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The thermodynamic properties of Al, Ni, NiAl, and Ni3Al were studied using the first-principles approach. The 0-K total energies are calculated using the ab initio plane wave pseudopotential method within the generalized gradient approximation. The contribution to the free energy from the lattice vibration was calculated using the phonon densities of states derived by means of the ab initio linear-response theory. The thermal electronic contribution to the free energy was obtained from the one-dimensional numerical integration over the electronic density of states. With the deduced Helmholtz free-energy, the thermal expansion and enthalpy as a function of temperature were calculated and compared with the experimental data. Our calculations show that the enthalpies of formation are slightly temperature dependent with a slope of −1.6 J/mol/K for NiAl and −1.2 J/mol/K for Ni3Al. For Ni, the inclusion of thermal electronic excitation results in a 10% increase in thermal expansion and 15% increase in enthalpy at 1600 K.

The coarsening kinetics of c 0 precipitates in binary Ni–Al alloy is studied using three-dimensional (3D) phase-field simulations. The bulk thermodynamic information and atomic diffusion mobilities are obtained from databases constructed using the CALPHAD approach, while the experimental values for the interfacial energy, elastic constants and lattice mismatch are directly employed in the phase-field model. Specifically, we predict the morphological evolution, average precipitate size, and size distribution as a function of time for a given temperature and composition. Comparison of the phase-field simulation results with experiments shows good quantitative agreement in both time and length scales. 2004 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Despite numerous investigations, all previous efforts on thermodynamic modeling of Al–Sr have suffered from inaccurate energetics of either the solid-state compounds or of the liquid alloy. Here, we demonstrate a method yielding simultaneously, accurate solid-state and liquid energetics, as given by first-principles density functional calculations and experimental measurements, respectively. Via first-principles methods, we have investigated the T =0 K energetics of not only the reported ground state compounds in Al–Sr (“the usual suspects”), but also of a wealth of other possible crystal structures observed in isoelectronic alloy systems (somewhat more “unusual suspects”). We find: (i) LDA calculations surprisingly show that Al 2 Sr in the C 15 structure is slightly lower in energy than the observed CeCu 2 -type structure. However, GGA predicts the opposite order, consistent with the observed CeCu 2 -type/ C 15 stability. (ii) An as-yet-unreported Al 5 Sr 4 compound (observed in Al–Ba) is found to be on the T =0 K ground state hull. (iii) An Al 3 Sr 8 phase, isostructural with the recently discovered Al 3 Ca 8 compound, is predicted to lie above the ground state hull and is not a T =0 K ground state. Using the first-principles formation enthalpies along with experimental thermodynamic and phase stability information, we have performed a new CALPHAD modeling of Al–Sr, including the three observed intermediate compounds as well as a hypothetical compound Al 3 Sr 8 . Two different models of the liquid phase were considered: an associate and a random solution model. The descriptions resulting from the two liquid models are critically evaluated with respect to experimental data in the literature and the present first-principles results.

The phase equilibria and thermodynamic properties of the Mg–Ca–Zn ternary system were analyzed and a complete thermodynamic description of the system was obtained using a computerized optimization procedure. Based on the experimental data, one ternary intermetallic compound was considered for the model, while another ternary intermetallic compound was speculated. The calculated results were compared with the experimental data in the literature.

An MgB2 thin film deposition technology is the first critical step in the development of superconducting electronics utilizing the 39 K superconductor. It turned out to be a challenging task due to the volatility of Mg and phase stability of MgB2, the low sticking coefficients of Mg at elevated temperatures, and the reactivity of Mg with oxygen. A brief overview of current deposition techniques is provided here from a thermodynamic perspective, with an emphasis on a very successful technique for high quality in situ epitaxial MgB2 films, the hybrid physical–chemical vapour deposition. Examples of heterostructures of MgB2 with other materials are also presented.

A three-phase miscibility gap including the austenite and two carbonitrides is presented to describe the phase equilibria between the austenite matrix and carbonitride precipitates. It is demonstrated that the three-phase equilibrium has a lower Gibbs energy than the conventional two-phase equilibrium of austenite and one carbonitride, and is more consistent with experimental data in the literature.

