178 research outputs found
Combining thermodynamics with tensor completion techniques to enable multicomponent microstructure prediction -- codes
No full textThis dataset contains the codes and input data used to generate the results presented in the paper "Combining thermodynamics with tensor completion techniques to enable multicomponent microstructure prediction", Yuri Amorim Coutinho, Nico Vervliet, Lieven De Lathauwer, Nele Moelans", in npj Computational Materials (doi: 10.1038/s41524-019-0268-y). The codes assume the use of MATLAB in combination with the TC toolbox (ThermoCalc) and Tensorlab (https://www.tensorlab.net/). You can find more information in the readme.txt scripts included in the dataset
Bounding box framework for efficient phase field simulation of grain growth in anisotropic systems
No full textA sparse bounding box algorithm is extended to perform efficient phase field simulations of grain growth in anisotropic systems. The extended bounding box framework allows to attribute different properties to different grain boundary types of a polycrystalline microstructure and can be combined with explicit,
implicit or semi-implicit time stepping strategies. To illustrate the applicability of the software, the simulation
results of a case study are analysed. They indicate the impact of a misorientation dependent boundary energy formulation on the evolution of the misorientation distribution of the grain boundary types and on the individual growth rates of the grains as a function of the number of grain faces.sponsorship: Nele Moelans thanks the Research Foundation-Flanders (FWO-Vlaanderen) for financial support. (Research Foundation-Flanders (FWO-Vlaanderen))status: Publishe
Combining thermodynamics with tensor completion techniques to enable multicomponent microstructure prediction -- codes
No full textThis dataset contains the codes and input data used to generate the results presented in the paper "Combining thermodynamics with tensor completion techniques to enable multicomponent microstructure prediction", Yuri Amorim Coutinho, Nico Vervliet, Lieven De Lathauwer, Nele Moelans", in npj Computational Materials (doi: 10.1038/s41524-019-0268-y). The codes assume the use of MATLAB in combination with the TC toolbox (ThermoCalc) and Tensorlab (https://www.tensorlab.net/). You can find more information in the readme.txt scripts included in the dataset
Ontwikkeling van een methode voor de bepaling van het oplosbaarheidsgebied van intermetallische fasen in metaal-metaal verbindingen
No full textMy PhD research is focused on hetero-junctions of dissimilar materials, for example, the integrated and composite material structures used in micro-electronic and photovoltaic devices.The growth of intermetallic compound (IMC) layers and precipitates at and near the interfaces is the main topic to study their influence on the reliability and life time of these devices.
Research Activities:
In the frame work of my PhD research, a combined modeling approach for the growth of IMC phases will be derived and implemented based on the phase-field method for microstructure evolution simulations and the CALPHAD method for the prediction of phase equilibria and thermodynamic properties in multi-component systems. The new simulation method will be used, integrated with experimental research, to study the growth of IMC layers and precipitates and predict diffusion paths in multi-component hetero-junctions of materials with 3 and 4 components.
The major activities are listed as follows:
more extensive study of the existing phase-field models for alloys and CALPHAD approaches for Gibbs energies and diffusion mobilities
implementation and validation of coupled phase-field/CALPHAD approaches for intermediate phases with low solubility
application of the coupled phase-field/CALPHAD approach on microstructure evolution and interdiffusion in a ternary system
validation of of the coupled phase-field/CALPHAD approach on microstructure evolution and interdiffusion in a quaternary systemstatus: Publishe
A quantitative and thermodynamically consistent phase-field interpolation function for multi-phase systems
No full textThe aimed properties of the interpolation functions used in quantitative phase-field models for two-phase systems do not extend to multi-phase systems. Therefore, a new type of interpolation functions is introduced that has a zero slope at the equilibrium values of the non-conserved field variables representing the different phases and allows for a thermodynamically consistent interpolation of the free energies. The interpolation functions are applicable for multi-phase-field and multi-order-parameter representations and can be combined with existing quantitative approaches for alloys. A model for polycrystalline, multi-component and multi-phase systems is formulated using the new interpolation functions that accounts in a straightforward way for composition-dependent expressions of the bulk Gibbs energies and diffusion mobilities, and interfacial free energies and mobilities. The numerical accuracy of the approach is analyzed for coarsening and diffusion-controlled parabolic growth in Cu-Sn systems as a function of R/l, with R grain size and l diffuse interface width. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.status: Publishe
