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

Precipitation is a natural phenomenon that is known to play an important role in the strengthening of Al–Li alloys. Cluster dynamics is powerful and effective in modeling the precipitation kinetics of precipitates in heat-treatable metallic materials, especially in the early stage. In this work, a cluster dynamics model with cluster mobility is further developed by redefining the effective monomer diffusivity for self-consistently modeling multicomponent and multiphase precipitation. The precipitation kinetic data for Al₃Sc in Al–Sc binary alloys and Al₃Li in Al–Li binary alloys are systematically reviewed and evaluated. The metastable fcc_A1/Al₃Li two-phase equilibria are reoptimized using the split four sublattice compound energy formalism to accommodate both the related phase equilibrium measurements and precipitation kinetic measurements. One set of precipitation kinetic parameters is respectively assessed for each of the two precipitate phases. The improved cluster dynamics model, together with the assessed model parameters, can reasonably reproduce the reliable experimental precipitation kinetic data of the two phases. The model parameter determination includes extensive sensitivity studies to use physically reasonable values, and the present work also studies the use of cluster mobility in modeling the early stage precipitation kinetics. The present work indicates that the obtained model parameters can be used to develop the fundamental informative CALPHAD-type precipitation kinetic database.

THE CALPHAD L 2023 conference was held in Boston, MA, USA from June 25^th to 30^th, 2023. We have 176 attendees from 23 countries. The activities in CALPHAD L 2023 included 84 oral presentations, 138 student posters, and two software workshops. The topics covered during the conference were gathered in nine categories.

In this study computational methods are used to derive thermochemical data for Sc, Fe, Co, Ni, and Hf hydroxides and oxyhydroxides. As done previously, molecular geometries and vibrational modes were derived with DFT methods; for the enthalpies of formation more computationally intensive coupled cluster methods were necessary. For each species Δ_fH^o(298), S^o(298), and C_p in the form A + BT + CT² + D/T + E/T² with A, B, C, D, and E fitted constants are presented. These are combined with previously reported calculations for Al, Cr, Si, Ta, Al, Zr, Y, Yb, Gd, and Mn to build a compound database for metal hydroxides and oxyhydroxides. Sample calculations for applications where high temperature water vapor is encountered are shown. The majority of the database was generated from ab initio calculations; however, experiments were critical benchmarks for many of the species.

The study presents a pressure-dependent CALPHAD-based model for assessment of the Al, Cu and Li unary systems, focusing on phase changes under varying pressures. By incorporating the Murnaghan equation of state and ab initio phonon calculations, the thermal properties for stable and metastable phases are accurately predicted. To ensure a comprehensive representation of the system's response to pressure changes; compressibility, volumetric thermal expansion coefficient as a function of temperature, the derivative of bulk modulus with pressure, and molar volume for the condensed phases are integrated in the framework. The model provides essential insights into pressure-induced transformation, aiding in the understanding of solid-state processing, such as high-pressure torsion and extrusion. The results from this work are in excellent agreement with the experimental literature and can be utilized to enhance phase predictions under non-equilibrium conditions.

The phase equilibria of the Sm-Fe-B ternary system at 873 K and 1073 K were experimentally investigated by equilibrated alloy method using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD). Four ternary intermetallic compounds, Sm₂Fe₁₄B with a Nd₂Fe₁₄B-type structure and space group P4₂/mnm, Sm₁₇(Fe₄B₄)₁₅ with a RE_l.1Fe₄B₄-type structure and space group P4₂/n, SmFeB₄ with a YCrB₄-type structure and space group Pbam and Sm₅Fe₂B₆ with a Pr₅Co₂B₆-type structure and space group $R\bar{3}m$ , were confirmed by the SEM-EDS results and the XRD Rietveld refinements. The isothermal sections of this ternary system at 873 K and 1073 K were established. Furthermore, in the combination with the previous assessments of the Sm-Fe, Sm-B and Fe-B binary systems and the measured and reported experimental results, thermodynamic calculation of the Sm-Fe-B ternary system was performed using the CALPHAD method. The calculated isothermal sections at 873 K and 1073 K are in good agreement with the determined experimental results. Thermodynamic parameters of the Sm-Fe-B ternary system were obtained finally, which would provide a good basis for the development of a thermodynamic database of RE-Fe-B-based magnetic alloys.

