Search Results (204)

Slags generated from pyrometallurgical processing of spent Li-ion batteries are reservoirs of Li compounds that, on recycling, can reintegrate Li into the material stream. In this context, γ-LiAlO₂ is a promising candidate that potentially increases recycling efficiency due to its high Li content and favorable morphology for separation. However, its solidification kinetics depends on melt compositions and cooling strategies. The Engineered Artificial Minerals approach aims to optimize process conditions that maximize the desired solid phases. To realize this goal, understanding the coupled influence of external cooling kinetics and internal kinetics of solid/liquid interface migration and mass and thermal diffusion on solidification is critical. In this work, the solidification of γ-LiAlO₂ from a Li₂O-Al₂O₃ melt is computationally investigated by applying a non-equilibrium thermodynamic model to understand the influence of varying processing conditions on crystallization kinetics. A strategy is illustrated that allows the effective utilization of thermodynamic information obtained by the CALPHAD approach and molecular dynamics-generated diffusion coefficients to simulate kinetic-dependent solidification. Model calculations revealed that melts with compositions close to γ-LiAlO₂ remain comparatively unaffected by the external heat extraction strategies due to rapid internal kinetic processes. Kinetic limitations, especially diffusion, become significant for high cooling rates as the melt composition deviates from the stoichiometric compound. Full article

Crack-free Stellite-6 alloy was fabricated using the laser powder bed fusion technique equipped with a heating module as the first attempt. Single tracks were printed with a build plate heated to 400 °C to identify the processing window. Based on the melt pool dimensions, two combinations (sample A: 300 W/750 mm/s and sample B: 275 W/1000 mm/s) were identified to print the cubes. The as-printed microstructure comprised FCC-Co dendrites with M₇C₃ in the interdendritic region. W-rich M₆C particles were found in the overlapping regions between the melt pools, matching the Scheil simulations. However, gas pores were observed due to the higher nitrogen and oxygen content of the feedstock requiring hot isostatic pressing (HIP) at 1250 °C and 150 MPa for 2 h. Sample A was partially recrystallized with slightly coarsened M₇C₃, while sample B underwent complete recrystallization followed by grain growth along with higher coarsening of the M₇C₃ after HIP. The varying recrystallization behavior can be attributed to the difference in residual stresses and grain aspect ratio in the as-built condition dictated by laser power and scanning speed. The microhardness after HIP was slightly higher than its wrought counterpart, indicating no severe impact of post-processing on the properties of Stellite-6 alloy. Full article

This paper presents equations derived from thermodynamic equations for calculating the liquidus and solidus temperatures, the liquidus slope, and the partition ratio for solidification simulations. The constants of these equations can be easily determined from measurement data obtained by digitalisation from known diagrams or can be calculated using a CALPHAD-based software. ESTPHAD has a hierarchical system; the developed functions of the binary systems are used in the calculation of the functions of the ternary systems, the functions of the ternary systems in the calculation of the function of quaternary systems, and so on. The developed method is demonstrated by processing the liquidus and solidus of Si–Ge isomorphous and Al–Mg and Al–Si eutectic equilibrium phase diagrams. The use of this method for calculating the functions of ternary systems will be shown in Part II. The advantages of this method are that the equations are simple, can be determined very quickly, and can be built into the simulation software very easily. The most significant advantage is that the calculation time is shorter by some order of magnitude than that of a CALPHAD-type calculation. Full article

In this study, a new lightweight Al-Ti-Ta alloy was developed through a synergistic approach, combining CALPHAD methodology and entropy-driven design. Following compositional optimization, the Al_87.5Ti_6.25Ta_6.25 (at.%) alloy was fabricated and isothermally heat-treated at 475 °C for 24 h to attain equilibrium. X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses revealed a dual-phase microstructure comprising a 50 vol.% FCC matrix enriched in Al and 50 vol.% Al₃(Ti,Ta)-type intermetallic phase (IP). Notably, the FCC phase exhibited a high-melting transition temperature of 660 °C, surpassing conventional Al-Si cast alloys. Phase-specific nanomechanical properties were evaluated using Nanoindentation. Microindentation tests demonstrated exceptional microhardness of approximately 3300 MPa. These results indicate the alloy’s superior hardness compared to conventional alloys such as Al-Si (A390), 7075 Al alloy, and CP-Ti, even exceeding Ti-64 alloy at a 15% lower density. The alloy’s stability under prolonged heat treatment at 475 °C, reflected by stable phases, microstructure, and mechanical properties, highlights its enhanced thermal stability, which can be attributed to entropy-driven phase stabilization. This study underscores the effectiveness of integrating entropy-driven design strategy with CALPHAD predictions for the accelerated development of advanced Al-based alloys. Full article

