Numerous efforts have contributed to the study of phase-change problems for over a century|both analytical and numerical. Among those numerical approximations applied to solve phase-transition problems, phase-field models attract more and more attention because they not only capture two important effects, surface tension and supercooling, but also enable explicitly labeling the solid and liquid phases and the position of the interface. In the research of this dissertation, a phase-field model has been employed to simulate 2-D dendrite growth of pure nickel without a flow, and 2-D ice crystal growth in a high-Reynolds-number lid-driven-cavity flow. In order to obtain the details of ice crystal structures as well as the flow field behavior during freezing for the latter simulation, it is necessary to solve the phase-field model without convection and the equations of motion on two different scales. To accomplish this, a heterogeneous multiscale method is implemented for the phase-field model with convection such that the phase-field model is simulated on a microscopic scale and the equations of motion are solved on a macroscopic scale. Simulations of 2-D dendrite growth of pure nickel provide the validation of the phase-field model and the study of dendrite growth under different conditions, e.g., degree of supercooling, interface thickness, kinetic coefficient, and shape of the initial seed. In addition, simulations of freezing in a lid-driven-cavity flow indicate that the flow field has great effect on the small-scale dendrite structure and the flow eld behavior on the large scale is altered by freezing inside it.

SixGe1-x is a promising alloy semiconductor material that is gaining importance in the semiconductor industry primarily due to the fact that silicon and germanium form a binary isomorphous system and hence its properties can be adapted to suit the needs of a particular application. Liquid phase diffusion (LPD) is a solution growth technique which has been successfully used to grow single crystals of SixGe1-x. The first part of this thesis discusses the development of a fixed grid solver to simulate the LPD growth under zero gravity condition. Initial melting is modeled in order to compute the shape of the initial growth interface along with temperature and concentration distribution. This information is then used by the solidification solver which in turn predicts the onset of solidification, evolution of the growth interface, and temperature and concentration fields as the solidification proceeds. The results are compared with the previous numerical study conducted using the dynamic grid approach as well as with the earth based experimental results. The predicted results are found to be in good qualitative agreement although certain noticeable differences are also observed owing to the absence of convective effects in the fixed grid model. The second part investigates the effects of crucible translation on the LPD technique using the dynamic grid approach. The case of constant pulling is examined first and compared with the available experimental results. Then a dynamic pulling profile obtained as a part of simulation process is used to achieve the goal of nearly uniform composition crystal. The effect of crucible translation on the interface shape, growth rate, and on the transport process is investigated. Finally, the effect of magnetic field on the LPD growth is examined. / Graduate

