Today, the main raw material for vanadium production is vanadium containing steelmaking slags. The yield of the vanadium extraction process is affected by the composition of the slag, which in turn determines the phases present, the fractions of the phases and the distribution of the elements between the phases. The aim of this thesis was to experimentally investigate the effect of Al2O3, CaO and SiO2 on the phase relations in vanadium containing slags at 1673 K. Synthetic slags, in which the contents of Al2O3, CaO and SiO2 were varied individually, were equilibrated at 1673 K in a vertical resistance furnace. Closed molybdenum crucibles were used to set the oxygen potential of the individual samples.  The phases present, the phase compositions and the phase fractions of the samples were studied using SEM-EDS and LOM combined with an image analysis software. The results indicate that the samples consisted of a mixture of a vanadium and iron rich spinel phase and an iron and silicon rich liquid phase at 1673 K. Practically all the vanadium was concentrated into the spinel phase while no free silica or solid phases into which both calcium and vanadium concentrate to a significant extent were observed. The effect of Al2O3 on the phase compositions and the phase fractions was seen to be limited in the range studied. CaO primarily affected the composition of the liquid phases, while the effect on the phase fractions was small. SiO2 affected both the composition and fraction of the phases. The main effect was a decreased fraction of spinel phase, with an increasing vanadium content in the spinel phase as consequence.

Electric arc furnace (EAF) slags are basic characteristic slags that include approximately 40 % iron oxide compounds. Iron oxide can be recycled and re-used in the process to decrease amount of waste product besides reducing loss of raw materials. According to result of survey performed by The European Association Representing Metallurgical Slag Producers and Processors (EUROSLAG) in 2010, 8.5 million tons of EAF slag is produced in Europe. High percentage of EAF slag is re-used in road construction as aggregate. However it can be re-cycled in the internal use for metallurgical processes as well. In order to re-use EAF slag in the process as a raw material, direct reduction is a new approach. Direct reduction is reduction of iron containing raw materials with gas or solid reductants without melting of charge. In this study, reduction conditions of 39 % Fe2O3 containing EAF slag in tube furnace was examined. As the reducing agent, metallurgical coke was used. EAF slag was milled and pelletized in raw material preparation step. Pellets were charged to fixed bed type tube furnace in a graphite boat at 1050, 1100 and 1150°C respectively with 150 and 200% of stoichiometrically required amount of metallurgical coke. 5, 10, 15, 30, 60, 90 and 120 minutes process durations were performed. Direct reduced pellets were milled to be characterized by using X-Ray Diffraction (XRD) and chemical analysis methods. Results indicate that increased temperature, process duration and stoichiometry have a positive impact on direct reduction of EAF slag in terms of iron metallization. 90 % metallization degree has been achieved as the result of the study with the process conditions of 200 % stoichiometry and 90 minutes process duration at 1150 °C.

Trough the following pages a comprehensive study of open structures will be shown, including mono-vacancy calculations and open surfaces. These are electronic structure calculations using density functional theory within the exact muffin tin method. First we investigate the accuracy of five common density functional approximations for the theoretical description of the formation energy of mono-vacancies in three closepacked metals. Besides the local density approximation (LDA), we consider two generalized gradient approximation developed by Perdew and co-workers (PBE and PBEsol) and two gradient-level functionals obtained within the subsystem functional approach (AM05 and LAG). As test cases, we select aluminium, nickel and copper, all of them adopting the face centered cubic crystallographic structure. This investigation is followed by a performance comparison of the three common gradientlevel exchange-correlation functionals for metallic bulk, surface and vacancy systems. We find that approximations which by construction give similar results for the jellium surface, show large deviations for realistic systems. The particular charge density and density gradient dependence of the exchange-correlation energy densities is shown to be the reason behind the obtained differences. Our findings confirm that both the global (total energy) and the local (energy density) behavior of the exchange-correlation functional should be monitored for a consistent functional design. Last we show the vacancy formation energies of paramagnetic Fe-Cr-Ni alloys as a function of chemical composition. The theoretical predictions obtained for homogeneous chemistry and relaxed nearest-neighbors are in line with the experimental observation. In particular, Ni is found to decrease and Cr increase the vacancy formation energy of the ternary system. / QC 20110929

No description available.

There is much that is unknown concerning the creation of Viking age brooches. Recreating these brooches in the same way they would have been created in the Viking age to try to understand how they were created is a time consuming project for experimental archaeologists.   This study has been done in order to find out if the time spent can be reduced and at the same time gain a better understanding of the creation of a Viking age brooch using 3D scanning and computer simulations. Casting simulations of a real Viking age brooch have been done using Magma5, a state of the art simulation software.   Simulations were run with several different casting systems, initial metal and mould temperatures, and both with as well as without the brooches distal figurines attached.   It was found that the initial metal and mould temperatures has got impact on the final result of the brooch, but the alloy and casting system has a much greater effect on the final result. The casting system that yielded the best result has the pouring basin directly above the medial part of the brooch and two sprues leading to gates on the north and south medial sides. / Det är mycket som inte är känt om tillverkningen av vikingatida broscher. Att försöka återskapa dem på samma sätt som vikingarna antagligen skapat dem för att öka kunskapen kring broscherna är ett tidsödande jobb.   Denna studie har gjorts för att ta reda på om den tiden kan reduceras och samtidigt öka kunskapen kring broscherna med hjälp av modern teknik som 3D skanning och datorsimuleringar. Gjutsimuleringar av ett äkta vikingatida spänne har skett i Magma5, ett kraftfullt simuleringsprogram.   Simuleringar utfördes med hjälp av flera olika gjutsystem, stor variation i smältans och formens initiala temperaturer, och både med och utan broschens distal figuriner.   Studien har funnit att smältans och formens temperaturer har påverkan på broschens slutresultat, men legeringen som används och gjutsystemet har betydligt större påverkan på slutresultatet. Gjutsystemet som gav bäst slutresultat har ett inlopp som är placerat direkt över mitten på den mediala delen, och sedan förgrenar sig i två delar och ansluter till den norra och södra delen av formkaviteten.

