only macroscopic interaction between the electromagnetic field and the matter. If irreversible currents such as diffusion and ionic currents are observed, these currents and their coupling can dominate the behaviour. Then, to describe that system it is necessary to start with a macroscopic description, which remains valid outside of the equilibrium. A macroscopic description of these currents is used to deduce a very simple model for an electrolytic actuator.
Influence of Pulsed Magnetic Field on the Al-Heterodiffusion in α-Fe
Authors: Pokoev A.V. , Verjakovskaya M.A.
Published: September 2009

Based on the X-ray method an experimental research has been carried out aimed to estimate the pulsed magnetic field influence on the heterodiffusion of Al in -Fe within the temperature interval of 700-820 °С and at the amplitude intensity of the magnetic field pulse equal to 0–557.2 kА/m and its frequency ranging from 0 to 8 Hz. It is established that the pulsed magnetic field changes noticeably the value of the measured coefficient of Al diffusion in -Fe. Possible mechanisms of the pulsed magnetic field influence on the diffusion process are considered on taking into account the interaction of moving domain walls, dislocations and impurity atoms.
First Study of Oxygen Diffusion in a ZnO - Based Commercial Varistor
Authors: Sabioni Antônio Claret Soares , Daniel Antônio Márcio J.M. , Metz Renaud , Huntz Anne Marie , Jomard François
Published: September 2009

Oxygen diffusion coefficients were determined in a commercial ZnO-based varistor by means of the gas-solid exchange method using the isotope 18O as the oxygen tracer. The diffusion annealings were performed at 892, 942, 992 and 1092oC, in an Ar + 18O2 atmosphere under an oxygen partial pressure of 0.2 atm. After the diffusion annealings, the 18O diffusion profiles were established by secondary ion mass spectrometry (SIMS). The results show an increase of the oxygen diffusion in the varistor, both in bulk and in grain boundaries, when compared to the oxygen diffusion in undoped ZnO. The increase of the oxygen bulk diffusion in the varistor agrees with an interstitial mechanism for the oxygen diffusion. The results also show that the grain boundary is a fast path for the oxygen diffusion in the varistor. However, the oxygen diffusion in the grain boundaries of the varistor seems to depend on several chemical and microstructural parameters and does not allow a simple explanation.
Dynamics of Mobile Oxygen Ions in Disordered Pyrochlore-Type Oxide-Ion Conductors
Authors: Díaz-Guillén M.R. , Moreno Karla J. , Díaz-Guillén J.A. , Fuentes A.F. , Garcia-Barriocanal J. , Santamaría J. , Leon C.
Published: September 2009

We investigate the effect of cation size in the dc activation energy needed for oxygen ion conductivity, Edc, in highly disordered pyrochlore-type ionic conductors A2B2O7. Twenty compositions of general formula Ln2Zr2-yTiyO7 (Ln = Y, Dy and Gd) and Gd2-yLayZr2O7, were prepared by mechanical milling and their electrical properties measured by using impedance spectroscopy at different temperatures. We also evaluate, by using Ngai’s Coupling Model, the effect of cation radii RA and RB, on the microscopic potential-energy barrier, Ea, that oxygen ions encounter when jumping into neighboring vacant sites. We find that for a fixed B-site cation radius RB, both activation energies decrease with increasing A-site cation size, RA, as a consequence of the increment in the unit cell volume. In contrast, and for a given RA size, the dc activation energy Edc of the Ln2Zr2-yTiyO7 series increases when the average RB size increases. The latter behavior is explained in terms of the enhanced interactions among mobile oxygen ions as the structural disorder increases when RB approaches RA.
Triple-Defect B2 Binary Intermetallics: Bragg-Williams Solution and Monte Carlo Simulations
Authors: Biborski Andrzej , Zosiak L. , Abdank-Kozubski Rafał Leszek
Published: September 2009