Muddringsprojekt är en global företeelse och görs av flera olika anledningar, till exempel för miljömässiga aspekter och för breddning av farleder. För att få en hållbar utveckling är det viktigt att finna bra lösningar på frågan hur förorenade sediment skall hanteras . I Mälaren kommer olika muddringsprojekt att genomföras för att bredda farleden från slussen i Södertälje till hamnarna i Köping och Västerås. Muddringsprojekten skall genomföras av Sjöfartsverket, Köpings kommun och Västerås stad. En metod för att omhänderta muddermassorna är att stabilisera/solidifiera dem genom att blanda i ett bindemedel bestående av en blandning av cement, masugnsslagg och aktivt kol och låta dem härda. Detta görs för att förbättra materialets geotekniska egenskaper samt för att immobilisera föroreningar. Syftet med detta examensarbete var att undersöka om det går att använda krossade stabiliserade/solidifierade muddermassor ovan vattenytan till exempel i vägkonstruktioner alternativt som fyllnadsmaterial. Möjligheten för användandet av de stabiliserade/solidifierade materialet utvärderades genom att materialets geotekniska och miljömässiga egenskaper undersöktes. Den miljöpåverkan som de stabiliserade/solidifierade materialet skulle kunna ha på den omgivning där de används har undersökts genom analyser av totala föroreningshalter samtkoncentrationer vid lakning. Detta gjordes dels genom egna skakförsök och dels genom utvärdering av resultat från undersökningar som Statens geotekniska instituts (SGI)miljölaboratorium gjort. När det gäller materialets geotekniska egenskaper utvärderades resultat från undersökningar genomförda av SGIs geotekniska laboratorium. Stabiliseringen/solidifiering gjorde att de undersökta metallerna som förekommer som katjoner immobiliserades, vilket ledde till att lakningen minskade. Däremot fungerade imobiliseringen inte för anjoner; om det skulle ha förekommit höga halter av toxiska anjoner som till exemple arsenik, vanadin och molybden skulle dessa ha lakats ut. Ur ett miljömässigt perspektiv skulle det gå bra att använda det undersökta materialet då koncentrationen i lakvätskan låg under de båda gränsvärden som används; gränsvärden för inert avfall och gränsvärden för mindre än ringa risk vid användning av avfall för anläggningsändamål. När det gäller hållfasthet uppfyllde materialet efter 28 dagars härdning inte kraven som ställs för användning i vägkonstruktion. Däremot hade materialets geotekniska egenskaper förbättrats jämfört med de obehandlade sedimenten. / Dredging is a global phenomenon carried out for several different reasons, e.g. environmental remediation and expansion of shipping lanes. A sustainable solution to the problem of how contaminated sediment should be handled is thus important to achieve a more sustainable development. Several dredging projects will be implemented in the lake Mälaren to widen the shipping lane from the lock in Södertälje to the ports of Köping and Västerås. The dredging will be carried out as a joint effort by the Swedish Maritime Administration, the City of Västerås and Köping municipality. One method used for treating dredged sediments is stabilization/solidification. This is carried out to improve the geotechnical properties of the material and to immobilize contaminants. The method works as follows: Sediments are dragged form the lake, mixed with a binding agent consisting of cement, granulated blastfurnace slag and active carbon and then left to harden. The objective of this master thesis was to investigate the feasibility of using the stabilized/solidified material on land above the water surface. Examples of applications for the crushed material are in road construction or as fillers for vegetation surfaces. The stabilized/solidified material was evaluated with respect to environmental factors and geotechnical properties to determine if it was appropriate to use for these applications. To investigate the potential impact of the stabilized/solidified material on the surrounding environment, analysis of total contamination content and leaching tests were evaluated. In this thesis, batch-leaching tests for metals were performed as well as evaluation of lab results from surveys conducted in the environmental laboratory at the Swedish Geotechnical Institute. The geotechnical properties of the material were evaluated based on results from experimentsconducted by the geotechnical laboratory at the Swedish Geotechnical Institute. The results from the treatment with stabilization/solidification showed that most of the studied metals were immobilized, and the leaching of these metals decreased. From an environmental perspective it would be feasible to use the material, as the results of the leaching test were below the limit values used in the assessment; limits for inert waste and limits for less than small risk (‘mindre än ringa risk’) in use of waste for construction purposes. In terms of the geotechnical features, after 28 days of hardening the material did not meet the requirements for use in road construction. However, the material's geotechnical properties such as strength had improved compared to the untreated sediments.

Additive manufacturing (AM) offers reduced material waste and energy usage, as well as an increase in precision. Direct metal AM is used not only for prototyping, but to produce final production parts in the aerospace, medical, automotive and other industries. Process mapping is an approach that represents process outcomes in terms of process input variables. Solidification microstructure process maps are developed for single bead and thin wall deposits of Ti-6Al-4V via an electron beam wire feed and electron beam powder bed AM process. Process variable combinations yielding constant beta grain size and morphology are identified. Comparison with the process maps for melt pool geometry shows that by maintaining a constant melt pool cross sectional area, a constant grain size will also be achieved. Additionally, the grain morphology boundaries are similar to curves of constant melt pool aspect ratio. Experimental results are presented to support the numerical predictions and identify a proportional size scaling between beta grain widths and melt pool widths. Results demonstrate that in situ, indirect control of solidification microstructure is possible through direct melt pool dimension control. The ability to control solidification microstructure can greatly accelerate AM process qualification potentially allow for tailored microstructure to the desired application.

