This thesis work concerns about the importance of the cast surfaces, surface phenomenon such as the formation of the oscillation marks and exudation and related defects including cracks and segregation that happened during the continuous casting. All of the investigated materials were collected during the plant trials while an in-depth analysis on these materials was performed at the laboratory scale with certain explanations supported by the schematic and theoretical models. The work consists on different material classes such as steels and phosphor bronzes with a focus on the surface defects and their improvements. In order to facilitate the theoretical analysis which could be capable of explaining the suggested phenomenon in the thesis, a reduced model is developed which required lesser computational resources with lesser convergence problems. / <p>QC 20160527</p> / Oscilation mark formation during continous casting of steel

The term Nanoceramics is well known in the ceramic field for at least two decades. In this project a detailed study was performed on the synthesis of α-alumina nanopowders. High solids content nanoalumina suspensions were prepared and used to form green bodies using both wet and dry forming routes. The green bodies were then sintered using both conventional single and two-step sintering approaches. Synthesis: Two different synthesis methods, viz. precipitation and hydrothermal treatment, were used to synthesize fine α-alumina powders from aluminium chloride, ammonia solution and TEAH (Tetraethyl ammonium hydroxide). XRD, TEM and FEG-SEM were used to characterise the powders produced. The presence of commercial α-alumina powder as seed particles did not affect the transformation to α-alumina phase during the hydrothermal treatment at 220˚C in either basic or acidic environments. The results obtained from the precipitation route showed that the combined effect of adding α-alumina seeds and surfactants to the precursor solution could lower the transformation temperature of α-alumina from about 1200˚C for unseeded samples to 800˚C, as well as reducing the level of agglomeration in the alumina powders. The difference in transformation temperature mainly resulted from the nucleation process by the α-alumina seeds, which enhanced the θ → α transformation kinetics. The lower level of agglomeration present in the final powders could be due to the surface modifying role of the surfactants preventing the particles from growing together during the synthesis process. By introducing a further high-temperature step for a very short duration (1 minute) to the low-temperature heat treatment route (800˚C/12 h), the unseeded sample with added surfactant transformed into pure α-alumina phase. The newly-added step was shown to be an in-situ seeding step, followed by a conventional nucleation and growth process. The best final powder was compared with a commercial α-alumina nanopowder. Processing of alumina ceramics: The effect of low-molecular weight ammonium dispersants including Dispex-A40, Darvan-C and Dolapix-CE64, on high solids content nanoalumina suspensions was investigated. The nanosuspension prepared using the most suitable dispersant, Dolapix-CE64, was slip cast into ~53% dense, very homogeneous green bodies. This nanosuspension was also spray freeze dried into crushable granules using Freon as a foaming agent. Green compacts with density of ~53.5% were then formed by dry pressing the 2 vol% Freon-added spray freeze dried granules at 40 MPa. Both slip cast and die pressed green bodies were sintered using conventional single-step and two-step routes followed by characterising the density and grain size measurement of final dense compacts. The results have been compared with that of a submicron alumina ceramic prepared using a commercial α-alumina suspension. Highly dense alumina with an average grain size of ~0.6 μm was fabricated by means of spark plasma sintering at 1200˚C. The application of 500 MPa allowed achieving almost fully dense alumina at temperature as low as 1200˚C for 30 minutes with no significant grain growth.