Surprisingly low rate of “order-order” kinetics in stoichiometric NiAl intermetallic known of very high vacancy concentration suggested a specific triple-defect mechanism of ordering/disordering in this system [1]. This mechanism implies a correlation between the concentrations of antisite defects and vacancies; the latters being trapped in triple defects and thus, inactive as atomic migration agents. The process was modelled by means of Monte Carlo (MC) simulations recognised as a powerful tool for such tasks [2], but requiring now the implementation of thermal vacancy thermodynamics. Temperature dependence of vacancy concentration in an AB B2 binary system was determined within an Ising-type model solved first in Bragg-Williams approximation [3] and then by means of MC simulation of a Grandcanonical Ensemble. Without any a priori assumptions concerning the formation of particular types of point defects the model yielded temperature domains where the concentrations of antisite defects and vacancies were proportional. The effect associated with the formation of triple defects appeared for specific values of atomic pair-interaction energies. Moreover, non-stoichiometric A-B systems with the same atomic pair-interaction energies showed the existence of constitutional vacancies at low temperatures. Monte Carlo simulations of “order-order” (disordering) kinetics in B2 AB systems modelled with triple-defect-promoting atomic pair-interaction energies were run with temperature-dependent concentra-tion (i.e. number) of vacancies given by the above model. The simulated relaxations showed two stages: (i) rapid formation of triple defects engaging almost all vacancies present in the system, (ii) very slow process of further generation of antisite defects until the equilibrium concentration was reached. The result reproduced very well the experimental observations [1].
Diffusion of Titanium and Nickel in B2 NiTi
Authors: Divinski Sergiy V. , Stloukal Ivo , Král Lubomir , Herzig Christian
Published: September 2009

Diffusion of both titanium and nickel was measured in the near stoichiometric Ni-49.4at.%Ti alloy with the B2 ordered structure. The radiotracer technique and the 44Ti and 63Ni isotopes were applied in the temperature interval from 900 to 1300 K. The penetration profiles were determined by precision parallel grinding or by ion beam sputtering at larger and smaller penetration depths, respectively. Titanium and nickel diffusivities were found to follow linear Arrhenius dependencies with the pre-exponential factors of 2.710-7 and 4.710-9 m2/s and the activation enthalpies of 205 and 143 kJ/mol, respectively. A vacancy mediated diffusion mechanism is suggested to provide diffusion of both nickel and titanium in the compound NiTi.
Characterisation of the Oxide/Metal Interface of Fluorine Treated Titanium Aluminides
Authors: Masset Patrick J. , Laurent Mathieu , Schütze Michael
Published: September 2009

Surface modifications with well defined amounts of fluorine have proven to improve significantly the oxidation resistance of titanium aluminides and to offer the potential to decrease the sensibility of TiAl-based alloys against environmental embrittlement. By means of combined EPMA and SEM analyses the formation of an oxide layer on fluorine treated specimens was characterised. The thicknesses of the external oxide layer as well as the oxygen and nitrogen-rich subsurface layer were measured. Their growth kinetics was found to follow a cubic and a parabolic law, respectively. By subtracting the mass variation due to the ingress of oxygen and nitrogen into 2-Ti3Al, underneath the alumina layer, this allowed calculating the true value of the kinetic constant for the growth of a pure alumina layer on titanium aluminides.
A Thermodynamic Approach of the Mechano-Chemical Coupling during the Oxidation of Uranium Dioxide
Authors: Creton Nicolas , Optasanu Virgil , Montesin Tony , Garruchet Sébastien , Desgranges Lionel
Published: September 2009

The aim of the present work is to introduce a thermodynamic model to describe the growth of an oxide layer on a metallic substrate. More precisely, this paper offers a study of oxygen dissolution into a solid, and its consequences on the apparition of mechanical stresses. They strongly influence the oxidation processes and may be, in some materials, responsible for cracking. To realize this study, mechanical considerations are introduced into the classical diffusion laws. Simulations were made for the particular case of uranium dioxide, which undergoes the chemical fragmentation. According to our simulations, the hypothesis of a compression stress field into the oxidised UO2 compound near the internal interface is consistent with the interpretation of the mechanisms of oxidation observed experimentally.
Oxidation Behaviour of Stainles Steel Matrix with TiC and TiC+TiB2 SHS Powders in a Thermal Spray Process
Authors: Fernández Javier , Isalgue Antonio , Cano Irene G. , Guilemany J.M.
Published: September 2009

Thermal spray coatings provide good tribological and corrosion-resistant properties. Coatings with carbides or diborides improve resistance to oxidation. However, depending on the thermal spray conditions some carbide and diboride oxidation takes place. The aim of this study is to analyze the oxidation of TiC or TiC+TiB2 powders embedded into a stainless steel matrix.

