<p>In the large family of carbon-based coatings there are members capable of providing a rare and very desirable combination of high wear resistance and low friction. The field of application for this kind of coatings is steadily increasing which, naturally, give raise to new questions and demands.</p><p>Coatings of this type can be produced in a number of different ways, but the parameter influencing their properties most is the chemical composition. To facilitate investigations of the compositional impact on the synthesis and properties of coatings, a way to alloy magnetron-sputtered thin films was developed in this thesis. It does not involve the use of reactive gases or additional material sources; instead metallic foils are attached onto the magnetron target surface and thus sputtered alongside the target material. This co-sputtering route was later used to synthesize carbon coatings alloyed with Ta, Zr, W and Al in various amounts and configurations.</p><p>It was shown that the co-sputtering method could be used to alloy coatings in a very simple and straightforward manner, with excellent possibilities of controlling the amount of alloying elements. The process temperature could be kept as low as 70 °C.</p><p>Carbon coatings alloyed with transition metals (MeC:C) displayed polycrystalline nanocomposite structures with 5 nm metal carbide crystallites in a matrix of near-amorphous carbon. Alloying with Ta resulted in a radical 80 % reduction in friction coefficient during dry sliding in air, from 0.22 for pure carbon to 0.04 for TaC:C. This was found to be due to facilitated graphitization and the formation of lubricating surface oxides. Al additions to TaC:C resulted in a transformation of the TaC phase to a metastable, previously unreported Ta_1-χAl_χC. The coefficient of friction remained unaltered, but the oxidation rate compared to TaC:C was significantly reduced due to the formation of AlTaO₄ instead of Ta₂O₅.</p>

<p>Demands on lower fuel consumption, reduced pollution, increased operating times, etc. force the automotive industry to constantly improve the performance of critical machine elements. In this development various carbon based coatings have proven very promising, mainly because of their low friction and high wear resistance in dry sliding contacts. The contact conditions can be very different in various machine element applications, e.g. both rolling and sliding contacts. Additionally, most contacts are usually lubricated. Hence, other properties of the coating may be required in order to obtain low friction and wear, as for instance a beneficial running-in ability. </p><p>In lubricated contacts the very high wear resistance of carbon coatings can cause fatigue damage resulting in delamination of the coating, especially when deposited on rough substrates. In rolling contacts the fatigue damage can be reduced simply by using smoother surfaces, but the thickness of both the coating and the interlayer also has a strong influence on fatigue damage.</p><p>In lubricated sliding contact tests it was found that the running-in ability could be improved by modifying the coating and/or by using an appropriate surface preparation prior to coating deposition. An increased Cr-content in the top-layer of the carbon coating reduced the friction due to the formation of a stable tribo-layer on the uncoated counter body. An even further reduced friction could be obtained by employing a fine wet-blasting of the substrate giving sharp surface asperities. The friction reduction is thought to be a result of a transition towards a higher degree of full film lubrication, due to a very fine smoothening process of both the coating and the counter body during the running-in process.</p>

The understanding of the hardenability is important in steel development with respect to weldability of steels as well as to the design of quenched and tempered steels.The common way to judge if steel is suitability to welding is the use of a carbon equivalent, which reflects the alloy content to the hardenability of the heat affected zone (HAZ). Most common of these equivalent is the IIW carbon equivalent wich has been in use for decades. However, this is an empirical equivalent, developed for CMn steels, and it doesn't say anything about the mechanical properties obtained in the HAZ. As a guideline a maximum HAZ hardness of 350 HV is normally put to avoid cold cracking in the HAZ. Numerous carbon equivalents have been published during the years, but few have been accepted and used. A drawnback of all these equivalents is that they have been evaluated for a set of chemical compositions which may be quite narrow, or that they have been evaluated on steels produced having other cleanliness, residual element levels etc. as is common in modern steelmarketing. The hardenability of steel designated to quenching and tempering is normally evaluated using either Jominy testing or using a calculation using the Grossmann formalism. As the hardenability described in the carbon equivalents used in welding and the hardenability of quenched and tempered steels using the Grossmann formalism are two different descriptions of the same phenomenon the aim of this thesis is to link these two formalisms together and use the knowledge from the HAZ hardenability to design quenched and tempered steels. The goal is to produce such steel grades having a much better weldability as compared with standard grades available at the market. In this work the hardenability in the heat affected zone (HAZ) in weldments in high strength low alloyed steels (HSLA steels) having a yield strength of 350 MPa. This part microalloying elements on the phase transformations which take place during cooling from the peak temperature of the welding cycle. These results have been linked to the mechanical properties of the HAZs. In the second part of this thesis the development of tool steel grades with respect to optimise both hardenability with respect to; - matrix hardenability (i.e the Grossmann approach) - an enhanced weldability of such new steels due to a lower alloying content than is usual in such grades

