Approximate thermodynamic solution phase data for steels

Approximate thermodynamic data based on a minimum amount of experiments are optimized for liquid, ferrite and austenite of some iron-based systems not assessed earlier, for a more accurate calculation of phase equilibria between these phases in multicomponent steels. The new data are shown to improve the correlation between calculated and measured liquidus temperature, solute partition and primary phase data in typical stainless steels.     

Reassessed thermodynamic solution phase data for ternary Fe-Si-C system

New thermodynamic solution phase data have been optimized for the Fe-Si-C system to improve the correlation between experiments and calculations obtained in an earlier assessment. New values were optimized for a binary Fe-Si interaction parameter of liquid phase and ternary Fe-Si-C interaction parameters of liquid, bcc and fcc phases applying experimental measurements on mixing enthalpies, solute activities, phase equilibria and solute partition.     

Simulation of solidification paths in high chromium white cast irons for wear applications

Thermodynamic calculations of the solidification paths in the Fe-Si-Cr-C system using the CALPHAD approach have been used for the interpretation of the solidification microstructures of high chromium white cast irons containing high silicon contents. The results show a reasonable agreement between experiments and calculations for alloys up to 2 wt% Si. The results suggests that the stability of the cementite phase is underestimated in the thermodynamic database. The calculations predict a change in the topology of the phase diagram, with the cementite primary field disappearing in favour of a new ternary eutectic involving liquid, austenite, graphite and M₇C₃ carbide, this is partially in agreement with the observed microstructures for the alloys containing 4 wt%Si. The calculations predict the existence of a complex invariant peritectic reaction involving liquid, graphite, austenite, cementite and M₇C₃ carbide in the Fe-Si-Cr-C system.     

ZnX_2-AgX(X=Cl,Br)体系的热力学评估

锌银的卤化物熔盐在电池、光学玻璃等方面具有重要的用途,而含卤化锌熔盐因其强烈吸水性和易玻璃化,相图实验测试大受限制。本文利用CALPHAD(Calculation of Phase Diagram)技术,热力学评估计算了ZnX_2-AgX(X=Cl,Br)体系在整个成分范围内的平衡相图,建立了相图与热力学数据库。评估过程中均采用双亚晶格离子溶液模型(Ag~+)_p:(X~-,ZnX_2)_Q描述体系液相结构。通过对已有的相图和热力学实验数据的精确评估,优化计算了ZnCl_2-AgCl体系在768 K,ZnBr_2-AgBr体系在773 K时的液相混合焓,分别获得自洽的热力学参数,计算结果与实验值非常吻合。     

Equilibrium characterization and thermodynamic calculations on highly alloyed refractory steels

A comparison has been made between the phase equilibrium calculated within the Calphad method with different thermodynamic databases (TCFE7, TCNI5, TTNI7) and experimental data obtained on a Nb–Ti-modified industrial HP grade. The experimental measurements include phase equilibrium data at different temperatures and liquidus/solidus determination. The obtained agreement between experiments and calculations is generally good. Conclusions are made concerning the most suitable thermodynamic database to describe highly alloyed austenitic refractory steels.     

Thermodynamic reassessment of the Au–Dy system supported by first-principles calculations

Based on the available experimental phase equilibria and thermodynamic data and enthalpies of formation computed via first-principles calculations, thermodynamic reassessment of the Au–Dy system was carried out by means of the CALPHAD method. The enthalpies of formation at 0 K for AuDy₂, αAuDy, βAuDy, Au₂Dy, Au₃Dy, Au₅₁Dy₁₄ and Au₆Dy were computed via first-principles calculations to supply the necessary thermodynamic data for the modeling in order to obtain the thermodynamic parameters with sound physical meaning. The solution phases, i.e. liquid, (Au), (αDy) and (βDy), were described by the substitutional solution model, and all the intermetallic compounds in the Au–Dy system were treated as stoichiometric phases. A set of self-consistent thermodynamic parameters for the Au–Dy system was finally obtained. The calculated phase diagram and thermodynamic properties agree reasonably with the literature experimental data and the present first-principles calculations.     

Third-generation CALPHAD description of pure GeO2 at 1 atm

The thermodynamic properties of crystalline and liquid/amorphous phases of germanium dioxide have been evaluated using DFT calculations and third-generation CALPHAD models. The values for the standard entropies of crystalline and amorphous phases were reassessed through use of the Planck-Einstein approach. This allowed a more physically-based representation of the set of thermodynamic properties of germanium dioxide to be obtained.     