The starting powders were obtained by Self-propagating High-temperature Synthesis (SHS). Oxidation was studied at two temperatures, 700°C and 800°C. The results aid our understanding of the powders’ behaviour during coating and use. An open electric furnace was used, and the samples were analyzed using a SEM coupled with an EDS. Thermal treatment time ranged from 2 minutes to 9 hours. A continuous oxidized layer was observed for the TiC particles. This was not the case for TiB2. The decomposition/oxidation of TiB2 begins before the oxidation of TiC. An oxidized layer of around 4 m is formed at a temperature of 800°C after 690 s, when using a powder of 45 m mean size.
Metal Dusting Corrosion of 9Cr-1Mo Steel in Propane-Butane Gas Mixture
Authors: Grzesik Zbigniew , Danielewski Marek , Mrowec Stanisław
Published: September 2009

The kinetics and mechanism of metal dusting corrosion of 9Cr-1Mo steel, commonly used in CCR platforming units, have been studied as a function of temperature (773 – 1173 K) in propane-butane atmosphere, being the mixture of 70 vol. % of propane and 30 vol. % of butane with the total pressure equal 105 Pa. The kinetics of corrosion have been studied thermogravimetrically in the apparatus enabling the mass changes of corroded sample to be followed continuously with the accuracy of the order of 10-6 g. It has been found that metal dusting corrosion in this atmosphere, modeling in some way industrial environments in petrochemical industry, is complex and two-stages of linear kinetics may be distinguished. In the first stage, which may be considered as an incubation period, the reaction proceeds with rather low rate, which increases dramatically in the second stage, the beginning of which depends strongly on temperature. Linear course of reaction indicates that chemical reactions and not diffusion processes determine the rate of corrosion. This conclusion is confirmed by the fact, that the layer of corrosion products is not compact but considerably porous.
Diffusion in Metal Dusting Processes
Authors: Young David J. , Motin M.A.A. , Zhang J.
Published: September 2009

Dusting of iron results from partial disintegration of a cementite scale which grows on the metal surface during reaction with carbon-supersaturated gas. Scaling kinetics are shown to be consistent with diffusion of carbon through the cementite. Further diffusion of carbon into the iron supersaturates it to a very high degree. Dusting of nickel and austenitic alloys leads to no carbide formation. Instead graphite grows into the metal, supported by diffusion of dissolved carbon to growth sites. Variations in rate with alloy iron content reflect the known effects of iron on carbon solubility and diffusivity. Alloying with copper also changes coking and dusting rates, although copper does not affect carbon permeability. The effect is shown to be due to interaction of copper with graphite nucleation sites.
Oxygen Uptake and Diffusion in Mayenite
Authors: Kilo Martin , Swaroop Sathya , Lerch Martin
Published: September 2009

Oxygen uptake and oxygen diffusion in Mayenite (Ca12Al14O33) were investigated using the stable tracer 18O2. Mayenite contains one intrinsic, highly mobile oxygen anion. It was shown that for high temperatures (above 700 °C), the diffusion goes through a interstitialcy mechanism, where the interstitial oxygen anion knocks out a lattice oxygen anion. The activation enthalpy for this process is around 0.9 eV, suggesting that the ionic migration is very fast.
Study of Oxygen Diffusion in Polycrystalline ZnO by SIMS
Authors: Sabioni Antônio Claret Soares , Daniel Antônio Márcio J.M. , Huntz Anne Marie , Ferraz Wilmar Barbosa , Jomard François
Published: September 2009

