Calphad-computer Coupling of Phase Diagrams and Thermochemistry最新文献

The Sn–Zr system was re-assessed thermodynamically. Gibbs free energies of the intermetallic compounds of this system were calculated by DFT phonon calculations which can give more reliable information owing to considering the contributions of lattice vibration and electric thermal excitation. Newly published valuable experimental data of liquidus, solidus and invariant reactions of this system were used for the first time in the optimization of the model parameters. It is shown that the previous thermodynamic models, where the Gibbs free energies of formation at different temperatures were replaced by energies of formation at 0 K, overestimated obviously the stability of all the compounds of this system. The thermodynamic model for the Sn–Zr system established in this work would give more solid prediction of phase structures and thermodynamic properties for materials containing Sn–Zr system.

Co–Fe–Ge is an important material system for magnetic and catalyst applications. However, phase equilibria information of the Co–Fe–Ge ternary system is limited. Ternary Co–Fe–Ge alloys equilibrated at 950 °C were prepared. The microstructures, chemical compositions and crystal structure of each phase were determined. The phase equilibria isothermal section at 950 °C of the Co–Fe–Ge ternary system was then proposed. A continuous solid solution phase was formed between the Co₅Ge₃ and Fe₅Ge₃ phases and was labeled the β(Co,Fe)₅Ge₃ phase. There are five three-phase regions in the system at 950 °C. A wide α₂ single-phase, and liquid phase regions with large composition ranges being confirmed at the Ge-poor and Ge-rich sides, respectively.

The partial phase equilibria of the Ni–Al−Dy ternary system have been systematically investigated via experimental analyses and thermodynamic modeling. Using the equilibrated alloy method, the 1150 °C and partial 800 °C isothermal sections of the Ni–Al−Dy ternary system and related Al–Dy binary system were constructed based on scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. Twelve three-phase regions were confirmed and four three-phase equilibria regions were speculated at 1150 °C, eight three-phase regions were determined at 800 °C, and five kinds of primary solidification regions, DyAl₂, τ7, τ5, NiAl and Ni₂Al₃ were observed. A new ternary compound τ12 was discovered, which was stable at 800 °C and disappeared at 1150 °C, the τ1 phase was not stable at 800 and 1150 °C isothermal sections; the ternary compound τ11 was confirmed to be stable at 800 °C. In addition, the primary solidification phases were also identified, and five different primary solidification phases were found. Based on the experimental results available in this study and the literature, the thermodynamic modeling of the Ni–Al–Dy ternary system was obtained using the CALPHAD method. A set of self-consistent thermodynamic parameters for the Ni–Al–Dy ternary system was first obtained with a satisfactory agreement between the experimental and calculated results.

The phase diagram of the Gd-Mn-Ga ternary system is a very important tool for the exploration and development of rare earth Heusler alloys with excellent physical properties, such as magnetic properties, half-metallic properties, ferromagnetic shape memory effect, magnetocaloric effect, ect. In this study, the alloy samples were prepared using a vacuum arc melting furnace, and the 873 K isothermal section of the Gd-Mn-Ga (≤50 at.%Ga) ternary alloy phase diagram was determined by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy spectrometry (EDS). The isothermal section consists of 22 single-phase regions, 44 two-phase regions, and 23 three-phase regions with the presence of 6 ternary compounds, GdMnGa, Gd₂MnGa₆, Gd₂Mn₁₅Ga₂, Gd₂Mn₁₁Ga₆, GdMn_0.56Ga_1.44, and GdMn_0.37Ga_1.63. The solid solubility ranges of Ga in β-Mn and Gd₂Mn₁₅Ga₂ are 5.0–18.1 at.%Ga and 10.5–25.0 at.% Ga. The maximum solid solubility of Ga in α-Mn, GdMn₁₂, and Gd₆Mn₂₃ are 2.0, 2.7, and 7.3 at.% Ga, respectively. The maximum solid solubility of Mn in GdGa₂ is determined to be 13.1 at.% Mn.

Ti–Al–V alloys have received considerable attention owing to their excellent high-temperature mechanical properties. After conducting a critical review of the available experimental data for the ternary Ti–Al–V system, a thermodynamic assessment of the system was carried out over the entire composition and a wide temperature range utilizing the CALPHAD method. The extensive homogeneity ranges of the ${\alpha }_2$ and $\gamma$ phases were satisfactorily reproduced. Of particular significance was the first accurate description of the phase equilibria at 1573 K. The model parameters obtained in this study well represented the thermochemical properties and phase equilibria of the experimental data. Furthermore, the enthalpies of the widely used Ti alloy Ti–6Al–4V were reproduced using the thermodynamic description established in this study. Thus, this study provides a reliable basis for guiding the development and design of Ti–Al–V alloys.

