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

Thermodynamic modeling of the La₂O₃-SiO₂, Dy₂O₃-SiO₂ and Er₂O₃-SiO₂ systems is part of a broader effort to obtain thermodynamic databases of the rare earth silicates that can help offer insight on designing the environmental barrier coatings in gas turbine engines. The main aim of the present work is to focus on obtaining a set of self-consistent thermodynamic parameters of La₂O₃-SiO₂, Dy₂O₃-SiO₂ and Er₂O₃-SiO₂ systems. The ionic two-sublattice model was accepted to express the liquid phase, and all the binary phases were described as stoichiometric compounds due to the negligible solubility. After a critical literature review on the experimental phase diagrams data and thermodynamic properties for the La₂O₃-SiO₂, Dy₂O₃-SiO₂ and Er₂O₃-SiO₂ systems, thermodynamic optimizations were performed by means of the CALPHAD (CALculation of PHAse Diagram) method. The modeling was done using Thermo-Calc software with PARROT module. The comprehensive comparison between the experimental results and our calculations exhibits that the calculated phase diagrams and thermodynamic properties were in good agreement with the available experimental data, except for experimental data with doubtful quality. This means that our thermodynamic descriptions were reasonable and could provide a reliable basis for thermodynamic calculations in RE₂O₃-SiO₂-based higher-order systems.

The prediction of the characteristic Martensite Start (M_s) temperature and Austenitic Nose Tip Temperature (ANTT) in steels is of scientific and technological importance; however, it faces significant challenges due to multiphysical complexity.

In this study, we introduced a structured framework for data classification and hierarchical iterations aimed at predicting Ms (Martensite start temperature) and ANTT (Austenite non-transforming temperature). This framework was incorporated into two optimization models, leading to enhancements in accuracy, extrapolation capabilities, and generalization performance. First, we classified the collected Ms datasets hierarchically based on the alloying elements presented in steels, including carbon, austenite stabilizers, non-austenitization elements, and data credibility. Regression analyses of Ms temperatures concerning chemical compositions were then carried out using phenomenological variables from binary systems to multi-component systems in alignment with the spirit of CALPHAD modeling, which is renowned for its robust extrapolation abilities. By iteratively fitting the hierarchically classified datasets and implementing hierarchical iterations, we developed the CALPHAD-guided phenomenological variable (CGPV) Ms regression model. This model achieved improved accuracy levels, with R² values of 0.9 for training and 0.87 for testing, surpassing most conventional regression models that do not account for compositional interactions. Furthermore, the CALPHAD-guided machine learning (CGML) model, constructed based on the classified datasets and hierarchical iterations but without utilizing phenomenological variables, demonstrated strong performance with R² values of 0.98 and 0.86 for training and testing, respectively. The CGML model was demonstrated not only to reliably filter out problematic data in a dataset but also to unveil the unnoticed coupling between carbon and other alloying elements on M_s. Finally, the CGML method has been readily transferred to predict ANTT with high accuracy as well.

The isothermal section at 900 °C of the Ti-poor part of the Ni−Ti−Ru ternary system was measured experimentally, combined with SEM-EDS, XRD, TEM and DSC techniques. Four three-phase equilibria regions were confirmed at 900 °C isothermal section and a ternary compound τ with Face-centered-cubic structure can existed stably. The isothermal section at 900 °C measured in this study and the experimental data from our previous work were adopted in the present optimization. The calculated Ni−Ti−Ru ternary system was summarily presented in the form of isothermal sections, liquids projection and reaction scheme, with appropriate comparisons with available experimental data.

As a core of the high entropy alloys, the Co-Cr-Fe-Ni system has been widely investigated. In the present work, the thermodynamics of the Co-Cr-Fe-Ni system and the atomic mobilities of its fcc phase have been evaluated by means of the CALPHAD approach. First-principles calculations were performed to obtain the total energies for the end-member compounds of the σ phase in the Co-Cr-Fe-Ni system. Combining with the experimental data and thermodynamic modeling of the sub-systems from the literature, a set of self-consistent thermodynamic parameters were derived and extrapolated to obtain a thermodynamic description of the Co-Cr-Fe-Ni quaternary system. In order to verify the accuracy of the model parameters, the phase equilibria of a series of the CoCr_xFeNi alloys with different Cr contents were determined using DSC, BSE and XRD analysis. Subsequently, based on the diffusion experimental data, the atomic mobilities of the fcc Cr-Fe-Ni alloys were reassessed using the DICTRA software. A mobility database for the fcc Co-Cr-Fe-Ni quaternary system was constructed by directly extrapolating the atomic mobilities of all sub-systems, and comprehensive comparisons prove the consistency between the present assessments and the experiments. In addition to the direct extrapolation approach, extra four-body interaction parameters concerning all four components were added and assessed. The results demonstrate that the extra interaction contributions are ignorable, so that the direct extrapolation from the sub-systems to the quaternary system is feasible in the fcc Co-Cr-Fe-Ni quaternary system.

In a previous paper a method was developed to define Einstein temperatures for metastable phases of the elements and their relation to the so-called lattice stabilities used in the past, and also the variation of the Einstein temperature with composition to account for the composition dependence of the excess entropy. This approach was demonstrated successfully for the Al–Zn system. In this paper this approach is extended to cover the Al–Si and Si–Zn binary systems. The phase diagram for the Al–Si–Zn ternary system was then predicted from the thermodynamic description of the binary subsystems only without any ternary interaction parameters. Agreement with the experimental data is shown to be very good.

