Journal of Phase Equilibria and Diffusion最新文献

In the present work, the thermodynamic assessment of the U-Ti-Zr ternary system was performed by using the CALPHAD (Calculation of Phase Diagrams) method based on phase diagram data as well as the reliable thermodynamic descriptions of the U-Ti, U-Zr, and Ti-Zr binary systems. The calculated isothermal sections and vertical section of the U-Ti-Zr system are in good agreement with the experimental results. Subsequently, based on the available experimental diffusion data, the atomic mobility parameters of the U-Ti binary system were assessed by means of DICTRA software. The calculated interdiffusion coefficients and composition profiles of the bcc U-Ti alloys are consistent with the experimental data. On this basis, the kinetic database of the bcc U-Ti-Zr alloys was constructed by extrapolation in combination with reliable atomic mobility parameters of the U-Zr and Ti-Zr binary sub-systems from the literature.

Differential scanning calorimetry (DSC) is a well-known experimental technique for measuring transformation temperatures such as liquidus and solidus in steels. Precise determination of these temperatures is crucial for accurately setting the solidification model of a large-size casting ingot. Therefore, the objective of this article is to discuss the results obtained with DSC to study the accuracy of determining solidus and liquidus temperatures. In the present study the influences of sample mass, cooling rates and chemical composition were the subject of examination to assess their effects on the variation and reliability of the measured solidus and liquidus for an as-cast steel alloy. The DSC experiments were conducted on two ingot-extracted steel compositions that showed variations, due to macrosegregation. Optical microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy and microhardness measurements were employed to investigate microstructure evolution. Thermodynamic calculations performed using FactSage^® software showed a significant difference in comparison with the experimental obtained liquidus and solidus temperatures. A 20 mg mass difference increased the solidification interval by 6 °C. Change in the cooling rate resulted in more influence on the deviation of the liquidus temperature than the solidus. Observations revealed an increase in undercooling with the rise in cooling rate, which resulted in shifting the solidification temperature range to lower temperatures. DSC results showed a mass loss after multiple thermal cycles, resulting in notable differences in the liquidus and solidus temperatures, peak shapes, and amplitudes. The results are discussed in terms of their impact in the optimization of large steel ingot casting.

Gibbs energy modeling of high temperature bornite is carried out from liquidus to mediate temperatures at a total pressure of one bar. A three sublattice approach using the compound energy formalism is developed which is consistent with a recently reported critical assessment and optimization of the Cu-S sulfide digenite. The first comprehensive comparison with experimental phase diagram data can be carried out on the basis of an adequate reproduction of the homogeneity range of high-temperature bornite which emanates from digenite into the Cu-Fe-S phase space with a substantial iron solubility. Ternary heat capacity data at the composition of Cu₅FeS₄, considered for the first time for Gibbs energy modeling, provides the basis for a reliable extrapolation to lower temperatures. A recently presented two-sublattice model for high-temperature pyrrhotite is adapted for accordance with its limited but relevant copper solubility. Eleven phase diagram sections of the Cu-Fe-S system – five isopleth and six isothermal sections – are calculated over the total ternary composition range for comparison with experimental data available in the literature. Together with further development of the Cu-Fe-S liquid phase model agreement between calculation and experimental data is achieved in a fair to a very satisfactory manner.

Kinetic Monte Carlo (KMC) simulations of the diffusion couple experiments were performed with the assumption that the vacancy composition in the system equilibrates much faster than the atomic configuration. Within this approach, the consistent atomistic simulation model with immediate vacancy equilibration mechanism was developed by incorporating a physical model of vacancy sources and sinks into the KMC algorithm. The Semi-Grand Canonical Monte Carlo (SGCMC) algorithm determined equilibrium vacancy composition and configuration in a system and, when implemented with the KMC code, generated on-line vacancy compositions locally equilibrated according to the atomic configuration in the sample. The values of the interdiffusion coefficients were determined by means of the Boltzmann-Matano formalism applied to the simulated composition profiles along the diffusion couple. The simulations also clearly reproduced the Kirkendall effect expected to appear in the simulated systems. Validity and reliability of the approach was assessed by comparing the results with the predictions of the Darken-Manning theory.

The Te–O phase diagram and the TeO₂ thermodynamic properties are of interest for many industrial fields: nuclear applications, steel making industry and chalcogenide glass processes. Both, the thermodynamic properties and phase diagram of this relevant binary system were reviewed and assessed using the Calphad method. From this assessment, the standard Gibbs free energy and corresponding heat capacity of the binary oxides are calculated as:

The phase equilibria in the V-rich region of the V-Si-B system, including the V₈SiB₄ phase, have been experimentally investigated. Eleven alloys with key compositions were produced by arc-melting or levitation-melting. The samples were then annealed at 1400 °C for 100/200/300 h under high vacuum condition. The as-cast and heat-treated alloys were investigated by scanning electron microscopy, electron backscatter diffraction, energy-dispersive x-ray spectroscopy and x-ray diffraction. The isothermal section at 1400 °C of the V-rich V-Si-B system was determined and compared with the one at 1600 °C. The determined isothermal section can be applied to the design of V-Si-B alloys.

