Z.P. Jin

Diffusion coefficients of some solutes in fcc and liquid Al: critical evaluation and correlation

The diffusion coefficients of several transition elements (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) and a few non-transition elements (Mg, Si, Ga, and Ge) in fcc and liquid Al are critically reviewed and assessed by means of the least-squares method and semi-empirical correlations. Inconsistent experimental data are identified and ruled out. In the case of the elements, for which plentiful experimental data are available in the literature, the least-squares analysis gives rise to the activation energies and pre-exponential factors in an Arrhenius equation. For the elements with limited experimental data or no data at all, the diffusion parameters are estimated from two semi-empirical correlations. In one correlation, the logarithmic pre-exponential factors are plotted against the activation energies for various elements in Al. In the other correlation, the activation energies are shown as a function of valences relative to Al. The diffusion coefficients calculated by using the evaluated diffusion parameters agree reasonably with the reliable experimental data. The proposed semi-empirical correlations are used to predict the diffusion coefficients of a few elements in liquid Al. A satisfactory agreement between the predicted and measured diffusion coefficients is obtained.

The Fe-Cu system: A thermodynamic evaluation

Thermochemical and phase diagram data in the Fe-Cu system have been critically evaluated by using phenomenological models for the Gibbs energy of various phases. A set of thermodynamic parameters more consistent with most of the selected experimental data than previous assess-ments has been obtained by a computerized least-squares method. Stable and metastable phase equilibria,T0 curves, and thermodynamic properties are calculated with the optimized param-eters. The calculated liquid/face-centered cubic (fcc)T0 curve and metastable liquid spinodal seem to permit an accurate prediction of maximum solid solubility obtained upon melt quenching in this system.

Thermodynamic reassessment of the AuIn binary system

Through CALPHAD method, the AuIn binary system has been thermodynamically reassessed. The excess Gibbs energies of the solution phases, liquid, fcc, α1, and hcp were formulated with Redlich-Kister expression, while the γ and Ψ phases with narrow homogeneity ranges were described with sublattice models, and other intermetallic phases were treated as stoichiometric compounds. A set of self-consistent parameters has been obtained, which can reproduce most experimental data of thermodynamic properties and phase diagram of this binary system. Additionally, the standard formation enthalpies of all intermediate phases have also been calculated.

Thermodynamic properties of the Al–Nb–Ni system

Abstract This paper provides a consistent thermodynamic data set for the whole Al–Nb–Ni ternary system via thermodynamic modeling. The order/disorder transitions between disordered bcc_A2 and ordered bcc_B2 phases as well as between disordered fcc_A1 and ordered L1 2 phases are treated using a two-sublattice model. The calculations indicate that the disordered and ordered phases can be described with a single equation. All of the experimental phase diagram data available from the literature are critically reviewed and assessed using thermodynamic models for the Gibbs energies of individual phases. Inconsistent experimental information is identified and ruled out. Optimal thermodynamic parameters are then obtained by considering reliable literature data. Comprehensive comparisons between the calculated and measured phase diagrams show that almost all the accurate experimental information is satisfactorily accounted for by the present thermodynamic description.

Thermodynamic re-assessment of Fe-Ti binary system

The Fe–Ti binary system was re-assessed using the CALPHAD method in order to improve the capability of being extrapolated to a ternary or higher-order system. Compared with previous assessments, the main focus was put on the thermodynamic description of the two intermetallic compounds Fe2Ti and FeTi. The C14_Laves phase Fe2Ti was described by the two-sublattice model, which is widely used at present. By checking the homogeneity range on the boundary of the ternary systems involving the binary, the phase boundary of this compound was further confirmed. The FeTi phase with a BCC_B2 crystal structure was treated as the ordered phase of the BCC_A2 phase and a unified Gibbs energy function was used to describe both the ordered and disordered phases. Reproduction of the specific heat capacities of these compounds was another aspect paid particular attention to. Comprehensive comparisons of the calculated and experimental results regarding the phase diagram and thermodynamic properties show a good agreement between them and prove the validity of the present thermodynamic description.