This study investigates the effects of the external magnetic field on the microstructure and mechanical property aluminum alloy 6061-T6 and 7075-T651 resistance spot welding joints. The melting behavior of 6061 and 7075 was analyzed via the calculation of the phase diagram (CALPHAD) technique. The CALPHAD results indicate that, for the 6061 aluminum alloy, the liquid fraction shows a minimal increase at the beginning stage during the solid–liquid phase transition process but with a sharp rise at the ending stage (near the liquidus). In contrast, for the 7075 aluminum alloy, the liquid fraction gradually increases throughout the entire solid–liquid phase transition process. The differences in melting behavior between the 6061 and 7075 alloys lead to different liquation crack morphologies in their spot-welded joints. In the 6061 alloy, the cracks tend to be “eyebrow-shaped”, allowing the liquid metal in the nugget to feed the gaps, and this does not significantly compromise the mechanical properties of the joint. In contrast, the 7075 alloy develops slender cracks that extend through the partially melted zone (PMZ), making it difficult for the liquid metal to feed these gaps, thereby significantly deteriorating the joint’s mechanical strength. Compared to conventional resistance spot-welding joints, the heat exchange between the nugget and the workpiece is enhanced under the external magnetic field, leading to a wider PMZ. This exacerbates the detrimental effects of liquation cracks on the mechanical properties of the 7075 joints. Lap-shear tests indicate that the mechanical properties of the 6061 aluminum alloy joints are improved under electromagnetic stirring. For 7075 aluminum alloy joints, the mechanical properties improve when the welding current is below 34 kA. However, when the welding current exceeds 34 kA, because the widening of the PMZ increases the tendency for liquation cracks, the joint’s mechanical property is deteriorated. Full article

Welding current is an essential parameter for submerged arc welding process. In submerged arc welding, the enormous heat generated by the current promotes the decomposition of the oxides in the flux, releasing oxygen and increasing the oxygen level in the metal, which further affects the microstructure and mechanical properties of the weld joint. Although previous studies have developed various models to evaluate oxygen content, the thermodynamic mechanism by which current influences oxygen levels in metal remains inadequately understood. This study integrates CALPHAD technology with welding thermodynamics to predict and simulate the impact of the welding current on oxygen content in metals. By combining experimental data with thermodynamic modeling, the research investigates how different current settings affect oxygen content in the metal across various welding zones, specifically when using CaO-Al₂O₃ fluxes with low and high basicity indices for the welding of typical carbon steel. This study selected two current values, 300 A and 600 A, for modeling analyses of the welding process, along with two typical fluxes with basicity indices of 1.6 and 0.4. The results indicate that the proposed method outperforms the BI model and can predict the metallurgical effects of current on oxygen content in the droplet and molten pool zones. The thermodynamic mechanisms that govern the metal oxygen level are also evaluated. These findings aim to enhance the understanding of the thermodynamic mechanism that governs oxygen behavior under different current conditions, thereby contributing to the optimization of submerged arc welding process. Full article

New developments in nickel-based superalloys and production methods, such as the use of additive manufacturing (AM), can result in innovative designs for turbines. It is crucial to understand how the material behaves during the AM process to advance the industrial use of these techniques. An analytical model based on reaction–diffusion formalism is developed to better explain the solidification behavior of the material during laser metal deposition (LMD). The well-known Scheil–Gulliver theory has some drawbacks, such as the assumption of equilibrium at the solid–liquid interface, which is addressed by this method. The solidified fractions under the Scheil model and the pure equilibrium model are calculated using CALPHAD simulations. A differential scanning calorimeter is used to measure the heat flow during the solid–liquid phase transformation, the result of which is further converted to solidified fractions. The analytical model is compared with all the other models for validation. Full article