Magnesium alloys have been extensively used for structural and functional applications due to their low densities. In order to improve the mechanical properties, grain refinement of the microstructures of magnesium alloys has been studied for many years. However, an effective and efficient grain refiner or refinement technique hasn’t been achieved yet, especially for those with aluminium contained. In this study, solution for this problem has been discovered through further understanding of the solidification process, including the potency and the efficiency of nucleation particles, the role of solute, and the role of casting conditions. First of all, the study suggested that MgO particles can act as nuclei in magnesium alloys by measuring and analyzing the differences in cooling curves with various amount of endogenous MgO particles. The differences indicated that the number density of MgO particles has a huge influence on the microstructure. This idea has been fatherly proved by the inoculation of MgO particles in magnesium alloys because the microstructures have been significantly refined after the inoculation. A new kind of refiner (AZ91D-5wt%MgO) has been developed based on such understandings. Secondly, the study discovered that the role of solute has much smaller effect on the grain size than it was suggested in traditional understandings. The inverse-proportional relationship between the grain size and the solute is highly suspected and the major role of solute is to cause columnar- equiaxed transition. The role of casting conditions has also been studied in order to provide experimental evidence for the existence of melt quenching effect in magnesium alloys. It is shown that various casting conditions, such as pouring temperatures and mould temperatures, have large influence on the critical heat balance temperature after rapid pouring. In this study, a theoretical model based on the analysis of cooling curves is presented for grain size prediction. An analytical model of the advance of equiaxed solidification front is developed based on the understanding of the role of casting conditions. Eventually, all these understandings have been applied to magnesium direct-chill (DC) casting. The refined microstructure of DC cast ingots can further assist in understanding the mechanism of advanced shearing achieved by MCAST unit. The comparison of the ingots with and without melt shearing indicated that the advance shearing device can disperse MgO film into individual particles.

Self-assembled nonionic alkyl glycoside surfactants are of interest for creating functional adsorption and catalytic sites at the surface of mesoporous metal oxides, but they typically impart poor long-range order when used as pore templates. Improved order and control over the functional site density may be achieved by mixing them with a cationic surfactant. To confirm this hypothesis, we investigate the lyotropic liquid crystalline (LLC) phase behavior of aqueous solutions of the functional nonionic surfactant n-dodecyl β-D-maltoside (C12G2) and cationic cetyltrimethylammonium bromide (C16TAB). A ternary phase diagram of the C16TAB-C12G2-water system is developed at 50 °C. By replacing the volume of water in the phase diagram with an equivalent volume of silica, ordered mesoporous materials are prepared by nanocasting with variable C12G2/C16TAB ratios. Metal oxide mesophases can almost always be predicted from the ternary phase diagram, except that silica prepared with high C12G2/C16TAB ratios are very weakly ordered, perhaps due to differences in hydrogen bonding or rate of assembly. Based on the ternary phase diagram of the system, a systematic approach is taken to the incorporation of titania sites via complexation to the maltoside headgroup of C12G2. Complexation to a saccharide is expected not only to guide titanium to the pore surface, but also to prevent uncontrolled hydrolysis and condensation of the (usually quite reactive) titanium precursor. Tetrahedrally coordinated titanium atoms incorporated into a silica network are believed to be the active oxidation sites required for heterogeneous silica-supported titania oxidation catalysts. To promote well-ordered materials and to allow control over titania site density, the mixed C12G2 / C16TAB system is used for pore templating. Series of Si-Ti mixed oxide thin films and bulk materials are synthesized with different amounts of titanium loading by utilizing pre-complexation between C12G2 and titanium isopropoxide. The degrees of homogeneity (indicated by tetracoordinated Ti) in these films are superior to those of films synthesized with the same loading of titanium but without C12G2 or without pre-complexation. Transition metal-carbohydrate complexation provides highly dispersed, tetrahedrally coordinated titanium atoms rather than the octahedral sites found without saccharide complexation.

<p>Aluminum alloys are widely used in many manufacturing areas due to good castability, lightness and mechanical properties. The purpose of this research is to investigate copper’s influence on an Al-Si-Mg alloy (A356). Copper in the range of 0.6 – 1.6 wt. % has been used in an A356 aluminum based alloy. In this work a simulation of three different casting processes, sand-, die- and high pressure die-casting has been employed with the help of gradient solidification equipment. The microstructure of the samples has been studied by optical and scanning electron microscopy. Materials in both as-cast and heat treated states have been investigated through tensile test bars  to get the mechanical properties of the different conditions.</p><p> </p><p>Questions that have been subjected to answer are what influence does copper have on the plastic deformation and on fracture behavior and whether there is a relationship between the content of copper and increased porosity or not; and in that case explore this relationship  between the amount of copper and the mechanical behaviour.</p><p> </p><p>It has been analyzed that a peak of mechanical properties is obtained with a content about 1.6 wt. % copper. The increment of copper seems to have a remarkable impact on the mechanical properties and especially after the aging process showing a large raise on the ultimate tensile strength and yield strength.</p><p>Relationship between the copper content and increased porosity could not be found.</p>

