Showing papers in "Calphad-computer Coupling of Phase Diagrams and Thermochemistry in 2017"

Critical reassessment of the Fe-Si system

Abstract: The Fe-Si system has been studied extensively due to its importance in steelmaking and electrical-magnetic applications. Thermodynamic and phase diagram data of the Fe-Si system available in the literature were critically evaluated and re-optimized to improve the thermodynamic description of this system. Two sets of optimized model parameters were obtained to reproduce the available and reliable literature data. In each set of parameters, the liquid phase was described using the modified quasi-chemical model or the Bragg-Williams random mixing model. The A2/B2 and B2/D03 order-disorder transitions were also taken into account in the present study.

Modified embedded-atom interatomic potential for Fe-Ni, Cr-Ni and Fe-Cr-Ni systems

Abstract: A semi-empirical interatomic potential formalism, the second-nearest-neighbor modified embedded-atom method (2NN MEAM), has been applied to obtaining interatomic potentials for the Fe-Ni, Cr-Ni and Fe-Cr-Ni systems using previously developed MEAM potentials of Fe and Ni and a newly revised potential of Cr. The potential parameters were determined by fitting the experimental data on the enthalpy of formation or mixing, lattice parameter and elastic constant. The present potentials generally reproduced the fundamental physical properties of the Fe-Ni and Cr-Ni alloys. The enthalpy of formation or mixing of the disordered phase at finite temperature and the enthalpy of mixing of the liquid phase are reasonable in agreements with experiment data and CALPHAD calculations. The potentials can be combined with already-developed MEAM potentials to describe Fe-Cr-Ni-based multicomponent alloys. Moreover, the average diffusivities in the unary, some binary and ternary alloys were simulated based on present potential. Good agreement is obtained in comparison with experimental data.

Experimental investigation and thermodynamic description of the Cu-Cr-Zr system

Abstract: The Cu-Cr-Zr ternary system was investigated via thermodynamic modeling coupled with key experiments. The isothermal section of the Cu-Cr-Zr system at 1123 K was determined by means of optical microscopy, X-ray diffraction and electron probe microanalysis, and the phase transformation temperatures were measured by differential scanning calorimetry. The Cu-Cr sub-binary system was re-assessed with a substitutional solution model for the solution phases to ensure its compatibility in multi-component system. A set of self-consistent thermodynamic parameters for the Cu-Cr-Zr systems was obtained using the CALPHAD (CALculation of PHAse Diagram) approach, and the calculated phase diagram is in a satisfactory agreement with the present experimental results and literature information. An increase of the thermodynamic stability for the CuZr and Cr 2 Zr phases due to the ternary solubility is verified by calculation.

Software tools for high-throughput CALPHAD from first-principles data

Abstract: We present a set of software tools that largely automate the process of converting ab initio data into thermodynamic databases that can readily be imported into standard thermodynamic modeling softwares. These tools are based on the Special Quasirandom Structures (SQS) formalism, extended to transparently handle, not only traditional fcc, bcc and hcp solid solutions, but also multiple-sublattice structures with possible sublattice disorder. A large database of pre-generated SQS is provided that covers over 30 of the most common multi-sublattice structures and spans the composition ranges of each of their sublattices. In addition, we exploit a theoretically justified and robust method to address the issue of assigning free energies to mechanically unstable “virtual” phases, thus providing a compelling solution to a long-standing problem in CALPHAD modeling, especially in the context of ab initio data. We also propose a simple low-order approximation scheme to include short-range order effects that requires no additional ab initio input. The resulting thermodyamic database seamlessly combines ab initio data (formation energies and, optionally, vibrational free energies) with elemental Scientific Group Thermodata Europe (SGTE) data. The proposed tools provide a clear path to expand the coverage of high-throughput efforts towards non-stoichiometric phases and non-zero temperatures. The generated free energy models can also provide very good starting points to perform complex thermodynamic assessments, especially in cases where the available experimental data poorly constrain some thermodynamic parameters. The Cu-Pt-W phase diagram is calculated as an example.

