Patrick Wollants

Thermodynamic optimization of the B-Fe system

Abstract The B–Fe binary system has been optimized using the CALPHAD method, utilizing published experimental thermochemical and phase diagram data. Two models for the solid solubility of B in b.c.c. Fe and in f.c.c. Fe are presented, B as a interstitial, and B as a substitutional constituent. Thermodynamic calculations based on the interstitial and the substitutional model were in good agreement with experimental data.

Thermodynamic assessment of the TiZr system and calculation of the NbTiZr phase diagram

Abstract Equilibrium phase relationships in the NbTiZr system are computed using the Calphad approach. SGTE-recommended lattice stability expressions for the pure elements are used. The thermodynamic model parameters for NbTi and NbZr are taken from recent assessments. A new thermodynamic description of TiZr is obtained by optimizing available experimental thermochemical and phase diagram data. Phase diagrams of the three limiting binaries, liquidus projection, solidus projection and a number of isothermal sections are computed.

Thermodynamic calculation of Nb-Ti-V phase diagram

Abstract Phase equilibrium in Nb-Ti-V system is calculated using thermodynamic descriptions of the lower-order systems. The thermodynamic descriptions of Nb-Ti and Nb-V are obtained by optimising available experimental information. The parameters for Ti-V are taken from a recent assessment. Phase diagram of the limiting binaries, liquidus projection, solidus projection, and two isothermal sections are computed.

Thermodynamic optimization of the lead-free solder system Bi–In–Sn–Zn

Abstract The Bi–In–Sn–Zn system is an important alloy system in lead-free soldering. Thermodynamic descriptions for the ternary systems Bi–In–Sn, Bi–In–Zn, Bi–Sn–Zn and In–Sn–Zn are optimized, using the CALPHAD method and combined to obtain a description of the quaternary Bi–In–Sn–Zn. All available experimental data from the literature are taken into consideration in the optimization. Calculated liquidi, isothermal and vertical sections and thermodynamic properties are compared with experimental data. Ternary and quaternary invariant reactions are also calculated.

Some guidelines for thermodynamic optimisation of phase diagrams

Thermodynamic optimisation of phase diagrams is a procedure that requires considerable experience and skill. The purpose of this article is to furnish certain guidelines that might facilitate the work and improve the quality of the thermodynamic optimisation of phase diagrams using the Calphad method. Some particulars regarding experimental data, Gibbs energy models, constraints on model parameters, and performing the optimisation are discussed.

Thermodynamic assessment of the Fe-Nd-B phase diagram

A thermodynamic description of all stable phases of the Fe-Nd-B system is presented. This description was obtained by the optimization of experimental thermochemical and phase diagram data from literature using a least-square method. Previous assessments of the three limiting binary systems were incorporated. A reassessment of the Nd-B phase diagram is performed, taking into account the experimental information of the ternary system. The calculated results are in excellent agreement with the experimental data. A reaction scheme is presented, accounting for all invariant reactions in the system. This leads to some differences with earlier suggestions regarding the phase relations in composition regions where the amount of experimental data is limited. It is expected that the present description could therefore provide an answer to some of the remaining conflicts between phases one would expect from the previously suggested phase diagrams and what is actually observed.

Quantitative analysis of grain boundary properties in a generalized phase field model for grain growth in anisotropic systems

A good choice of model formulation and model parameters is one of the most important and difficult aspects in mesoscale modeling and requires a systematic and quantitative analysis. In this paper, it is studied how the model parameters of a generalized phase field model affect the landscape of the free-energy density functional, the phase field profiles at the grain boundaries, and the corresponding trajectory along the free-energy landscape. The analysis results in quantitative relations between the model parameters, on one hand, and grain boundary energy and mobility, on the other hand. Based on these findings, a procedure is derived that generates a suitable set of model parameters that reproduces accurately a materials grain boundary energy and mobility for arbitrary misorientation and inclination dependence. The misorientation and inclination dependence are formulated so that the diffuse interface width is constant, resulting in uniform stability and accuracy conditions for the numerical solution. The proposed model formulation and parameter choice allow us to perform quantitative simulations with excellent controllability of the numerical accuracy and therefore of the material behavior.

Thermodynamic evaluation of Fe-Sn phase diagram

Abstract The thermodynamic descriptions for all the stable phases in the Fe-Sn system are obtained by a least-square optimisation of the thermochemical and the phase diagram data from literature. The latest recommended of expressions for Gibbs energies of pure elements are used. The calculated phase diagram and thermochemical properties are compared with the experimental data.

Non-metallic inclusions in aluminium killed steels

Abstract Heats of medium carbon aluminium killed, low carbon silicon-aluminium killed, and low carbon aluminium killed steels were sampled with short time intervals during ladle metallurgy. Non-metallic inclusions were extracted from the steel matrix and investigated using scanning electron microscopy and energy dispersive spectrometry. Six inclusion morphologies were recognised, i.e. spherical, faceted, platelike, and dendritic shapes, as well as clusters and aggregates. For each sample also the total oxygen content was measured. Spherical inclusions were most abundant, but clusters, aggregates, and large faceted inclusions made up most of the oxide volume fraction. The present research shows that clusters, which are formed during the deoxidation operation, are removed within ~15 min after aluminium addition. Aggregates and large polyhedra appear after 5-10 min and their sizes increase with holding time. Small, mainly spherical and polyhedral, and to some extent also platelike, inclusions do not show evolution in size or in composition.

Water-cooled probe technique for the study of freeze lining formation

Furnace protection by water-cooled freeze linings becomes increasingly important as the metal producing industry attempts to achieve higher process intensities. Systematic investigations of the growth and the resulting microstructure and compositional profile of freeze linings are necessary to understand the behavior of freeze linings, their relation with the industrial process, and their interaction with the wall cooling system. We have developed a technique based on the submergence of a water-cooled probe into a liquid slag bath. Freeze linings of two industrial nonferrous slags have been produced using this technique and their growth, microstructural, and compositional profiles as a function of submergence time were determined. Thermodynamic equilibrium for the investigated slag systems was calculated and compared with the observed microstructures. The freeze linings form in approximately 15 minutes. Close to the water cooling, the freeze linings are predominantly amorphous in structure. With increasing distance from the water cooling, the proportion of crystalline phases increases and bath material is entrapped in the microstructure. Cellular crystals are observed close to the bath. The freeze linings exhibit an approximate homogeneous composition. The results demonstrate that the technique is a successful tool in obtaining information on the growth, microstructure, and composition of freeze linings in industrial water-cooled furnaces.