Investigation of diffusion behavior in Cu–Sn solid state diffusion couples
No full textThe diffusion behaviors and diffusion parameters of intermetallic compounds (IMCs) formed in Cu-Sn diffusion couples were investigated at the temperature range of 130 °C–200 °C. Interdiffusion coefficients of IMCs were calculated based on the measured composition profiles of the diffusion zones. Considering the wavy type of the diffusion layers and the narrow homogeneity range of the IMCs (Cu₃Sn and Cu₆Sn₅), the integrated method was performed to evaluate the integrated interdiffusion coefficients based on the measured thicknesses of the IMCs layers. The transient initial growth stage was excluded by considering two diffusion times where the growths of both IMCs are in the diffusion control stage. The activation energies for diffusion of the IMCs were evaluated from the integrated diffusion coefficients. The growth behavior of Cu₃Sn suggested the existence of a transient growth regime for Cu₃Sn at the initial stage in cold-bonded Cu-Sn diffusion couple. The intrinsic diffusion coefficients of Cu and Sn in Cu₆Sn₅ were estimated based on the integrated diffusion coefficients. Sn was found to be the faster diffusion component in the Cu₆Sn₅ phase. Phase-field simulations combined with the experimentally measured diffusion coefficients and steady-state growth-rate coefficients were performed to estimate the homogeneity range of IMCs. The estimated results are consistent with the experimental results from this study as well as those from literature experimental values and showed that the homogeneity ranges of Cu₃Sn and Cu₆Sn₅ phases in the Cu-Sn system are almost temperature independent.sponsorship: Authors thank the foundation from Fonds Wetenschappelijk Onderzoek - Vlaanderen (FWO). The corresponding author, Yuan Yuan, is a FWO Pegasus Marie Curie Fellow of the Research Foundation - Flanders (FWO - Vlaanderen) and European Commission. The funding is in the European Union's Seventh Framework Program for research, technological development and demonstration under grant agreement No. 267216. This work was under the collaboration between the group of Prof. Nele Moelans in KU Leuven and the group of Prof. Hans Jurgen Seifert in Karlsruhe Institute of Technology. The simulations were performed using the VSC - Flemish Supercomputer Center, which is managed by the Hercules Foundation in partnership with five Flemish university associations. Yuan Yuan greatly appreciates Prof. Hans Jurgen Seifert for the kindly host. The SEM analysis done by Ms. Materna-Morris, the AES analysis done by Mr. Tobias Weingaertner and the EPMA analysis done by Mr. Pieter L'hoest are highly appreciated. (European Union|267216)status: Publishe
Ontwikkeling van een elastoplastisch faseveldmodel voor meerfasigesystemen
No full textThe microstructure of a material largely determines its properties at the macroscale. Tailoring the microstructure to obtain desirable properties, and thereby, high performance of a material, is a challenge faced by the manufacturing sector. Increasingly, in order to avoid and reduce time-consuming and expensive experiments, computer simulations are being used to predict the microstructure of a material under the set of conditions the material is exposed to during processing or service. Phase-field modelling is one such tool that is used to simulate the evolution of the microstructure and other characteristics such as composition, strain, and stress in a material at the micron and sub-micron length scales. This is a powerful tool for simulating coupled mechanical and chemical behaviour, which is of utmost importance in solid-state multi-phase materials such as solder alloys, turbine materials, and steels, wherein the presence of strain affects phase transformations. In this work, we aimed to identify or develop a quantitative phase-field model for multi-phase systems that considers elastic and plastic deformation. To this end, we first evaluated the existing schemes for including elastic effects and found that the properties calculated using them deviated from the analytical solution. This was due to unphysical excess energy generated at the interfaces, which was an artefact of the models due to interfacial conditions that were different from local equilibrium conditions. Therefore, we developed a new scheme that takes into account local chemical and mechanical equilibrium conditions at the interface. This scheme was then validated for different configurations in 2D and 3D showing good agreement with analytical solutions. We then applied this model to the microstructure evolution in Sn-Cu/Cu solder joint, wherein the formation of brittle intermetallic phases affects the reliability of the solder joint. In order to simulate such a system using experimentally measured or theoretically estimated