Oxygen diffusion coefficients were measured in polycrystalline ZnO by means of the gas-solid exchange method using the isotope 18O as the oxygen tracer. The diffusion annealings were performed at 892oC and 992oC, in an Ar+18O2 atmosphere under oxygen partial pressures from 0.1 to 1atm. After the diffusion annealings, the 18O diffusion profiles were established by secondary ion mass spectrometry (SIMS). Increasing the oxygen pressure leads to an increase of the oxygen diffusion in ZnO. The bulk diffusion coefficients depends on oxygen pressure according to , at 882oC, or , at 992oC, which indicates that the oxygen bulk diffusion mechanism should preferentially take place by means of interstitial oxygen having a null effective charge. The grain boundary diffusion coefficients show little dependence on oxygen pressure at 882oC, given by , which should correspond to a diffusion mechanism by means of interstitial oxygen, with a double negative charge, but at 992oC this dependence is corresponding to a diffusion mechanism by interstitial oxygen having a null effective charge. The results also show that the grain boundary is a fast path for the oxygen diffusion in polycrystalline ZnO.
Oxygen and Silicon Diffusion in Silica under Varying Ambient Conditions
Authors: Sunder Kirsten , Bracht Hartmut
Published: September 2009

Diffusion of oxygen (O) in amorphous silicon dioxide (SiO2) was investigated by means of Si3N4/natSinatO2/28Si18O2/28Si isotope heterostructures grown by thermal oxidation and plasma enhanced chemical vapour deposition. Diffusion experiments with and without a silicon nitride (Si3N4) cap, which serves as diffusion barrier for the gasses in the ambient, were performed. In particular, we determined the impact of the ambient gas, of the thickness of the isotopically enriched SiO2 layer, and of the annealing time and temperature on diffusion. Our results are compared with data given in the literature on oxygen and silicon diffusion in silica and are discussed in the framework of the experimental conditions established at the sample surface and at the buried 28Si18O2/28Si interface. Taking into account a point defect model that is predicted by recent atomistic simulations all experimental results can be explained consistently.
The Oxide Scale Growth Mechanism on Fe20Cr5Al+RE Alloy in SO2+O2
Authors: Jedlinski Jerzy , Żurek Zbigniew , Homa Martah , Smoła G. , Camra J.
Published: September 2009

The oxidation mechanism of FeCrAl (+RE), RE: reactive elements: Y and Hf) thin foils was studied at temperatures ranging from 1093 K to 1173 K in SO2+1%O2 atmosphere. Materials were subjected to isothermal and thermal cycling exposures as well as to the so-called two-stage-oxidation. In the latter, an oxygen isotope 18O2 was used as a tracer. Starting materials and scales were characterized using Grazing Angle X-Ray Diffraction (GA-XRD), EDX, SEM, XPS and High Spatial Resolution Secondary Ion Mass Spectrometry (HSR-SIMS). The obtained results showed within the studied range of exposure conditions the scales on all the studied alloys grow via outward mechanism typical for transient oxides and not for the -Al2O3 which is consistent with phase composition results and scale morphology and/or microstructure. It was also found that ‘as received’ foils are not bare metals but complex oxide-on-metal systems resulting from their manufacturing procedure.
The obtained results are discussed in terms of the diffusion-related transport properties of the scale and of the scale phase composition.
Interface Diffusion in Cu Processed by Means of Surface Mechanical Attrition Treatment
Authors: Wang Z.B. , Wang K. , Lu K. , Wilde Gerhard , Divinski Sergiy V.
Published: September 2009

A nanostructured surface layer with a gradient microstructure was produced on a Cu plate by means of the surface mechanical attrition treatment (SMAT). Diffusion of Ni in the nanostructured layer was investigated by the radiotracer technique at temperatures from 383 to 438 K. The measured diffusion profiles consist of two distinct sections with different slopes, the steep one corresponding to the top surface layer with the grain size of 10 to 25 nm and the shallow one corresponding to a subsurface layer with a grain size of 25 to 100 nm. The effective diffusivities derived from both sections are more than 2 orders of magnitudes higher than the grain boundary diffusivities in coarse-grained Cu. The significantly accelerated diffusion rates are expected to be associated with the “non-equilibrium” states of interfaces in the nanostructured surface layer induced by SMAT. The difference between the diffusivities in the top and sub- surface layer might result from the fact that most interfaces developed from twin boundaries in the former while produced by dislocation activities in the latter.
Self Diffusion in Liquid Titanium: Quasielastic Neutron Scattering and Molecular Dynamics Simulation
Authors: Meyer Andreas , Horbach Jürgen , Heinen O. , Holland-Moritz Dirk , Unruh T.
Published: September 2009