A systematic first-principles calculation for the total energies of 78 pure elemental solids has been performed at zero Kelvin using the projector augmented-wave method within the generalized gradient approximation. The total energy differences, i.e. lattice stabilities, among the face-centered-cubic (fcc), body-centered-cubic (bcc), and hexagonal-close-packed (hcp) crystal structures are studied and compared with the Scientific Group Thermodata Europe (SGTE) database developed by the CALPHAD method. For non-transitional elements, favorable comparison is observed, while for the majority of transition elements, particularly the V, Cr, Mn, Fe, and Co group elements, significant discrepancies exist. The Bain/tetragonal distortion analysis between fcc and bcc structures shows that when one structure is stable, the other is unstable, and the higher the energy of the unstable structure, the larger the discrepancy. Through analysis of the alloying effect in binary systems, we conclude that the lattice stability of unstable structures obtained through extrapolation of first-principles calculations in binary systems is close to the SGTE lattice stability obtained by the CALPHAD method.

To quantitatively simulate microstructural evolution in real systems, we investigated three different interface models: a sharpinterface model implemented by the software DICTRA and two diffuse-interface models which use either physical order parameters or artificial order parameters. A particular example is considered, the diffusion-controlled growth of a c 0 precipitate in a supersaturated c matrix in Ni–Al binary alloys. All three models use the thermodynamic and kinetic parameters from the same databases. The temporal evolution profiles of composition from different models are shown to agree with each other. The focus is on examining the advantages and disadvantages of each model as applied to microstructure evolution in alloys. 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In this paper, we describe initial results of an ongoing research activity involving materials scientists, computer scientists, mathematicians, and physicists from academia, industry and a national laboratory. The present work aims to develop a set of integrated computational tools to predict the relationships among chemistry, microstructure and mechanical properties of multicomponent materials systems. It contains a prototype grid-enabled package for multicomponent materials design with efficient information exchange between structure scales and effective algorithms and parallel computing schemes within individual simulation/modeling stages. As part of our multicomponent materials design framework, this paper reports the materials simulation segment in developing materials design knowledgebase, which involves four major computational steps: (1) Atomic-scale first-principles calculations to predict thermodynamic properties, lattice parameters, and kinetic data of unary, binary and ternary compounds and solutions phases; (2) CALPHAD data optimization approach to compute thermodynamic properties, lattice parameters, and kinetic data of multicomponent systems; (3) Multicomponent phase-field approach to predict the evolution of microstructures in one to three dimensions (1–3D); and (4) Finite element analysis to generate the mechanical response from the simulated microstructure. These four stages are to be integrated with advanced discretization and parallel algorithms and a software architecture for distributed computing systems.

The thermodynamic properties of the ternary Mg-Al-Ca system are investigated in this article, based on the Al-Ca, Al-Mg, and Ca-Mg binary systems. The equilibrium phases in the Mg-Al-Ca alloys studied are the primary magnesium matrix and Cl5-Al2Ca, as indicated by the calculated ternary phase diagrams. The experimental results are in good agreement with the thermodynamic calculations using Thermo-Calc software.

The structure–property relationship of a spray formed Al–Y–Ni–Co alloy with two sets of processing conditions was investigated. Significant differences in tensile strength, yield strength, and high temperature ductility were observed with respect to the microstructural changes. Fracture toughness values were determined for both sets of specimens and found to be 7.5 and 5.8 MPa·m 1/2 , respectively. Three intermetallic phases were observed in the matrix and constitute a volume fraction of approximately 75%. It is believed that the specimens failed during fracture toughness testing by the mechanism of cleavage, observed in the Al 3 Y intermetallic particles.

The MgB2 compound has a superconducting temperature of 39 K and its film has been successfully deposited by means of the hybrid physical chemical vapor deposition (HPCVD). In this paper, the CALPHAD technique was applied to study the reactivity of magnesium with several substrate materials during the HPCVD process. The calculated results showed that MgO, SiC, AlN and TaN are stable in the current HPCVD process. The Si, ZrO2, TiN, SiO2, Al2O3 and GaN substrates were also investigated. It was found that Mg reacts with these substrates under current HPCVD conditions. However, if the Mg vapor is low enough but still in the stability range of the MgB2 compound, the Si, ZrO2 and TiN substrates can be stable in the HPCVD process. The methodology used in the present work can be extended to other systems, and the current findings may be useful to guide other MgB2 thin film deposition processes.