The size and morphology of the dendrite growth patterns are simulated for laser powder deposition of Ti-Nb alloys under steady-state and transient growth conditions. A phase field model using an adaptive grid technique was employed to simulate the steady-state growth of dendrites on rather small domains, in which fixed local solidification conditions are present. For simulation of dendrite growth patterns at transient conditions, a cellular automaton model was used along with a virtual front tracking technique on larger domains, containing various initial orientations of the solid-liquid (SL) interface. To obtain the required input thermal data, i.e., the temporal distribution of temperature, a finite element analysis was performed along with a novel numerical approach for the real-time addition of new deposition material in each time step, thus building the deposition geometry momentarily. Using the output of the thermal model, the motion and morphology of the SL interface was determined through tracking the isotherm of the solidification temperature. First, in this study, the appropriate set of processing parameters was found through an optimization process using a new concept, laser supplied energy Es, which combines the effects of the energy and powder density in the process. With the developed analytical/experimental procedure, crack and pore-free coatings of Ti-Nb with continuous beads were produced by examining the effects of a few sets of processing parameters, including laser power, laser scan velocity, laser beam diameter and powder feed rate. The results of the thermal model for the optimized set of parameters matched with the thermocouple temperature measurements with only ~5% deviation. The thermal model was able to predict realistic profiles for the temporal development of deposition geometry, thus predicting meaningful morphologies of the SL interface. The model output was easily treated for extraction of local processing parameters, such as the temperature gradient and solidification velocity. These data are very useful when simulating the dendrite growth patterns at steady-state conditions in directional solidification of selected regions in the microstructure. In order to define transient growth conditions, the simulated distribution of temperature can be also directly fed into the microstructure model at each solution time step. Phase field simulations of steady-state growth of dendrites during directional solidification showed a remarkable agreement with the experimental observations for the local dendrite arm spacing across the microstructure. Also qualitatively agreeing with the experiment, the simulated dendrite spacing exhibited a minimum around the mid-height region of the microstructure, which is explained by the counter effect of the temperature gradient and solidification velocity along the height of the sample. On a large domain containing different initial orientations of the SL interface, cellular automaton simulations for transient growth patterns of dendrites could reproduce most qualitative features observed in the microstructure. The dendrite arm spacing gradually decreased from the top of the microstructure. The competition was won by the dendrites growing in areas with higher cooling rates, i.e., in the regions closer to the top of the microstructure. The secondary arms of the primary dendrites, which are initially inclined on the vertical axis, grew extensively only along the overall growth direction and eventually became primary arms in some cases.

Finite element solution of solidification process in 2-D Cartesian and axisymmetric geometries is investigated. The use of finite element may result in spurious increase of temperature in the field and the selection of the mushy zone range when used as a numerical tool along with the selection of the mesh size results in large errors in the predicted solidification time. The approach works best for problems where the mushy zone range is finite and the thermal conductivities of both phases are high.

In this study an experimental spray-rolling set-up is designed in order to produce rapidly solidified Al-Fe-V-Si flat product. Al-Fe-V-Si alloys produced by rapid solidification powder metallurgy (RSP/M) methods are mostly used in high temperature applications in aerospace and automotive industries. The RSP/M technique used is spray deposition, which is desirable because of the high cooling rates achieved, as a result fine silicide dispersoids and intermetallics are observed in the microstructure which are known to contribute to the mechanical properties i.e. high strength at elevated temperatures, thermal stability, fracture toughness, corrosion resistance. Since spray deposition is a droplet consolidation process a considerable amount of porosity is expected in the final product. In this work, spray rolling process, which consists of spray deposition and subsequent hot twin-rolling stage, is designed and developed by interpreting the results obtained from SEM, XRD, tensile, three point bending and hardness tests of the specimens formed in several design stages. Two original intermetallic phases characterized in this study are V3Si and V2Mg3Al18 .