Seed bubbles trigger boiling heat transfer in silicon microchannels

The smooth channel surface of microsystems delays boiling incipience in heated microchannels. In this paper, we use seed bubbles to trigger boiling heat transfer and control thermal non-equilibrium of liquid and vapor phases in parallel microchannels. The test section consisted of a top glass cover and a silicon substrate. Microheater array was integrated at the top glass cover surface and driven by a pulse voltage signal to generate seed bubbles in time sequence. Each microheater corresponds to a specific microchannel and is located in the microchannel upstream. Five triangular microchannels with a hydraulic diameter of 100 μm and a length of 12.0 mm were etched in the silicon substrate. A thin platinum film was deposited at the back surface of silicon chip with an effective heating area of 4,500 × 1,366 μm, acting as the main heater for the heat transfer system. Acetone liquid was used. With the data range reported here, boiling incipience was not initiated if wall superheats are smaller than 15°C without seed bubbles assisted. Injection seed bubbles triggers boiling incipience and controls thermal non-equilibrium between liquid and vapor phases successfully. Four modes of flow and heat transfer are identified. Modes 1, 2, and 4 are the stable ones without apparent oscillations of pressure drops and heating surface temperatures, and mode 3 displays flow instabilities with apparent amplitudes and long periods of these parameters. The four modes are divided based on the four types of flow patterns observed in microchannels. Seed bubble frequency is a key factor to influence the heat transfer. The higher the seed bubble frequency, the more decreased non-equilibrium between two phases and heating surface temperatures are. The seed bubble frequency can reach a saturation value, at which heat transfer enhancement attains the maximum degree, inferring that a complete thermal equilibrium of two phases is approached. The saturation frequency is about a couple of thousand Hertz in this study.     

Thermodynamic modeling of the Mg–Ge–Pb system

All available thermodynamic and phase diagram data of the Mg–Ge and Mg–Pb binary systems, and the Mg–Ge–Pb ternary system have been critically evaluated and all reliable data have been simultaneously optimized to obtain one set of model parameters for the Gibbs energies of the liquid and all solid phases as functions of composition and temperature. The liquid phase was modeled using the Modified Quasichemical Model in order to describe the strong ordering in Mg–Ge and Mg–Pb liquid. Mg₂Ge–Mg₂Pb solid solution phase was modeled with consideration of a solid miscibility gap. All calculations were performed using the FactSage thermochemical software.     

Thermodynamic modeling of the Mg–Si–Sn system

All available thermodynamic and phase diagram data of the Mg–Si and Mg–Sn binary systems, and the Mg–Si–Sn ternary system have been critically evaluated and all reliable data have been simultaneously optimized to obtain one set of model parameters for the Gibbs energies of the liquid and all solid phases as functions of composition and temperature. The liquid phase was modeled using the Modified Quasichemical Model in order to describe the strong ordering in Mg–Si and Mg–Sn liquids. The Mg₂Si–Mg₂Sn solid solution phase was modeled with consideration of the solid miscibility gap. All calculations were performed using the FactSage thermochemical software.     

A critical thermodynamic assessment of the Mg–Ni, Ni–Y binary and Mg–Ni–Y ternary systems

A thorough review and critical evaluation of phase equilibria and thermodynamic data for the phases in the Mg–Ni–Y ternary system have been carried out over the entire composition range from room temperature to above the liquidus. This system is being modeled for the first time using the modified quasichemical model which considers the presence of short range ordering in the liquid. The Gibbs energies of the different phases have been modeled, and optimized model parameters that reproduce all the experimental data simultaneously within experimental error limits have been obtained. For the liquid phases, the modified quasichemical model is applied. A sublattice model within the compound-energy formalism is used to take proper account of the structures of the binary intermediate solid solutions. The Mg–Ni and Ni–Y binary systems have been re-optimized based on the experimental phase equilibrium and thermodynamic data available in the literature. The optimized thermodynamic parameters for the Mg–Y system are taken from the previous thermodynamic assessment of the Mg–Cu–Y system by the same authors. The constructed database has been used to calculate liquidus projection, isothermal and vertical sections which are compared with the available experimental information on this system. The current calculations are in a good agreement with the experimental data reported in the literature.     

Micro-ECM for production of microsystems with a high aspect ratio

The most used processes for production of microsytem components are basically from the semiconductor technology. The material properties of used silicon often dont achieve the demands of for example: micro-surgery, biotechnology life science, fluidics or high temperature environment. For microstructuring of highly stressed metals, like stainless and heat resisting steels, cold work tool steels, hot work tool steels and nickel-base-alloys and a variety of metals there is no manufacturing-process. An interesting possibility for structuring this type of materials are the electrochemical machining processes (ECM). Some new developed ECM-sinking-processes are working with oscillating tool-electrode, to improve shape accuracy.