Constitutional liquation means the local eutectic melting of second-phase particles in a matrix at temperatures above the eutectic temperature and below the solidus of the alloy, which may occur in the heat-affected zone (HAZ) during welding. In the present paper, the constitutional liquation in the Al–Cu system was computationally investigated using the DICTRA program coupled with critically assessed thermodynamic and kinetic databases. Computer simulated results are in quantitative agreement with existing experimental data. The computational procedures for obtaining the critical heating rate to avoid constitutional liquation are demonstrated. The critical heating rate was found to be inversely proportional to the square of the precipitate size. The present computational procedures can be readily extended to predict the susceptibility of multicomponent commercial alloys to constitutional liquation during welding with available thermodynamic and kinetic databases.

Thermodynamic modeling of the Ca-Sr and Sr-Zn binary systems and the prediction of the Ca-Sr-Zn ternary system were done using the CALPHAD technique and a computerized optimization procedure. The thermodynamic descriptions of pure Ca, Sr, and Zn elements were taken from the literature. Based on the experimental phase diagram and thermodynamic information, a set of parameters describing the Gibbs energies of the different phases in this ternary system was obtained. The calculated results were compared with the experimental data in the Ca-Sr and Sr-Zn binary systems, and the phase equilibria of the Ca-Sr-Zn ternary system was predicted.

We have carried out thermodynamics studies of the Mg-B system with the calculation of phase diagrams (CALPHAD) modeling technique and found that the superconductor MgB/sub 2/ phase is thermodynamically stable only under fairly high Mg pressures at elevated temperatures. This has lead us to the investigation of chemical vapor deposition in which the pressure during the film deposition can be high. Although the initial effort on metal-organic chemical vapor deposition (MOCVD) was not successful due to carbon contamination, a unique hybrid physical-chemical vapor deposition (HPCVD) technique has successfully produced high quality in situ MgB/sub 2/ films. The epitaxially-grown MgB/sub 2/ films show high transition temperature and low resistivity comparable to the best bulk samples, and their surfaces are smooth. In this paper, the details of the technique and the results of the HPCVD films are presented.

The recently discovered superconductor MgB2 with Tc at 39 K has great potential in superconducting electronics. In this paper, we review the deposition techniques used for MgB2 thin films in the light of a thermodynamic study of the Mg-B system with the calculation of phase diagrams (CALPHAD) modeling technique. This thermodynamic study identifies a growth window in the pressure–temperature phase diagram, in which the magnesium pressure is very high for likely in situ growth temperatures. A Hybrid Physical–Chemical Vapor Deposition (HPCVD) technique that successfully achieves such a high Mg pressure is shown to produce in situ epitaxial MgB2 thin films with bulk superconducting properties.

The thermochemical and phase-equilibrium data of the In-Pd binary system were critically reviewed. A self-consistent thermodynamic description of the system was obtained using the CALPHAD approach. Eight intermetallic compounds were considered in the system. The InPd(B2) compound was described by a two-sublattice model. The compounds In7Pd3, In3Pd2, In3Pd5, αInPd2, and αInPd3, with negligible homogeneity ranges, were modeled as stoichiometric compounds. βInPd2 and βInPd3 were treated as stoichiometric compounds due to a lack of experimental information. Model calculations agreed satisfactorily with most existing experimental data. The thermodynamic factor for the InPd(B2) compound was also predicted based on the present thermodynamic description.

The phase equilibria and thermodynamic properties of the Re-Ta-W system are analyzed, and a complete thermodynamic description of the ternary system is obtained with the calculation of phase diagrams (CALPHAD) technique using a computerized optimization procedure. The thermodynamic modeling of intermetallic compounds σ and χ phases with three sublattices is discussed in terms of the effects of a large number of interaction parameters in the phases. The ternary parameters ΔG Re:Ta:W and ΔG Re:W:Ta of the σ and χ phases are assumed to be linear combinations of the binary parameters ΔG Re:Ta:Ta and ΔG Re:W:W of the σ and χ phases. The ternary-interaction parameters of the liquid and bcc phases are optimized using available experimental data. The calculated phase diagrams show good agreement with the experimental data.