Self diffusion in liquid titanium was measured at 2000K by quasielastic neutron scattering
(QNS) in combination with container less processing via electromagnetic levitation. At small
wavenumbers q the quasielastic signal is dominated by incoherent scattering. Up to about 1.2 °A−1 the
width of the quasielastic line exhibits a q2 dependence as expected for long range atomic transport,
thus allowing to measure the self diffusion coefficient DTi. As a result the value DTi = (5.3± 0.2)×
10−9 m2s−1 was obtained.With a molecular dynamics (MD) computer simulation using an embedded
atom model (EAM) for Ti, the self diffusion coefficient is determined from the mean square displacement
as well as from the decay of the incoherent intermediate scattering function at different q.
By comparing both methods, we show that the hydrodynamic prediction of a q2 dependence indeed
extends up to about 1.2 °A−1. Since this result does not depend significantly on the details of the interatomic
potential, our findings show that accurate values of self diffusion coefficients in liquid metals
can be measured by QNS on an absolute scale.
Grain Boundary Diffusion in Recrystallizing Nanocrystalline Materials
Authors: Klinger Leonid , Amouyal Y. , Divinski Sergiy V. , Rabkin Eugen
Published: September 2009

A model that considers diffusion in nanocrystalline materials undergoing recrystallization was developed. Application of this model enabled us deriving 63Ni radiotracer diffusion coefficients along the grain boundaries in ultrafine grain copper produced by equal channel angular pressing from the experimentally measured radiotracer penetration profiles.
Impact of Carbon on the Diffusion of Donor Atoms in Germanium
Authors: Bracht Hartmut , Brotzmann S. , Chroneos Alexander
Published: September 2009

We report experiments on the diffusion of n-type dopants in isotopically controlled Ge multilayer structures doped with carbon. The diffusion profiles reveal a strong aggregation of the dopants within the carbon-doped layers and a retarded penetration depth compared to dopant diffusion in high purity natural Ge. Dopant aggregation and diffusion retardation is strongest for Sb and similar for P and As. Successful modeling of the simultaneous self- and dopant diffusion is performed on the basis of the vacancy mechanism and additional reactions that take into account the formation of carbon-vacancy-dopant and dopant-vacancy complexes. The stability of these complexes is confirmed by density functional theory calculations. The overall consistency between experimental and theoretical results supports the stabilization of donor-vacancy complexes in Ge by the presence of carbon and the dopant deactivation via the formation of dopant-vacancy complexes. These results help to develop concepts to suppress the enhanced diffusion of n-type dopants and the donor deactivation in Ge. Both issues hamper the formation of ultra shallow donor profiles with high active dopant concentrations that are required for the fabrication of Ge-based n-type metal oxide semiconductor field effect transistors.
Effect of a Low-Concentration H3PO4 Solution Application on High-Temperature Behaviour of Ti and Ti-Al Alloys
Authors: Brou S.Y. , Bonnet G. , Grosseau-Poussard Jean Luc
Published: September 2009

TiAl, TA6V and titanium coupons were treated by a phosphoric acid solution by dipping. They were then submitted to a heat treatment and, in the case of TiAl and TA6V, to high temperature discontinuous oxidation under laboratory air. The H3PO4 treatment allowed to decrease the mass gains for TiAl and TA6V, in particular during the first 100 hours. XRD analyses demonstrated for the three substrates the formation of a pyrophosphate layer during the heating period. This pyrophosphate evolved towards TiO2 with oxidation time increase, quicker for smaller aluminium content (or higher titanium content) in the metallic substrate. The decrease of mass gains was attributed to a diffusion barrier effect of the pyrophosphate layer as long as it was present.
Atomic Diffusion and its Relation to Thermodynamic Forces in Al-Ni Melts
Authors: Griesche Axel , Zhang Bo , Horbach Jürgen , Meyer Andreas
Published: September 2009

We make use of a novel X-ray radiography method to measure chemical diffusion in capillaries in binary Al-Ni melts. Data are compared to self diffusion coefficients of Ni obtained by quasielastic neutron scattering as well as diffusion and thermodynamic data obtained by molecular dynamic simulations. Interdiffusion compared to self diffusion is enhanced with a maximum at Al40Ni60. We show that this enhancement is caused by thermodynamic forces as described by the Darken-Manning equation. In liquid Al-Ni alloys the Manning factor that is smaller than one can be attributed to collective cross correlations.
Concentration Characteristics of Diffusion-Induced Recrystallization
Authors: Schmitz Guido , Kruse B. , Baither D. , Kim T.H.
Published: September 2009

