<p>Challenges in the realisation of a miniature robot are both to handle the complexity of such a system, and to cope with effects of the actual reduction in physical size of all the parts. In particular, the mechanisms for locomotion have to be analysed.</p><p>The main achievements presented in the thesis are the evaluation and the development of fabrication techniques for miniature multilayer piezoceramic actuators, the evaluation of different motion mechanisms for miniature robots, and the development of building techniques for piezo-based miniature robots.</p><p>New piezoelectric drive units for miniature robots were designed and fabricated. To realize these monolithic devices, the fabrication technique for multilayer piezoceramic structures was further developed and evaluated with respect to the potential for miniaturisation. Introducing milling in the green state as a technique for shaping piezoceramic actuators gave a geometrical freedom without impairing the possibility of miniaturisation. A rapid prototype process was also developed. In this process, green machining in a milling machine was not only used to shape the multilayer structure, but also to pattern the internal electrodes. The first prototype was a multilayer telescopic actuator, which proved to have a displacement amplification of about 5 compared to a multilayer stack.</p><p>The drive units were used to evaluate different motion mechanisms. Experiments showed that for a mass corresponding to a typical miniature robot, i.e. 1-10 g, it is possible to use both dynamic and quasistatic motion mechanisms. Artefacts due to vibrations were identified as the main reason for non-ideal behaviour when the movable mass is small. Design criteria for robots with small masses are presented.</p><p>A tethered cm3 miniature robot for micromanipulation was successfully built. Application specific integrated circuits and two drive units were integrated with a particular building technique. Three-axial positioning and manipulating operations were demonstrated, allowing for a 5-axial movement of a tool.</p>

<p>This thesis presents the results from the development process of a ceramic dental filling material based on calcium aluminate cement. The main focus of the work concerns dimensional changes during setting, hardening and curing and the understanding of the factors controlling the dimensional stability of the system. A range of compositions for research purposes and the composition of Doxadent™ – a dental product launched on the Swedish market in October 2000 – were evaluated. Furthermore hardness characteristics, flexural strength, porosity and microstructure studies are presented. The studies of dimensional changes led to a thorough investigation of the measuring devices used and their relevance. A split pin expander technique, very simple in function, has been evaluated and improved. The technique is considered to be adequate for detecting dimensional stability in restrained samples, thus mimicking the case for real fillings in most tooth cavities. The dimensional changes in the calcium-aluminate based cement system are mainly controlled by the grain size, the exact composition and the compaction degree. The expansion of the calcium-aluminate cement system was in the early work decreased from several percent down to only tenths of a percent. Results show that Doxadent™ has less than 0.2% in linear expansion after 200 days of storage in water. However, long-term tests have been unable to verify whether expansion stops with time. Long-term in-vitro studies of dimensional changes also affect the test equipment used, which is why the long-term behavior of the dimensional stability has to be clinically evaluated. The material integrates excellently with the tooth structure, has hardness and thermal properties similar to those of enamel and dentine, and is also biocompatible during hardening. A patented process for the preparation of wet compacted specimens was also developed.</p>

<p>This thesis mainly treats the fabrication and applications of micro-optical elements in the semiconductor materials gallium arsenide (GaAs) and diamond.</p><p>The recent trend in high-capacity data transfer using light as the information carrier creates new demands on the optoelectronic systems, such as small size, low cost and the integration of many components. Micro-optical components are key elements for building compact optoelectronic systems and are well suited for integration with other devices. Another area where micro-optical elements can play an important role is the use of lasers in medicine, industrial machining, metrology, etc. In most cases, the laser beam characteristic is not directly suited for the application and external optics is needed to focus, shape or split the laser beam.</p><p>In the first part of this thesis, the fabrication of continuous-relief diffractive optical elements, such as diffractive lenses and blazed gratings, in GaAs is examined. The manufacturing technology uses electron-beam lithography followed by plasma etching in an inductively coupled plasma etching system. In the next step, these diffractive elements were monolithically integrated with vertical-cavity surface-emitting lasers.</p><p>In the second part of this thesis a novel topic is examined, diamond micro-optics. Diamond is a unique material in many aspects, it is the hardest material mankind knows, it has an extremely wide optical transmission window, and it possesses the highest thermal conductivity of all solids. Until today, due to difficulties in machining diamond, the realization of diamond optics has been limited. By using the same technology we earlier developed for the fabrication of GaAs optics we demonstrate for the first time continuous-relief structures in diamond of optical quality. Several diamond micro-optical structures are presented; sub-wavelength gratings for reduction of unwanted Fresnel reflections, diffractive fan-out elements used to split a CO₂-laser beam and refractive microlens arrays.</p><p>The accuracy of the fabrication process by plasma etching was evaluated by optical and topographical measurements, in all cases the optical components were of very high quality. </p>