physical and chemical parameters from literature, the new elastic scheme developed in this work was coupled with a scheme to include plastic deformation and extended to multi-phase systems. Moreover, ab initio calculations of stiffness tensors of Cu and Cu3Sn were also performed because of large variations among existing values in literature. Simulations of intermetallic growth in the solder joint showed that strains play a significant role in the growth kinetics and composition evolution. The development of the new phase-field model in this work drives forward the growing interest and research in performing predictive simulations of microstructure evolution in complex multi-phase industrial alloys where strain plays a significant role in phase transformations.status: Publishe
Methodology Development and Experimental Determination of the Origin of Sticking Copper Droplets in Pyrometallurgical Slags
No full textCopper is one of the first metals ever extracted and used by mankind. Due to its excellent properties, such as formability, corrosion resistance, thermal and electric conductivity, copper has been an important metal throughout history and is still used in a wide variety of applications. Consequently, the copper demand remains high and is expected to continuously increase in the future. Therefore, the urge for further process optimization remains relevant for both primary and secondary copper production. Within copper producing industry, the process efficiency is to a large extent related with copper losses throughout the production process. Copper is mainly produced via pyrometallurgical processes, where sedimentation is frequently applied to obtain a phase separation between different pyrometallurgical phases (slag, matte and metal). During sedimentation, phase separation is driven by the difference in density, but is often suboptimal, leading to copper losses in the slag. Due to its economic importance, this phenomenon remains an important issue in copper production and a lot of research is already performed on this topic. Currently, it is generally accepted that there are two types of losses: chemical and mechanical losses. Chemical losses refer to copper which is dissolved in the slag in its oxidic or sulfidic form. Mechanical losses refer to entrained copper droplets in the slag which did not settle into the underlying matte or metal phase. Four main causes are frequently mentioned in literature explaining the presence of these entrained droplets:
I. Charging or tapping operations
II. Gas-producing reactions that disperse the metal into the slag
III. Precipitation of copper due to a local decrease in copper solubility in the slag
IV. The attachment of metal droplets to spinel solids in slags
The first three reasons have been extensively studied in literature. Concerning the last reason, although it has been clearly observed, limited experimental and industrial data or fundamental knowledge is available. In order to further increase our knowledge and to improve the copper recovery efficiency, it would be a significant step forward to acquire fundamental understanding concerning this phenomenon. This lack of knowledge determined the basis for this PhD-research as the goal is indeed to gain fundamental insights, knowledge and understanding concerning the phenomenon of sticking copper droplets to spinel solids in pyrometallurgical slags.
At first, a suitable methodology had to be developed to tackle this problem. A wide variety of experimental approaches have been described to study metal losses in slags in general. However, no method has focused on the phenomenon of sticking droplets. Therefore, a suitable methodology was developed starting from two complementary approaches.
First, the spinel-Cu-slag interactions were studied using the sessile drop method for copper-spinel, slag-spinel and slag-copper-spinel combinations, respectively. For this purpose, MgAl2O4 and ZnFe2O4 substrates, representing the spinel solids in industrial slags, were produced using powder based methodologies. Attempts were made to produce Fe3O4, but it appeared to be experimentally very difficult to keep this spinel structure stable throughout the substrate production, which would therefore also be a problem during the sessile drop experiment. Pure copper and copper-silver alloys (5, 12.5 and 30 wt% Ag) were selected to represent the sticking droplets and an industrial relevant synthetic (PbO-CaO-SiO2-Cu2O-Al2O3-FeO-ZnO) slag was chosen with a composition in the spinel primary phase field. To perform the sessile drop experiment, two methodologies were used: an adapted heating unit of the confocal scanning laser microscope and a set-up built around a horizontal tubular furnace.
Secondly, two experimental set-ups were developed to study the attachment of copper droplets in the slag. For these experiments, the synthetic slag was used as well. One set-up was specifically developed to study the effect of the sedimentation time, while the second set-up allowed examining the sticking droplets gradient over the slag height.