The newly discovered 39-K superconductor MgB2 holds great promise for superconducting electronics. Like the conventional superconductor Nb, MgB2 is a phonon-mediated superconductor, with a relatively long coherence length. These properties make the prospect of fabricating reproducible uniform Josephson junctions, the fundamental element of superconducting circuits, much more favourable for MgB2 than for high-temperature superconductors. The higher transition temperature and larger energy gap of MgB2 promise higher operating temperatures and potentially higher speeds than Nb-based integrated circuits. However, success in MgB2 Josephson junctions has been limited because of the lack of an adequate thin-film technology. Because a superconducting integrated circuit uses a multilayer of superconducting, insulating and resistive films, an in situ process in which MgB2 is formed directly on the substrate is desirable. Here we show that this can be achieved by hybrid physical-chemical vapour deposition. The epitaxially grown MgB2 films show a high transition temperature and low resistivity, comparable to the best bulk samples, and their surfaces are smooth. This advance removes a major barrier for superconducting electronics using MgB2.

The thermodynamic properties of the binary Al–Ca system are investigated. The assessment is carried out by means of the computer program Thermo-Calc, using models for the Gibbs energy of individual phases. In the present study, both associate and random solution models are tested for the system to better reproduce the experimental data. The results from the two models are compared with each other and with experimental data in the literature.

A three-dimensional phase-field model is proposed with the thermodynamic and kinetic parameters directly extracted from existing databases using the CALPHAD method. We modelled the γ′ precipitate microstructure evolution in a Ni-base alloy, particularly a single precipitate morphology at different sizes using independently assessed thermodynamic, kinetic and structural parameters.

A new barium polytitanate Ba1.054Ti0.946O2.946 was synthesized by a citrate chemical route. The X-ray powder pattern of this compound was indexed to a hexagonal system, with space group P63/mmc and lattice parameters a=5.722(4) and c=13.996(8) A. Prolonged annealing of the Ba1.054Ti0.946O2.946 in air at temperatures above 1150°C leads to a peritectoid decomposition reaction yielding Ba2TiO4 and cubic-BaTiO3, consistent with the known phase diagram. A thermal stability study of this compound demonstrates it to be a stable phase under ambient conditions and metastable under low oxygen partial pressures.

The recently discovered superconductor MgB2 with Tc at 39 K has great potential in superconducting microelectronics. Thermodynamics studies with the calculation of phase diagrams (CALPHAD) modelling technique show that due to the high volatility of Mg, MgB2 is only thermodynamically stable under fairly high Mg overpressures for likely in situ growth temperatures. This provides a helpful insight into the appropriate processing conditions for MgB2 thin films, including the identification of the pressure–temperature region for adsorption-controlled growth. The initial MgB2 thin films were made by pulsed laser deposition followed by in situ annealing. The cross-sectional transmission electron microscopy reveals a nanocrystalline mixture of textured MgO and MgB2 with very small grain sizes. A zero-resistance transition temperature of 34 K and a zero-field critical current density of 1.3 × 106 A cm−2 were obtained. The qualities of these films are limited by the thermodynamic stability conditions, which favour deposition techniques that can maintain a high flux of Mg.

The stability and evolution of ferroelectric domain structures in thin films are studied. Elastic solutions are derived for both elastically anisotropic and isotropic thin films with arbitrary domain structures, subject to the mixed stress-free and constraint boundary conditions. These solutions are employed in a three-dimensional phase-field model to investigate simultaneously the effect of substrate constraint and temperature on the volume fractions of domain variants, domain-wall orientations, surface topology, domain shapes, and their temporal evolution for a cubic-to-tetragonal ferroelectric phase transition. A specific example of a [001] orientated film heteroepitaxially grown on a [001] cubic substrate is considered. It is shown that the shapes of a-domains with tetragonal axes parallel to the film surface are significantly different from those of c-domains with tetragonal axes perpendicular to the film surface. For the substrate constraints and temperatures under which both a- and c-domains coexist, both types of a-domains are present with their tetragonal axes perpendicular to each other, and the domain wall orientations deviate from the 45 orientation generally assumed in thermodynamic analyses. It is demonstrated that a substrate constraint results in sequential nucleation and growth of different tetragonal domains during a ferroelectric phase transition.

