Thermodynamic assessment of the phase diagrams of the Cu-Sb and Sb-Zn systems

Thermodynamic assessments have been made for the Cu-Sb and Sb-Zn binary systems by means of the CALPHAD technique. The Gibbs energies of the liquid, bcc, and fcc phases are described by a substitution solution model and a Redlich-Kister formalism. All of the compounds were treated as stoichiometric compounds. Moreover, the liquidus temperatures of the Zn-rich portion in the Sb-Zn system were measured to check the unusual shape reported by previous work. It was confirmed that the liquidus line is not peculiar but smooth. A consistent set of the thermodynamic parameters was optimized to obtain a better fit between calculated results and experimental data including phase diagram and thermodynamic quantities.     

Thermodynamic assessments of the phase diagrams of the hafnium-vanadium and vanadium-zirconium systems

Thermodynamic assessments have been made for the hafnium-vanadium (Hf-V) and vanadium-zirconium (V-Zr) systems using the Calphad-Thermocalc approach. The Gibbs energies of the liquid, body-centered cubic, and close-packed hexagonal phases were described by a substitution solution model with a Redlich-Kister formalism to express the excess Gibbs energy. The C15-Laves phase was treated first as stoichiometric and then with a composition range. A consistent set of optimized thermodynamic parameters was obtained, and calculated phase equilibria were compared with the experimental data. The enthalpy of formation of the C15-Laves phase was calculated equal to approximately −3 and −5 kJ/mol, respectively, in the Hf-V and V-Zr systems, which is in good agreement with predicted values.     

Thermodynamic database of the phase diagrams in Cu-Fe base ternary systems

A thermodynamic database of the Cu-Fe-X [X: aluminum (Al), cobalt (Co), chromium (Cr), manganese (Mn), molybdenum (Mo), niobium (Nb), nickel (Ni), vanadium (V)] systems was developed by the CALPHAD (Calculation of Phase Diagrams) method, where the Gibbs energies of solution phases such as the liquid, face-centered-cubic (fcc), body-centered-cubic (bcc), and hexagonal-close-packed (hcp) phases are described by the subregular solution model, while the those of the bcc phase in the Cu-Fe-Al system and of all compounds are described by the sublattice model. The thermodynamic parameters describing Gibbs energies of the different phases in this database were evaluated by fitting the experimental data for phase equilibria and thermodynamic properties. On the basis of this database, much information concerning stable and metastable phase equilibria of isothermal and vertical sections, molar fractions of constituent phases, the liquidus projection, etc., can be predicted. This database is expected to play an important role in the design of Cu-Fe base alloys.     

Thermodynamic database of the phase diagrams in the Mg-Al-Zn-Y-Ce system

The Mg-Al-Zn-Y-Ce system is one of the key systems for designing high-strength Mg alloys. The purpose of the present article is to develop a thermodynamic database for the Mg-Al-Zn-Y-Ce multicomponent system to design Mg alloys using the calculation of phase diagrams （CALPHAD） method, where the Gibbs energies of solution phases such as liquid, fcc, bcc, and hcp phases were described by the subregular solution model, whereas those of all the compounds were described by the sublattice model. The thermodynamic parameters describing Gibbs energies of the different phases in this database were evaluated by fitting the experimental data for phase equilibria and thermodynamic properties. On the basis of this database, a lot of information concerning stable and metastable phase equilibria of isothermal and vertical sections, molar fractions of constituent phases, the liquidus projection, etc., can be predicted. This database is expected to play an important role in the design of Mg alloys.     

Au-Ag-Al系相图的热力学优化和计算

使用计算相图方法(CALPHAD)计算Au-Ag-Al的三元相图时,三个边际二元相图(Au-Al,Au-Ag,Ag-Al)的准确性对三元相图的计算有很大的影响,目前Au-Al边际二元相图存在着一定的矛盾。在综合评估Au-Al体系实验数据的基础上,优化和计算了Au-Al合金体系的平衡相图,使用置换式溶体溶液模型描述Au-Al体系中液相、Bcc和Fcc相的吉布斯自由能,分别用亚点阵模型(Al)(Au)4、(Al)3(Au)8、(Al)(Au)2、(Al)(Au)和(Al,Au)2(Al,Au)描述AlAu4、Al3Au8、AlAu2、AlAu和Al2Au相,通过Pandat软件优化得到一组各相的热力学参数,计算得到的Au-Al相图与实验数据和热力学数据相吻合。结合Au-Ag和Ag-Al的热力学参数,计算了Au-Ag-Al液相面投影图和等温截面图,液相面投影图显示该三元系存在8个四相平衡反应,对Au-Ag-Al合金的研究具有指导意义。     

The phase diagrams of the Sc---Sn and Sc---Pb systems

The phase diagrams of the Sc---Sn and Sc---Pb systems have been investigated using differential thermal analysis (DTA), metallographic analysis, X-ray diffraction (XRD) and electron microscopy.

The Sc-rich side of both systems (0–30 at.% Sn or Pb) has not been studied owing to the high melting temperatures of the corresponding alloys and contamination of the samples by the container material (Mo).