Diffusion-induced recrystallization (DIR) is investigated in Au/Cu and Ag/Pd thin-film interdiffusion couples. It is experimentally demonstrated that several generations of new grains are formed inside the diffusion zone by a cascade-like process. Each generation is distinguished by a characteristic composition level. In order to understand the observed composition levels quantitatively, a thermo-mechanic model has been derived, which determines the thermo-elastic driving force to the grain boundary. By the model, it is shown that those grains dominate the diffusion zone, which develop the maximum possible stress in front of the moving boundary.
Computer Simulation of Diffusion in Dilute Al-Fe Alloys
Authors: Mendelev Mikhail , Rodin Alexey , Bokstein Boris S.
Published: September 2009

We present results of the molecular dynamics study of Al selfdiffusion, Al and Fe diffusion in Al-Fe dilute alloys. We found that addition of Fe does not change the vacancy formation energy but considerably slows down Al diffusion. We also found that Al and Fe migration energies, i.e. energies of vacancy exchange with Al and Fe atoms, differ very strongly. Both activation energies for Al and Fe diffusion are in satisfactory agreement with available experimental data.
Oxygen Diffusion and Surface Exchange in Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Ceramics at Low Temperatures
Authors: Kowalski Kazimierz
Published: September 2009

Oxygen self-diffusion and oxygen surface exchange investigations in the yttria-stabilized zirconia (3 and 8 mol% of Y2O3) and in the gadolinia-doped ceria (10 and 20 mol% of Gd2O3) ceramics in the temperature range from 250 to 450°C were performed by means of the 18O isotopic labeling and the SIMS profiling methods. The activation energies of these processes were determined. The results were discussed in comparison with the literature data extrapolated from higher temperatures.
Structural Investigations of Solidification and Heat Treatments Influence on High Alloyed Cast Irons Grades with Nb-V-Ti Additions
Authors: Lecomte-Beckers Jacqueline , Tchoufang Tchuindjang Jérôme
Published: September 2009

Two High Alloyed Cast Irons (HACI) were studied, both belonging to the Fe-C-Cr-Si-X system where X represented a strong carbide forming element. One of these alloys was obtained after adding Nb, V and Ti to the chemical composition of the other alloy.
Raw materials originated from spun cast rolls for hot strip mill were submitted to different heat treatments routes, in order to study the influence of alloying elements on the microstructure.
Both HACI grades contained a mixture of martensite and retained austenite matrix in the as-cast conditions and after quenching.
Differential Thermal Analysis was carried out on the heat treated samples in order to determine the phase transformations occurring during re-melting and subsequent solidification sequence.
Diffusionless transformations leading to various types of martensite were found in the matrix.
Bulky NbC carbides precipitating at the beginning of the solidification process strongly influence the nature and the rate of the subsequent diffusional phase transformations, particularly for HACI grade with Nb, V and Ti additions.
Quantitative metallography was done to determine graphite, NbC carbides, cementite and matrix volume fraction in HACI studied grades.
Influence of Beta Stability on Hydrogen Diffusion in Various Beta Titanium Alloys
Authors: Christ Hans-Jürgen , Schmidt Peter
Published: September 2009

The prediction of the applicability range of beta titanium alloys in hydrogen containing environments and the systematic study of hydrogen effects on the microstructure during heat treatment require reliable information about the hydrogen diffusion coefficient DH in the respective titanium alloy. Up to now the little information available on hydrogen diffusivity in commercial titanium alloys indicates a higher hydrogen diffusion coefficient in beta titanium alloys as compared to alpha and alpha + beta titanium alloys. In the present study, the hydrogen diffusion coefficients were determined systematically by means of electrochemically charging the half length of thin titanium rods and subsequent annealing, thereby enabling hydrogen diffusion. The Matano technique was applied in order to identify any effect of hydrogen concentration on DH. The hydrogen diffusion coefficients determined were correlated with results from microstructure examination applying optical and electron microscopy. Since molybdenum and vanadium are the most important beta-stabilizing alloying elements, binary titanium alloys of the Ti–Mo and the Ti–V systems at various contents of the respective alloying element were systematically studied in addition to commerical beta titanium alloys. The results of the experiments revealed the strong effect of beta stability and phase composition on hydrogen diffusion.
Grain Boundary Diffusion of Ni in Ultra-Fine Grain Copper-Lead Alloy Produced by Equal Channel Angular Pressing
Authors: Ribbe Jens , Schmitz Guido , Estrin Yuri , Divinski Sergiy V.
Published: September 2009