Thermodynamic re-assessment of the Al-Co-W system

Abstract: The Al-Co-W system and its binary sub-systems Al-Co, Al-W and Co-W were critically reviewed. The thermodynamic description of the Al-Co-W system including all three binaries was developed considering thermodynamic and constitutional data of the systems. Results from density functional theory calculations were employed to improve reliability of the descriptions. The Gibbs energy for the thermal vacancy (GVa) in the BCC_A2 phase is discussed. The revised descriptions obtained for the Al-W and Co-W systems describe the thermodynamic and phase equilibrium data well and are free of undesired artefacts for temperatures below 6000 K. The ordered γ’ phase of the Al-Co-W system is described as a metastable phase in the entire temperature range. The calculated Gibbs energy of the γ’ is only slightly above that of the equilibrium state, which indicates that there is good possibility of stabilizing the γ’ phase with the addition of γ’-stabilizing elements, such as Ti, Ta, Hf, Nb and Ni.

Thermodynamic assessment of the Al-C-Fe system

Abstract: The Al-C-Fe system was assessed in the framework of the CALPHAD approach Through the critical review of thermochemical properties of liquid Al-Fe alloys, the binary Al-Fe description was revised t

The exponential excess Gibbs energy model revisited

Abstract: The exponential model for the temperature (T) dependence of the excess Gibbs energy of liquid solutions within the framework of the Redlich-Kister polynomials is proven to be an efficient tool to avoid high-T artefacts, such as an artificial inverted miscibility gap, caused by the linear model. However, it has been claimed that the exponential model can lead to a low-T artefact, i.e. to the artificial low-T re-stabilization of the liquid solution. As shown here, this claim is un-supported for all the 15 binary systems studied so far by the exponential model in the literature. Still, the artefact might appear for other systems, or for lower temperatures, as the 15 systems were modelled at and above 298 K. To make sure the low-T artefact does not appear, this paper introduces a new, low-T polynomial, which is matched with the exponential model at temperature T*, defined as the lowest liquidus temperature of the given system. The low-T model is described by a four parameter polynomial, obtained analytically from the two fitted parameters of the exponential model, ensuring that the four excess functions (the excess Gibbs energy, the heat of mixing, the excess entropy and the excess heat capacity) are continuous functions of T in the whole T-interval at any composition. When the complexity of the liquid alloy requires more than two semi-empirical parameters, the combined linear-exponential model should be used instead of the exponential model, with the same matching low-T polynomial. The inherently inconsistent nature of the recent LET function (see S.M. Liang, P. Wang, R. Schmid-Fetzer, Calphad 54 (216) 82–96) is discussed, as it was introduced to replace the exponential model. It is proven by the new simplified assessment of the Mg-Si system that the exponential model can be applied to this system without any artifact, contrary to the claim of Schmid-Fetzer et al., Calphad 31 (2007) 131–142.

Phase equilibria, thermodynamics and microstructure simulation of metastable spinodal decomposition in c–Ti1−xAlxN coatings

Abstract: Based on the experimental equilibrium data on spinodal decomposition in the literature together with the newly measured data in the present work, a complete metastable phase diagram for the pseudo-binary c–TiN/c-AlN system was constructed for the first time, from which a self-consistent thermodynamic description was then established by means of CALculation of PHAse Diagram (CALPHAD) method with the aid of first-principles computed free energies. By coupling with the CALPHAD thermodynamic database, two- and three-dimensional quantitative numerical simulations of microstructure evolution in metastable c–Ti1−xAlxN coatings during spinodal decomposition were performed using Cahn-Hilliard model. Three sets of diffusivity data available in the literature were carefully screened by comparing the simulated microstructures with the experimental ones, and one of them was chosen for the final simulations. The simulated composition wavelengths during spinodal decomposition at different temperatures agree with the experimental data. Moreover, the effect of the composition fluctuation on the microstructure evolution during spinodal decomposition was also comprehensively investigated.

Second nearest-neighbor modified embedded-atom method interatomic potentials for the Pt-M (M = Al, Co, Cu, Mo, Ni, Ti, V) binary systems

Abstract: Interatomic potentials for Pt-M (M = Al, Co, Cu, Mo, Ni, Ti, V) binary systems have been developed on the basis of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The parameters of pure Mo have also been newly developed to solve a problem in the previous 2NN MEAM potential in which the sigma and α-Mn structures become more stable than the bcc structure. The potentials reproduce various materials properties of alloys (structural, thermodynamic and order-disorder transition temperature) in reasonable agreements with relevant experimental data and other calculations. The applicability of the developed potentials to atomistic investigations for the shape and atomic configuration of Pt bimetallic nanoparticles is demonstrated.