Vanadium and its alloys have potential for application as fuel cladding in new fast breeder reactors cooled by sodium. Diffusion aluminide coatings could be a solution of choice in providing protection against high-temperature corrosion by liquid sodium or residual oxygen for these materials. In this work, multilayered coatings were formed on V and V-44Al substrates by halide activated pack cementation, using CrCl₃ as transport agent and pure aluminum (high activity) as master alloy. Two types of diffusion couples, V/Al and V-44Al/Al, were investigated in order to determine the growth kinetics of the aluminide compounds in the 800-1000 °C temperature range. The growth of the saturated V_ss as well as of the VAl₃ and V₅Al₈ layers was controlled exclusively by solid state diffusion following a parabolic law, allowing the determination of the parabolic growth constants. Wagner’s analysis was adopted to calculate the integrated interdiffusion coefficients, resulting in values ranging approximately from 10⁻¹⁰ to 10⁻¹² cm²/s for temperatures between 800 and 1000 °C. In general, VAl₃ has the highest ({widetilde{text{D}}}_{text{int}}) values in relation to those of the other two layers, considering the nominal temperatures (except for 1000 °C).

With zero-flux boundary conditions imposed at both ends, amounts of components in a system cannot change as a result of a unidimensional diffusion in it. With appropriately chosen time steps, the Crank-Nicolson scheme can dependably track a temporal evolution of an initial discrete concentration profile, but an invariance of an area below a continuously changing concentration vs. position curve is not guaranteed. In this work, a heuristic yet mathematically sound technique of incorporating a "constant integral" requirement into the Crank-Nicolson method is proposed.

Phase diagrams of the ternary Tm-Co-Fe and boundary binary systems Tm-Co and Tm-Fe were constructed in the entire composition ranges using differential thermal analysis, powder x-ray diffraction, microscopic examination and electron probe microanalysis. The Tm-Co phase diagram was plotted for the first time. A new binary compound Tm₁₂Co₇ was found and its crystal structure was established. The Tm-Fe phase diagram was revised: all invariant temperatures were updated, and disagreements with previously reported data were resolved. The Tm-Co-Fe system was studied for the first time. The results are given in the form of liquidus and solidus projections, isothermal sections at 1200 and 1000 °C, and Scheil reaction scheme. Ternary compounds are not formed in the system. Instead, the isostructural phases of Tm-Co and Tm-Fe systems form continuous solid solutions (αCo,γFe), Tm₂(Co,Fe)₁₇, Tm(Co,Fe)₃, Tm(Co,Fe)₂ at all studied temperatures. The Tm₆Fe₂₃ phase dissolves up to 45 at.% Co. The solubility of Fe in Tm-Co compounds is much lower. Five three-phase regions are present on the solidus projection, which form from one eutectic and four transition (U) type invariant reactions. The boundaries of the primary crystallization regions of phases, types and coordinates of invariant and monovariant equilibria are determined. Isothermal sections differ from the solidus projection by: (i) the presence of wide areas of melt, resulting in the absence of Tm₃Co and Tm₁₂Co₇ compounds and (ii) the absence of TmCo₅ compound. As a result, there are two three-phase regions at 1200 and 1000 °C.

The phase equilibria of the Y-Co-Cu ternary system were investigated experimentally by scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction. The experimental results did not indicate any ternary intermetallic compounds and revealed that the YCo₅ and YCu₆ binary intermetallic compounds form the continuous solid solution phase Y(Co, Cu)₅ because of having the same space groups. According to the measured phase compositions at 873 K, the solid solubilities of Co in fcc(Cu), YCu₄, Y₂Cu₇ and YCu₂ are 8.6, 1.7, 44.0 and 8.6 at.%, respectively, while those of Cu in fcc(Co), Y₂Co₁₇, Y₂Co₇, YCo₃, YCo₂, Y₂Co₃, Y₆Co₇, Y₄Co₃, Y₈Co₅ and Y₃Co were determined to be 15.8, 6.4, 8.1, 13.5, 7.9, 1.2, 1.4, 3.9, 7.6 and 10.6 at.%, respectively. Furthermore, at 1073 K the solid solubilities of Co in fcc(Cu), YCu₄, Y₂Cu₇ and YCu₂ were measured to be 3.9, 2.5, 40.0 and 10.8 at.%, respectively, while those of Cu in fcc(Co), Y₂Co₁₇, Y₂Co₇, YCo₃, YCo₂, Y₂Co₃ and YCo were determined to be 13.6, 9.4, 7.4, 13.7, 10.3, 2.3 and 31.4 at.%, respectively. Two isothermal sections of the Y-Co-Cu ternary system at 1073 K and 873 K were established finally.