A fundamental quantum mechanical modelling approach is used for calculating liquid diffusion parameters in cemented carbides. Up to now, no detailed description of diffusion for alloying elements in a liquid Co matrix is available. Neither are experimental measurements found in the literature for the self- or impurity diffusion in the liquid Co system. State of the art application is the description of gradient formation in cemented carbide systems using DICTRA. In this work it is assumed that diffusion during sintering of cemented carbides takes place mainly in the liquid Co binder phase. With this assumption one can calculate the diffusion coefficient for different alloying elements like W, Ti, N and C in a liquid Co matrix phase. The mean square displacement (MSD) of the diffusing atoms is used to obtain the diffusion coefficients which could be simulated by Ab initio Molecular Dynamics (AIMD). By fitting the computed temperature dependence with the Arrhenius relation one can determine the frequency factor and the activation energy which allows to give a quantitative description of the diffusion. Three methods will be used for validating the data from this work. Available estimated literature values based on calculations (scaling laws, a modified Sutherland equation and classical molecular dynamics) will be used to compare the results in a first instance. The general agreement for diffusion in liquid metals will be done by comparison with experimental data for the liquid Fe system. In a last step, the diffusion values obtained by this work will be used to create a kinetic database for DICTRA. The gradient simulations will be compared with experimentally measured gradients. The AIMD simulations are performed for binary diffusion systems to investigate the diffusion between the liquid Co matrix and one type of alloying element. In a second approach the diffusion for a multicomponent systems with Co, W, Ti and C has been performed. The results from the present AIMD simulations could be shown to be in good agreement with the literature. Only two DICTRA simulations could be performed within the timeframe of this work. Both are predicting a ~3 times bigger gradient zone whereas the initial choice of the labyrinth factor λ = f could be identified as a possible source of disagreement. A labyrinth factor of λ = f2 with the calculated mobility values from the AIMD calculations should give improved results. Although the results from those simulations are not available to this date. The two approaches of the diffusion simulations in the binary and multicomponent system are giving matching results. The non-metallic elements C and N are diffusing two times faster than the fastest metallic element Co. The diffusivity of Ti is slightly lower than Co and W could be identified as the element with the slowest diffusion within the liquid Co matrix. Further investigations of the liquid structure could indicate the tendency to form bonds between C and W and between C and Ti. This gives slowed down diffusion of C in the multicomponent system compared to the diffusion in the binary Co-C system.

This project is a feasibility study for Hydro Extrusion Sweden AB, a company that produces extruded aluminium profiles. The main purpose of this project was to analyse the difference of Mg2Si particle sizes in aluminium alloys when varying parameters, such as cooling rate and composition, in aluminium extrusion, particularly the EN AW 6082 alloy. The Mg2Si particles have a great impact on the product’s mechanical properties. This was done in order to investigate whether real-time process parameter control is possible or not. The main software used was Thermo-Calc and the add-on module DICTRA. Thermo-Calc was used to do equilibrium calculations and gather data for the alloy and its phases. Based on this information and data from Hydro, simulations in DICTRA could be performed. The results were then plotted with respect to time and radius. The findings indicate that the cooling rate significantly influences the particle size. As the process becomes more intricate and involves a greater number of trace elements, adjusting the cooling rate could potentially be employed as a means to address this issue. The results also showed that trace elements had a minimal effect on the particle size. However, this probably does not match the reality since other phases affect and block the growth of Mg2Si.The overall results indicate a positive outcome for using DICTRA in determining particle sizes. However, further research needs to be done in correlation with more experiments before this could be a viable research method for Hydro. / Det här projektet är en förstudie för företaget Hydro Extrusion Sweden AB som producerar extruderade aluminiumprofiler. Det huvudsakliga syftet med projektet var att analysera skillnaden på Mg2Si-partiklarnas storlek i aluminiumlegeringar när olika parametrar som kylhastighet och sammansättning användes vid aluminiumextrudering, mer specifikt legeringen EN AW 6082. Mg2Si partiklarna har stor betydelse för produktens mekaniska egenskaper. Syftet med detta var att undersöka huruvida det är möjligt att styra process parametrarna i realtid. Mjukvaran som användes var Thermo-Calc och tilläggsmodulen DICTRA. Thermo-Calc användes för att göra jämviktsberäkningar och samla in data för legeringen samt dess faser. Baserat på denna information och data från Hydro kunde simuleringar i DICTRA utföras. Resultaten plottades sedan med avseende på tid och radie. Partikelstorleken påverkas avsevärt av kylningshastigheten enligt resultaten. I framtiden, när processen blir mer avancerad med fler spårämnen, kan det vara möjligt att justera kylningshastigheten för att hantera detta. Resultaten visade också att spårämnen hade en mycket liten effekt på partikelstorleken. Detta stämmer dock förmodligen inte med verkligheten eftersom andra faser påverkar och blockerar tillväxten av Mg2Si. De övergripande resultaten pekar på ett positivt resultat för att använda DICTRA för att bestämma partikelstorlekar. Ytterligare forskning måste göras i samband med fler experiment innan detta kan vara en genomförbar forskningsmetod för Hydro.

The development of alternative binder systems for tungsten carbide (WC) based cemented carbides has again become of relevance due to possible changes in EU regulations regarding the use of Cobalt (Co). A framework for the ICME (Integrated Computational Materials Engineering) based Materials Design is presented to accelerate the development of alternative binder systems. Part one of this work deals with the design of the cemented carbide composite hardness. It has been shown that the intrinsic binder hardness is comparable to a bulk metal alloy and that based on the binder solubilities a solid solution strengthening model developed in this work can be employed. Using a method presented in this work the non-equilibrium, frozen-in binder solubilities can be obtained. Both the design of the binder phase and composite hardness is presented based on a general Materials Design approach. Part two deals with a multiscale approach to model the surface gradient formation. The experimentally missing data on liquid binder diffusion has been calculated using AIMD (Ab initio Molecular Dynamics). The diffusion through the liquid cemented carbide binder has to be reduced to an effective diffusion value due to the solid carbides acting as obstacles that increase the diffusion path. The geometrical reduction of the diffusion has been investigated experimentally using the SIMS (secondary ion mass spectroscopy) technique in WC-Nickel-58Nickel diffusion couples. The geometrical contribution of the so-called labyrinth factor has been proven by the combination of the experiments and in conjunction with DICTRA simulations using the precise liquid AIMD diffusivities. Unfortunately, despite the improved kinetic database and the geometrical diffusion reduction, the surface gradient formation cannot be explained satisfactory in complex cemented carbide grades. Additional, but so far unidentified, contributions have to be considered to predict the surface gradient thickness. / <p>QC 20170919</p>

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