Phase formations in low density high entropy alloys

Abstract: Phase formations in high entropy alloys (HEAs) with at least two light elements in literature are predicted by CALPHAD (CALculation of PHAse Diagrams) thermodynamic calculations and the results are compared with experimental observations. The comparison suggests that the applicability of traditional CALPHAD calculations depends on the manufacturing processes of HEAs. Factors such as solute trapping, energies of defects need to be considered while predicting phases in HEAs prepared by non-equilibrium processes. The effects of light elements (Al, Ti, Si, alkali and alkaline earth metals) on the phase formations in HEAs are discussed. Especially, intermetallics predicted for Si-containing HEAs by traditional CALPHAD calculation can be suppressed in rapid solidification process, due to the solute trapping effect. Mg or other alkali and alkaline earth metals can lead to the formations of various intermetallics in HEAs prepared by conventional casting, but could be dissolved into solid solutions by non-equilibrium processes such as mechanical alloying. It is proposed that non-equilibrium processes may be an effective way to introduce light elements Si, alkali and alkaline earth metals into HEAs.

Thermodynamic and diffusion kinetic studies of the Fe-Co system

Abstract: The phase equilibria, thermodynamic properties and diffusion mobilities of the Fe-Co system were carefully assessed through the CALPHAD methods. As an indispensable tool, the first-principles calculations were carried out to study the magnetic moments and the enthalpies of mixing of the bcc_A2, bcc_B2, fcc_A1 and hcp_A3 phases as well as the point defect types of the bcc_B2 phase. In order to verify the heat capacities reported in the literature, new measurements were conducted in a high-temperature calorimetric apparatus using the three-dimensional calorimetric method. Because of the revision of the thermodynamic parameters in the present work, the diffusion mobilities for the fcc_A1 phase were reassessed. The diffusion mobilities for the bcc_A2 phase were established for the first time based on the experimental diffusion coefficients. For the low-temperature bcc_B2 phase, the diffusion couple experiments conducted in the present work show that the diffusion process is sluggish and the interdiffusion coefficients are difficult to determine. Therefore the tracer diffusivities of Co and Fe in the Fe-Co alloys were used to assess the diffusion mobilities for the bcc_B2 phase, while the composition-distance profile of one diffusion couple was served as a validation of its diffusion mobilities.

Critical evaluation of thermodynamic properties of rare earth sesquioxides (RE = La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y)

Abstract: In order to develop the thermodynamic database containing rare earth sesquioxides (RE2O3), accurate thermodynamic descriptions of all stable and metastable RE2O3 phases are required. Rare earth sesquioxides have five polymorphs, which are (from low to high temperature) the cubic phase (C), the monoclinic phase (B), the hexagonal phase (A), the high temperature hexagonal phase (H), and the high temperature cubic phase (X). However, the thermodynamic property data of all polymorphs available in the literature are insufficient. In particular, the thermodynamic data for the phases stable only at high temperatures and for metastable phases are not well investigated. In this study, all ∆ H 298 K o , S 298 K o , CP (or heat content) and phase transition temperature (Ttr) data available in the literature for each rare earth sesquioxide were collected and critically evaluated based on the sample preparations, experimental procedures and characterization techniques. Relationships between ∆ H 298 K o , S 298 K o , and Ttr against the ionic radii of the entire rare earth cations were then established and missing thermodynamic information was predicted based on the general trends. In these ways, the accurate and consistent Gibbs energies of all stable and metastable RE2O3 phases (RE = La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc) were prepared. These Gibbs energy data can be readily used for the development of a comprehensive thermodynamic database containing rare earth oxides.