The present work reports on the effect of Mn-, Zr- and Sc-additions upon hot deformation properties, recrystallization properties and mechanical properties for different temper conditions of Al-Mg alloys. It can be stated that the addition of Mn, Zr and Sc improves the recrystallization properties and the mechanical properties of Al-Mg alloys. It should be emphasised that the precipitation of the metastable cubic Al3Zr and the stable cubic Al3(Sc,Zr) is favourable in an aluminium-magnesium matrix due to a close similarity of the lattice structures. The Al3(Sc,Zr)-phase is similar to the equilibrium Al3Sc-phase and has a high thermal stability and thus the coherency with the aluminium matrix is retained to very high temperatures. The present work has demonstrated the beneficial features of the Al3(Sc,Zr)- phase upon recrystallization and strength. This also results in an increase in the deformation resistance and a reduction in the hot ductility. In particluar, manganese reduces hot ductility. After casting most of the Zr and Sc remained in solid solution. The Mn was partly present in large primary constituent particles and partly in solid solution. Segregations of all three elements were detected. Decomposition of solid solutions of these elements resulted in the formation of dispersoids of the type Al3Mn (orthorombic), Al3Zr (cubic) and Al3(Sc,Zr) (cubic). It was found that the flow stress increased in the presence of the dispersoids. As compared to the alloy without dispersoids, the presence of Al6Mn and Al3Zr or Al3(Sc,Zr) increased the flow stress by 20-100% depending on the temperature and strain rate. The effect of the particles decreases as the Zener- Hollomon parameter increases. Extrusion experiments also confirm these results. In addition, manganese reduces the hot ductility considerably. Furthermore, the present work has demonstrated that the recrystallization properties of Al-Mg alloys may be affected considerably by introducing Mn, Zr and Sc. The recrystallization behaviour after hot deformation may be effectively determined by the Zener drag exhibited by the dispersoids on grain boundaries. Al6Mn showed to be least effective while Al3(Sc,Zr) is extremely effective in retarding recrystallization. After cold deformation, however, the recrystallization behaviour is different due to a higher amount of stored energy. In the alloy without dispersoids, recrystallization occurred by classical nucleation at microstructural heterogeneities, while particle stimulated nucleation operates in the other alloys. Recrystallization of cold rolled material resulted in an extremely finegrained microstructure. Once recrystallized, extensive grain growth occurs in alloys containing Al6Mn and/or Al3Zr. Contrary, alloys containing Al6Mn and Al3(Sc,Zr) are very stable and the fine-grained structure seems to be very stable up to 550°C. This clearly proves that Al3(Sc,Zr) are thermally stable and efficiently pin grain boundaries up to very high temperatures. In the last part of this thesis the mechanical properties of the investigated alloys were mechanically tested in several temper conditions. It was found that the presence of Al6Mn and Al3(Sc,Zr) caused an increase in the flow stress of 36 MPa in the O-temper condition, probably due to the Orowan mechanism. The effect of Al6Mn and Al3Zr alone or in combination was less pronounced. Furthermore, the retained deformation microstructure after extrusion was associated with the Zener drag forces exhibited by the dispersoids and resulted in considerable strengthening. For instance, the combination of Al6Mn and Al3(Sc,Zr) increased the strength by approximately 100 MPa compared to the dispersoid free alloy. Again the effect of Al6Mn and Al3Zr is less pronounced due to the lower capacity in retarding recrystallization. The capability of the dispersoids to retard recrystallization should be an opportunity to increase the strength of the heat-affected zone after fusion welding. This is an important aspect since strain hardened conditions are used commercially. However, it has been demonstrated that a complete utilisation of the strength increase in the base material is not achieved as long as the weld metal is the weakest part in the weldment. However, a yield strength of 160 MPa was achieved for the material containing both Al6Mn and Al3(Sc,Zr), while somewhat lower values were obtained for the alloys with Al6Mn and/or Al3Zr.