High-entropy ceramics (HECs) represent an emerging class of materials composed of at least five different cations or anions in near-equiatomic proportions, garnering significant attention due to their extraordinary functional and structural properties. While multi-component ceramics have played a crucial role for many years, the concept of high-entropy materials was first introduced eighteen years ago with the synthesis of high-entropy alloys, and the first high-entropy nitride films were reported in 2014. These newly developed materials exhibit superior properties over traditional ceramics, such as enhanced thermal stability, hardness, and chemical resistance, making them suitable for a wide range of applications. High-entropy carbides, borides, oxides, oxi-carbides, oxi-borides, and other systems fall within the HEC category, typically occupying unique positions within phase diagrams that lead to novel properties. HECs are particularly well suited for high-temperature coatings, for tribological applications where low thermal conductivity and similar heat coefficients are critical, as well as for energy storage and dielectric uses. Computational tools like CALPHAD streamline the element selection process for designing HECs, while innovative, energy-efficient synthesis methods are being explored for producing dense specimens. This paper provides an in-depth analysis of the current state of the compositional design, the fabrication techniques, and the diverse applications of HECs, emphasizing their transformative potential in various industrial domains. Full article

Existing thermodynamic descriptions of the whole Cr–Fe–P system are insufficiently accurate for understanding the thermodynamic behavior of the Cr–Fe–P materials during the manufacturing process. To construct a more precise and consistent thermodynamic database of the Cr–Fe–P system, thermodynamic modeling of the Cr–P and Cr–Fe–P systems was conducted using the CALculation of PHAse Diagrams (CALPHAD) approach based on critical evaluation of the experimental data. The modified quasichemical model and compound energy formalism were employed to describe the liquid and solid solutions, respectively. The Gibbs energies of stoichiometric compounds Cr₃P(s), Cr₂P(s), CrP(s), and CrP₂(s) were carefully determined based on reliable experimental data. The ternary (Cr,Fe)₃P, (Cr,Fe)₂P, and (Cr,Fe)P phosphides were modeled as solid solutions considering mutual substitution between Cr and Fe atoms. In addition, the phase equilibria of BCC_A2 and FCC_A1 solutions and the liquid phase of the ternary Cr–Fe–P system were also optimized for more accurate descriptions of existing phase equilibria and thermodynamic properties data. As an application of the present database, the experimentally unexplored thermodynamic properties and phase diagrams of the Cr–Fe–P system are predicted. Full article

This study, based on the analysis of existing experimental data, presents a third generation Calphad description of lithium, covering all temperature ranges, using nonlinear least squares in Matlab. We have expanded the SGTE database’s description of lithium phases (face-centered cube, body-centered cube, liquid) down to 0 K with reasonable accuracy, taking into account the significant effort required to reconstruct the database for each element. During the evaluation process, it was determined that the low-temperature phase of lithium is fcc. The heat capacity of crystalline Li was accurately described using the extended Debye model. The third generation Calphad description of lithium utilized the two-state model and the extended Einstein model, leading to improved agreement with experimental data compared to previous assessments. Full article

Recent developments in metallic additive manufacturing (AM) processes for the production of high-performance industrial pieces have been hampered by the limited availability of reliably processable or printable alloys. To date, most of the alloys used in AM are commercial grades that have been previously optimized for different manufacturing techniques. This study aims to design new alloys specifically tailored for AM processes, to minimize defects in the final products and to optimize their properties. A computational approach is proposed to design novel and optimized austenitic alloy compositions. This method integrates a suite of predictive tools, including machine learning, calculation of phase diagrams (CALPHAD) and physical models, all piloted by a multi-objective genetic algorithm. Within this framework, several material-dependent criteria are examined and their impact on properties and on the occurrence of defects is identified. To validate our approach, experimental tests are performed on a selected alloy composition: powder is produced by gas atomization and samples are fabricated by laser powder bed fusion. The microstructure and mechanical properties of the alloys are evaluated and its printability is compared with a commercial 316L stainless steel taken as a reference. The optimized alloy performs similarly to 316L in terms of coefficient of thermal expansion, hardness and elongation, but has a 17% lower yield strength and ultimate tensile strength (UTS), indicating that further optimization is required. Full article

