The goal of the project work has been to study the symmetry of the phonons in 4H and 6H-SiC for different measuring geometries by using two experimental techniques, Raman and infrared absorption (IR) spectroscopy, and a theoretical model. The Raman spectra were measured in different scattering configurations in order to obtain experimental data for detailed investigation of the phonon symmetries. The gross features of the spectra obtained in different geometries can be explained using general group-theoretical arguments. Using a lattice-dynamics model, we have also calculated the angular dependence of the phonon energies near the centre of the Brillouin zone, as well as the phonon displacements in some high-symmetry directions. The theoretical results are used to interpret the Raman lines in different configurations, and it was possible to estimate that if ionicity of the bonding of 12% is taken in the theoretical model for 4H-SiC, the splitting of the polar TO mode and the shift of the polar LO mode observed in our spectra are well reproduced theoretically. It was also observed that these polar modes have to be classified as longitudinal and transversal with respect to the direction of phonon wave vector, while the rest of the modes remain longitudinal or transversal with respect to the c-axis of the crystal. The Raman lines in the case of 4H SiC have been tentatively labelled with the irreducible representations of the point group of the crystal (C6v).

A new NOx sensor for high-temperature applications has been developed and thouroghly characterised. The sensor layers are a mixed oxide of CoO, MgO and MgO2 deposited by thermal evaporation with a porous platinum gate on top, deposited by thermal evaporation or sputtering. The sensitivity and selectivity of the sensor is promising and is shown to depend upon the ratio between Co and Mg in the film and a number of competing mechanisms are shown to take place on the sensor surface. Response and recovery of the device is still slow and there are some drift, which are suggested to be due to a restructuring sensor surface during operation that was found by SEM-studies. Finally,the oxide surface has been characterized by XPS and a novel process for deposition of the sensor layers by lift-off technique has been developed.

<p>In the first part of this thesis, the FE program MSC.Marc is applied for coupled thermomechanical simulations of wire-rod rolling. In order to predict material behaviour of an AISI 302 stainless steel at high strain rates generated during wire-rod rolling, a material model based on dislocation density is applied. Then, the evolution of temperature, strain rate and flow stress is predicted in the first four rolling passes of a wire block.</p><p>In the second part of the thesis, an alternative approach to simulation of shape rolling is evaluated. The approach is applied in order to save the computational time in cases where many shape-rolling passes are to be simulated. The approach is a combination of the slab method and a 2D FEM with a generalized plane-strain formulation. A number of various isothermal shape-rolling passes are simulated applying the simplified approach. The simulations are carried out using an in-house 2D FE code implemented in Matlab. The results are compared to fully 3D FE analyses. The comparison shows that the simplified approach can predict roll forces and roll torques with a fair accuracy, but the predicted area reductions are a bit underestimated. The reasons for the deviations between the simplified approach and the 3D FEM are discussed.</p>

<p>This licentiate study was initiated by copper, zinc and galvanized steel producers in Europe, who felt a need to assess runoff rates of copper and zinc from the pure metals and commercial products at marine exposure conditions. Their motive was the increasing concern in various European countries and the on-going risk assessments of copper and zinc within the European commission. Also the circumstance that available runoff rates so far, had been reported for mainly urban exposure conditions, rather than marine. A collaboration was therefore established with the French Corrosion Institute, which runs a marine test site in Brest, and a set of vital questions were formulated. Their answers are the essence of this licentiate study.</p><p>Based on the ISO corrosivity classification and one-year exposures, the marine atmosphere of Brest is fairly corrosive for zinc (class C3) and highly corrosive for copper (C4). Despite higher corrosivity classifications for both metals in Brest compared to the urban site of Stockholm, used as a reference site, nearly all runoff rates assessed for copper, zinc and their commercial products were lower in Brest compared to Stockholm. This was attributed to a higher surface wetting in Brest and concomitant higher removal rate of deposited chloride and sulphate species from the marine-exposed surfaces. The comparison shows that measured corrosion rates cannot be used to predict runoff rates, since different physicochemical processes govern corrosion and runoff respectively.</p><p>For copper, the runoff rate in Brest was approximately 1.1 g m^-2 yr^-1 with cuprite (Cu2O) as main patina constituent. During periods of very high chloride and sulphate deposition, paratacamite (Cu₂Cl(OH)₃) formed which increased the runoff rate to 1.5 g m^-2 yr^-1. For zinc, with hydrozincite (Zn₅(CO₃)2(OH)₆) as the main patina constituent, the runoff rate was relatively stable at 2.6 g m^-2 yr^-1 throughout the year, despite episodes of heavy chloride and sulphate deposition.</p><p>The application of organic coatings of varying thickness on artificially patinated copper or on different zinc-based products resulted in improved barrier properties and reduced runoff rates that seem highly dependent on thickness. The thickest organic coating (150 µm thick), applied on hot dipped galvanized steel, reduced the runoff rate by a factor of 100. No deterioration of organic coatings was observed during the one-year exposures. Alloying zinc-based products with aluminium resulted in surface areas enriched in aluminium and concomitant reduced zinc runoff rates.</p><p>The release rate and bioavailability of copper from different anti-fouling paints into artificial seawater was also investigated. It turned out that the release rate not only depends on the copper concentration in the paint, but also on paint matrix properties and other released metal constituents detected. Far from all copper was bioavailabe at the immediate release situation. In all, the results suggest the importance of assessing the ecotoxic response of anti-fouling paints not only by regarding the copper release, but rather through an integrated effect of all matrix constituents.</p>