This thesis deals with the preparation, optical characterization and analyses of experimental work and theoretical modeling on selective solar absorbers used in solar thermal collectors. The overall goal has been to obtain efficient absorbers by optimizing the optical properties, and to improve their durability using cost-effective techniques. A Ni-Al2O3 absorber was pyrolytically coated with SnO2 to improve its coating quality. Undesirable increase of solar reflectance obtained as a result of the SnO2 was reduced by applying a silica antireflection layer produced by a dipping technique from colloidal silica sol. Annealing of Ni particles in an Al2O3 matrix was also carried out and compared to particles heated without the matrix. Due to the Al2O3 matrix, a much slower oxidation rate was found for the embedded particles. In addition, the optical performance of commercial Ni-Al2O3 and Ni-NiOx absorbers were experimentally compared at oblique incidence. A better solar-absorptance of the Ni-Al2O3 at higher angles of incidence was found. This is due to enhanced optical interference in the double-layer structure of Ni-Al2O3, which could not be achieved in the graded index film of Ni-NiOx. The optical properties of Si-Al2O3 films of different thicknesses have been investigated by preparing the films using an integral coloration method. The solar-absorptance and thermal-emittance were found to increase with increasing film thickness. Due to high thermal-emittance, the Si-Al2O3 coating shows non-selective absorbing properties. Its feasibility for a selective solar absorber was studied by modeling the coating as a function of coating thickness for different particle size and volume fraction using four-flux theory. The results indicated that the Si-Al2O3 coating is not a suitable candidate for selective solar absorbers. Scattering and absorption cross-sections of FeMnCuOx and black carbon pigments have been obtained from reflectance and transmittance measurements in the solar wavelength range. The cross-sections were determined by using pellets consisting of low pigment volume fractions dispersed in KBr matrix. The cross-sections exhibit linear dependence of the volume fraction, indicating that single scattering dominates. The cross-sections were used to model the optical properties of solar selective paints using four-flux model resulting in good agreement between calculations and experiments.

An angle-resolved scatterometer and an integrating sphere for reflectance measurements at oblique angles of incidence have been designed and evaluated. The integrating sphere has a centre-mounted sample holder and the detector sits at the end of the sample holder and therefore always faces the same sphere wall area. The sphere geometry plays an important role for the modelling of detected signals and the reflected intensity has to be divided into a specular and a diffuse component. These components must be treated separately in the modelling. These two instruments, as well as traditional spectrophotometers, have been used for the evaluation of solar energy materials. Scattering as well as non-scattering surfaces have been studied, requiring different measurement techniques. By using angle-resolved scatterometry it has been demonstrated that a solar reflector does not need to be perfectly specular provided the concentration factor is low. Thus it is possible to use inexpensive aluminium foil as the reflector material. The possibility of increasing the reflectance of aluminium with thin dielectric films of silicon and titanium oxides for pv-cell and solar thermal collector application has been investigated. Particular attention has been paid to the angular optical properties since thin films strongly affect them owing to interference effects. In an under-glazing application for pv-cells, the use of aluminium coated with titania and silica is recommended. The long-term stability of several reflector materials has been studied and anodised aluminium protected by a UV-stabilised polymer coating is recommended for solar collector reflectors. Antireflective films consisting of porous silicon oxide for solar collector cover glazings have been studied. The films were prepared by a dip-coating process using a suspension of nano-sized silicon oxide particles. This treatment increased the solar transmittance by 5.5 percentage points. It has also been shown that it is possible to temper antireflection treated glazings without seriously affecting the optical performance. The tempering also strongly improves the mechanical stability of the film.Some of the measurements presented in this thesis were used as input data to simulation programs, which calculate the collected annual energy as a function of the optical properties of the different components. It was found that spectrophotometric laboratory measurements agree well with outdoor collector testings.

During recent decades, huge amount of radioactive waste has been dumped into the earth's surface environments. 129I (T1/2 = 15.6 My) is one of the radioactive products that has been produced through a variety of processes, including atomic weapon testing, reprocessing of nuclear fuel and nuclear accidents. This thesis describes development of the Accelerator Mass Spectrometry (AMS) ultra-sensitive atom counting technique at Uppsala Tandem Laboratory to measure 129I and discusses investigations of its distribution in the hydrosphere (marine and fresh water) and precipitation. The AMS technique provides a method for measuring long-lived radioactive isotopes in small samples, relative to other conventional techniques, and thus opens a new line of research. The optimization of the AMS system at Uppsala included testing a time of flight detector, evaluation of the most appropriate charge-state, reduction of molecular interference and imporvement of the detection limit. Furthermore, development of a chemical procedure for separation of iodine from natural water samples has been accomplished. The second part of the thesis reports investigations of 129I in natural waters and indicates that high concentrations of 129I (3-4 orders of magnitude higher than in the pre-nuclear era) are found in most of the considered natural waters. Inventory calculations and results of measurements suggest that the major sources of radioactive iodine are the two main European nuclear reprocessing facilities at Sellafield (U.K.) and La Hague (France). This information provides estimates of the transit time and vertical mixing of water masses in the central Arctic Ocean. Results from precipitation, lakes and runoff are used to elucidate mechanisms of transport of 129I from the point sources and its pathways in the hydrological environment. This study also shows the need for continuous monitoring of the 129I level in the hydrosphere and of its future variability.