<p>Die casting is a very cost-efficient method of forming thin-walled and complex near net-shaped products with close geometric tolerances and good surface finish. A permanent die tool is used to make large quantities of identical products. The performance and tool life are limited by several mechanisms, e.g. thermal fatigue cracking, erosion, and corrosion. To develop new and more resistant tool materials for die casting detailed knowledge of the actual casting conditions and the tool failure mechanisms are essential. This thesis contributes to an increased knowledge of tool failure in die casting by investigating and simulating actual casting conditions and tool failure mechanisms.</p><p>A method to record the temperature fluctuations in a cavity insert during actual brass die casting was developed, and details of the temperature conditions were obtained. Also, a test method based on cyclic induction heating and internal cooling of hollow cylindrical test rods was developed, where the surface strain during thermal cycling could be measured. This method reproduced the characteristic type of surface cracking observed on die casting tools, and proved to give information of the strains and stresses behind the fatigue failure.</p><p>In actual die casting, the dominant tool failure mechanism is thermal fatigue cracking. The formation of the cracks is associated to accumulation of the local plastic strain that occurs during each casting cycle. Initial crack growth is facilitated by oxidation of the crack surfaces, and proceeded growth is facilitated by this oxidation in combination with crack filling of cast material, and by softening of the tool material. In addition, local enrichment of Pb at the crack front from the cast alloy melt was also observed to promote the crack growth in die casting of brass.</p><p>In an investigation of thermal fatigue of two hot work tool steels, quenched and tempered to different conditions, it was found that low-cycle fatigue occurs, although the estimated tensile stress never exceed the initial yield strength of the steel. The reason is a gradual softening of the steel during the thermal cycling, and the presence of stress raising defects. The resistance against thermal cracking improves with initial tool steel hardness, because any initial ranking in hardness among the steels is unaffected by the thermal cycling.</p><p>Another investigation on a selection of surface engineered tool steels, including common diffusion treatments, PVD coatings and combinations of these, showed that surface engineering generally reduce the resistance against thermal cracking as compared to untreated references, since the engineering processes influence negatively on the mechanical properties of the hot work tool steels.</p><p>Finally, corrosion tests of CrN PVD-coated tool steels by exposing them to molten aluminium revealed the mechanisms of initiation and progress of liquid metal corrosion of this material combination, and that the corrosion resistance improves with the CrN coating thickness.</p>

<p>Microfluidics can be used to increase performance, reduce reagent consumption and increase throughput in chemical analysis. With the forthcoming development of more advanced microfluidic systems, the integration of actuating elements becomes essential, giving the ability to control and manipulate fluid flow as well as sample or other components. This thesis addresses miniaturisation of piezoceramic actuators, in particular important technological issues when actuators are integrated in microfluidic systems. Thick film multilayer fabrication technology for piezo­ceramics has been further developed, e.g. by introducing techniques for integration of microfabricated channel structures and via interconnects in multilayer components. New building techniques have been incorporated to allow miniaturisation of devices. A rapid prototyping technique for advanced multilayer actuators based on mechanical machining has also been developed and used in subsequent work.</p><p>When interfacing the macro and the micro world in miniaturised chemical analysis systems, non-contact sample dispensing methods such as ink-jet technology are needed. Thus a piezoactuated flow-through microdispenser, suitable for high-speed on-line chemical sample handling has been investigated. A new miniaturised actuator has been developed and integrated in the microdispenser, simplifying assembly and demonstrating an improved performance of the device.</p><p>With the prospect of performing automated and highly parallel analysis in reusable microarray devices, a new concept for dynamic arraying is presented. Non-contact trapping of particle or bead clusters in a microfluidic system is demonstrated utilising acoustic radiation forces in standing ultrasonic waves. The integration of piezoceramic micro­transducers has been shown to render possible localised and spatially controlled trapping of individually addressable particle clusters in micro­fluidics. The importance of the acoustic near field in miniaturised devices has been identified and utilised to give strong trapping forces. By making use of disposable chemically activated microbead arrays within a flow-through device, a flexible system is emerging with e.g. applications in proteomics.</p>

<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.