The beginnings of metallurgical activity have intrigued scholars for decades. In this dissertation, I explore early metallurgical activity on the Iranian Plateau represented by the evidence at Tal-i Iblis in southern Iran, and Seh Gabi and Godin Tepe in central northern Iran. Together, these sites offer a diachronic view of metal production on the Plateau as well as a view of metallurgical activities practiced at different scales of production. The metallurgical materials from Tal-i Iblis are firmly dated to the late 6th to early 5th millennia BCE, and this corpus includes hundreds of crucible fragments excavated from multiple trash dumps. Seh Gabi and Godin Tepe offer a smaller range of production materials from the 4th through 2nd millennia BCE, but they also include a large collection of finished metal objects. These later materials differ in style and process from the Iblis debris.Thorough examination of these artifacts, combined with comparison to a series of carefully controlled casting experiments, has returned numerous significant results. The metallurgy of the Iranian Plateau does not fit the standard model of early metallurgical development. The Iblis crucibles do not reflect an early "experimental" stage in copper production. Rather, these artifacts represent a carefully controlled, production process with a narrow range of variability in both temperature and reducing atmosphere. Further, there is clear evidence for the preference of arsenical-copper alloys at Tal-i Iblis. These ancient craftspeople sought high-quality ores from a source (the Talmessi copper deposit) over 500 km from their production facility.Metallurgical production on the Iranian Plateau is also characterized by the long-term use of crucibles as the primary reaction vessel well into the 2nd millennium BCE. There are some production centers on the Iranian Plateau that see the use of furnaces during the 3rd millennium, but crucible use persists at many sites. At Godin Tepe--a site with significant evidence for contact with the Mesopotamian lowlands--variability in crucible form increases in later periods to include an Egyptian-style crucible during the 2nd millennium BCE. The presence of this crucible suggests that there was contact with foreign metallurgical processes, but the preference for small, portable reaction vessels persisted.

This thesis revolves around my work Desirable Objects, an installation in glass and other materials, which deals with objectification based on female and animal trophies. The topics included are those that have been crucial to my working process; craft, post-colonial studies and European hierarchical dualism, where woman and nature are seen as connected, but inferior. My motivation has been to get a better understanding of underlying power structures, and put this knowledge in relation to my own work. This process has led me to make a full body casting of my own body as a method of self-exploitation, in an attempt to expose myself to a similar power perspective. By making the dualistic connection between woman and nature, I am commenting a phenomenon that in my view has resulted in a similar exploitation of both. / Åtråvärda objekt

Composites have been developed with great success by the use of fiber reinforcements in metallic materials. Fiber reinforced metal matrices possess great potential to be the next generation of advanced composites offering many advantages compared to fiber reinforced polymers. Specific advantages include high temperature capability, superior environmental stability, better transverse modulus, shear and fatigue properties. Although many Metal Matrix Composites (MMCs) are attractive for use in different industrial applications, Aluminium Matrix Composites (AMCs) are the most used in advanced applications because they combine acceptable strength, low density, durability, machinability, availability, effectiveness and cost. The present study focuses on the fabrication of aluminium matrix composite plates by squeeze casting using plain weave carbon fiber preform (AS4 Hexcel) as reinforcement and a matrix of wrought aluminium alloy 1235-H19. The objective is to investigate the process feasibility and resulting materials properties such as hardness at macro- and micro-scale, impact and bend strength. The properties obtained are compared with those of 6061/1235-H19 aluminium plates that were manufactured under the same fabrication conditions. The effect of fiber volume fraction on the properties is also investigated. Furthermore, the characterization of the microstructure is done using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) in order to establish relationships between the quality of the fiber/aluminium interface bond and mechanical properties of the composites. In conclusion, aluminium matrix composite laminate plates were successfully produced. The composites show a good chemical bond between the fiber and the aluminium matrix. This bond resulted from heterogeneous precipitation of aluminium carbides (Al4C3) at the interface between aluminium matrix and carbon fiber. The hardness at macro- and micro-scale of the composites increases by over 50% and the flexural modulus increases by about 55%. The toughness of the composite decreases due to the presence of brittle phases which can be improved by better oxidation prevention. Also, an optimal carbon volume fraction was observed that provides optimal properties including peak hardness, peak stiffness and peak toughness.

