Journal of Phase Equilibria and Diffusion最新文献

Reliable thermodynamic and kinetic databases are essential for designing and developing novel magnesium (Mg) alloys for elevated-temperature applications in the automotive and aerospace industries. This study investigated diffusion behaviors of HCP Mg-Ag-Sn alloys by four sets of three diffusion couples annealed at 450, 500, and 550 °C, respectively. Interdiffusion and impurity diffusion coefficients at the three annealing temperatures were extracted using the forward-simulation method. The determined diffusion coefficients, combined with prior results in the literature, were then used to assess atomic mobilities for the HCP phase of the Mg-Ag-Sn system. This assessment was conducted using the DICTRA and the TCMG5 thermodynamic database within the Thermo-Calc software. Comprehensive comparisons between calculated and experimental diffusion coefficients yielded an excellent agreement. The atomic mobilities were also further validated by appropriate predictions of concentration profiles and diffusion paths observed in independent diffusion couple experiments performed at 525 °C for 18 hrs. It has been found that the addition of Sn and Ag both increase the diffusivity of Ag in HCP Mg and Sn in HCP Mg in the stable temperature range of HCP Mg, respectively. This improved understanding of the kinetics in the Mg-Ag-Sn ternary system is essential for controlling diffusion-dependent properties such as coarsening and, therefore, the mechanical properties of Mg-Ag-Sn alloys at elevated temperatures.

Exploring the correlation between the density and the thermo-physical properties of the Al₂O₃-CaO-MgO-SiO₂ quaternary slag system is a subject of great interest in the domain of high alumina slag systems. This work attempts to establish correlations between (a) molar volume/density with enthalpy of mixing and (b) molar volume/density with slag viscosity, for the quaternary slag systems. The former is targeted based on existing models to determine the slag density and enthalpy of mixing first and then to develop machine-learning models which can suitably extrapolate the enthalpy of mixing as a function of slag composition, temperature and density. The volume shrinkage and the exothermic enthalpy of mixing between the slag constituent components are correlated in the current work. The later part would involve the conjunction of two hybrid machine-learning models, one for predicting slag viscosity as a function of slag compositions and temperature, and the other which predicts slag viscosity with the incorporation of slag density. The work will facilitate the establishment of two novel quantitative relationships that could provide better insights into the blast furnace quaternary slag systems.

Interactions of Ag and Sb(III) and Sn(IV) sulfides were investigated by x-ray diffraction, differential thermal analysis and microstructure analysis methods. The quaternary compound Ag₁₁Sb₃SnS₁₂ was found for the first time in the Ag₂S-Sb₂S₃-SnS₂ system at 500 K (227 °C) at the intersection of AgSbS₂-Ag₈SnS₆ and Ag₃SbS₃-Ag₂SnS₃. The compound melts congruently at 920 K (647 °C) and has a polymorphous transition at 646 K (373 °C). The quasi-ternary system is characterized by solid solution ranges of the binary compounds Ag₂S, Sb₂S₃, SnS₂, ternary Ag₃SbS₃, AgSbS₂, Ag₈SnS₆, Ag₂SnS₃ and quaternary compound Ag₁₁Sb₃SnS₁₂. The separation of the composition triangle into 10 single-phase, 18 two-phase, and 9 three-phase fields was established. Seven vertical sections were investigated of which five are quasi-binary (Ag₃SbS₃-Ag₈SnS₆, Ag₃SbS₃-Ag₂SnS₃, AgSbS₂-Ag₈SnS₆, AgSbS₂-Ag₂SnS₃, AgSbS₂-SnS₂). The AgSbS₂-Ag₄Sn₃S₈ and AgSbS₂-Sb₂SnS₅ sections are non-quasi-binary due to peritectic formation of Ag₄Sn₃S₈ and Sb₂SnS₅. The liquidus surface projection of the Ag₂S-Sb₂S₃-SnS₂ system consists of 10 fields of primary crystallization of the solid solutions α-Ag₂S, β-Sb₂S₃, γ-SnS₂, δ-Ag₃SbS₃, ε′-AgSbS₂, ζ-Ag₈SnS₆, η-Ag₂SnS₃, σ-Ag₁₁Sb₃SnS₁₂ and compounds Ag₄Sn₃S₈ and Sb₂SnS₅. These are separated by curves of monovariant equilibria that converge at 9 ternary invariant points (7 eutectic (E₁-E₇) and 2 quasi-peritectic (U₁, U₂)).