Au-Ni nanoparticles: Phase diagram prediction, synthesis,characterization, and thermal stability

Abstract: The Au-Ni nanoparticles (NPs) were prepared by oleylamine solvothermal synthesis from metal precursors. The Au-Ni phase diagram prediction respecting the particle size was calculated by the CALPHAD method. The hydrodynamic size of the AuNi NPs in a nonpolar organic solvent was measured by the dynamic light scattering (DLS) method. The average hydrodynamic sizes of the nanoparticle samples were between 18 and 25 nm. The metallic composition of the AuNi NP samples was obtained by inductively-coupled plasma atomic emission spectroscopy (ICP-OES). The metallic fraction inside AuNi NPs was varied Au-(30-70)wt%Ni. The steric alkylamine stabilization was observed. The individual AuNi NPs were investigated by transmission electron microscopy (TEM). The dry nanopowder was also studied. The structures of the aggregated samples were investigated by scanning electron microscopy (SEM). The AuNi NPs reveal randomly mixed face-centered cubic (FCC) crystal lattices. The phase transformations were studied under inert gas and air. The samples were studied by differential scanning calorimetry (DSC).

PrecHiMn-4 - A thermodynamic database for high-Mn steels

Abstract: This paper concerns a Calphad database that was developed to describe precipitation of cubic carbides and nitrides (V, Nb and Ti) in high manganese steels and to describe phase equilibria in high manganese steels with high aluminium content. The database has also been shown to be useful for calculations on medium manganese steels and low-density steels with varying aluminium additions. Thus the database covers a significant fraction of the steels that are termed advanced high strength steels (AHSS) of the second and third generation. A number of systems were assessed (or reassessed) for the database, namely Fe–Mn–Al, Fe–Mn–C, Fe–Nb, Mn–Nb, Fe–Mn–Nb, Fe–Nb–V, Fe–Nb–C, Mn–Nb–C, Fe–Mn–Nb–C, Nb–N, Fe–Mn–Nb–N. The remaining systems were taken from published assessments. The database covers the elements Fe, Mn, Al, Si, V, Nb, Ti, C and N.

Thermodynamic modeling of Ti-Fe-Cr ternary system

Abstract: Previous work of the Ti-Fe-Cr ternary system and its related binary systems are reviewed. Based on the thermodynamic descriptions of the Ti-Fe, Ti-Cr and Fe-Cr systems available in the literature, and also the ternary experimental data previously reported, the Ti-Fe-Cr ternary system is reassessed in this work by means of the Calphad method. Isothermal sections at 923 K, 1073 K and 1273 K and three invariant reactions as well as the vertical section TiCr2-TiFe2 are calculated. It is shown that the present calculated results are in good agreement with most of the experimental data.

Thermodynamic modeling of the Cu-Fe-Cr and Cu-Fe-Mn systems

Abstract: All the thermodynamic and phase diagram information available in the literature on the Cu-Cr system, Cu-Fe-Cr system, and Cu-Fe-Mn system were critically evaluated and used in the thermodynamic optimization to obtain a set of consistent thermodynamic model parameters for the systems. The liquid solutions for the Cu-Cr, Cu-Mn, Fe-Cr, Cu-Fe-Cr, and Cu-Fe-Mn systems were described using the Modified Quasichemical Model (MQM) with pair approximation. The solid solution phases were modeled using the Bragg-Williams random mixing model. Accurate reproduction of all the reliable phase diagram and thermodynamic property data indicates the high reliability of the present thermodynamic optimizations.

Thermodynamic modeling of the quaternary Al-Cu-Mg-Si system

Abstract: Based on the critically evaluated thermodynamic and phase diagram information available in the literature, thermodynamic modeling of the Cu-Mg, Al-Cu-Mg, Al-Cu-Si, and Cu-Mg-Si systems were conducted using the CALPHAD (CALculation of PHAse Diagrams) technique. The liquid phase was described using the Modified Quasi-chemical Model (MQM), and the solid solution phases were modeled with the Compound Energy Formalism (CEF). Based on the newly obtained and the previously published thermodynamic descriptions of the subsystems, a set of self-consistent thermodynamic description for the Al-Cu-Mg-Si quaternary system was constructed. Comprehensive comparison between the calculated and measured thermodynamic and phase diagram information indicated that most of the reliable experimental data in the quaternary system can be satisfactorily reproduced by the presently obtained thermodynamic description. The optimized thermodynamic parameters can be used for the calculations of the phase diagram and thermodynamic properties of any composition and temperature range in the Al rich Al-Cu-Mg-Si quaternary system.

