Computational Thermodynamic Approach Research Articles

Physics-coupled Data-driven Design of High-Temperature Alloys

We present a materials design loop, which streamlines physics-coupled machine learning (ML) surrogate models to discover new alloy chemistries with improved properties. The efficacy is demonstrated by discovering a high-temperature alumina-forming austenitic (AFA) stainless steel with enhanced creep, followed by experimental validation. The ML models have been trained using a well-curated, highly consistent experimental dataset augmented with synthetic microstructural features from a computational thermodynamic approach. We have populated a large number of hypothetical AFA alloys to explore the high-dimensional composition space and have predicted their creep properties by providing the same synthetic input features obtained from the trained ML models. Uncertainties from the ML training were taken as thresholds for truncating predicted results to identify alloys with improved or deteriorated creep. Individual elemental compositions have been determined via probability density distribution analysis from the group of alloys at the top and bottom of the predicted creep values for further virtual and experimental validations. We anticipate that this workflow can be applied to screen desired conditions, such as chemistry and processing parameters, in high-dimensional space through physics-guided data analytics.

Computational thermodynamics-guided alloy design and phase stability in CoCrFeMnNi-based medium-and high-entropy alloys: An experimental-theoretical study

A computational thermodynamics approach has been employed to design CoCrFeMnNi-based medium- and high-entropy alloys (M/HEAs) with systematically varied compositions (Co((80-X)/2)Cr((80-X)/2)FeXMn10Ni10 with x = 30, 40, and 50 at.%) and phase stability. Since the formation of sigma phase, usually brittle and undesirable, is a common concern, when this class of alloys is subjected to elevated temperatures (600–1000 °C), predicting its formation becomes essential. Thus, its formation and the phase equilibria were studied using the CALPHAD method, and two empirical methods, namely, valence electron concentration (VEC) and paired sigma-forming element (PSFE). Isothermal aging treatments at 900–1100 °C for 20 h were performed, since CALPHAD and VEC/PSFE predictions diverged. Both prediction methods were compared with experimental characterization by a combination of scanning electron microscopy and high-energy synchrotron X-ray diffraction. The predictions from the VEC/PSFE and CALPHAD calculations (depending on the database used) were shown to be quite accurate.

WITHDRAWN: Optimization of Thermochemical Stability of La-based/Zr-based Dual-Phase Composites for Oxygen Transport Membranes via Computational Thermodynamics

The current investigation deploys a computational thermodynamics approach to develop new materials for dual-phase composites. The chemical stability of (La0.9Sr0.1)0.95CrxFe1-xO3-δ and (La0.8Sr0.2)0.95CrxFe1-xO3-δ (x=0.5, 0.7, 0.8, and 0.9) with three fluorite phases of 8YSZ, 10Sc1YSZ, and 10Sc1CeSZ has been examined. The changes in the Sr-content and the Cr: Fe ratio in the perovskite phase have also been investigated under oxidizing and reducing atmospheres at elevated temperatures. The results show that SrZrO3 as the dominant secondary phase together with limited formations of (La0.5Zr0.5)O1.75 and La2O3. The experimental results have been incorporated into simulations performed by computational thermodynamics. Involved mechanisms to improve the chemical stability have been discussed based on correlations between the content of dopants and applied conditions. The results promote knowledge for the development of ceramic-based dual-phase composite membranes.

Highly Concentrated Electrolytes for Lithium Sulfur Batteries – the Role of the Anion(s)

Lithium-sulfur batteries (Li-S) have attracted a lot of attention as a alternative/complement to lithium-ion batteries (LIBs) – due to both high energy density, availability, and inexpensive materials used.[1]Yet, dissolution of sulfur from the C/S cathode and subsequent shuttling of lithium polysulfides (LiPS) to the anode as well as the instability of the Li metal anode itself are true scientific and technological challenges. Advancing in the field of electrolytes is one promising way to overcome both issues.Switching from the standard 1 M electrolyte design of LIBs to highly concentrated electrolytes (HCEs) may both prevent the dissolution of LiPSs and hinder dendrite formation at the lithium metal anode.[2]Here we combine experimental methods and computational approaches to investigate several HCEs based on various Li-salts in several standard organic solvents. Experimentally we targeted electrochemical properties, local electrolyte structure, and physico-chemical properties, with focus on the role(s) of the Li-salt anions. Furthermore, to predict the solubility of sulfur the conductor like screening model for real solvents (COSMO-RS), a computational fluid phase thermodynamic approach, was used.[3] Overall, the challenges and opportunities associated with the use of HCEs in Li-S batteries will be addressed, also highlighting potential areas for future research and development.References Peng et al., "Drastic effect of salt concentration in ionic liquid on performance of lithium sulfur battery." Journal of the Electrochemical Society 169.5 (2022): 050515.Suo et al., "A new class of solvent-in-salt electrolyte for high-energy rechargeable metallic lithium batteries." Nature communications 4.1 (2013): 1481.Jeschke and P. Johansson, "Predicting the Solubility of Sulfur: A COSMO‐RS‐Based Approach to Investigate Electrolytes for Li–S Batteries." Chemistry–A European Journal 23.38 (2017): 9130-9136.

