Application Of Computational Thermodynamics Research Articles

Applications of Computational Thermodynamics in Materials Science Courses

Abstract Computational thermodynamics is an important tool used to predict the phase equilibria, phase compositions, transformation temperatures, solubility limits and many thermodynamic properties of multi-component materials. In this contribution, the possibilities of how to introduce computational thermodynamics into the university Materials Science courses using Thermo-Calc software are described. Also, the application of computational thermodynamics in materials research and development of new materials is shortly outlined.

The Third Law of Thermodynamics: Phase equilibria and phase diagrams at low temperatures

Great progress has been made over the recent decades in the application of computational thermodynamics (Calphad) and theoretical methodologies (CVM) including so-called first principles approaches to modeling thermodynamic properties and the calculation of phase diagrams of materials. The aim of this paper is to call attention to considerations of the THIRD LAW OF THERMODYNAMICS when evaluating these results when applied to low temperature phase equilibria. In this effort we call attention to the essential content of the modern version of this third principle of thermodynamics using an historical and pedagogical approach. An appreciation of the constraints of the THIRD LAW is shown to be valuable in projecting possible low temperature phase fields and boundaries and predicting thermodynamically consistent phase diagram configurations as T→0 K. The ideas of Simon regarding aspects or subsystems are shown to be of paramount importance in assessing the thermodynamic properties of materials at low temperatures.

Application of computational thermodynamics to Fe/Ni, Fe-3%Si/Ni and 316L/Ni systems produced by powder metallurgy

ABSTRACTThe commercial simulation software packages, Thermo-Calc and DICTRA, are widely used to predict phase formation and diffusion in materials prepared by traditional metallurgical processes. The goal of this work was to clarify whether the software can also be applied to materials produced by powder metallurgy techniques. For this purpose, diffusion couples of the material combinations Fe/Ni, Fe-3%Si/Ni and 316L/Ni were prepared by two techniques: co-pressing of powders followed by co-sintering and joining of two sintered parts followed by annealing. Thermo-Calc and DICTRA were used to predict interface formation and phase transformations during heat treatments. Scanning electron micrography and energy-dispersive X-ray spectrometry showed the formation of interdiffusion interfaces. The diffusion rate was higher in co-sintered couples, resulting in broader interdiffusion zones than those predicted by simulations, but the annealed couples exhibited interdiffusion profiles similar to those predicted by DICTRA simulations. In general, simulations and experimental results showed the same tendencies.

The Application of Computational Thermodynamics in the Understanding and Control of Clogging and Scum in Continuous Casting of Steel

Non-metallic inclusions are present in small volume fractions in steel products. A significant portion of them is associated to the deoxidation process. The type and form of inclusions is, in general, directly connected to the deoxidation practice and to eventual reoxidation during processing. Besides influencing the steel properties, non-metallic inclusions can have an important effect on their processability. In this work, we review the processability questions associated with inclusions in the continuous casting of steel, with emphasis on long products. When solid inclusions are present during the casting of steel they may agglomerate and clog the valves used in the continuous casting equipment, limiting the number of sequential heats that can be casted and reducing casting speeds. Additionally, in some conditions, solid non-metallic inclusions may agglomerate and form surface defects in the continuous casting products, sometimes referred to as scum. As productivity and quality are essential to the profitability of steelmaking, avoiding these conditions is of paramount importance. Thus, we review the main thermodynamic conditions that may lead to the clogging of continuous casting valves, and discuss, from the thermodynamic point of view, the measures that can be taken to avoid the occurrence of these various conditions. Furthermore, we discuss the conditions that might cause to the formation of scum and the thermodynamics of its formation and elimination. It is concluded that the analysis of steelmaking conditions via computational thermodynamics can have an important role in avoiding problems in continuous casting and helping ensure productivity and quality in the process.