The proton mean kinetic energy, Ke(H), of water confined in nanocavities of beryl (Be3Al2Si6O18) at 5 K was obtained by simulating the partial vibrational density of states from density functional theory based first-principles calculations. The result, Ke(H) = 104.4 meV, is in remarkable agreement with the 5 K deep inelastic neutron scattering (DINS) measured value of 105 meV. This is in fact the first successful calculation that reproduces an anomalous DINS value regarding Ke(H) in nano-confined water. The calculation indicates that the vibrational states of the proton of the nano-confined water molecule distribute much differently than in ordinary H2O phases, most probably due to coupling with lattice modes of the hosting beryl nano-cage. These findings may be viewed as a promising step towards the resolution of the DINS controversial measurements on other H2O nano-confining systems, e.g., H2O confined in single and double walled carbon nanotubes.

A Na-ion solid-state electrolyte, Na3 P0.62 As0.38 S4 , is developed with an exceptionally high conductivity of 1.46 mS cm-1 at 25 °C and enhanced moisture stability. Dual effects of alloying element As (lattice expansion and a weaker AsS bond strength) are responsible for the superior conductivity. Improved moisture stability is regulated by shifting low-energy moisture reactions to high-energy ones due to As.

Interest in additive manufacturing (AM) has dramatically expanded in the last several years, owing to the paradigm shift that the process provides over conventional manufacturing. Although the vast majority of recent work in AM has focused on three-dimensional printing in polymers, AM techniques for fabricating metal alloys have been available for more than a decade. Here, laser deposition (LD) is used to fabricate multifunctional metal alloys that have a strategically graded composition to alter their mechanical and physical properties. Using the technique in combination with rotational deposition enables fabrication of compositional gradients radially from the center of a sample. A roadmap for developing gradient alloys is presented that uses multi-component phase diagrams as maps for composition selection so as to avoid unwanted phases. Practical applications for the new technology are demonstrated in low-coefficient of thermal expansion radially graded metal inserts for carbon-fiber spacecraft panels.

Charge transfer among individual atoms is the key concept in modern electronic theory of chemical bonding. In this work, we present a first-principles approach to calculating the charge transfer. Based on the effects of perturbations of an individual atom or a group of atoms on the electron charge density, we determine unambiguously the amount of electron charge associated with a particular atom or a group of atoms. We computed the topological electron loss versus gain using ethylene, graphene, MgO, and SrTiO3 as examples. Our results verify the nature of chemical bonds in these materials at the atomic level. © 2015 Wiley Periodicals, Inc.

Mg-Al-Ca alloys exhibit appealing creep strength at temperatures over 100°C. It is believed that it is due to the substitution of the γ-Al12Mg17 phase by laves phases of higher thermal stability. In the literature, the C15-Al2Ca phase in the Al-Ca binary system and the C14-Mg2Ca phase in the Ca-Mg binary system have been reported. Their relative stability in the ternary system may play an important role in the development of the Mg-Al-Ca alloys. Furthermore, recent experiments and first-principles calculations in the literature revealed the existence of a C36 laves phase in the Al2Ca-Mg2Ca pseudo-binary system in addition to the C14-Mg2Ca and C15-Al2Ca laves phases. In the present work, special quasirandom structures (SQS) for all three laves phases were constructed. The structures possess local pair and multisite correlation functions that mimic those of the corresponding random structures. First-principles calculations were carried out based on the SQS developed to predict the enthalpy of formation in the Al2Ca-Mg2Ca pseudo-binary system. It was observed that the enthalpy of formation of C36 is very close to that of C14 at the Mg2Ca end and decreases with the addition of small amount of Al, while the enthalpy of formation of C14 increases with the addition of Al. It is thus energetically plausible the C36 is stable in the Al2Ca-Mg2Ca pseudo-binary system. Experimental investigations were done using diffusion couple of Mg-Ca alloy and pure Al. EPMA analysis of the diffusion zone found the existence of two ternary phases (Mg,Al)2Ca and Al2(Mg,Ca).