Thermophysical properties of LiF–LiCl–Li2CO3 eutectic mixture/multi-walled carbon nanotubes for thermal energy storage

Latent heat thermal energy storage based on solid-liquid phase change material has a huge potential in dealing with mismatch between energy demand and supply. LiF–LiCl–Li 2 CO 3 ternary system was screened out for high temperature energy storage material due to its good thermophysical properties. Its eutectic composition ( X LiF = 28.41 mol%, X LiCl = 55.09 mol% and X Li2CO3 = 16.50 mol%) was predicted based on the developed thermodynamic model and verified experimentally. The melting point, phase change latent heat, heat capacity, thernal diffusivity, thermal conductivity and thermal stability of LiF–LiCl–Li 2 CO 3 eutectic mixture were measured. And the influence of the addition of multi-walled carbon nanotubes (MWCNTs) were analyzed. It was found that adding MWCNTs could increase the latent heat, specific heat capacity, thermal diffusivity and thermal conductivity of LiF–LiCl–Li 2 CO 3 eutectic mixture, while didn't significantly change the melting temperature. • An innovation molten salt is successfully designed via computational thermodynamic approach. • Thermophysical properties of the eutectic salt are determined experimentally. • Composite phase change material (CPCM) was prepared and characterized. • Thermal conductivity and heat capacity can be enhanced by doping nanoparticles.

Experimental design for chemical mixtures: A case study on a molten salt system conductivity

Experimental studies in many fields such as chemistry, biochemistry, food and environmental sciences require very well designed experimental strategies to achieve the best results at minimum cost. At this point experimental design means application of statistical methods to the selection of experimental process factors and to the modelling of system responses to them. Models in which experimental results are expressed depending on experimental factors are also called response surface functions. Mixture designs as a special type of response surface function are also a very effective method for determining the proportions of components in mixtures and are also of great importance in chemical industries like paint, food, glass, ceramic and polymer. Physicochemical properties such as thermal-physical properties, fusion enthalpy, heat capacity, density, thermal stability and conductivity for pure materials or their mixture can be determined experimentally by thermal analysis methods depends on their ingredients. In this study to design molten salt mixtures for thermal energy storage, computational thermodynamics approach has been applied on an experimental design sample. For this purpose conductivities of a molten salt system with three components were measured experimentally depending on the relative ratio of each component, and the effect of these ratios on the conductivity of the mixture was investigated. Here, mixture design model chosen for optimization of process parameters is Simplex Lattice, and Design Expert 700 software were used for statistical analysis. After the model selection for experimental design and transformation of the all factors, the correlation coefficients of the response surface function with linear, quadratic and cubic terms based on all factors for experimental measurements and pseudo and real factors were determined separately. Comparing with the others the best fit of the response surface function sufficient for optimization of process parameters to the experimental measurements was found out for that of with quadratic terms.

Understanding and modelling the thermodynamics and electrochemistry of lithiation of tin (IV) sulfide as an anode active material for lithium ion batteries

Tin (IV) sulfide is a promising anode active material for lithium ion batteries due to its relatively high reversible capacity of 644 mAh/g, which is more than one and a half times that of graphite. During lithiation of tin (IV) sulfide, an inert Li2S matrix is formed in the first discharge cycle, which serves to accommodate the mechanical stresses associated with the volume expansion of tin during the successive LixSn alloying and de-alloying reactions. In order to improve the electrochemical performance of tin (IV) sulfide further, fundamental understanding and insights into the thermodynamics, phase formation, and driving forces for the lithiation reactions are still required. Therefore, in this work, a computational thermodynamics approach was combined with ex-situ XRD investigations of electrodes during the discharge reaction as well as galvanostatic intermittent titration technique (GITT) experiments in order to clarify the lithiation thermodynamics of tin (IV) sulfide. Based on the experimental data, a one-phase mechanism was suggested for the intercalation of lithium into SnS2, a thermodynamic model was developed to describe the intercalation reaction and the expected open circuit voltages were calculated.