The two systems are very similar to one another; with tin, however, two more intermediate phases are formed. Sc₅X₃ and Sc₆X₅ compounds are isomorphous, Mn₅Si₃ and Ti₆Ge₅ types respectively. ScSn₂ is a new intermetallic compound with a new structure type. The impossibility of finding single crystals for XRD prevented the determination of the structure and then of the exact stoichiometry for ScSn which was assigned taking into account the results of DTA, XRD, optical and electronic microanalysis. Sc₅X₃, different from the other intermediate phases, shows appreciable solid solution range towards compositions richer in X.     

Thermodynamic analysis of some binary phase diagrams involving liquid crystals

A computer-coupled thennodynamic/phase diagram analysis was performed on the phase diagram data of seven binary systems involving liquid crystals. These include five systems based on a homologous series of compounds and two others having 1:1 intermediate compounds. The excess Gibbs energies of the solution phases were thereby calculated, and evaluated phase diagrams were generated that are thermodynamically self-consistent. The results are discussed in the light of what is known about excess solution properties in such systems. The usefulness of the thermodynamic analysis is examined with respect to the prediction of the eutectics of ternary and higher order liquid crystal mixtures. The “Equal G Analysis” is also briefly discussed with reference to the estimation of the nonidealities of mesophase solutions.     

Thermodynamic analysis of some binary phase diagrams involving liquid crystals

A computer-coupled thennodynamic/phase diagram analysis was performed on the phase diagram data of seven binary systems involving liquid crystals. These include five systems based on a homologous series of compounds and two others having 1:1 intermediate compounds. The excess Gibbs energies of the solution phases were thereby calculated, and evaluated phase diagrams were generated that are thermodynamically self-consistent. The results are discussed in the light of what is known about excess solution properties in such systems. The usefulness of the thermodynamic analysis is examined with respect to the prediction of the eutectics of ternary and higher order liquid crystal mixtures. The “Equal G Analysis” is also briefly discussed with reference to the estimation of the nonidealities of mesophase solutions.     

Phase equilibria and phase diagrams in carbide systems

Experimental data on phase equilibria in the Co-Ni-W-C, Fe-Ni-W-C, and Co-Ti-W-C systems are presented. This information includes the equilibria between the liquid phase at 1350 °C and tungsten carbide (WC) in the Fe-Ni-W-C system as well as the solubility of graphite in these liquids. Information on the solubility of graphite in the Co-Ni-W-C liquid is also presented. The majority of this information was used earlier for phase diagram evaluations by the ThermoCalc group at the Royal Institute of Technology in Stockhohn in collaboration with LTPCM-ENSEEG in Grenoble. Comparisons are made between calculated phase equilibria based on the results of their evaluations and the experimental phase equilibria. Heat treatments of Co-Ti-W-C alloys at 1100 °C resulted in the precipitation of a hexagonal tungsten-titanium carbide with a composition corresponding to the formula W₄Ti₂C_3-x:. To our knowledge, this carbide has not been mentioned in the literature. B. Uhrenius is now at AB Sandvik Hard Materials, S-126 80 Stockholm, Sweden. K. Forsén is now at Ericsson Oy, Helsinki, Finland. I. Andersson is now at Elektrokoppar AB, Helsingborg, Sweden.     

The phase diagrams and thermodynamics of the ZrO2-CaO-MgO and MgO-CaO systems

The phase diagram of the ZrO₂-CaO-MgO system was studied both experimentally and computationally. Using the newly developed isoplethal map method, the partial isotherms of the system at 1523,1573,1683, and 1773 K were determined with better accuracy than reported in the literature. The enthalpies of formation of the fluorite cubic structure, with reference to the monoclinic zirconia and the periclase CaO and MgO, were measured calorimetrically. With optimized binary data for the systems ZrO₂-MgO and ZrO₂-CaO, which were reported elsewhere, and the data for MgO-CaO briefly discussed in this paper, the thermodynamics and phase diagram data of the ternary system were assessed by means of computational optimization. Good agreement between the experimental and computational results were obtained. The liquidus surface was also predicted and compared with the available experimental results.     

Thermodynamic study of CVD–ZrO2 phase diagrams

Chemical vapor deposition (CVD) of zirconium oxide (ZrO₂) from zirconium acetylacetonate Zr(acac)₄ has been thermodynamically investigated using the Gibbs’ free energy minimization method and the FACTSAGE program. Thermodynamic data Cp°, ΔH° and S° for Zr(acac)₄ have been estimated using the Meghreblian–Crawford–Parr and Benson methods because they are not available in the literature. The effect of deposition parameters, such as temperature and pressure, on the extension of the region where pure ZrO₂ can be deposited was analyzed. The results are presented as calculated CVD stability diagrams. The phase diagrams showed two zones, one of them corresponds to pure monoclinic phase of ZrO₂ and the other one corresponds to a mix of monoclinic phase of ZrO₂ and graphite carbon.     

Correlations between phase diagrams and thermodynamic data for metal hydride systems

A series of correlations between the phase diagrams and enthalpic data are developed for metal hydride systems. The value of these correlations lies in their providing criteria for checking the consistency of the thermodynamic behavior for these systems. The correlations are illustrated using some experimental thermodynamic data and the accompanying phase diagrams for metal hydrides from the literature.