The microsystem processing of today is based on an assortment of diverse and contrasting fabrication techniques, sprung from the microelectronic industry. Microsystem technology has primarily been developed to meet the demands for scaled down low-cost sensor and actuator systems. These devices are based on a number of contrasting principles, e.g. capacitance of mechanical membranes, microfluidic or piezoelectric actuation, electrostatic or heat deflection, etc. Clearly the disparate designs of these devices require microfabrication processes that are flexible and unrestricted, allowing deep and vertical structures to be obtained. The scope of this thesis is microstructuring and microsystem fabrication of primarily polymer materials by means of ion track lithography. Ion track lithography in combination with microstructuring unwraps unique and untouched grounds. The available building blocks in these microsystems include high aspect ratio (depth-to-width ratio) capillaries and metal wires of nanometric width, deep vertical cavities as well as conventional double-sided thin film lithographic patterns. The blocks have been combined to materialise a few technology demonstrators integrated in flexible polyimide foils and laminates, commercially attractive materials with excellent mechanical, temperature, and high frequency electronic properties. A magnetic field sensing structure based on the magnetoresistance as well as inductor coils for microwave circuitry have been fabricated and characterised. The various fabrication processes have been evaluated with respect to resolution, aspect ratio, and verticality. We can present a deep vertical micro? and nanofabrication technique, overriding the natural anisotropy or isotropy of many of the diverse materials employed in the microsystem field. We have obtained pores, capillaries with aspect ratios of up to 400, clusters of electrodeposited magnetic and non-magnetic nanowires with similar aspect ratio, solid complex structures with close to vertical walls as well as through hole microvias in flexible printed circuitboards.

In the modern process of continuous Direct Chill (DC) hot top casting of aluminium extrusion ingot with gas slip, poor surface quality of the cast ingot can still be a problem. In the worst cases pronounced surface wrinkling may occur coupled with periodic zones of reduced grain size, macrosegregation and exudation at the surface. The observed surface irregularities are believed to be linked to periodic oscillations or folding of the free molten aluminium surface in the mould, the meniscus, resulting in varying solidification conditions. The focus of this work is to gain a better understanding of the dynamics of the meniscus and the effect it has on ingot surface formation.

Thermal spraying is the name of a large group of coating deposition techniques used to deposit thick layers for a variety of applications. The principle is to melt the material, and rapidly propel the droplets towards a substrate where they flatten and solidify. When properly used, the substrate is not significantly heated. Spraying enables deposition of practically any material with a stable molten phase, on any solid material. Sprayed ceramics are used to reduce wear by sliding and by hard particles. However, due to the defect-filled microstructure resulting from spraying, the coatings typically have poor mechanical and tribological properties compared to dense, sintered materials. By varying the spraying parameters, the microstructure of the coatings was influenced, and also the wear rate and cohesion, which is difficult to quantify. Improved tribological properties resulted from spraying with axial particle injection equipment and using narrowly size distributed, spherically shaped powder particles, compared to conventional equipment and powder particles. A new method to seal the open pores of sprayed ceramic coatings by electrolysis is proposed and evaluated. It was found that almost complete sealing could be obtained, in some cases giving a drastically improved wear behaviour. The studied electrolytically deposited sealants were Pb, Sn, Cu and Ni. The latter was found to give the best performance. It also proved possible to apply PVD coatings to the sprayed ceramics, and it was shown that sprayed and Ni-sealed alumina can be superior to ball bearing steel to support thin, low friction PVD coatings.

The lateral double-diffused MOS (LDMOS) transistor has traditionally been a high-voltage device used in switching applications. The use as a high-frequency device has become more important lately since the LDMOS offers an low cost solution for telecommunication applications. An important property of the LDMOS concept is that it can be manufactured in virtually the same process used in standard CMOS production. It only requires one extra process step, which is easily implemented. The other important aspect that gives the LDMOS the good high-frequency performance is that the channel length is a process parameter and not a lithography parameter. This thesis investigates the LDMOS transistor primarily from two aspects. The first is the high-voltage performance. For a high-voltage device the most important parameter is the breakdown voltage. The second most important parameter is the on-resistance that has the property of being in contradiction of the breakdown voltage and usually trade-offs are made to achieve acceptable performance. In the thesis several methods to improve the breakdown voltage/on-resistance relation are presented. The other part covers the high-frequency behavior of the LDMOS transistor. High-frequency characterization has been made to gain valuable information for the fundamental understanding of the physical mechanisms inside the transistor. A large part of the thesis covers modeling and parameter extraction of the devices. A new general method for parameter extraction of small-signal equivalent circuit models is presented, which has the appealing properties of not needing any approximation during the extraction which is common with other techniques.