High Pressure Die Casting (HPDC) has very high demands on toughness and tempering resistance of the tool. A typical hardening cycle for this purpose consists on austenitizing and quenching in a vacuum furnace followed by three temperings at 600°C. In this work the possibility of optimizing the toughness and tempering resistance in Uddeholm Dievar by adding an extra tempering at the beginning and/or the end of the tempering process is investigated. Extra temperings were performed at 300-400° and hardness levels, impact toughness and tempering resistance were evaluated. Microstructural investigations as well as thermodynamical calculations were also carried out. Results showed no feasible differences between the results of the here conducted tests and those from the common tempering procedures.

Phase interface and stacking fault are two common planar defects in metallic materials. In the present thesis, the interfacial energy and the generalized stacking fault energy of random alloys are investigated using density functional theory formulated within the exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA).The interfacial energy is one of the key physical parameters controlling the formation of the Cr-richα’ phases during the phase decomposition in Fe-Cr ferrite stainless steels. This decomposition is believed to cause the so-called“475°C embrittlement”. Aluminum addition to ferritic stainless steels was found to effectively suppress the deleterious 475oC embrittlement. The effect of Al on the interfacial energy and the formation energy of Fe-Cr solid solutions are studied in this thesis. The interface between the decomposed Fe-rich α and Cr-rich α phases carries a positive excess energy, which represents a barrier for the process of phase separation. Our results show that for the α-Fe70Cr20Al10/α0-Fe100−x−yCryAlx(0≤x≤10, 55≤y≤80) interface, the Al content(x) barely changes the interfacial energy. However, when Al is partitioned only in the alpha phase, i.e. for the α-Fe100−x−yCryAlx/α0-Fe10Cr90(0≤x≤10,0≤y≤25) interface, the interfacial energy increases with Al concentration due to the variation of the formation energies of the Fe-Cr alloys upon Al alloying. The intrinsic energy barriers (IEBs) of the γ surface (also called generalized stacking fault energy, GSFE) provide fundamental physics for understanding the plastic deformation mechanisms in face-centred cubic metals and alloys. In this thesis, the GSFEs of the disordered Cu-X (X=Al, Zn, Ga, Ni) and Pd-X (X=Ag,Au) alloys are calculated. Studying the effect of segregation of the solutes to the stacking fault planes shows that only the local chemical composition affects the GSFEs. Based on the calculated GSFEs values, the previously revealed “universal scaling law” between these IEBs is demonstrated to be well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, Al, Zn and Ga increase the twinnability, while Ni decreases it. Aluminum and gallium yield similar effects on the twinnability. Our theoretical predictions are in line with the available experimental data. These achievements open new possibilities in understanding and describing the plasticity of complex alloys. / <p>QC 20141104</p>

The research presented in this thesis explores the structure, alloying and stability of the carbides in the Co-Cr-C system by using the CALPHAD approach supported by experimental measurements and ab initio calculations. WC-Co based cemented carbide materials consist of hard WC grains and a ductile Co-based binder. Cr is usually added to cemented carbides for the purpose of reducing grain growth during sintering or to increase corrosion resistance. The Co-Cr-C system is highly relevant for Cr-containing cemented carbides. For example, it determines the allowable C-content interval in the quaternary W-Co-Cr-C system with respect to the formation of unwanted Cr-based carbides. The CALPHAD method is based on critical assessment of model parameters constituting phenomenological expressions of the Gibbs energy and its derivatives, e.g. enthalpy, entropy and heat capacity. A thermodynamic assessment based on the CALPHAD method relies heavily on the available experimental or ab initio calculated information. The crystal structures of Cr23C6 and Cr3C2 have previously been accurately determined. However, various authors reported different crystal structures for the Cr7C3 carbide. A combined experimental and ab initio investigation of the crystal structure of Cr7C3 and M7C3 (M=Co,Cr) was thus performed. Furthermore, the stabilities of all end-member compounds of the mixed carbide at 0 K were determined by ab initio calculations. Available experimental information on phase equilibria with carbides in the Co-Cr-C system was found to be insufficient to describe all the features in the phase diagram. Therefore, the liquid + M23C6 + M7C3 and M7C3 + M3C2 + graphite equilibria (M=Co,Cr) were investigated experimentally with focus on the solubility of Co in the M23C6, M7C3 and M3C2 carbides. Finally, a reassessment of the thermodynamic description of the Co-Cr-C system was performed, which resulted in a set of thermodynamic models and parameters that accurately describe all of the considered information. Applied experimental methods and theoretical models are explained throughout the thesis. Important examples from the appended papers are also given. / <p>QC 20140212</p>

The possibility of cluster formation during solidication of steel is explored to explain structures that are seen on the fracture surface of the steel. A hypothesis is built that postulates porosities provide favourable locations for inclusions to agglomerate and form clusters.  A thermodynamic model is constructed to describe precipitation of porosity and inclusions. Formation of inclusions follow a nucleation and growth mechanism. Porosities on the other hand are the product of pressure balance in the liquid.  Motion of pores and inclusions is analysed based on the drag force and  surface  stresses. Gradient of surface tension is also identied as a driving force which acts on the pore surface and would cause motion. It is shown that relative motion of pores and inclusions coupled with  the inclusion tendency to get attached on pore surface makes or a viable mechanism explaining agglomeration of inclusion particles to clusters / <p>QC 20150930</p>

No description available.