The thermodynamic optimization of the Gd-Cd binary system was carried out with the help of CALPHAD (CALculation of PHAse Diagram) method., GdCd₃, Gd₁₃Cd₅₈ and GdCd₈ have been treated as stoichiometric compounds while a solution model has been used for the description of the liquid, HCP_A3 (αGd), BCC_A2 (βGd) and HCP_A3 (Cd) phases. The intermetallic compounds GdCd,α-GdCd₂, β-GdCd₂, Gd₁₁Cd₄₅ and GdCd₆, which have homogeneity ranges, were treated by a two-sublattice model. The calculations based on the thermodynamic modeling are in a good agreement with the phase diagram data and experimental thermodynamic values.

The energy crisis and climate change have promoted a growing interest in non-fossil sources, such as nuclear, with uranium carbides being seen as potential fuel candidates for Generation IV nuclear reactors. However, the need of accurate thermophysical data for the fuel and its compatibility with core materials during the extreme fission conditions is still an issue. Here a study of the ternary uranium-iron-carbon system performed at 1100 °C using powder x-ray diffraction and Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry is presented. The U-Fe-C isothermal section is characterized by two ternary compounds, thirteen 3-phase regions and five 2-phase regions. UFeC₂ and ~ U₁₁Fe₁₂C₁₈ were confirmed to be present at 1100 °C and crystallize in structures related to the binary uranium carbides. UFeC₂ crystallizes in an original structure type, a distorted variant of the UCoC₂ structure, with space group P4/n and a = 3.503(5) Å and c = 7.405(5) Å lattice parameters. ~ U₁₁Fe₁₂C_18, has a crystal structure related to the Th₁₁Ru₁₂C₁₈ structure-type (space group I (overline{4 }) 3m) with the lattice parameter a ≈ 10 Å. Furthermore, an island of a α-UC₂-based phase with 32U:4Fe:64C composition was found in the 1100 °C isothermal section, indicating the inclusion of Fe in the α-UC₂ binary compound.

Ternary alloys samples with 22, 25 and 23 different compositions were prepared for determining isothermal sections at 1123, 1223 and 1373 K, respectively. The microstructures, phase constituents and phase compositions of the annealed Cu-Nb-Ni alloys were analyzed by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD) methods. Two three-phase regions, (text{fcc} + {text{NbNi}_{{3}}}+{text{Nb}_7}{text{Ni}_6}), fcc + bcc(Nb) + Nb₇Ni₆, and three two-phase regions, (text{fcc} + {text{NbNi}_{{3}}},{text{Nb}_7}{text{Ni}_{{6}}}+{text{NbNi}_{{3}}}), fcc + Nb₇Ni₆, are determined for isothermal sections at 1123 and 1223 K. Two three-phase regions, (text{liquid} + {text{NbNi}_{{3}}}+{text{Nb}_7}{text{Ni}_6}), liquid + bcc(Nb) + Nb₇Ni₆, and three two-phase regions, (text{fcc} + {text{NbNi}_{{3}}},{text{Nb}_7}{text{Ni}_{{6}}}+{text{NbNi}_{{3}}}), liquid + Nb₇Ni₆, are determined for isothermal sections at 1373 K. The solubilities of Cu in NbNi₃ and Nb₇Ni₆ were determined to be ~ 9.6 at.% and ~ 11.4 at.% at 1123 K, ~ 10.8 at.% and ~ 12.4 at.% at 1223 K and ~ 11.2 at.% and ~ 12.8 at.% at 1373 K, respectively. No ternary compounds were found. Based on the experimental phase equilibria data from the literature and the present work, a thermodynamic description of the Cu-Nb-Ni system was carried out by CALPHAD method. The substitutional solution model and sublattice model were employed to describe the solution phases and intermediate phases, respectively. A set of self-consistent thermodynamic parameters of the Cu-Nb-Ni system was conclusively obtained. Most of the reliable experimental data were reproduced by the present thermodynamic modeling.