Improved microstructure and mechanical properties for sintered NdFeB permanent magnet/steel soldered joints by Nd addition

Abstract Sintered NdFeB permanent magnets with excellent magnetic properties are widely used in electromagnetic devices. The effect of Nd addition on microstructure and mechanical properties of sintered NdFeB permanent magnet/steel soldered joints was investigated by computational thermodynamics approach and coefficient of thermal expansion. The formation of NdSn3 after doping minor Nd into Zn-Sn-Bi solder improved the mechanical properties of soldered joints. On the one hand, NdSn3, as a low Gibbs free energy phase, promoted the heterogeneous nucleation of the β -Sn, resulting in the grain refinement. On the other hand, NdSn3 with lower coefficient of thermal expansion was beneficial for relaxing the residual stress.

A combined numerical approach for the thermal analysis of a piston water pump

Abstract The paper proposes a numerical model for the investigation of a piston water pump under different operating conditions. In particular, the lubricating system is analysed and modelled. The study accounts for the lubrication and friction phenomena, heat transfer, multiphase fluid approach and motion simulation. A computational thermo fluid dynamics approach has been adopted to develop a numerical tool able to simulate the behaviour of the oil during the machine working phases. The CFD approach simulates the moving metal components by means of moving meshes techniques; the friction phenomenon is estimated on the basis of formulations available in literature. The numerical model evaluates the heat transfer between moving metal parts and oil during the operating phases of the system. Furthermore, the heat transfer between oil and environment is calculated, accounting for conduction through the metal crankcase walls. A multiphase fluid approach is used for the simulation of the oil and air mixing during the crank rotation. The heat transfer coefficient predicted by the CFD approach are employed in a lumped and distributed numerical model; the reliability and accuracy of the proposed numerical approach is addressed and validated against experimental results. Experimental data have been collected by means of a thermographic camera and thermocouples. Finally, the tool's predictive capabilities are addressed by simulating different working conditions.

Formation of high purity uranium via laser induced thermal decomposition of uranium nitride

Producing gram quantities of uranium metal in a controlled manner by traditional methods is challenging due to the complex chemistry of precursor material and extreme thermal requirements. In this article, a novel approach is reported that combines modeling and an advanced experimental technique for extracting uranium from a uranium-containing compound. Using uranium nitride as an example, a computational thermodynamic approach identified a decomposition pathway to convert uranium nitride to uranium metal at temperatures exceeding 2500 K under conditions of rapid material cooling. To realize these extreme conditions, laser-induced heating, which enables fine control of process location and rapid cooling, was utilized for high-temperature modification of material. Uranium nitride was irradiated by a controlled laser under several gaseous conditions including high-vacuum, argon, and nitrogen environments, resulting in uranium metal at yields up to 96%. The complete decomposition leading to pure uranium metal occurs at the high temperature surface region, where laser-based heating induces a surface depression and molten pool of material. The observed kinetic phase behaviors in this study fundamentally differ from previous uranium decomposition studies where small uranium metal precipitates from the nitride bulk are formed at the surface of uranium nitride.

High-throughput thermodynamic screening of carbide/refractory metal cermets for ultra-high temperature applications

Carbide/refractory metal cermets possess attractive combinations of thermal and mechanical properties for ultra-high temperature structural applications. Using a high-throughput computational thermodynamic approach, 16 carbide/refractory metal cermet systems were identified, out of 1808 possible combinations, that could be fabricated by the displacive compensation of porosity (DCP) method using molten copper alloys as infiltrators at 1300 °C. Experimental results for ZrC/W and ZrC/Mo, and other proposed systems in the literature provide a level of validation to this approach. We found that copper alloys are more suitable for DCP than aluminum alloys owing to the low melting temperature of copper alloys (e.g., Zr2Cu and Ti2Cu), and the minimal chemical reaction as well as very limited mutual solid solubility of copper with refractory metals. Our results show that high-throughput thermodynamics calculation is a robust approach for systematically and thoroughly identifying refractory metal cermets that are suitable for DCP.