Ab initio-assisted assessment of the CaO-SiO2 system under pressure

Abstract: We present the results of an ab initio-assisted assessment of melting and subsolidus phase relations in the system CaO-SiO2 up to high pressure conditions. All solid compounds known to nucleate in the system have been treated as purely stoichiometric and the liquid resolved in the framework of a simple polymeric model. Mixing properties of the binary liquid phase are fully described by a single-parameter purely enthalpic chemical interaction plus a strain energy contribution. The latter is required to predict liquid immiscibility of SiO2-rich liquid compositions at ambient conditions and becomes irrelevant at P > 2 GPa. A detailed survey of thermodynamic properties of silica polymorphs and calcium oxide and silicates in a broad range of P-T conditions reveals quite controversial stability relations and melting behavior. First-principles calculations on CaO and SiO2 pure liquid components and solid phases (lime and stishovite) have been used, along with a sound assessment of first- and second-order phase transitions, to reconcile thermochemical data with topological details of the observed phase diagrams. A physically-consistent coupling between thermodynamic and thermoelastic properties (viz. compressibility and thermal expansion) turns out to be of fundamental importance to infer reliable stability relations both at subsolidus and melting conditions. Pressure effects shift the composition of the main invariant points in the CaO-SiO2 system and also change the melting behavior of the CaSiO3 metasilicate in a complex manner.

Critical thermodynamic re-evaluation and re-optimization of the CaO–FeO–Fe2O3–SiO2 system

Abstract: Comprehensive literature review, critical re-assessment and thermodynamic re-optimization of phase diagrams and thermodynamic properties of all phases have been carried out for the CaO–FeO–Fe2O3–SiO2 system. Thermodynamic assessments of this system were previously published, however some of them were incomplete or described only limited range of compositions. In addition, more recent important experimental data have been available after previous assessments. The Modified Quasichemical model is used to describe the Gibbs energy of the liquid slag. The monoxide, wollastonite, α-Ca2SiO4 and α’-Ca2SiO4 solid solutions are described using the random mixing Bragg-Williams model. Spinel, olivine, pyroxene and melilite solid solutions are modelled using sublattice model based on the Compound Energy Formalism. A set of optimized parameters for the thermodynamic models has been obtained which reproduces all available experimental data within the experimental uncertainties from sub-solidus to above the liquidus temperatures at all compositions and atmosphere conditions.

Thermodynamic model for prediction of binary alloy nanoparticle phase diagram including size dependent surface tension effect

Abstract: Considering the size effect of nanoparticles on surface tension, a new CALPHAD type thermodynamic model was developed to predict phase diagram of binary alloy nanoparticle systems. In contrast to conventional model, the new model can be applied to the nanoparticles smaller than the critical size (5 NM in radius). For an example, the model applied to Ag – Au binary system and the results were compared with experimental data as well as conventional CALPHAD model and molecular dynamics simulation results.

Diffusion study in bcc_A2 Fe-Mn-Si system: Experimental measurement and CALPHAD assessment

Abstract: Based on the recently developed numerical inverse method, high-throughput measurement of the composition-dependent interdiffusivity matrices in the bcc_A2 Fe-Mn-Si alloys at 1173, 1273 and 1373 K was performed in the present work. To verify the reliability of the presently determined interdiffusivities, the ternary interdiffusivities evaluated by the traditional Matano-Kirkaldy method at the intersection points of the diffusion paths were employed to make a direct comparison. Subsequently, on the basis of the presently obtained interdiffusivities together with the thermodynamic descriptions for bcc_A2 phase in the Fe-Mn-Si system, atomic mobilities of Fe, Mn and Si in bcc_A2 Fe-Mn-Si alloys were assessed by means of DICTRA (DIffusion Controlled TRAnsformatim) software package. The comprehensive comparison between various calculated/model-predicted diffusion properties, including interdiffusivities, concentration profiles, interdiffusion fluxes and diffusion paths, and the experimental data indicates that most of the experimental data can be well produced by the presently obtained atomic mobilities. Moreover, the reliability of the present atomic mobilities was further validated by reproducing the experimental composition profiles which were not utilized in the assessment procedure.