Combination of the experimental measurements of diffusion behavior and kinetic computational simulation provides a unique tool to probe the design of multi-component refractory alloys with excellent properties. In this work, for the first time, the determination of the interdiffusion coefficients of bcc phase in Mo-Zr system and Mo-Nb-Zr ternary system as well as the relevant atomic mobility parameters of Mo, Nb and Zr in BCC phase are investigated systematically. The interdiffusion coefficients of bcc phase in Mo-Zr binary alloys and Mo-Nb-Zr ternary alloys at 1423-1523 K were measured by solid-phase diffusion couple method combined with Boltzmann-Matano method and Matano-Kirkaldy method, respectively. Simultaneously, the quite steep Mo concentration gradients of the corresponding ternary diffusion couples in the Mo-Nb-Zr system are observed in this study, and the contributions of which are carefully evaluated in the subsequent extraction of the ternary interdiffusion coefficients for the Mo-Nb-Zr system. On the basis of the determined interdiffusion coefficients of Mo-Zr system and Mo-Nb-Zr system in this work, along with the relevant thermodynamic parameters, the atomic mobility parameters of Mo, Nb and Zr in BCC phase were evaluated, which are incorporated into the atomic mobility database of bcc phase in Nb-Mo-Ti-Zr multi-component system. In addition, the component distance curves of a series of diffusion couples are simulated by applying the established atomic mobility database. The consistency between the simulated results and the measured values further verifies the reliability of the work.

The Sm–Ni–Al phase relationships at 800 °C have been investigated by using several well–focused experimental techniques such as X–Ray Powder Diffraction (XRPD), Light Optical Microscopy (LOM) and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Microprobe Analysis (EPMA). The isothermal section of the Sm–Ni–Al system at 800 °C was constructed according to the present experimental results. More than 50 alloys have been synthesized and characterized in the 30–100 at.% Al region. At 800 °C, 9 intermetallic phases have been confirmed, characterized and their relationships have been established. In the Al-rich corner, the presence of two ternary invariant reactions have been postulated whilst along the 16.67 at.% Sm isopleth, the presence of two structurally related extended solid solutions have been observed. The determined phase equilibria at 800 °C are discussed and compared with the isothermal section at 500 °C already reported in literature.

In the steam turbine circuit of advanced ultra supercritical power plants dissimilar joints of alloy 617 and 10Cr steel are unavoidable due to economic reasons. In these joints diffusional interaction causing change in microstructure is identified as possible reason for failure during service. To investigate the interdiffusion driven structural changes, alloy 617/10Cr steel diffusion couples were fabricated. To achieve good metallurgical bond between Fe- and Ni-based alloys and to study diffusional transformations under accelerated conditions, diffusion couples were prepared by annealing in the temperature range of 1000-1100 °C for 3-8 h. For all conditions heat treatment interaction zones were wider in alloy 617 (150-200 μm at 1050 °C, 8 h) than in 10Cr steel (15-16 μm at 1050 °C, 8 h) and the phase stability at the interface was studied using electron microprobe and x-ray diffraction. Average effective interdiffusion coefficients were calculated using Dayananda’s approach. While the diffusivities of substitutional solutes were similar in alloy 617 (0.31-0.42 × 10⁻¹⁵ m²/s at 1050 °C), they differed in 10Cr steel in the following sequence: (tilde{D}_{{{text{Cr}}}}) > (tilde{D}_{{{text{Fe}}}})≈(tilde{D}_{{{text{Ni}}}}) > (tilde{D}_{{{text{Co}}}}.) Further, multicomponent interdiffusion profiles were predicted using homogenization model in DICTRA and an integrated approach combining DICTRA with Thermo-Calc helped in understanding the experimental observations on the interface microstructure.

A new thermodynamic assessment of the Co–Ti system is presented on the basis of the literature data concerning phase equilibria and thermodynamics. A set of parameters of Gibbs-energy expressions for phases is obtained by means of CALPHAD approach. Excess Gibbs energy of fcc, bcc, and hcp disordered solutions is modeled using Redlich-Kister polynomials. The thermodynamic properties of liquid alloys are described using the associate solution model. Compound Energy Formalism is used to describe the thermodynamic properties of Laves C15 and C36 phases and order-disorder transformations L1₂-A1 and B2-A2 by applying of the corresponding two-sublattice models. The CoTi₂ compound is treated as stoichiometric. The phase diagram, coordinates of invariant equilibria, and thermodynamic properties of liquid and solid phases are calculated. Metastable phase transformations with the participation of supercooled liquid alloys and boundary solid solutions are analyzed.