Magnesium alloys are considered as promising materials for use as biodegradable implants due to their biocompatibility and similarity to human bone properties. However, their high corrosion rate in bodily fluids limits their use. To address this issue, amorphization can be used to inhibit microgalvanic corrosion and increase corrosion resistance. The Mg-Zn-Ga metallic glass system was investigated in this study, which shows potential for improving the corrosion resistance of magnesium alloys for biodegradable implants. According to clinical tests, it has been demonstrated that Ga ions are effective in the regeneration of bone tissue. The microstructure, phase composition, and phase transition temperatures of sixteen Mg-Zn-Ga alloys were analyzed. In addition, a liquidus projection of the Mg-Zn-Ga system was constructed and validated through the thermodynamic calculations based on the CALPHAD-type database. Furthermore, amorphous ribbons were prepared by rapid solidification of the melt for prospective alloys. XRD and DSC analysis indicate that the alloys with the most potential possess an amorphous structure. The ribbons exhibit an ultimate tensile strength of up to 524 MPa and a low corrosion rate of 0.1–0.3 mm/year in Hanks’ solution. Therefore, it appears that Mg-Zn-Ga metallic glass alloys could be suitable for biodegradable applications. Full article

Complex concentrated alloys, including high-entropy alloys (HEAs) and medium-entropy alloys (MEAs), offer another pathway for developing metals with excellent mechanical properties. However, HEAs/MEAs of different structures often suffer from various drawbacks. So, investigations on the effect of phase and microstructure on their properties become necessary. In the present work, we adjust the phase constitution and microstructure by Al addition in a series of (Ti₂ZrHf)_100−xAl_x (x = 12, 14, 16, 18, 20, at.%, named Al_x) MEAs. Different from traditional titanium, Al shows a β-stabilizing effect, and the phase follows the evolution of α′(α)→α″→β + ω + B2 with Al increasing from 12 to 20 at.%, which could not be predicted by the CALPHAD (Calculate Phase Diagrams) method or the Bo-Md diagram because of the complex interactions among composition elements. At a low Al content, the solid solution strengthening of the HCP phase contributes to the extremely high strength with a σ_0.2 of 1528 MPa and σ_b of 1937 MPa for Al14. The appearance of α″ deteriorates the deformation capability with increasing Al content in the Al16 and Al18 MEAs. In the Al20 MEA, Al improves the formations of ordered B2 and metastable β. The phase transformation strengthening, including B2 to BCC and BCC to α″, together with the precipitation strengthening of ω, brings about a high work-hardening ratio (above 5 GPa) and improvements in ductility (6.8% elongation). This work provides guidelines for optimizing the properties of MEAs. Full article

With the advancement of the manufacturing industry, performing submerged arc welding subject to varying welding heat inputs has become essential. However, traditional thermodynamic models are insufficient for predicting the effect of welding heat input on elemental transfer behavior. This study aims to develop a model via CALPHAD technology to predict the influence of heat input on essential elements such as O, Si, and Mn when typical SiO₂-bearing fluxes are employed. The predicted data demonstrate that the proposed model effectively forecasts changes in elemental transfer behavior induced by varying welding heat inputs. Furthermore, the study discusses the thermodynamic factors affecting elemental transfer behavior under different heat inputs, supported by both measured compositions and thermodynamic data. These insights may provide theoretical and technical support for flux design, welding material matching, and composition prediction under various heat input conditions subject to submerged arc welding processes when SiO₂-bearing fluxes are employed. Full article

The high-temperature oxidation behaviour and phase stability of equi-atomic high entropy AlCrCoFeNi alloy (HEA) were studied using in situ high-temperature X-ray diffraction (HTXRD) combined with ThermoCalc thermodynamic calculation. HTXRD analyses reveal the formation of B2, BCC, Sigma and FCC, phases at different temperatures, with significant phase transitions observed at intermediate temperatures from 600 °C–100 °C. ThermoCalc predicted phase diagram closely matched with in situ HTXRD findings highlighting minor differences in phase transformation temperature. ThermoCalc predictions of oxides provide insights into the formation of stable oxide phases, predominantly spinel-type oxides, at high p(O₂), while a lower volume of halite was predicted, and minor increase observed with increasing temperature. The oxidation behaviour was strongly dependent on the environment, with the vacuum condition favouring the formation of a thin, Al₂O₃ protective layer, while in atmospheric conditions a thick, double-layered oxide scale of Al₂O₃ and Cr₂O₃ formed. The formation of oxide scale was determined by selective oxidation of Al and Cr, as further confirmed by EDX analysis. The formation of thick oxide in air environment resulted in a thick layer of Al-depleted FFC phase. This comprehensive study explains the high-temperature phase stability and time–temperature-dependent oxidation mechanisms of AlCrCoFeNi HEA. The interplay between surface phase transformation beneath oxide scale and oxides is also detailed herein, contributing to further development and optimisation of HEA for high temperature applications. Full article