After the methodology development, the set-ups were used to study the spinel-copper-slag interactions. At first, the copper-spinel and slag-spinel interactions were evaluated with the sessile drop set-up. The copper-spinel interaction was examined by different sets of sessile drop experiments in which the wetting behaviour between Cu/Cu-Ag alloys and MgAl2O4 substrates was studied for an oxygen partial pressure range between 10-13 and 10-8 atm. For all alloys, a non-wetting behaviour was observed, with a maximal contact angle for the Cu-12.5 wt% Ag alloy. It was also observed that pure copper displays an improved wetting for an oxygen partial pressure of 10-8 atm. A less explicit effect of the oxygen partial pressure was observed for the Cu-Ag alloys, indicating a combined influence of the oxygen partial pressure and the alloy composition on the wetting behaviour. Subsequently, the effect of the composition of the spinel substrate was studied. Therefore, the wetting of pure copper on ZnFe2O4 and MgAl2O4 was evaluated using sessile drop experiments with different interaction times under a protective Ar-atmosphere. A low wettability of the copper was observed for both types of spinel substrates, but the contact angle for ZnFe2O4 (88°) was smaller than for MgAl2O4 (123°). The interaction time had no significant influence on the wetting behaviour.
The spinel-slag interaction was examined between MgAl2O4 and the synthetic slag. In contrast to copper, slag displayed a reactive wetting with the formation of an (Mg,Zn,Fe)(Al,Fe)2O4 interaction layer at the MgAl2O4-slag interface. More focus was put on the origin of the interaction layer and its evolution as a function of the interaction time. Therefore, MgAl2O4 substrates were immersed for different times in the synthetic slag (10 s, 30 s, 1 min and 3 min). Already after 10 s an interaction layer could be observed, indicating the fast nucleation and formation kinetics of this layer. Within the first minute, a significant increase in thickness of the interaction layer was observed. Subsequently, the formation speed slowed down, probably due to a local depletion of the spinel forming elements in the slag.
Additionally, an adapted sessile drop experiment was performed to study the copper-slag-spinel interaction, in which both copper and slag were molten on a MgAl2O4 substrate. The slag positioned itself in between the copper droplet and the spinel substrate. Similar to the slag- MgAl2O4 experiment, a (Mg,Zn,Fe)(Al,Fe)2O4 interaction layer was formed at the slag-spinel interface. The positioning of the slag allowed no direct interaction between the copper droplet and the MgAl2O4 substrate. At the slag-copper droplet interface, an interaction layer of copper oxide was present and copper dissolution into the slag was observed. However, the presence of small copper droplets in the slag sticking to spinel solids was also observed.
In a next step, the phenomenon of sticking droplets was studied in the synthetic slag system using the two set-ups developed in the methodology section. In both experiments, a significant part of the present mechanically entrained copper droplets was attached to spinel solids. A clear decrease of the amount of mechanical entrained droplets was noticed in the upper slag layer as a function of time, together with a variation of the amount of mechanically entrained droplets as a function of slag height. Similar observations could be made for the spinel solids present in the slag.
Within the slag system, two different types of spinel phases were present: an Al-rich spinel and an Fe-rich spinel. Throughout all experiments, it was observed that copper droplets were only attached to Fe-rich spinel solids. Furthermore, it was also observed some copper droplets were completely surrounded by spinel solids present in the slag system.
It has been noted throughout the sessile drop experiments that slag exhibits a better wetting than copper on spinel substrates. The origin of the phenomenon of the sticking copper droplets requires consequently that an energy barrier has to be overcome to break up a slag layer surrounding the spinel solid. Two different ways are suggested to explain the origin of the copper droplets sticking to spinel solids. Firstly, extensive stirring could be sufficient to remove the slag layer and induce the attachment. Secondly, it is suggested that the sticking droplets find their origin in a chemical reaction, occurring when the system evolves towards a thermodynamically more stable state. While the first assumption seems to be less likely as sticking droplets are also observed in experiments without any stirring, the second option was explored in more detail. A reaction scheme was proposed, including two possible pathways where the spinel solids form together with the copper droplets or form around the copper droplets depending on the local conditions of the system. In both pathways, redox reactions involving copper (oxides) are essential and within the applied synthetic system, Fe and Fe-oxides have a crucial role. The proposed mechanism can explain the presence of droplets sticking to spinel particles in the copper-slag-MgAl2O4 sessile drop experiments and the presence of copper droplets fully surrounded by spinel substrates.