O63] Application of Computational Thermodynamics in Solid Oxide Fuel Cell

A bi-structured gadolinia doped ceria (GDC) interlayer, which has a dense layer combining tightly with yttria-stabilized zirconia (YSZ) film and a porous layer with rough surface for contacting closely with the cathode, is prepared from a two-step sputtering process. Compared to the cell with a dense GDC interlayer, the single cell with the bi-structured GDC interlayer depicts greatly reduced ohmic and polarization resistances and increased electrochemical performance.

The Application of Computational Thermodynamics for the Determination of Surface Tension and Gibbs-Thomson Coefficient of Aluminum Ternary Alloys

Casting simulation requires high quality information about the thermophysical properties of the alloy, but the number of alloys for which such information is available is limited. In this paper, a solution of Butler’s formulation for surface tension is presented for Al-Cu-Si ternary alloys and consequently, permitting the Gibbs-Thomson coefficient to be determined. The importance of the Gibbs-Thomson coefficient is related to the reliability of predictions furnished by predictive microstructure growth models and of numerical computations of solidification thermal variables, which will be strongly dependent on the values of the thermophysical properties adopted in the calculations. The Gibbs-Thomson coefficient for ternary alloys is seldom reported in the literature. A numerical model based on Powell hybrid algorithm and on a finite difference Jacobian approximation was coupled with a ThermoCalc TCAPI interface to assess the excess Gibbs energy of the liquid phase, permitting the surface tension and Gibbs-Thomson coefficient for Al-Cu-Si hypoeutectic alloys to be calculated. The computed results are presented as a function of the alloy composition.

The application of computational thermodynamics and a numerical model for the determination of surface tension and Gibbs–Thomson coefficient of aluminum based alloys

In this paper, a solution for Butler's formulation is presented permitting the surface tension and the Gibbs–Thomson coefficient of Al-based binary alloys to be determined. The importance of Gibbs–Thomson coefficient for binary alloys is related to the reliability of predictions furnished by predictive cellular and dendritic growth models and of numerical computations of solidification thermal variables, which will be strongly dependent on the thermophysical properties assumed for the calculations. A numerical model based on Powell hybrid algorithm and a finite difference Jacobian approximation was coupled to a specific interface of a computational thermodynamics software in order to assess the excess Gibbs energy of the liquid phase, permitting the surface tension and Gibbs–Thomson coefficient for Al–Fe, Al–Ni, Al–Cu and Al–Si hypoeutectic alloys to be calculated. The computed results are presented as a function of the alloy composition.

Application of Computational Thermodynamics for superalloys

Application of Computational Thermodynamics for superalloys

Critical investigation of high temperature gas nitriding of a PM tool steel

AbstractThe nitrogen uptake of high-alloyed steels, especially tool steels, from gaseous atmospheres at elevated temperatures is a well known effect. Besides, for instance, the nitrogenbased case hardening, one application arises in the field of powder metallurgy. Here, introducing nitrogen containing atmospheres during sintering of high-alloyed powder metallurgically produced tool steels could lead to an optimization of the sintering process and an improvement of the materials properties. In this context, several works deal with the application of computational thermodynamics for considering the nitrogen uptake. The scope of this contribution is to investigate in detail the agreement of calculated and experimentally found nitrogen contents. Therefore, one typical gas-atomized powder of a ledeburitic cold work steel was sintered at a temperature of 1230°C, varying the nitrogen partial pressure during sintering between 0.02 MPa and 0.2 MPa. The measured nitrogen contents are compared with values obtained from equilibrium calculations. Additionally, the distribution of nitrogen in the microstructure is investigated by time-resolved optical emission spectrometry and energy dispersive X-ray spectrometry measurements. The results exhibit good agreement between calculated and measured values for low partial pressures of less than 0.1 MPa and an increasing deviation for higher partial pressures. Furthermore, the transformation of vanadium-containing MC carbides to M(C, N) carbonitrides was verified.