Thermodynamic re-assessment of the Fe-Gd and Fe-Sm binary systems

Abstract: Thermodynamic re-assessment of the Fe-Tm and Fe-Ho binary systems were carried out with the help of the CALPHAD method based on the previous optimizations and the critical review of the available experimental information in the published literature. The substitutional solution model was used to describe liquid phase and fcc-Fe, bcc-Fe, hcp-Tm, bcc-Ho and hcp-Ho solid solution phases and their excess terms of Gibbs energies were expressed with the Redlich-Kister polynomial. The intermetallic compounds, Fe17Tm2, Fe23Tm6, Fe3Tm, Fe2Tm, Fe17Ho2, Fe23Ho6, Fe3Ho and Fe2Ho, were treated as stoichiometric compounds considering the experimental heat capacity of two intermetallic compounds (Fe2Tm and Fe2Ho) in the low temperature range. Self-consistent thermodynamic parameters to describe the Gibbs energies of various phases in the Fe-Tm and Fe-Ho binary systems were obtained finally. The calculated results in this work are in good agreement with available phase equilibira data and thermodynamic data.

Experimental investigation of phase equilibria in the Ti-Fe-Cr ternary system

Abstract: Phase equilibria in ternary Ti-Fe-Cr system at 873 and 1173 K were investigated in this work. Based on the phase constitutions and phase compositions in 32 samples prepared using the equilibrated alloys, the isothermal sections of the Ti-Fe-Cr ternary system were established. For this system, there were six three-phase regions at both 873 and 1173 K, the phase relations at the studied two temperatures are almost the same. Thereinto, two tentative three-phase regions of βCr2Ti + β(Ti) + (Fe, Cr)2Ti and βCr2Ti + β(Ti) + αCr2Ti were deduced near the Ti-Cr side at 1173 K. The (Fe, Cr)2Ti phase has a large solubility of Cr, up to 59.1 at% at 873 K and 59.5 at% at 1173 K. Moreover, at 873 and 1173 K, the homogeneity ranges of the nearly linear ternary compounds τ1 were measured to be 49.9–72.1 at% Fe and 52.7–77.2 at% Fe, respectively, and the solubility of Cr in (Fe, Cr)Ti were 9.0 at% and 10.6 at%.

Critical evaluation and thermodynamic assessment of the MgO-V2O5 and CaO-V2O5 systems in air

Abstract: The MgO-V2O5 and CaO-V2O5 systems in air have been critically evaluated and thermodynamically assessed based on available experimental data. The liquid phase is described by the modified quasichemical model and all intermediate phases are treated as stoichiometric compounds. A set of self-consistent model parameters for all phases in both systems is obtained. The experimental phase equilibria and thermodynamic data in air are well reproduced within experimental error limits.

Thermodynamic modelling of Ti-Zr-N system

Abstract: Thermodynamic modelling of Ti-Zr-N system is performed using Calphad method coupled with ab initio calculations. The energies of formation of stable and metastable end-members of sublattice formulations of solid phases in Zr-N system and enthalpy of mixing of the mixed nitride (Ti, Zr)N ( δ ) are calculated using ab initio method. Phonon calculations are used to compute the Gibbs energies of stoichiometric ZrN and the mixed nitride δ . With the aid of experimental thermochemical and constitutional data from the literature along with the results of ab initio calculations, thermodynamic optimization is carried out to obtain the Gibbs energy model parameters.

First-principles calculations and thermodynamic modeling of the Sn-Ta system

Abstract: A thermodynamic description of the Sn-Ta system was developed using the CALPHAD (CALculation of PHAse Diagram) approach in combination with first-principles calculations. A positive enthalpy of mixing of the body centered cubic phase was predicted, using special quasirandom structures (SQS), indicating the tendency to form a miscibility gap. The finite temperature thermodynamic properties of Ta3Sn and TaSn2 were calculated by the Debye-Gruneisen model as well as phonon calculations using the supercell approach. The results from first-principles calculations along with the previously reported decomposition temperature of TaSn2, 868 °K, were used to evaluate the Gibbs energy parameters of the TaSn2, Ta3Sn intermetallics and the liquid phase. No decomposition temperature of Ta3Sn has previously been reported in the literature but was predicted in this work to be 2884 °K. The calculated phase diagram agrees well with available experimental information of the Sn-Ta system and also compares well with similar systems such as Nb-Sn and V-Sn.