By the introduction of machine elements made of light metals, e.g. Al or Mg alloys, which are coated with a material providing high wear resistance and low friction coefficient, both economical and environmental benefits can be gained. A high resistance against wear results in increased lifetime and lower costs for spare parts and maintenance. This also means fewer production stops and less machine downtime. Moreover, a vehicle of lower weight and with reduced friction losses will consume less fuel. The light metal alloys display low hardness and elastic modulus and in addition they have a high tendency to stick to the countersurface in sliding contact. Hence, to be used in tribologically demanding applications, they must be coated with a material providing low friction and wear. Due to the thin and brittle nature of the available coatings an intermediate load-carrying layer has to be introduced to protect the base material from large deformations and the brittle surface coating from cracking. In this thesis both experiments and theoretical simulations has shown that the load-carrying layer between the soft and compliant base material and the thin brittle coating should have high elastic modulus and hardness as well as a for the contact situation sufficient thickness. A number of vapour deposited coatings have been investigated regarding their tribological behaviour with special emphasis on the mechanisms providing low friction. When sliding against steel, it was found that carbon-rich coatings show much lower friction and wear of the countersurface than nitrogen-rich coatings. The explanation is that steel has a tendency to stick to nitrogen-rich coatings, leading to steel against steel contact, but not to carbon-rich coatings. Another explanation is that material is transferred from a carbon-rich coating to the steel and this gives an easily sheared contact with low friction coefficient.

This thesis deals with studies of thin films using soft x-ray emission spectroscopy. Thin films are frequently used in optical, semiconductor and magnetic applications, and along with the development of thin film deposition techniques, there is a growing need for thin film characterisation and production control. Soft x-ray spectroscopy provides elemental as well as chemical bonding information and has the advantage of being relatively insensitive to electric and magnetic fields. It may thus be used in-situ during deposition for monitoring sputtering deposition. Thin films of TiVN were reactively co-sputtered using two targets, and soft x-ray spectroscopy and optical emission spectroscopy were used to determine the film composition in-situ. These measurements were compared with ex-situ elemental analysis as well as with computer simulations. The results agree qualitatively and indicate that soft x-ray spectroscopy can be used for in-situ determination of film composition. In another study, the composition of chromium nitride was studied in-situ under varying deposition conditions. The fraction of different stoichiometric phases in the deposited films as a function of nitrogen flow was determined in-situ. The thesis also deals with the angular dependence of soft x-ray emission spectroscopy. The angular dependence of the emission was measured and compared to simulations for layered samples consisting of different transition metals, one sample consisting of Fe(50Å)/Cu(100Å)/V(100Å)/Si and another set of samples consisting of Fe(XÅ)/V(100Å)/MgO, where X = 25, 50 and 100 Å. The measured angular variation can be described qualitatively by calculations including refractive effects. For measurements below the critical angle of reflection, only the top layer corresponding to the evanescent wave region of 20-50 Å is probed, whereas for larger grazing angles the probe depth reaches thousands of Å. This demonstrates the feasibility of using the angular dependence as a way of studying composition and layer thickness of thin films.

This thesis treats angle-resolved optical properties and the energy efficiency of windows. A theoretical evaluation of optical and thermal properties of windows is briefly surveyed and the energy performance of a large selection of windows, under different conditions, is examined. In particular, angle dependent optical properties are analysed. A new model assessing angle dependence of the total solar energy transmittance, g, of windows is presented. A comparison of simple models for angle-dependence prediction has been performed, including both fictitious and measured real window glazings. The new proposed model illustrates low errors for both the real and the fictitious glazings. The impact of inaccuracy in the angle dependence of the g-factor has been assessed and found to be clearly noticeable but not necessarily critical. A simple model for comparing the energy efficiency of different windows in different types of buildings and different climates has been further developed and analysed for several conditions. The energy performance of a large number of windows has been analysed using this model, and also by using other building and window simulation models. Typical savings when changing from a standard double glazed window to the optimal window for the investigated case is in the order of 100-150 kWh/m2yr. The annual energy balance of modern low emittance windows illustrates that they can be annual energy savers rather than energy losers, unlike traditional windows. However, it is shown that it is not important to argue about small changes (~0.01) of the thermal emittance value. Furthermore, advance solar control glazings effectively reduce solar transmittance with maintained high light transmittance. AR-coatings and low-iron glazings can increase the transmittance of glazings considerably. In fact, a "super" low emittance window with a U-value below 1 W/m2K can have higher light transmittance than a common double-glazed unit. Windows with variable transmittance, switchable windows, are compared with high-performing solar control windows, illustrating some degree of potential energy savings compared to high performing static solar control windows, depending on the type of control that is used. This is accompanied by the potential for automatic thermal comfort- and glare control. Different models for energy rating of windows have been evaluated, demonstrating that a simple linear rating depending on the U and g-factor of the window may be sufficient with certain restrictions. Division into climate zones is essential. In all, the results demonstrate that energy-efficient windows provide huge energy-saving potentials on a large (regional, national, global) scale.