Based on the observed interactions between the slag and copper droplet on the spinel substrates, the copper-spinel interaction seems not stable in the presence of a slag. This is in contradiction with the observed presence of small entrained sticking droplets in the slag. On the one hand, it is possible that the determining interfacial tensions in the sessile-drop set-up, where the experiment is carried out in an argon atmosphere, are different from those of sticking droplets which are fully surrounded by a synthetic slag. On the other hand, it is also possible that, if the sticking droplets originate from a chemical reaction, a reactive wetting behaviour occurs as long as the reactions takes place. This confirms the explanation that a chemical reaction mechanism might induce the phenomenon of sticking droplets.
Finally, the sedimentation behaviour of the droplet/spinel entity is evaluated. A model is developed to calculate the sedimentation rates based on an adapted form of the Stokes’ equation. Although the model is based on a number of simplifying assumptions, interesting insights are gained concerning the influence of the sticking interaction between spinel solids and copper droplets on the settling behaviour. It is noted that the attachment of the copper droplets to spinel particles hinders the complete sedimentation, since the average density of the ‘copper droplet – spinel’ entity is lower than that of the underlying copper. Additionally the presence of attached spinel particles can hinder the coagulation of smaller droplets, which also hinders the settling rate.status: Publishe
Isothermal Crystallization of Metallurgical Slags: Phase Field Simulations Combined with In Situ Experiments
No full textCrystallization of metallurgical slags occurs in many industrial pyrometallurgical processes. Important examples are the application of freeze linings, refractory degradation and the usability of the solidified slag. To extend the fundamental knowledge of these phenomena, this research focuses on the simulation and in situ observation of crystallizing minerals in oxide melts. Modeling of slag crystallization can bring valuable insight into phenomena that are difficult to measure or observe, such as solute diffusion and growth kinetics of minerals in liquid slags. In this work, the phase field technique is used because it has proven its capabilities for microstructure evolution in metals, such as solidification, coarsening and solid-state transformations. A state-of-the-art multi-phase and multi-component model is extended to simulate crystallization of oxide melts. Therefore, the model is linked with thermodynamic databases for oxides, the phase field mobility is made dependent on the interface orientation to allow faceted crystal growth, and a new boundary condition is developed to treat redox dependent behavior of multivalent cations when the melt is in contact with an oxygen-containing atmosphere. The phase field model is applied to the isothermal dendritic crystallization of Wollastonite (CaO.SiO2) in a ternary CaO-Al2O3-SiO2 melt, and the crystallization of Magnetite spinel (FeO.Fe2O3) in a FeO-Fe2O3-SiO2 melt, under an oxidizing atmosphere. Besides the simulations, the crystallization behavior of Wollastonite in a CaO-Al2O3-SiO2 melt is also observed experimentally, using a confocal scanning laser microscope (CSLM). Relating the simulation to experimental results allows an estimation of the solid-liquid interfacial energy of Wollastonite in a CaO-Al2O3-SiO2 melt, which is difficult to measure directly. The developed model is also used to answer a longstanding issue regarding ternary two-phase diffusion couples, in which multiple analytical solutions exist. Using the phase field model, this work shows that the diffusion path depends on the Gibbs energies of both phases as well as their interfacial energy.status: Publishe
Metal droplet entrainment by solid particles in slags : a combined phase field-experimental approach
No full textThis doctoral work investigated metal droplet entrainment by solid particles in slags with a combination of two experimental set-ups and two phase field models. The binary model with limited complexity already clarified our view of the interaction between metal droplets and nonreacting solid particles to a great extent. For example, the fact that the movement of one phase with respect to the others influenced the apparent wetting regime is very interesting for the interpretation of experimentally obtained results. Moreover, the two different types of experiments confirmed that a chemical reaction might lay at the origin of the attachment, but that it requires nucleation sites in the form of metal droplets before it takes place. However, the first phase field model assumed nonreactive solid particles. Thus, a model concerning the growth of the solid phase in a realistic quaternary oxide system was also considered. Future work needs to consider the interaction of reacting metal droplets with reacting solid particles in a realistic liquid slag
- …