Analysis of microstructure formation in cast Zn alloys derived from computational thermodynamics of the Zn–Al–Cu–Mg system

A self-consistent thermodynamic description of the Zn–Al–Cu–Mg quaternary alloy system is developed. The as-cast microstructures of key Zn–Al–Cu–Mg samples in the low-alloyed range are studied experimentally. These are interpreted by computational thermodynamic analysis applying both Scheil and equilibrium simulations. Contradictions concerning the variation of apparent fraction of primary (Zn) phase, the eutectic structure and visibly larger fractions of eutectoid structure with increasing Mg content can be resolved by these detailed calculations. Two series of dedicated experimental work found in this journal on as-cast microstructures of such quaternary Zn alloys in the high-alloyed range, including also thermal analysis data, were also analyzed. The viability of this computational thermodynamic approach is demonstrated by providing a detailed analysis going beyond the explanations and interpretations in the original publications. The coverage of a larger Zn alloy composition range suggests a predictive capability of this approach.

Modern data analytics approach to predict creep of high-temperature alloys

A breakthrough in alloy design often requires comprehensive understanding in complex multi-component/multi-phase systems to generate novel material hypotheses. We introduce a modern data analytics workflow that leverages high-quality experimental data augmented with advanced features obtained from high-fidelity models. Herein, we use an example of a consistently-measured creep dataset of developmental high-temperature alloy combined with scientific alloy features populated from a high-throughput computational thermodynamic approach. Extensive correlation analyses provide ranking insights for most impactful alloy features for creep resistance, evaluated from a large set of candidate features suggested by domain experts. We also show that we can accurately train machine learning models by integrating high-ranking features obtained from correlation analyses. The demonstrated approach can be extended beyond incorporating thermodynamic features, with input from domain experts used to compile lists of features from other alloy physics, such as diffusion kinetics and microstructure evolution.

La2O3 addition for improving the brazed joints of WC-Co/1Cr13

The effects of lanthanum oxide (La2O3) as an interlayer component on microstructures and mechanical properties of brazed joints of tungsten carbide/cobalt (WC-Co) cemented carbides and the 1Cr13 stainless steel are investigated by an integrated experimental and computational thermodynamics approach. A carbide solid solution phase (CSSP) is experimentally identified adjacent to the detrimental η phase (Co3W3C) due to the addition of La2O3. Such a CSSP is observed to suppress the formation of η phase. The underlying inhibition mechanism is then explained thermodynamically by comparing the Gibbs free energy of the austenite, CSSP and η phases. The added La2O3 is also found to effectively promote the heterogeneous nucleation of the austenite phase, which results in the grain refinement and the uniform distribution of the austenite phase. The shear strength (∼340 MPa) of the brazed joints with La2O3 addition outperforms the counterparts without La2O3.

Utilization of brittle σ phase for strengthening and strain hardening in ductile VCrFeNi high-entropy alloy

General design concept used in high-entropy alloys (HEAs) have deviated from forming an fcc single phase to utilizing hard intermetallic phases in ductile fcc matrix. Here, we effectively exploited strengthening effects of a brittle intermetallic sigma (σ) phase to improve cryogenic tensile properties of a non-equi-atomic ductile VCrFeNi four-component HEA. We preferentially selected vanadium as a candidate alloying element to efficiently produce the σ phase through computational thermodynamic approach. This σ phase has beneficial effects on grain refinement through retardation of grain growth due to grain-boundary pinning, thereby leading to yield strength of 0.79–0.93 GPa. The extensive strain hardening results in tensile strength of 1.33–1.49 GPa and ductility of 23–47% at cryogenic temperature, which are enabled by nano-sized dislocation substructures rather than deformation twinning. Our results demonstrate how the intermetallic σ phase, which has been avoided in typical HEAs because of ductility deterioration, could be used in high strength HEA design.

Modern Data Analytics Approach to Predict Creep of High-Temperature Alloys

A breakthrough in alloy design often requires comprehensive understanding in complex multi-component/multi-phase systems to generate novel material hypotheses. We introduce a modern data analytics workflow that leverages high-quality experimental data augmented with advanced features obtained from high-fidelity models. Herein, we use an example of a consistently-measured developmental high-temperature alloy creep dataset combined with scientific alloy features populated from a high-throughput computational thermodynamic approach. Extensive correlation analyses provide ranking insights for most impactful alloy features for creep resistance, evaluated from a large set of candidate features suggested by domain experts. We also show that we can accurately train machine learning models by integrating high-ranking features obtained from correlation analyses. The demonstrated approach can be extended beyond incorporating thermodynamic features, with input from domain experts used to compile lists of features from other alloy physics, such as diffusion kinetics and microstructure evolution.