First-principles study of the Cu-Pd phase diagram

Abstract: The equilibrium phase diagram of a Cu-Pd alloy has been computed using cluster expansion and Monte Carlo simulation methods combined with density functional theory. The computed phase boundaries show basic features that are consistent with the experimentally reported phase diagram. Without vibrational free energy contributions, the order-disorder transition temperature is underestimated by 100 K and the critical point is inconsistent with experimental result. The addition of vibrational free energy contributions yields a more qualitatively correct Cu-Pd phase diagram in the Cu rich region.

Thermochemical analysis for the reduction behavior of FeO in EAF slag via Aluminothermic Smelting Reduction (ASR) process: Part II. Effect of aluminum dross and lime fluxing on Fe and Mn recovery

Abstract: We investigated Fe recovery from EAF slag by means of aluminothermic smelting reduction (ASR) at 1773 K with Al dross as the reductant, especially the effect of the added amount of the fluxing agent CaO on the Fe recovery. The maximum reaction temperature calculated using FactSage™ 7.0 decreased with increasing CaO addition, but the experimentally measured maximum temperatures increased with increasing CaO addition. We calculated the amounts of various phases before and after Al dross addition under different conditions of added CaO. FeO and Al2O3 contents in molten slag sharply varied within the first 5 min of the reaction, stabilizing soon thereafter. The aluminothermic reduction of FeO appeared to proceed rapidly and in good stoichiometric balance, based upon the mass balance between the consumption of FeO and MnO (ΔFeO and ΔMnO) and the production of Al2O3 (∆Al2O3). Iron recovery from EAF slag was maximized at about 90% when 40 g of CaO was added to 100 g slag. Furthermore, Mn could also be reduced from the EAF slags by the metallic Al in the Al dross reductant. The solid compounds of spinel (MgO∙Al2O3) and MgO were precipitated from the slag during the FeO reduction reaction, as confirmed by means of XRD analysis and thermochemical computations. To maximize Fe recovery from EAF slag, it is crucial to control the slag composition, namely to ensure high fluidity by suppressing the formation of solid compounds.

Diffusivities and atomic mobilities for fcc Cu–Ni–Sn alloys

Abstract: Utilizing five groups of bulk diffusion couples together with electron probe microanalysis technique, the composition-dependent ternary interdiffusion coefficients in fcc Cu–Ni–Sn alloys at 1023 K were determined via the Whittle and Green method. The presently obtained interdiffusion coefficients at 1023 K as well as our previously measured ones at 1073 K were combined with the slightly modified thermodynamic descriptions of the fcc Cu–Ni–Sn phase to explore atomic mobilities of Cu, Ni and Sn in fcc Cu–Ni–Sn alloys within the CALPHAD framework. In order to be consistent with the thermodynamic description, atomic mobilities in binary fcc Ni–Sn alloys were re-evaluated in the present work. The quality of the assessed kinetic characteristics was confirmed by the comprehensive comparisons between various model-predicted diffusion behaviors and the experimental ones, including concentration profiles and diffusion paths.

Investigation of the phase equilibria in Ti-Ni-Hf system using diffusion triples and equilibrated alloys

Abstract: In present work, the phase equilibrium relations in the Ti-Ni-Hf ternary system, which are of great importance for the design of Ti-Ni based high temperature shape memory alloys, were investigated using diffusion triples and sixteen key equilibrated alloys. Based on the experimental results from electron-probe microscopy analysis (EPMA) and X-ray diffraction (XRD) techniques, two isothermal sections were constructed, which consist of 13 and 12 three-phase regions at 900 °C and 800 °C, respectively. Hf can substitute for Ti in TiNi and Ti 2 Ni phases increasing from 30, 62 at% at 800 °C to 36, 64 at% at 900 °C, respectively. The Hf 7 Ni 10 and Hf 9 Ni 11 phases show wide ternary composition ranges, while the solubility of Ti in HfNi 5 , Hf 2 Ni 7 , and HfNi phases are relatively limited. A new ternary phase of τ was detected for the first time, and the stoichiometry of τ phase is close to Ni:(Hf,Ti) = 11:14, with Ti substituting for Hf from ～5 at% to ～22 at%. The single-phase region of the τ phase became narrow as the decreasing of annealing temperature. Based on comparison of phase relations at 900 °C and 800 °C, it is speculated there is an invariant reaction TiNi + τ → HfNi + Ti 2 Ni at between 900 °C and 800 °C.