Thermodynamics has often been viewed applicable to states near equilibrium only although irreversible thermodynamics was already developed in 1950s. The CALPHAD technique of computational thermodynamics developed since early 1970s has helped to change this view. This technique couples the phase diagram and thermochemical properties to explicitly characterize all phases in a system, including stable, metastable, and unstable phases over a wide range of temperature, pressure and composition. The modeling of Gibbs energy of individual phases enables the calculation of driving forces between any intermediate non-equilibrium states for simulating dynamic microstructure evolutions.

We analyse the formalism of transport in a binary system especially focussing on a detailed consideration of the heat of transport parameter characterizing diffusion driven by a temperature gradient. We introduce the reduced heat of transport parameter Q_{c}^{{*}'} which characterizes part of the interdiffusion flux that is proportional to the temperature gradient. In an isothermal system Q_{c}^{{*}'} represents the reduced heat flow (pure heat conduction) consequent upon unit interdiffusion flux. We demonstrate that Q_{c}^{{*}'} is independent of reference frame and is practically useful for direct comparison of simulation and experimental data from different sources obtained in different reference frames. Then, we use equilibrium molecular dynamics simulations in conjunction with the Green-Kubo formalism to study the heat transport properties of a model of the liquid Ni_{50}Al_{50} alloy at three state points within the temperature range 1500 – 4000 K. Our results predict that in the liquid Ni_{50}Al_{50} alloy in the presence of a temperature gradient Ni tends to diffuse from the cold end to the hot end whilst Al tends to diffuse from the hot end to the cold end.

The formalism of thermotransport in a binary system is analysed. Focus is put on a detailed consideration of the heat of transport parameter characterizing diffusion driven by a temperature gradient. We introduce the reduced heat of transport parameter Q_{c}^{{*}'} , which characterizes part of the interdiffusion flux that is proportional to the temperature gradient. In an isothermal system Q_{c}^{{*}'} represents the reduced heat flow (pure heat conduction) consequent upon unit interdiffusion flux. It is demonstrated that Q_{c}^{{*}'} is independent of reference frame and is useful in a practical way for direct comparison of simulation and experimental data from different sources obtained in different reference frames. In the case study of the liquid Ni_{50}Al_{50} alloy, we use equilibrium molecular dynamics simulations in conjunction with the Green–Kubo formalism to evaluate the heat transport properties of the model within the temperature range of 1500–4000 K. Our results predict that in the presence of a temperature gradient Ni tends to diffuse from the cold end to the hot end whilst Al tends to diffuse from the hot end to the cold end.

The thermodynamic properties of alloys can be described from the knowledge of the underlying lattice and the atomic numbers of the alloy species by using a first-principles electronic structure approach based on the tight-binding linear muffin-tin orbital method within the coherent potential approximation (TB-LMTO-CPA) and the local density approximation of density functional theory. The generalized perturbation method (GPM) permits direct mapping of the configurational part of the effective one-electron Hamiltonian onto an Ising-like model thus insuring the necessary link between quantum mechanics and statistical thermodynamics. To test the practical application of this approach to multi-component alloys, data assessment has been successfully performed for the Cr-Ta-W alloy system by using the thermodynamic results derived from the TB-LMTO-CPA-GPM and the cluster variation method (CVM) in the tetrahedron approximation for Ta-W alloys as functions of temperature and concentration. These later results predict B2 ordering for the bcc-based Ta-W system with a maximum ordering temperature near 1000 K at 43 at.% Ta. The output thermodynamics were converted to a Redlich-Kister/Bragg-Williams format with an acceptable level of accuracy. The results were then combined with those of the CALPHAD description of the Cr-W and Cr-Ta systems to calculate isothermal sections of the ternary phase diagram of the Cr-Ta-W system.

The phase equilibria and thermodynamic properties of the Ca-Zn binary system were analyzed and a complete thermodynamic description of the system was obtained using a computerized optimization procedure. Based on the experimental data, eight intermetallic compounds were considered. A new interpretation of the decomposition of the phase CaZn 3 is presented. Good agreement was obtained between the calculated results and the experimental data for the binary system.