Thermodynamic assessment of the Au–Zn binary system

Abstract The phase diagram of the Au–Zn binary system may play an important role in developing new Au-base solders. In this paper, the Au–Zn binary system has been thermodynamically assessed with the CALPHAD method. Excess Gibbs energies of solution phases, liquid, fcc, hcp, and ϵ were formulated with the Redlich–Kister expression, while the intermediate phases were modeled with (Au,Zn)0.5:(Au,Zn)0.5 for β′, (Au)0.6:(Au,Zn)0.2:(Zn)0.2 for α1, (Au)0.64286:(Au,Zn)0.25:(Zn)0.10714 for α3, (Au,Zn)0.15385:(Au)0.15385: (Au,Zn)0.23077:(Zn)0.46153 for γ, and (Au)0.12:(Au,Zn)0.16:(Zn)0.72 for γ3, and the other phases including α2, ϵ′, Au5Zn3, γ2 and δ were treated as stoichiometric compounds according to their composition ranges. Based on the reported thermodynamic properties and phase boundary data, the thermodynamic parameters of these phases were optimized, which give a reasonable agreement between thermodynamic properties and phase diagram.

Thermodynamic optimization of Bi-Ni binary system

Based on the available experimental data, the Bi-Ni binary system was optimized thermodynamically by the CALPHAD method. The solution phases, including liquid, fcc_A1(Ni) and rhombohedral_A7(Bi), were described as substitutional solution phases, of which the excess Gibbs energies were expressed with the Redlich-Kister polynomial. The intermetallic compound, BiNi, was modeled using three sublattices (Bi) (Ni, Va) (Ni, Va) considering its crystal structure (NiAs-type) and the compatibility of thermodynamic database in the multi-component systems, while Bi3Ni was treated as a stoichiometric compound. Finally, a set of self-consistent thermodynamic parameters formulating the Gibbs energies of various phases in this binary system were obtained. The calculated results are in reasonable agreement with the reported experimental data.

A thermodynamic description of the B–Co system: modeling and experiment

Abstract The B–Co system is investigated via thermodynamic modeling and experiments. In the modeling section, all of the experimental phase diagram and thermodynamic data available from the literature were critically reviewed and assessed by using thermodynamic models for the Gibbs energies of individual phases. In the experimental section, 6 key alloys were prepared by arc melting Co slug and B pieces and annealing at 900°C for 9 days. Water-quenched samples were analysed by using X-ray diffraction, optical microscopy, electron probe microanalysis and differential thermal analysis techniques. The measured invariant reaction temperatures are: 1136 ± 2°C for Liquid (L) ↔ (αCo) + Co3B, 1157 ± 2°C for L + Co2B ↔ Co3B, 1263 ± 2°C for L ↔ Co2B + CoB, and 1358 ± 2°C for L ↔ CoB + B. A consistent thermodynamic data set for the B–Co system is finally obtained by considering the present experimental results and reliable literature data. Comparisons between the calculated and measured phase diagram and thermodynami...

Thermodynamic Modeling of the Au-Bi-Sb Ternary System

Based on the available experimental information, the Au-Bi binary system has been thermodynamically assessed using the CALPHAD method. The solution phases, including liquid, fcc_A1, and rhombohedral_A7, were modeled as substitutional solutions, while the intermediate compound Au2Bi was described as a stoichiometric compound. Combined with the available thermodynamic parameters of the Au-Sb and Bi-Sb binary systems, a thermodynamic description of the Au-Bi-Sb ternary system has been developed to reproduce the reported phase equilibria. The liquidus projection and several vertical and isothermal sections of this ternary system have been calculated, which are in reasonable agreement with the reported experimental data.

Development of an atomic mobility database for disordered and ordered fcc phases in multicomponent Al alloys: focusing on binary systems

Abstract An atomic mobility database for binary disordered and ordered fcc phases in multicomponent Al-Cu-Fe–Mg-Mn–Ni–Si–Zn alloys was established based on a critical review of diffusion data in various constituent binary systems via the DICTRA (DIffusion Controlled TRAnsformation) software package. The mobility parameters for self-diffusion in the metastable fcc structure were determined through a semi-empirical method. An effective strategy, which takes the homogeneity range and defect concentration into account, was used to optimize the atomic mobilities of L12 phase in the Fe–Ni system. Comprehensive comparisons between various calculated and measured diffusivities show that most of the experimental data can be well reproduced by the presently obtained atomic mobilities. The general agreement between the model-predicted concentration profiles and the experimental ones in the Al-Ni–Si, Al-Mg-Zn and Cu-Mn–Ni–Zn diffusion couples validates the potential application of the present atomic mobility database to predict the concentration profiles in higher order systems. An 8-elemental diffusion couple was also simulated with the present database.