Journal of Phase Equilibria and Diffusion最新文献

This study systematically investigates the solute-vacancy coupling diffusion mechanisms in aluminum alloys using atomic kinetic Monte Carlo simulations for 50 solute elements. The calculated self-diffusion coefficient of Al and solute diffusion coefficients agree well with density functional theory with harmonic transition state theory predictions and experimental data, validating the simulation reliability. Contrary to conventional understanding, transition metals (excluding IB/IIB groups) exhibit non-vacancy-mediated diffusion due to repulsive solute-vacancy interactions and high exchange barriers. Analysis of solute-vacancy drag ratios reveals that Mg consistently shows negative drag ratios (indicating inverse Kirkendall behavior), while other solutes transition from positive (vacancy drag) to negative (inverse Kirkendall) ratios with increasing temperature, following a Boltzmann function. The drag transition temperature correlates linearly with solute-vacancy binding energy (except for Cu). Lifetime analysis of solute-vacancy pairs identified optimal microalloying elements (such as Ge, In, Se, La) for aging control, demonstrating effective vacancy trapping during natural aging and millisecond-scale release during artificial aging. This work provides theoretical guidance for alloy design and heat treatment while elucidating the atomic-scale mechanisms of solute-vacancy dynamic coupling in aluminum alloys.

The thermodynamic description of the Al-Cu system is reassessed considering metastable states of Al based alloys in rapid solidification. In previous work, only an improved thermodynamic description of the FCC phase was presented based on experimental results from electromagnetic levitation and simulation results for free dendritic growth to be in accordance with existing thermodynamic descriptions of the liquid phase. The phase diagram thus obtained enabled the correction of the artificial miscibility gap when calculating metastable extensions of the FCC/liquid phase equilibria, the unphysical change of the slope of the solidus line on the Al-rich side and the artificial maximum on the Cu-rich side. However, the description did not well align with the most recent experimental results on the Cu-rich side. The new description reassessing FCC, liquid and the α′-phase demonstrates high consistency with these recent experimental results, reproducing all invariant reactions (temperatures) with an accuracy of ± 4 K and the experimental liquidus line with an accuracy of ± 10 K, all well within the experimental error. The results provide a robust framework for predicting phase behavior under metastable conditions, as confirmed by our experimental data.

This work focuses on the thermodynamic modeling of the binary indium-cerium (In-Ce) system. A thorough bibliographic review was conducted to gather relevant experimental and theoretical data. The CALPHAD (CALculation of PHAse Diagrams) approach was employed using Thermo-Calc software to develop an optimized thermodynamic description of the system. Additionally, ab initio calculations were performed with Quantum ESPRESSO to estimate the formation enthalpies of the intermetallic compounds. The resulting thermodynamic model successfully reproduces the phase diagram and key thermodynamic properties such as mixing enthalpies, partial enthalpies, activities, and compound formation enthalpies. The results are in good agreement with the available data. However, further experimental studies are recommended to improve and validate the accuracy of the model.

The present study revisits the first, second, and combined laws of thermodynamics by introducing partial internal energy in the first law, entropy production and partial entropy in entropy change, and partial volume in the context of work exchange. These developments yield a more rigorous and internally consistent thermodynamic framework, within which chemical potential is defined as the partial derivative of internal energy with respect to composition at constant entropy and volume, and is related to partial internal energy, partial entropy, and partial volume.

The effect of austenitization temperature (T_A) and cooling rate (CR) on microstructure and transformation kinetics of near eutectoid steel after continuous cooling transformation have been studied by dilatometry. The samples were austenitized at 800, 900, and 1000 °C for 20 min, and then cooled to room temperature at CR of 0.5, 1, and 2 °C/s. Increasing CR resulted in the lowering of interlamellar spacing (S), producing finer pearlite. Similarly, at a constant CR, S decreased with higher T_A. The nature of pearlite nucleation indicating site saturation was predicted through kinetic analysis, where the Kamamoto equation was applied to the dilatometric data of the fully pearlitic steels. The DICTRA simulations using the MobFe2 database confirmed the increased time for completion of transformation and decreased S with increased T_A at a CR of 2 °C/s, aligning well with the experimental data. Both experimental and simulated results also showed consistent trends in time for completion of transformation and S values across constant T_A of 1000 °C with varying CR conditions.

The Debye model for the heat capacity of solids is highly successful in modeling a wide variety of materials. Yet, it is not used in currently-developed CALPHAD (Calculation of Phase Diagrams) thermodynamic databases, just because it requires numerical integration and thus is inconvenient in implementation. Holzapfel et al. developed a simple closed-form approximation of the Debye model. The present work demonstrates the utility of Holzapfel’s expression for use in CALPHAD thermodynamic databases and software, with examples of modeling the Gibbs energy of the metallic elements Al and W. Advantages over previous work in CALPHAD modeling are pointed out.

The surface adsorption of B atoms on La-Doped and undoped α-Ti (0001) surfaces was systematically investigated using first-principles calculations. Concurrently, the bulk diffusion behavior of B atoms in La-Doped α-Ti and β-Ti was examined. The results demonstrate that boron atoms preferentially adsorb at the hollow site of the α-Ti (0001) surface. Our study reveals that La doping in the surface layer reduces the adsorption energy of boron on α-Ti (0001). In contrast, substituting La in the subsurface layer enhances the adsorption of boron atoms on the α-Ti (0001) surface. Furthermore, boron atoms are predicted to preferentially occupy the octahedral and tetrahedral sites in La-Doped α-Ti and β-Ti lattices. The analysis of boron diffusion behavior shows that La doping reduces the energy barrier for boron diffusion and penetration, thereby significantly promoting the boronization process of the titanium substrate. These findings provide a theoretical basis for understanding the boronization mechanism of the Ti surface with rare-earth doping.

Liquid Pb-Bi alloys are pivotal for next-generation nuclear and solar energy systems, yet predicting their thermodynamic and transport properties remains challenging due to complex atomic interactions. This study integrates electromotive force measurements with the molecular interaction volume model (MIVM) to accurately calculate Pb-Bi thermodynamic properties (activity coefficients, Gibbs free energy, and mixing entropy) while establishing direct links to surface tension and viscosity. We demonstrate that MIVM achieves high precision and, combined with Gąsior’s entropy model, successfully predicts viscosity across broad temperature and composition ranges. Surface tension predictions demonstrate excellent agreement with experimental measurements, highlighting the preferential segregation of Bi atoms at the interface and temperature-induced structural homogenization across varying compositions. The unified framework resolves discrepancies in prior models by leveraging excess entropy and molecular interactions, offering critical insights for optimizing liquid metal coolants in advanced reactor and energy systems.