It has been recently discovered that the compound MgB 2 possesses superconductivity at 39K. To better design and control the fabrication of the MgB 2 compound, a complete thermodynamic description of the system is desirable. In the present work, the phase equilibria and thermodynamic properties of the binary Mg-B system were analyzed and a complete thermodynamic description of the binary system was obtained by means of the CALPHAD technique using a computerized optimization procedure. The thermodynamic descriptions of pure Mg and B elements were taken from the literature. Based on the experimental data, three binary intermetallic compounds, MgB 2 , MgB 4 and MgB 6 , were considered. Good agreement was obtained between the calculated results and the available experimental data in the literature.

The phase equilibria and thermodynamic properties of the Re–Ta and Re–W systems were analyzed and complete thermodynamic descriptions of the two binary systems were obtained with the CALPHAD technique using a computerized optimization procedure. The thermodynamic descriptions of pure Re, Ta and W elements were taken from the SGTE database. Two binary intermetallic compounds were considered in both binary systems, namely σ phase and χ phase based on available experimental data. Good agreement was obtained between calculated results and experimental data in the two binary systems.

Computational approaches in materials science and engineering have progressed significantly in recent decades and are shifting the materials research paradigm to the integration of computation, processing, and characterization. This paper presents a brief overview of the state-of-the-art of computational approaches and their power in enhancing research and development of commercial materials.

The phase equilibria and thermodynamic properties of the binary Co-Ta system were analyzed and a complete thermodynamic description of the binary system was obtained with the CALPHAD technique using a computerized optimization procedure. The thermodynamic descriptions of pure Co and Ta elements were taken from the SGTE database. Based on the experimental data, six binary intermetallic compounds were considered. They are three Laves phases, μ phase, θ phase and Co 7 Ta 2 phase. The last two compounds are treated as stoichiometric compounds. Good agreement was obtained between calculated results and experimental data in the binary system.

The phase equilibria and thermodynamic properties of the ternary Al-Fe-Si system were analyzed and a complete thermodynamic description of the ternary system was obtained. The thermodynamic descriptions of the three binary systems were taken from the literature. Most of the binary intermetallic phases, except Al13Fe4(ϑ), FeSi2-L, and FeSi2-H, were assumed to have no ternary solubility. Based on the experimental data, seven stable ternary intermetallic phases were considered in the system. Two of them were treated as semistoichiometric compounds with homogeneity ranges for Al and Si, and the others were treated as stoichiometric compounds. Reasonable agreement was obtained between calculation results and experimental information in the ternary system.

The available thermodynamic databases for magnesium alloys are discussed in this paper. Of particular interest are the features of a magnesium database developed by the authors with 19 elements: Mg-Al-Ca-Ce-Cu-Fe-KLa-Li-Mn-Na-Nd-Pr-Si-Sn-Sr-Y-Zn-Zr. Using this database, two applications are presented. One is the phase evolution in AZ61 magnesium alloy including the variations of phase fractions, alloying compositions, and partition coefficients of alloying elements as a function of temperature (or solid fraction). The other is to understand sodium-induced high-temperature embrittlement in the Al-Mg alloy, which is ascribed to the formation of a liquid phase due to the presence of sodium traces.

The atomic mobilities of Au, In, Pb, and Sn in face-centered cubic Pb-Sn and Pb-In alloys are modeled using the available literature data. A set of parameters describing the composition and temperature dependence of diffusional mobility are provided. The calculated tracer diffusivities of Pb in ternary Pb-Sn-In and Pb-Sn-Au alloys are in very good agreement with the experimental data. Using the model parameters, both tracer and chemical diffusivities can be calculated in the composition and temperature ranges where experimental data is not available. On the assumption of local equilibrium, the simulation of dissolution kinetics of Pd in liquid Pb is demonstrated. The major source of discrepancy between the calculated and experimental diffusion profiles is the uncertainty of the atomic transport kinetics data in the liquid phase. The implications of current kinetic modeling are discussed briefly.