The term nanoceramics is well known in the ceramic field for at least two decades. Even though there are many reports that nanoceramics are superior in terms of mechanical and other properties, no comprehensive and conclusive study on the grain size dependent variation in mechanical properties. So this study was an attempt to study the property variation with grain size and yttria content for a well known ceramic, yttria stabilised zirconia. High solids content but low viscosity YSZ nanosuspensions have been slip cast into -52% dense, very homogeneous green bodies in sizes up to 60 mm in diameter. Sintering cycles have been optimised using both hybrid and conventional two-step heating to yield densities >99.5% of theoretical whilst retaining a mean grain size of <100 nm. The sintered samples have been characterised for hardness, toughness, strength, wear resistance and hydrothermal ageing resistance. The results have been compared with that of a submicron zirconia ceramic prepared using a commercial powder. The strength of the nanoceramics has been found to be very similar to that of conventional submicron ceramics, viz. -10Pa, although the fracture mechanism was different. Two toughness measurement approaches have been used, indentation and surface crack in flexure. The results indicate that the nano 1.5YSZ ceramics may be best viewed as crack, or damage, initiation resistant rather than crack propagation resistant; indentation toughness measurements as high as 14.5 MPa m 112 were observed. Micro-Raman mapping was demonstrated to be a very effective technique to map the phase transformations in zirconia. The wear mechanism of nanozirconia has been observed to be different compared to that in conventional, submicron YSZ and the wear rates to be lower, particularly under wet conditions. In addition, and potentially most usefully, the nan03YSZ ceramics appear to be completely immune to hydrothermal ageing for up to 2 weeks at 245°C & 7 bar; conditions that see a conventional, commercial submicron ceramic disintegrate completely within 1 hour.

The direct chill (DC) casting technique to produce billets for extrusion and ingots for rollingwas developed in the 1930s. The principle, which is still valid, is a two-stage cooling with a primary cooling at a mould surface followed by water spraying directly on the surface. Improvements of this technique have mainly focused on changes to the primary cooling, where a water-cooled metal mould has been replaced by different techniques to minimize cooling at this stage. The drive for development comes from the extrusion industry, which can increase the productivity and quality of extruded profiles by improving the billet surface appearance and structure. Hot top casting supported by airflow against the casting surface during the primary cooling is currently the standard procedure to achieve acceptable billet surfaces. The goal is to minimize the depth of the surface segregation zone, which is the governing factor for the appearance of different phases in the surface region. Billet surface quality is evaluated by quantifying surface appearance, segregation zone thickness, and  occurrence of large Mg2Si and β-particles near the surface. The β-Al5FeSi intermetallic phase and coarse Mg2Si particles have negative effects on extrudability and workability of 6xxx Al alloys billets. To achieve extruded products with a high surface quality the as-cast billets are  heat-treated before extrusion. During heat treatment the undesired intermetallic particles, i.e., β-AlFeSi platelets are transformed to rounded α-Al(FeMn)Si intermetallic phases. In this  research the formation of the surface segregation for smooth defect-free surfaces in both as-cast and homogenized billets was studied. In addition, the surfaces with defects such as wavy, spot and vertical drag defects were investigated and possible mechanisms for initiation of those defects were explained. Moreover, for a better understanding of the homogenization process in-situ studies of the heat treatment of 6082, 6005, 6060 and 6063 Al alloys were carried out by using a transmission electron microscope (TEM). Based on the observations, an explanation of the probable mechanisms taking place during transformation from β-to α-phase was presented. / <p>Vid tidpunkten för disputationen var följande delarbeten opublicerade: delarbete 5 manuskript, delarbete 6 inskickat och delarbete 7 inskickat.</p><p>At the time of the doctoral defence the following papers were unpublished: paper 5 manuscript, paper 6 submitted, paper 7 submitted.</p>