Interstitial metal hydrides (MHs) have attracted considerable attention in the field of hydrogen technology, particularly in the context of storage and compression applications. Because of their minor hysteresis effects, good cyclability, activation simplicity, and high volumetric storage density, ${\mathrm{LaNi}}_5$-based alloys are recognized as prominent candidates for hydrogen storage application. Additionally, the system’s thermodynamic and electrochemical properties can be modified to suit the requirements of a particular application by alloying specific substituents. To ascertain the thermodynamic effects of Ce addition within ${\mathrm{LaNi}}_5$, in this work the CeH and ${\mathrm{CeNi}}_5$ $H$ systems have been modeled with the CALPHAD method. For this reason, in this work, two different thermodynamic models have been developed and assessed using the same pressure-composition isotherms (PCIs) datasets obtained from literature and theoretical formation energies newly calculated employing periodic density functional theory (DFT). Direct comparison of the models against each other in terms of accuracy and physical plausibility revealed that extrapolation of thermodynamic properties to data-scarce regions is more reasonable with fewer model parameters and in agreement with other similar systems within the rare-earth ($\mathrm{RE}$) metal-hydride class. In addition, the ${\mathrm{CeNi}}_5$ $H$ system was investigated by assessing the ${\mathrm{(Ce)(Ni)}}_5{\left(\mathrm{V\; a,H}\right)}_7$ phase model, which could accurately predict hydrogen storage properties while being compatible with previously developed ${\mathrm{LaNi}}_5$ $H$ models. Ultimately, the models developed in this study may be employed and extended to describe multi-component $\mathrm{RE}$ $H$ systems and allow for thermodynamic computations that are highly desirable for accurate predictions of hydrogen absorption/desorption properties and degradation characteristics within the ${\mathrm{(La,Ce)Ni}}_5$ $H$ metal hydride family.

The high-pressure behavior of the alkali metals has attracted much attention in both experimental and theoretical aspects. This study is focused on the thermodynamic optimization of the temperature and pressure dependence of the molar volumes, the compressibility and phase diagrams of Li, Na and K according to the CALPHAD method. The pressure-temperature phase diagrams of lithium, sodium and potassium up to 50–100 GPa were calculated using the obtained thermodynamic parameters. The available experimental data, such as extremely low melting temperatures at high pressure, pressure-induced structural transitions between simple bcc and fcc crystals and the molar volume changes with the increasing pressure, were well reproduced in our calculations. The good agreements between our calculations and the experiments assessed in the literature indicated that our thermodynamic parameters are reasonable. Our thermodynamic calculations would assist to understand the phase transitions and structural properties of alkali metals at high pressure.

Aiming to evaluate the effect of refractory metal additions to a quinary AlCoCrFeNi High-Entropy Alloy (HEA), three novel equimolar AlCoCrFeNi-X (X = Mo, Ta, W) HEAs were designed, arc-melted, annealed, and characterized by SEM-EDS, XRD and microhardness measurements. CALPHAD thermodynamic calculations were exploited to design compositions and thermal treatments of the selected HEAs as well as to predict constitution and interpret microstructure of the samples. On the other hand, the experimental results contributed to the validation of the in-house built GHEA thermodynamic database (including the Al, Co, Cr, Fe, Ni, Mo, Ta, W elements) used for the calculations. No TCP intermetallic was found to form in the quinary AlCoCrFeNi alloy. However, the formation of σ, Laves-C14 and μ phases was observed in the samples containing Mo, Ta, and W, respectively, in agreement with the most accepted VEC-based phases stabilization criteria. The addition of the refractory metals led to a microhardness increase for all the investigated alloys. Overall, good agreement was observed between experiments and calculations, especially for compositional trends and phase amounts, allowing the database validation and supporting its applicability to phase equilibria simulation in the six-component HEAs belonging to the Al–Co–Cr–Fe–Ni-X (X = Mo, Ta, W) systems.

The thermodynamic description of the (LiF, NaF, KF, CrF₂)–CrF₃ systems has been revisited, aiming for a better understanding of the effects of Cr on the FLiNaK molten salt. First-principles calculations based on density functional theory (DFT) were performed to determine the electronic and structural properties of each compound, including the formation enthalpy, volume, and bulk modulus. DFT-based phonon calculations were carried out to determine the thermodynamic properties of compounds, for example, enthalpy, entropy, and heat capacity as functions of temperature. Phonon-based thermodynamic properties show a good agreement with experimental data of binary compounds LiF, NaF, KF, CrF₃, and CrF₂, establishing a solid foundation to determine thermodynamic properties of ternary compounds as well as to verify results estimated by the Neumann-Kopp rule. Additionally, DFT-based ab initio molecular dynamics (AIMD) simulations were employed to predict the mixing enthalpies of liquid salts. Using DFT-based results and experimental data in the literature, the (LiF, NaF, KF, CrF₂)–CrF₃ system has been remodeled in terms of the CALculation of PHAse Diagrams (CALPHAD) approach using the modified quasichemical model with quadruplet approximation (MQMQA) for liquid. Calculated phase stability in the present work shows an excellent agreement with experiments, indicating the effectiveness of combining DFT-based total energy, phonon, and AIMD calculations, and CALPHAD modeling to provide the thermodynamic description in complex molten salt systems.