<p>Over one million hip prostheses are implanted in patients worldwide each year and the need is increasing as the patient group of younger and more active patients is increasing. Many parameters affect the longevity of the implant, where aseptic loosening caused by wear debris is the most common reason for revision. To be able to monitor wear in vivo and also to predict the longevity of new materials for hip prostheses are therefore important issues in this interdisciplinary research area. This thesis comprise a true non-invasive 3D method for determination of acetabular cup wear using Computed Tomography (CT) intended for clinical routine use in order to plan for a revision. It also comprises investigations of the influence of surface roughness and sterilization method in wear testing of materials for hip prostheses. Mainly wear of ultra high molecular weight polyethylene (UHMWPE) was investigated since it is the most common soft bearing in hip prostheses. The 3D-CT method was found to be easy to use and showed an accuracy and repeatability at a clinical relevant level for acetabular cup wear. It should lend itself well to semi-automation. The influence of surface roughness was investigated with both a multidirectional pin-on-disk machine and with a hip simulator. A new low friction coating, Micronite, was also evaluated with the pin-on-disk machine. This coating showed potential for use in artificial joints, but further investigations are needed. In the hip simulator test, it was found that not only a rougher counter surface increased wear, but also sterilization by γ-irradiation increased wear of UHMWPE cups.</p>

<p>Very often defects are present in rolled products. For wire rods, defects are very deleterious since the wire rods are generally used directly in various applications. For this reason, the market nowadays requires wire rods to be completely defect-free. Any wire with defects must be rejected as scrap which is very costly for the production mill. Thus, it is very important to study the formation and evolution of defects during wire rod rolling in order to better understand and minimize the problem, at the same time improving quality of the wire rods and reducing production costs.</p><p>The present work is focused on the evolution of artificial defects during rolling. Longitudinal surface defects are studied during shape rolling of an AISI M2 high speed steel and a longitudinal central inner defect is studied in an AISI 304L austenitic stainless steel during ultra-high-speed wire rod rolling. Experimental studies are carried out by rolling short rods prepared with arteficial defects. The evolution of the defects is characterised and compared to numerical analyses. The comparison shows that surface defects generally reduce quicker in the experiments than predicted by the simulations whereas a good agreement is generally obtained for the central defect.</p>

<p>Commercial alloys are continuously developed to improve their performance. Therefore it is important to develop new optimisation software, which could be used in development of new materials or in materials selection. In this study the mechanical properties which are important in materials selection in mechanical design are investigated. Two types of materials are analysed, aluminium alloys and stainless steels but focus will be on the aluminium alloys.</p><p>Thermodynamic analysis has been used to evaluate the effect of the microstructure. Solid solution hardening has been successfully modelled for both aluminium alloys and stainless steels and follows the theories by Labusch and Nabarro. The precipitation hardening is most dominant for the hardenable aluminium alloys, but the non-hardenable alloys also increase their strength from precipitation hardening. The non-hardenable alloys are divided into tempers, which differ in the amount of strain hardening. This has also been modelled successfully.</p><p>Combining these fundamental results with multiple regression, models for mechanical properties have been created. Separate models are developed for wrought aluminium alloys and stainless steels. For the aluminium alloys this includes the solid solution hardening and the precipitation hardening. For the stainless steels the thickness, nitrogen content and ferrite content are included together with the solid solution hardening.</p>