The effect of stress on transformation is studied through a series of dilation experiments. The results obtained are used to modify models of transformation kinetics, transformation plasticity, and elastoplastic constitutive relations so as to predict residual stresses after quenching. Results of the simulation show that the modified models are fit to predict residual stresses after quenching, which agree well with experimental results if both transformation plasticity and stress induced transformation are taken into account.

The solute drag was discovered in connection with grain boundary migration during recrystallization, and it was suggested that the effect is caused by segregation of impurities to grain boundaries. This idea was later extended to the migration of phase interfaces during phase transformations. However, in a phase transformation, the phases often have different compositions. In order to maintain steady state conditions at the phase interface, a concentration profile must exist inside the moving interface if it has a finite width. This is realized by diffusion inside the phase interface, which consumes a part of the driving force. This concept does not necessarily involve the segregation to the boundary explicitly but is nevertheless often referred to as a solute drag effect. However, a complete solute drag model for phase transformations should of course also include the effect of phase-boundary segregation. Furthermore, the gradient energy may also need to be considered. In the present work, thermodynamics of interfacial adsorption will be discussed in conjunction with a solute drag model for phase transformations, recently modified to take into account the interfacial segregation of alloying elements. It will be shown that the classical interfacial adsorption treatment can be consistently included in the new modified solute-drag model. The gradient energy will be discussed, and an expression to evaluate its value from the Gibbs energy function will be presented.

The model for the solute drag effect in phase transformations has been applied to recrystallization, i.e., moving grain boundaries. In this model, the total driving force is dissipated by the interfacial energy, the finite interfacial mobility, the solute drag in boundaries, and diffusion in the matrix ahead of the interface, of which all are taken into account consistently. The effects of the Gibbs energy of segregation and the diffusivity of impurity atoms in boundaries were investigated. The results show that the Gibbs energy of segregation mainly affects the critical composition at which the drastic change in the boundary velocity appears, and the diffusivity of impurity atoms in boundaries mainly affects the velocity reduced by the solute drag effect. In other words, the Gibbs energy of segregation and the diffusivity of impurity atoms in boundaries can be evaluated from experimental data by means of the present model. This model was applied to the Al−Mg system, and the Gibbs energy of segregation and the diffusivity of Mg in boundaries were evaluated from experimental data. The evaluated Gibbs energy of segregation agrees with the estimate based on elastic energy considerations. The diffusivity estimated from this model is smaller than that measured along the grain boundary.

The steady state growth equation for a paraboloid of revolution and a parabolic cylinder, taking the interfacial energy into account, is revisited. Although the consideration of the interfacial energy was necessary, the growth equation was much more complicated than the original equation with a zero interfacial energy, since both the thermodynamics and kinetics of the growth are considered in one equation. In the present work, we take advantage of the development in computational thermodynamics and consider the thermodynamics and kinetics of the process in separate equations, but solve them simultaneously. A consistent framework to describe the phenomena and compare it with previous treatment of the interfacial energy will be presented.

An X Window user interface for Dictra has been developed based upon the user interface developed for Thermo-Calc. With this user interface, many useful simulations can be made in a simple way without mastering the commands of Dictra. It should thus be possible for people who are not specialists in Dictra to use the program. With this interface, it is possible to simulate certain virtual heat treatments of an alloy. One example is soft annealing and subsequent austenitising of an Fe-C-Cr alloy. The dissolution of M23C6 carbide in an Fe-Cr-C alloy and the solidification of an 18-8 stainless steel can also be simulated and many other simulations can similarly be made. With a little further programming work, it will be possible to combine various single simulations to simulate a series of heat treatments, such as solidification followed by homogenisation and then isothermal transformation or continuous cooling, etc. Other future goals are to include diffusion in dispersed systems, i.e. carburisation, ...

A recently modified solute drag model, taking into account the interfacial segregation of alloy elements, is applied to the decomposition of austenite into ferrite in Fe-Mo-C alloys. The calculations are carried out with assessed thermodynamic and kinetic data stored in databases. The effect of the Gibbs energy of segregation is discussed in connection with published experimental observations of the bay in the time-temperature-transformation (TTT) curve for initiation of transformation. The solute draglike effect suggested in the literature is discussed in comparison with the present quantitative calculation.