Aplicação da ferramenta termodinâmica computacional na simulação da produção de aço inoxidável

Esse trabalho, realizado com a aplicação da termodinâmica computacional, trata dos fundamentos da produção de aços inoxidáveis na aciaria. A compreensão dos equilíbrios termodinâmicos, que se estabelecem durante o processo, contribui para a melhoria do controle operacional e do rendimento do Cr, um insumo comparativamente caro. A metodologia consistiu em utilizar os bancos de dados e a rotina de minimização da Energia de Gibbs do software FactSage, para calcular os equilíbrios envolvendo os sistemas Fe-Cr-O e Fe-Cr-O-C-Ni. Os valores calculados para o teor de O em equilíbrio com o Cr são próximos aos resultados obtidos com base em equações e dados da literatura. Em relação ao teor de Cr limite, no qual o óxido sólido em equilíbrio muda de FeO·Cr2O3 para Cr2O3, os resultados desse trabalho aproximam-se dos valores estabelecidos na literatura, mas mostram discrepância em relação a trabalhos recentes. Ressaltam-se, além disso, alguns aspectos sobre os quais se embasa a tecnologia - o efeito do vácuo e da temperatura, durante a operação de refino.

Application of computational thermodynamics and kinetics to control of high Mn ductile iron austempering

To provide sufficient hardenability for austempering of ductile iron, alloying elements like Mn, Ni, Cu or Mo are frequently added. But the segregation of these alloying elements, occurring during solidification, changes the kinetics of austenitisation and austempering reaction. In this work, using the calculated alloying elements segregation profile, the related thermodynamics equations were used to calculate the Ae3 and A1 phase boundaries in the different regions of matrix. The results show the variation of austenitisation kinetics as a function of alloying elements segregation. Needles to say that as a consequence of alloying elements segregation and variation of austenitisation kinetics, kinetics of austempering should be a function of alloying elements local concentration. To verify the austempering kinetics, three high carbon Si-Mn steel compositions corresponding to three different parts of ductile iron matrix (i.e. near graphite nodules, intercellular regions and the area between these two regions) were prepared. The iron and steel samples were all subjected to different austempering cycles in dilatometry equipment. In addition, to predict time-temperature-transformation diagrams the classical nucleation theory and related equations were used to calculate the time of bainitic start transformation.

Welding: Solidification and microstructure

Parameters that control the solidification of castings also control the solidification and microstructure of welds. However, various physical processes that occur due to the interaction of the heat source with the metal during welding add a new dimension to the understanding of the weld pool solidification. Conventional theories of solidification over a broad range of conditions can be extended to understand weld pool solidification. In certain cases, because of rapid cooling rate effects, it is not unusual to observe nonequilibrium microstructures. Recent developments in the application of computational thermodynamics and kinetic models, studies on single-crystal welds, and advanced in-situ characterization techniques have led to a better understanding of weld solidification and microstructures.

Application of computational thermodynamics to the analysis of waste melting processes

The simulation system for the waste melting process (SWMP) has been developed through the combination of the multi-phase equilibrium calculation method and the thermodynamic database. The SWMP can be used to simulate reactions in waste melting processes with respect to equilibrium between various phases, identify the problems experienced by the process, and help develop strategies for process optimization. Examples of the application of the SWMP to two different types of waste melting processes are presented.

Thermodynamics of molecular electronics agents: the significance of highly mobile isomeric equilibria

The possible application of computational thermodynamics in relation to the design of bistable conformational systems for use in molecular electronics has been analysed. The search for these systems has revealed some conflicting requirements, namely, the relatively easy conversion of one structure into the other and vice versa, with the isomerisation equilibrium constants close to unity, but, at the same time, the need for both isomers to be sufficiently different to enable their easy differentiation. Using the example of the interconversions in the Si 6H 6 system characterised by means of recent theoretical calculations, the formulation and verification of the design criteria have been demonstrated using the computational approach.