In Rahmen dieser Arbeit wurde ein Simulationsprogramm für Gießprozesse weiterentwickelt. Zunächst wurden die Richtigkeit der mathematischen Lösung und die Sensibilität der Software bestätigt. Dazu wurde ein Vergleich der berechneten mit den experimentellen Werten durchgeführt. Zur Messung der Wanddicke des erstarrenden Gussteils wurde eine neue Methode zur Visualisierung der Berechnungsergebnisse erarbeitet. Anhand zweier Beispiele zur Berechnung eines dünnwandigen, komplizierten Al-Gussteils und eines exothermischen Speisers wurde eine korrekte Nutzung neuer Gießtechnologien aufgezeigt. Das Simulationssystem wurde speziell für das Stranggießen modifiziert. Die neu entwickelten Berechnungsalgorithmen sowie die Visualisierungsmöglichkeiten erlauben eine exakte Modellierung des Strangabzuges in der Gießmaschine. Auch in diesem Falle liefert der Vergleich zwischen den durchgeführten Berechnungen und den erzielten Versuchswerten die Richtigkeit und Exaktheit der neu eingesetzten Methode.

Compacted graphite iron (CGI) is rapidly becoming an attractive alternative material for engine components in the automotive industry, replacing lamellar graphite iron (LGI) in applications where high mechanical strength is desired. However, the gain in mechanical strength comes with a cost; thermal conductivity, process control and machining are three areas that are more challenging for CGI. This generates a need for research regarding various aspects concerning CGI. In this thesis the microstructure formation during solidification and solid state transformation will be the focus of interest. The phase transformations relevant for microstructure formation of importance to properties in CGI were studied. Experiments were performed in an industrial foundry giving this research direct relevance to regular production of CGI castings. Solidification of the grey (graphite/austenite) eutectic will be discussed, focusing on some relevant aspects influencing the graphite morphology of CGI. The formation of graphite nodules has been investigated by studying colour-etched microstructures. In a material containing mainly CGI cells it was found that nodules form either early during solidification as a consequence of high undercooling or late in the solidification sequence due to a combination of high undercooling and segregation of nodularising elements. Solidification of the white (cementite/austenite) eutectic was studied using chill wedges and the influence of some alloying elements on the amount of carbides was examined. To further enhance the understanding of carbide formation in CGI a commercial casting simulation software was used to correlate real castings to simulations. It was found that the alloying elements investigated influence the carbide formation in a similar way as in other graphitic cast irons and that high nodularity CGI is more prone to chill formation than low nodularity CGI. The solid state transformation was studied and a deterministic model was developed. The model divides a eutectic cell into layers, in order to take into account segregation of alloying elements, which was observed to be influential for the ferrite growth. Moreover, the effect of alloying elements on mechanical properties (tensile properties and hardness) was evaluated. Properties were correlated to microstructural features originating from both solidification and solid state transformations. The trends found generally confirmed previous results regarding properties in graphitic cast irons.

An improved crystallisation spectrometer has been designed, built and tested. It is to be used by others to gain new knowledge about the solidification of matter by study of the crystallisation of hard sphere colloid samples that are an established model for the behaviour of some aspects of atoms. In this crystallisation spectrometer, expanded and collimated green laser light is Bragg scattered from the colloidal crystals as they form, and the diffracted light is focused by a liquid filled hollow glass hemispherical lens onto low cost CCD array detectors that are rotated about the optical axis to average the intensities around the whole Debye-Scherrer cone of scattered light. The temperature of the sample is controlled to +/-0.1„a, and because of the ability to change the refractive index of the sample particles with temperature, this is utilised to control the amount of scattering from the sample Also, this spectrometer uniquely exploits the refractive index match of the colloidal particles, the solvent, the bath liquid, and the glass used for both the sample bottle and the hollow glass hemisphere. A unique facility has been incorporated to permit tumbling of the sample prior to the measurement commencing to shear-melt any pre-existing crystals. This ensures that the sample is completely fluid and is at the correct temperature at the start of the measurement. The instrument is assembled on an optical table and is computer controlled. Results presented show that this new spectrometer with its use of the whole Debye-Scherrer cone of Bragg scattered light and other enhancements gives insight into the crystallisation process more than one order of magnitude of time earlier than previous light scattering experiments, providing new knowledge about the crystallisation process.