Experimental investigation and thermodynamic modeling of an innovative molten salt for thermal energy storage (TES)

A novel computational thermodynamic approach based on thermodynamic principles was applied to design and develop innovative molten salt mixtures for thermal energy storage. In this work, the eutectic composition of the NaCl-NaF-Na2CO3 ternary system was predicted based on experimental data via computational thermodynamic approach. Substitutional solution model (SSM) was used to describe the Gibbs energies for all liquid phases. Thus, a set of self-consistent thermodynamic model parameters was obtained for three subsystems and the parameters were used to predict the eutectic composition of the NaF-NaCl-Na2CO3 ternary system. Results manifested that the predicted eutectic point of the ternary system were located at T = 849 K and XNaF = 21.66 mol%, XNaCl = 41.87 mol% and XNa2CO3 = 36.47 mol%. By means of Differential Scanning Calorimetry method, the predicted results were verified experimentally and the agreement between the measured and predicted values was satisfactory. Thermal-physical properties for eutectic salt mixtures, such as enthalpies of fusion, heat capacity, density and thermal stability, were also determined experimentally via thermal analysis methods in this work. Through computational thermodynamics approach, an innovative eutectic salt was designed and developed as thermal energy storage (TES) materials at high temperatures, especially it can be serve as candidate thermal energy storage materials for next generation concentrated solar power (CSP) plants.

Computational thermodynamic and first-principles calculation of stacking fault energy on ternary Co-based alloys

Theoretical calculation of stacking fault energy (SFE) needs to be investigated closely in each alloy system due to the complex effect between different elements. In this study, we have revealed that the computational thermodynamic approach and first-principles density-functional-theory (DFT) calculations are capable of calculating the SFE for developing and designing ternary Co-based alloys with low SFE and excellent mechanical properties. Interaction between Ni and Cr atoms in ternary systems can make a distinct effect to the SFE while interaction between Cr and Mo atoms gives more charge transfer then lower the SFE. Effect of alloying atom position and Cr concentrations of Co-Cr-W alloys was studied and explained regarding the electronic structure. In high Cr concentrations, Cr atoms that dispersing uniform are more useful to improving the strengthening effect than those dispersing segregatively.

Experimental investigation and thermodynamic modeling of the LiNO3-RbNO3-AgNO3 system and its subsystems

Computational thermodynamics approach based on experimental values is applied to evaluation and optimization of the LiNO3-RbNO3-AgNO3 system and its subsystems in this work. The substitutional solution model (SSM) was used to describe all liquid phase. All the intermediate compounds were treated as stoichiometric of which Gibbs energies comply with the Neumann-Kopp rule. A set of self-consistent database with thermodynamic model parameters obtained for the LiNO3-RbNO3-AgNO3 subsystems and this database were used to predict thermodynamic properties of the LiNO3-RbNO3-AgNO3 ternary system. The calculated results were verified experimentally using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques, and the agreement between the experimental values and predicted values is satisfactory. The phase diagram of the LiNO3-RbNO3-AgNO3 ternary system contain two eutectic types: one eutectic (Liquid ↔ α-AgNO3 + LiRb(NO3)2 + AgRb(NO3)2) at 385.3 ± 1.5 K and another eutectic (Liquid ↔ LiRb(NO3)2 + AgRb(NO3)2 + AgRb2(NO3)3) at 398.8 ± 1.5 K. Through computational thermodynamics approach, a multi-component system was successfully predicted and this approach will be applied to design and develop multi-component molten salt mixtures as thermal energy storage (TES) materials.

Lattice mismatch modeling of aluminum alloys

We present a theoretical framework to accurately predict the lattice mismatch between the fcc matrix and precipitates in the multi-component aluminum alloys as a function of temperature and composition. We use a computational thermodynamic approach to model the lattice parameters of the multi-component fcc solid solution and θ′-Al2Cu precipitate phase. Better agreement between the predicted lattice parameters of fcc aluminum in five commercial alloys (206, 319, 356, A356, and A356+0.5Cu) and experimental data from the synchrotron X-ray diffraction (SXD) has been obtained when simulating supersaturated rather than equilibrium solid solutions. We use the thermal expansion coefficient of thermodynamically stable θ-Al2Cu to describe temperature-dependent lattice parameters of meta-stable θ′ and to show good agreement with the SXD data. Both coherent and semi-coherent interface mismatches between the fcc aluminum matrix and θ′ in Al-Cu alloys are presented as a function of temperature. Our calculation results show that the concentration of solute atoms, particularly Cu, in the matrix greatly affects the lattice mismatch.