Ca₃TiFe₂O₈ (abbreviated as CTF), which is a significant mineral phase in the sinter of titanium-containing iron ore, was successfully prepared by solid-state reaction (calcined at 1553 K for 24 h) by using analytical reagents in this study. The metallurgical performance (melting performance and reduction behavior) was systemically characterized and the enthalpy change data of CTF was tested. The results show that softening temperature, melting temperature, and flowing temperature of CTF were 1691 K, 1734 K, and 1753 K, respectively. The non-isothermal reduction results revealed that CTF was reduced to Fe, CaO, and perovskite in a single step, and the CTF reduction was completed when the temperature reached 1423 K. The results of isothermal reduction shows that the reduction degree of CTF was 89% when reduced at 1173 K for 79.2 min, and the order of reduction performance was Fe₂O₃ > Fe₃O₄ > CaO∙2Fe₂O₃ > CaO∙Fe₂O₃> Ca₃TiFe₂O₈> 2CaO∙Fe₂O₃> Ca₃Fe₂Si_1.58Ti_1.42O₁₂.

A novel second-nearest-neighbor (2NN) modified embedded atom method (MEAM) potential for Zr–C system has been developed. The lattice constants, formation enthalpy, mechanical properties of stoichiometric ZrC have been reproduced. The melting point from the new 2NN-MEAM potential is 3436 K, which is coincident with the experimental melting point, ∼3530 K. The properties of sub-stoichiometric ZrC_x with ordered or disordered carbon vacancy have also been examined with the new potential. The results for ordered sub-stoichiometric ZrC_x agree well with the experimental data and/or first-principles calculations. The lattice parameter, elastic properties, thermodynamic properties change with the C/Zr ratio have been studied. The predicted relationships between the properties versus C/Zr ratio coincide with available experimental results. These results indicate the present 2NN-MEAM potential is suitable for atomic scale simulation of ZrC.

The Ta–Ge system was thermodynamically modeled for the first time using the CALPHAD method incorporating both literature-derived phase equilibria data and new enthalpy of formation values for the intermetallic compounds. Density Functional Theory (DFT) calculations were employed to accurately determine enthalpy of formation values for key Ta–Ge compounds. The stable intermetallic phases (i.e., αTa₃Ge, βTa₃Ge, βTa₅Ge₃, and TaGe₂) were described as stoichiometric phases while the Liquid (L), Ta-rich solid solution (BCC-A2), and Ge-rich solid solution (Diamond-A4) were modeled as solution phases using the Compound Energy Formalism. Excess terms were described by the Redlich-Kister polynomials. The present thermodynamic model accurately describes phase equilibria and thermodynamic data, providing a reliable guide for designing alloys containing Ta and Ge.

A description of the thermodynamic properties of FCC Pd above room temperature was developed by Dinsdale (1991) by relying on the heat capacity ($C_P$) measurements by Vollmer and Kohlhaas (1969). A subsequent assessment by Arblaster (1995) relied upon a combination of the enthalpy measurements by Cordfunke and Konings (1989) with the $C_P$ data reported by Miiller and Cezairliyan (1980). For temperatures in the range 400 K < T < 1200 K the $C_P$ values recommended by Dinsdale are smaller than those by Arblaster, with a maximum discrepancy of about 1.5 J/K.mol at 800 K. Later on, Milošević and Babić (2013) reported new $C_P$ data, which suggest that the discrepancy in the mentioned temperature range might be diminished. However, in the re-assessment reported by Arblaster (2018), the results by Milošević and Babić were not relied upon. Motivated by these various problems, exploratory Molecular Dynamics (MD) simulations of the thermal properties of FCC Pd were performed using the LAMMPS code and the Embedded Atom Model (EAM) interatomic potential developed by Sheng et al. (2011). The MD work predicted enthalpy values that are in reasonable agreement with the data of Milošević and Babić (2013). In view of this result, the full experimental database of $C_P$ and enthalpy measurements has been reanalyzed using a Maier-Kelley type thermodynamic model which accounts phenomenologically for the vibrational and electronic contributions to $C_P$. Systematic discrepancies between the enthalpy measurements and the direct determinations of $C_P$ are reported. An expression representing what is considered as the best possible account of the reliable experimental information available is presented.