This paper introduces an innovative theory for customizing photoluminescence (PL) emission wavelengths in rare earth ion (Eu²⁺⁾ doped alkaline earth metals (Ca, Mg) silicates, rooted in the entropy of fusion and configurational entropy of congruent and incongruent silicates, respectively, aiming to reveal dynamic deformation of the tetrahedral SiO₄ ligand within these materials. Using FactSage, we computationally calculate the fusion entropy of congruent silicates in the CaO-MgO-SiO₂ system. Synthesized ternary silicates confirm our theory by highlighting correlations between lower/higher fusion entropy (for congruent) and configurational entropy (for incongruent) silicates, leading to red/blue shifts in PL emission wavelengths. In binary silicate systems, we observe an inverse correlation between PL emission wavelengths and fusion entropy of congruent silicates or pseudo-congruent silicates like MgSiO₃, whose solid-liquid decomposition temperature is close to its melting point. Furthermore, the non-ideal liquid phase entropy of incongruent silicates positioned between congruent CaMgSi₂O₆ (Pyroxene) and congruent Ca₂MgSi₂O₇ (Akermanite) in the MgO-CaO-SiO₂ ternary phase diagram comprehensively explains diverse PL emission wavelengths. Beyond its scholarly impact, this work expands perspectives in lighting and photonic research, opening an exciting frontier in entropy-lighting research and enabling predictions of host chemical composition and tunable PL emission wavelengths, particularly relevant to LED technologies.

The formation of the η phase in two nickel-based superalloys that have similar amounts of titanium and aluminum but different Ti/Al ratios was investigated. The aging was carried out at 750 °C, 800 °C, and 850 °C for 10000 h. The microstructures were observed using SEM and TEM, and equilibria phases were calculated using a Thermo-Calc. equipped with TCNI11 database. Results showed that the number and size of η phase increased with aging temperature and Ti/Al ratios. The size of the γ′ phase was also found to be increased with aging temperature, but it was not significantly affected by the Ti/Al atomic ratio. However, the η phase was not predicted to be the thermodynamic equilibrium phase in the alloy using Thermo-Calc. with the TCNI11 database. The η phase was expected to be the equilibrium phase with Ti/Al ratios higher than 1.85 at 850 °C for Ni-27.0Cr-19.1Co-0.91Nb-0.29Mo-0.14C-xTi-yAl alloys. However, the result does not match the experimental observations or other literature. It is suggested that the effect of titanium on the formation of the η phase may be underestimated in the TCNI11 database. Therefore, it is necessary to enhance the accuracy of predicting the formation of the η phase by modifying at least one of the thermodynamic parameters, including the phase equilibrium of the ternary Ni-Ti-Al system.

Intense researches on new kinds of materials, especially those with marked multi-principal-element character, currently give rise to all-intricate multiphase environments, for which reliably predicting structure and stability becomes extremely difficult to achieve with macroscopic phenomenological modellings. The purpose of this work is to demonstrate how this issue can be overcome by sticking down to the atomic scale, through ab initio-based thermodynamics within the Independent-Point-Defect Approximation (IPDA), which offers an efficient framework to investigate systems involving various chemistries and crystallographies. As a case study of significant intricacy, we consider ternary AlBTi viewed as an approximant for Al-based alloys reinforced with TiB${}_2$ particles and including AlB${}_2$ and Al${}_3$Ti additional compounds. Firstly, our IPDA investigations reveal unexpected discrepancies among neighbouring metallic borides, and predict point defect structures at odds with earlier pictures commonly employed hitherto, which suggests that many complex compounds may suffer from inadequate phenomenological modellings. Furthermore, we show that far-reaching conclusions on phase stability can be drawn only if the scope of analysis is broadened up to encompass global multiphase IPDA-based thermodynamics, a task which constitutes the core and the methodological originality of this work. Our approach thus provides reliable arguments to interpret the occurrence of various kinds of poorly known compounds, as illustrated by the controversial behaviour of Al${}_3$Ti and AlB${}_2$ in TiB${}_2$-reinforced Al-based composites. Finally, our work allows to conclude that the robust and handsome IPDA approach can be extended to highly intricate multiphase situations, e.g. to investigate other classes of multiphase multi-principal-element materials, which due to the presence of complex crystal structures can hardly be explored by alternative methods.

To investigate the mechanism of slag formation during pellet consolidation, we combined thermodynamic calculations and experimental methods to study the effects of roasting temperature, basicity, and SiO₂ content on slag formation. The results indicate that as the temperature increases, the solid phases clinopyroxene, orthopyroxene, and melilite transform into slag within the pellet. The roasting temperature and basicity of slags formed by different particles varied considerably. At 1250 °C, the slag content is less than 5 % in low-silica fluxed pellets, less than 15 % in medium-silica fluxed pellets, and up to approximately 20 % in high-silica fluxed pellets. Phase diagram analysis showed that CaFe₂O₄ and Ca₂Fe₂O₅ formed in the pellet due to basicity differences SEM-EDS analysis showed that the slag in fluxed pellets primarily comprises the silicates Ca₃Fe₂(SiO₄)₃ and (Mg, Fe)₂SiO₄, as well as ferrate. The slag is distributed in a reticulated pattern within the pellets, with some quartz remaining undissolved in the slag phase and existing independently in pores.