Journal of Phase Equilibria and Diffusion最新文献

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.

Phase equilibria in the Pd rich region of the Au-Cu-In-Pd quaternary at 500 °C and 800 °C are investigated by SEM, EDX and XRD techniques. Part of the isothermal tetrahedron was constructed accounting for published data for bounding ternaries obtained earlier by the present authors. No quaternary phases were detected. The solubility of copper in the τ₁ phase of the Au-In-Pd ternary (AuCu₃ structural type) does not exceed 5 at.%. Gold solubility in the InPd₂Cu phase of the Cu-In-Pd ternary is not less than 18 at.% at 500 °C, and at least 15 at.% at 800 °C. Analytical description of the boundaries of the FCC solid solutions in the equilibrium with the InPd₃, InPd₂Cu and ternary τ₁ phase was performed for bounding Cu-In-Pd and Au-In-Pd ternaries as well as for the quaternary. The tie-lines of the equilibria, i.e. the compositions of the two phases in equilibrium, were described as a single entity. To this end, the approach used in the literature for regression analysis of phase compositions of the (γ + γ′) Ni based superalloys was modified. The parametric descriptions of the two-phase tie-lines’ centers and those of the distribution coefficients of the components between the phases were built. The choice of parametrization is discussed. In particular cases of the ternaries and quaternary studied using the content of one or two of the components as parameters proved to be quite satisfactory. Very good description of the solubility lines and solubility surface including rather fine details has been achieved.Please check and confirm the edit made in the article title.Ok

We have studied phase transformations in Cd_0.96Mn_0.04Te_0.98Se_0.02 solid solutions in the temperature range of 1080-1149 °C using differential thermal analysis (DTA). Following the "heating-dwell-cooling" procedure, we investigated the melt supercooling versus superheating, crystallization temperature versus dwell temperature, and crystallization rate versus crystallization temperature. We observed that the Cd_0.96Mn_0.04Te_0.98Se_0.02 alloy remained in a semi-liquid state over the dwell temperature range of 1089-1097 °C. Following a "heating-dwell-heating-cooling" procedure, we investigated the solid-phase volume fraction versus dwell temperature, melting temperature versus dwell temperature and melt crystallization rate versus dwell temperature. We observed that at dwell temperatures higher than 1097 °C, the solid phase completely disappeared in the sample, since the effect of melting was not observed, meaning that the sample was a single-phase melt. Despite the fact that the alloy was heated in every cycle up to 1147 ± 2 °C after the intermediate dwell, structural fragments formed during this intermediate dwell were still present even at higher temperatures and, as a result, affected the crystallization. The range of crystallization temperatures decreases with increasing intermediate dwell temperature. Such dependence can be interpreted as an alloy “memory” of its thermal history.