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 thermodynamic database for the Al-Fe-Mg-Mn-Si system is developed based on the constituent binary, ternary, and quarternary systems. The computed phase diagrams agree well with the experimental data. The obtained database is used to describe the solidification behavior of Al 356.1 (91.95Al-0.46Fe-0.3Mg-0.32Mn-6.97Si, in wt.%) and Al 356.2 (92.77Al-0.08Fe-0.35Mg-6.8Si, in wt.%) under equilibrium and Gulliver-Scheil non-equilibrium conditions. The reliability of the established thermodynamic database is also verified by the good agreement between calculation and experiment for both equilibrium and Gulliver-Scheil non-equilibrium solidifications. Microstructure and microsegregation of the directionally solidified Al 356.1 alloy are investigated with a growth rate of 0.04445 cm s-1 and a temperature gradient of 45K cm-1. Fractions of solids formed are measured by using quantitative image analysis of back-scattered electron, and solute redistribution in the primary (Al) is determined by means of an area scan approach with a total of 2400 electron probe microanalysis point counts. A micromodel, which includes solid-state diffusion, secondary dendrite arm coarsening, and dendrite tip and eutectic undercooling, is coupled with a multicomponent phase diagram calculation engine (PanEngine) to predict the microstructure and microsegregation of the solidified alloy. Quantitative agreement of the model prediction with the experiment is obtained for concentration distributions in the primary (Al), the types and amounts of phases formed, and the solidification path.

A method to estimate the thermodynamic properties of ternary alloys from those of constitutive binary alloys was proposed. The thermodynamic data of binaries were calculated by Miedema's theory. The asymmetry of constitutive binary alloys in the ternary system was considered in the present extrapolating procedure. The dependence of asymmetric constituent on the choice in Toop's model was overcome. The present method was used to calculate the formation enthalpies of Fe-Ni-V alloys. The agreement between the calculation and experiment is reasonable. So the formation enthalpies of Fe-Al-RE (RE=lanthanide metal) ternary alloys were calculated with the present method. The relative stability of RE(Fe1-xAlx)13, RE2(Fe1-xAlx)17 and RE5(Fe1-xAlx)17 were also studied with the present method.

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 L12 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 optimizations of the Mo-Nb, Mo-Ta, and Nb-Ta binary systems were performed by considering the experimental phase diagram and thermodynamic data available from the literature. The Mo-Nb-Ta ternary system was then synthesized from the descriptions of the binary sides. The calculated thermodynamic properties as well as phase diagrams for the binary systems agree well with the experimental ones. In the case of the ternary system, several isothermal sections were calculated by extrapolation from the three boundary systems. The model-predicted liquidus temperatures in the ternary system are in reasonable agreement with the experimental data. The computed liquidus projection and a set of model parameters describing the Gibbs energies of the assessed phases are also presented.

This paper provides a consistent thermodynamic data set for the whole Cr-Nb-Ni ternary system via thermodynamic modeling. 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. The ternary liquid and (Ni) phases are described with a regular solution model. The two-sublattice model is used to model the binary phases NbCr2(HT), NbCr2(LT), NbNi3, and Nb6Ni7. In order to reproduce the measured solid solubilities in the ternary system and to reduce the number of adjustable parameters, the third element is assumed to be anti-site atoms in only one sublattice. Optimal thermodynamic parameters are obtained by considering reliable literature data. Comprehensive comparisons between calculated and measured phase diagrams show that all the accurate experimental information is satisfactorily accounted for by the present thermodynamic description. The thermodynamic parameters obtained can also describe the diffusion paths observed for the diffusion couples between Nb and several Cr-Ni alloys annealed at 1002℃

The modified cluster-site approximation (CSA) model has been used to model the f.c.c. phases (ordered L12 and disordered A1) in the Ni-Al system. The CSA model has the advantage over the cluster variation method (CVM) in that the independent variables in the free energy functional are the site probabilities and not the cluster probabilities. Unlike the zeroth approximation, however, the CSA takes short-range order into consideration, an essential requirement for describing phases that undergo an order/disorder transition, as does the f.c.c. phase in the Ni-Al system. By using the modified CSA model, we have been able to obtain an improved phenomenological description of this system with the use of fewer model parameters than used in previous descriptions. The topology of the calculated metastable f.c.c. phase diagram is similar to the one obtained using a 'first-principles'-CVM approach, whereas the f.c.c. phase diagrams based on the previous phenomenological descriptions are unsatisfactory.

The Al-Be system is investigated via three steps. In the first step, all of the experimentally measured phase diagram and thermodynamic data available in the literature are critically reviewed. On the basis of the assessed phase diagram, in the second step, eight decisive samples are prepared by arc melting of Al and Be pieces and annealing at 600℃ for eight days. Water-quenched samples are analyzed using differential thermal analysis (DTA), X-ray diffraction (XRD), optical microscopy, and scanning electron microscopy (SEM) techniques. In the last step, an optimal thermodynamic data set for the Al-Be system has been obtained by considering the present experimental data and the reliable literature data. The calculated phase diagram and thermodynamic properties agree well with the accurate experimental values.

The isothermal section at 950℃ of the Co-Nb-Ti system was investigated using diffusion couples and six ternary alloys. The specimens were examined by means of optical microscopy, scanning electron microscopy and electron probe microanalysis. No ternary compound was found. Nine three-phase equilibria were observed. The binary intermediate phases NbCo3 and Nb2Co7, the existence of which is still controversial in the literature, were observed at 950℃. The solubilities of Ti in Nb2Co7, NbCo3, γ-NbCo2 and μ-Nb6Co7 were determined to be 1.9, 16.4, 14.4 and 17.4 at.%, respectively. The solubilities of Nb in TiCo3, TiCo2(h), TiCo2(c), TiCo and Ti2Co were determined to be about 5.7, 11.0, 2.6, 13.6 and 3.1 at.%, respectively.

The Al-Y system is reassessed based on a critical literature review involving recently measured phase diagram and thermodynamic data. In the thermodynamic optimization, the liquid phase is described by using a substitutional solution model. Al3Y, AlY, Al2Y3 and AlY2 are modeled as stoichiometric ones. A two-sublattice model (Al,Y)2(Al,Y)1 has been used to describe Al2Y. A set of self-consistent thermodynamic parameters for the Al-Y binary system has been obtained by means of a CALPHAD approach applied to the selected experimental data. The reliable experimental phase diagram data and thermodynamic properties are well reproduced with the optimal thermodynamic parameters. The observed solidification paths for as-cast alloys can also be described reasonably using the present parameters. Significant improvement has been made, compared with previous assessments.