<p>På dagens fönsterglasmarknad har produkter med samma funktioner och utseende fått olika namn. Detta är förvirrande och gör det svårt för en person som ska beställa fönsterglas att jämföra olika tillverkares produkter med varandra. Rapporten är tänkt som en översikt på de olika fönsterglasen som finns på marknaden idag och även på sådant som kan bli aktuellt i framtiden. Den berör också sådant som kan vara av värde att veta vid användning av fönsterglas. Målgruppen är alla som kan tänkas ha intresse i ämnet - alltifrån hobbybyggaren till fackmän i byggbranschen. Informationen är sammanställd från böcker, broschyrer, internet och experter på området fönsterglas.</p>

Cemented carbides are composite materials consisting of a hard carbide and a ductile binder. They are powdermetallurgically manufactured, where liquid-phase sintering is one of the main steps. The most common cemented carbide consists of WC and Co and it is widely used for cutting tools. Two of the most important factors controlling the mechanical properties are the WC grain size and the grain size distribution and thus it is of great interest to understand the grain growth behavior. In this thesis the grain growth during sintering at 1430 °C is studied both experimentally and through computer simulations. The grain growth behavior in cemented carbides cannot be explained from the classical LSW-theory. The WC grains have a faceted shape necessitating growth by 2-D nucleation of new atomic layers or surface defects. A new model based on 2-D nucleation, long-range diffusion and interface friction is formulated. Three powders having different average sizes are studied and both experiments and simulations show that a fine-grained powder may grow past a coarse-grained powder, indicating that abnormal grain growth has taken place in the fine-grained powder. Fine-grained powders with various fractions of large grains are also studied and it is seen that a faster growth is obtained with increasing fraction of large grains and that an initially slightly bimodal powder can approach the logaritmic normal distribution after long sintering times. The grain size measurements are performed on 2-D sections using image analysis on SEM images or EBSD analysis. Since the growth model is based on 3-D size distributions the 2-D size distributions have to be transformed to 3-D, and a new method, Inverse Saltykov, is proposed. The 2-D size distribution is first represented with kernel estimators and the 3-D size distribution is optimized in an iterative manner. In this way both negative values in the 3-D size distribution and modifications of the raw data are avoided. / QC 20110426

Most metals and alloys in the presence of oxygen and moisture will instantaneously react and form a thin (2-5 nm) surface oxide layer. For further reaction to occur, oxygen ions and/or metal cations often diffuse through the already formed oxide layer. The corrosion resistance of a metal in aggressive environments at high temperatures depends on the properties of the surface oxide scale. Zirconium-based alloys represent the main structural materials used in water-cooled nuclear reactors. For these materials, the formation of a thin, adherent oxide scale with long-term stability in high temperature water/steam under irradiation conditions, is crucial. In this thesis, the transport of oxygen and hydrogen through Zr-based oxide scales at relevant temperatures for the nuclear industry is investigated using isotopic gas mixtures and isotope-monitoring techniques such as Gas Phase Analysis and Secondary Ion Mass Spectrometry. Porosity development in the oxide scales generates easy diffusion pathways for molecules across the oxide layer during oxidation. A considerable contribution of molecular oxygen to total oxygen transport in zirconia has been observed at temperatures up to 800°C. A novel method for evaluation of the gas diffusion, gas concentration and effective pore size of oxide scales is presented in this thesis. Effective pore sizes in the nanometer range were found for pretransition oxides on Zircaloy-2. A mechanism for densification of oxide scales by obtaining a better balance between inward oxygen and outward metal transport is suggested. Outward Zr transport can be influenced by the presence of hydrogen in the oxide and/or metal substrate. Inward oxygen transport can be promoted by oxygen dissociating elements such as Fe-containing second phase particles. The results suggest furthermore that a proper choice of the second-phase particles composition and size distribution can lead to the formation of dense oxides, which are characterized by low oxygen and hydrogen uptake rates during oxidation. Hydrogen uptake in Zr-based materials during oxidation in high temperature water/steam can generate degradation due to the formation of brittle hydrides in the metal substrate. A promising method for the suppression of hydrogen uptake has been developed and is presented in this thesis. / QC 20100629