Kinetic characteristics of internal interfaces in ultrafine grained (UFG) materials represent an aspect that is central to their potential applications. Interface diffusion is strongly affected by ultrafine crystallinity and incorporated defects. In the present study the radiotracer technique was applied for measuring grain boundary (GB) diffusion of Ni in UFG Cu-1wt.%Pb alloy. The UFG specimens were prepared by equal channel angular pressing at room temperature. GB diffusion was investigated at room temperature in Harrison’s C kinetic regime under conditions in which Ni diffusion - even along general high-angle GBs in pure Cu - would hardly be measurable by the mechanical sectioning (as the corresponding penetration depths would be less than 100 nanometers). The present study highlights the existence of ultra-fast diffusion paths in severely deformed material. An atypical time dependence of the room-temperature diffusion data indicates a quite involved nature of these “fast” diffusion paths in the Cu-1wt.%Pb alloy.
Electronic States and Doping Effect of Carbon in the Kink of BCC Iron
Authors: Qiu Zheng Chen , Xia Can Fang , Chen Li Qun
Published: September 2009

By the use of the first-principles method, based upon density functional theory, we investigated the effect of C upon the electronic structure of a kink on the ½[111](1¯10) edge dislocation in bcc iron. The results show that C has a tendency to segregate towards the kink. The structural energies of some atoms of interest in the kink with C are lower than those of corresponding atoms in the clean kink. Furthermore, the interactions between C and the neighboring Fe atoms are very strong due to the hybridization between the C 2p state and the Fe 3d4s4p states. We find that there exists some charge accumulations between C and the neighboring Fe atoms. The analysis of the electronic structure indicates that the introduction of C can stabilize the kink system and impede the sideways motion of the kink. The C induces a strong pinning effect on the ½[111](1¯10) edge dislocation and may result in solid solute hardening.
Effect of Bi Additions upon the Physical Properties of Germanium Telluride Glassy Semiconductors
Authors: Sharma Ambika , Barman P.B.
Published: September 2009

The effect of bismuth (Bi) additions upon the physical properties, coordination number (m), constraints (Nc), density (ρ), molar volume (Vm), cohesive energy (CE), lone pair electrons (L) and glass transition temperature (Tg) of Ge20Te80-xBix (x = 0, 1.5, 2.5, 5.0) bulk glassy alloy has been investigated. The density and molar volume of the glassy alloys has been found to increase with increasing Bi content. The CE of the investigated samples has been calculated by using the chemical bond approach (CBA) and is correlated with a decrease in the optical band-gap with increasing Bi content. The glass transition temperature has been estimated by using the Tichy–Ticha approach and was found to increase with an increase in the Bi content.
A Study of the Variation of Monovacancy Formation Energy with the Parameter of Ashcroft's Potential and Different Exchange and Correlation Functions for Some Group-IIa and Group-VIII FCC Metals in the Active Divalent State
Authors: Ghorai Amitava
Published: September 2009

Graphs of monovacancy formation energy ( ) versus the parameter, , of Ashcroft's empty-core model potential (AECMP) and nine different exchange and correlation functions (ECF) are shown for two different group-IIa divalent fcc metals (Ca and Sr) and seven group-VIII divalent fcc metals in an active valence state (γ-Fe, β-Co, Rh, Ir, Ni, Pd and Pt). The criterion used is that is greater than the Bohr radius. There is a systematic increase and decrease in the fitted value of , and the calculated value of , respectively, in going from one ECF to other, as follows: Sham<K-K<G-V<Kle<Harr<V-S<Hub<Tay<M-D for group-IIa face-centered cubic metals and K-K<G-V<Sham<…..<Tay<Hub<M-D for group-VIII face-centered cubic metals; with a slight variation in between. It should be noted that the inherent simplicity of AECMP makes it difficult to have a universal parameter for all types of atomic property calculations.
Effect of Heat Treatment on the Structural, Morphological and Optical Properties of Tin-Doped ZnO (x=0.0 and x=0.05) Thin Films
Authors: Huda Abdullah , Norazia M.N. , Shaari S. , Khadum A.Amir
Published: September 2009

The sol-gel method was used to obtain ZnO films doped with Sn at different annealing temperatures, 400°C, 500°C and 600°C. As a starting material, zinc acetate dehydrate was used, with 2-methoxyethanol and monoethanolamine as the solvent and stabilizer, respectively. The dopant source was tin chloride. The amounts of dopant in solution were Zn1-xSnxO: x = 0 and 5at.%. The proportion of dopant and Zn atoms are not the same in the film and in the solution. In other cases, the dopant proportion in the film is less than that in the solution. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), UV-VIS spectroscopy and Raman spectroscopy were used to study the structural, surface morphological and optical properties of the films and the molecular bonding of the ZnO, respectively. It was concluded that the dopant amount, as well as the annealing temperature, modifies the film growth process and consequently the microstructure and surface morphology as well as the optical properties.
Non-Ohmic Behavior of Some ZnO Ceramic Defective Ions with Different Valences
Authors: El-Hofy M.
Published: September 2009

ZnO ceramic samples with the chemical formula, 97ZnO-2BaO-1(X)Mol% (where X= CuO, Fe2O3, TiO2, V2O5, MoO3) have been prepared by using conventional ceramics techniques. The samples were sintered at 1200°C for 1, 1.5 or 2h. The metal ions were chosen such that their ionic radii were just slightly different, whereas their ion valences varied from 2+ in case of Cu to 6+ for Mo. Room-temperature I-V characteristics, microstructures, linear scans and X-ray patterns were then studied. The microstructure and linear scan data revealed that, in the case of Cu-, Fe-, V- and Mo-doped ceramics, the doped ions resided mainly at the grain boundaries while, in case of Ti-doping, the ions resided mainly in the grain interior. The electrical measurements and the linear scan data showed that both the non-linearity parameter, α, and the rate of change of α with sintering time, (dα/dt), was exponentially proportional to the valence of the doped ion, where t is a sintering time in the range of 1 to 2h. The leakage current, JL, is linearly proportional to the amount of doped ion present in the grain interior, relative to that present at the boundaries. The X-ray data revealed that the obtained phase was the hexagonal ZnO phase, with traces of secondary phase related to the doped ion; the secondary phases were identified as being Fe2O3, BaTi5O11, Zn3(VO4)2 and (ZnMoO4) in case of Fe-, Ti-, V- and Mo-doped ceramics, respectively. The relative intensity of the X-ray peak at 2θ = 34.45, corresponding to the (0002) plane, was exponentially proportional to the valence of the doped ion; while α scaled with the relative intensity of the aforementioned X-ray peak.
Nanoscale through Substratum Topographic Cues Modulate Human Embryonic Stem Cell Self-Renewal
Authors: McFarlin D.R. , Finn K.J. , Nealey P.F. , Murphy C.J.
Published: September 2009

A major technological barrier to large-scale propagation of human embryonic stem (HES) cells is the persistence of spontaneous differentiation in culture. Our laboratory and others have previously reported that substrate topography, independent of surface chemistry, profoundly modulates fundamental cell behaviors. We hypothesized that topographic cues would also play a role in modulating HES cell behaviors. This hypothesis was tested on substrates containing nanoscale through micron scale grooves and ridges that were generated by soft lithography. Topographically patterned substrates improved maintenance of the self-renewing phenotype (p = 6.7x10-6) under culture conditions that promote stem cell self-renewal. Topographic cues were found to promote differentiation, however, under culture conditions that promote differentiation. To our knowledge these are the first experiments documenting that the physical topography of culture surfaces influences HES cell differentiation and self-renewal. Topographic cues should be considered a fundamental environmental factor that has relevance to emerging strategies of stem cell engineering.