QC 20101020

<p>The main objective of this industrially important work was to gain an increasing understanding of the properties of materials such as CMSX-4 nickel base super alloy, mould powder used in continuous casting of steel and coke used in blast furnace, with special reference to the thermal diffusivities. The measurements were carried out in a wide temperature range, solid, liquid, glassy and crystalline states.</p><p>For CMSX-4 alloy, the thermal conductivities were calculated from the experimental thermal diffusivities. Both the diffusivities and conductivities were found to increase with increasing temperature. Microscopic analysis showed the presence of intermetallic phases such as NiTi and NiTi2 below 1253 K. In this region, the mean free path of the phonons is likely to be limited by scattering against lattice defects. Between 1253 K and solidus temperature, these phases dissolved in the alloy adding to the impurities in the matrix, which, in turn, caused a decrease in the thermal diffusivity. This effect was confirmed by annealing the samples at 1573 K. The thermal diffusivities of the annealed samples measured at 1277, 1403 and 1531 K were found to be lower than the thermal diffusivities of non-annealed samples and the values did not show any noticeable change with time. It could be related to the attainment of equilibrium with the completion of the dissolution of γ and γ´ phases during the annealing process.</p><p>Liquid CMSX-4 does not show any change of thermal diffusivity with temperature. It may be attributed to the decreasing the mean free path being shorter than characteristic distance between two neighbouring atoms.</p><p>On the other hand thermal diffusivities of mould powder having glassy and crystalline states decrease with increasing temperature at lower temperature and are constant at higher temperature except for one glassy sample.</p><p>Analogously, the thermal diffusivity measurements of mould powder did not show any significant change with temperature in liquid state. It is likely to be due to the silicate network being largely broken down.</p><p>The thermal diffusivity is increased with increasing crystallisation degree of mould powder, which is expected from theoretical considerations.</p><p>The coke sample, taken from deeper level of the blast furnace, is found to have larger thermal diffusivity. This could be correlated to the average crystallite size along the structural <i>c</i>-axis, L_c, which is indicative of the higher degree of graphitisation. This was also confirmed by XRD measurements of the different coke samples. The degree of graphitisation was found to increase with increasing temperature. Further, XRD measurements of coke samples taken from different levels in the shaft of the blast furnace show that the graphitisation of coke was instantaneous between room temperature and 1473 K.</p>

No description available.

<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.</p><p>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. </p><p>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. </p><p>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. </p><p>In the second part of this thesis the development of tool steel grades with respect to optimise both hardenability with respect to; </p><p>- matrix hardenability (i.e the Grossmann approach) </p><p>- an enhanced weldability of such new steels due to a lower alloying content than is usual in such grades</p>

Experiments of directional solidification in a Hele-Shaw cell, 240 mm x 245 mm x 1 mm, were carried out to study the effects of convective flows and the evolution of structure in the "mushy layer", consisting of fluid and crystallites. Three different concentrations of ammonium chloride (NH₄Cl) solution, 26%, 27% and 28%, with a constant bottom cooling temperature ranging from 5°C to -20°C were used as an analogue model for metallic alloy systems. The experimental design included techniques using Peltier heat pumps along with PID feedback control for temperature regulation. A shadowgraphic visualization method made possible the simultaneous observation of the evolution of convection in the liquid region and the phenomena of chimney formation within the mushy layer. More than one hundred runs were carried out. Temperature information and simultaneously acquired digital images were recorded automatically. The time evolution of the solidification process was traced by image processing technique from the digital images. Results show that the phenomenon of intermittent plumes frequently occurs. The number of plumes near the liquid-mush interface decreases from a larger number in the beginning to about the same number of high plumes in the liquid region or chimneys in the mush. The number of chimneys is more static than that of plumes due to the relatively low speed of solidification or dissolution. The mush consists of three different layers. A thin layer of generally upward oriented crystal forms rapidly in the beginning, followed by a second layer aggregate gradually covering it. Finally a third layer of dendritic crystals dominates the top of the growing mush. Preliminary experiments in a Hele-Shaw cell inclined at 21 degrees caused the mush structures to develop differently than in the normal geometry. The significant differences include the dendritic crystal form, the lacunae of the mush, the shape of the chimneys, and the porosity changes of the structures. Directions for future research are suggested.

The assembly of nanoparticles at the interface of immiscible fluids holds promise for the preparation of new materials that benefit from both the physical properties of the nanoparticles and the chemistry associated with the ligands. Shaking nanoparticle solutions in organic solvents with water, results in the formation of nanoparticle-coated droplets that range in size from 10 µm to 200 µm. A strategy to control the size of these emulsions is described, by passing the droplets through commercial track-etch membranes with known pore sizes. Extrusion reduces the droplet size by breaking the droplets while passing theough the membrane pores, and reforming in the presence of excess nanoparticles in solution to form droplets as small as 1-5 µm. Crosslinking of nanoparticles at a liquid interface lends greater stability to the interfacial assembly, leading to ultrathin nanoparticle-based capsules, which possess mechanical integrity even after removal of the interface. Two approaches towards crosslinking are used in this thesis. Norbornene-functionalized CdSe/ZnS are used to afford facile capsule visualization by fluorescence confocal microscopy, as well as ease of crosslinking in mild conditions by means of ring-opening metathesis polymerization (ROMP). The crosslinked capsules can be used to encapsulate materials, and display size-selective retention capability, governed by the interstitial spaces between the nanoparticles. In a second approach to making hybrid capsules and sheets, horse spleen ferritin bionanoparticles and aldehyde-functionalized CdSe quantum dots are co-assembled at an oil-water interface. The cross-linked materials formed by reaction of the aldehyde functionality on the quantum dots with the surface-available amines on the ferritin bionanoparticles can be disrupted by addition of acid, thus leading to pH-degradable capsules and sheets. The driving force for assembly of nanoparticles at liquid interfaces is the reduction of the interfacial energy between the two liquids. The factors governing the amount of interfacial stabilization provided by the nanoparticles, namely the size and ligand coverage of the nanoparticles, are examined using the example of mixed assemblies of two different types of nanoparticles. Assemblies of 10 nm cobalt nanoparticles are disrupted upon the addition of 2.5 nm CdSe nanoparticles. The studies in this thesis demonstrate that the lower density of ligand coverage on CdSe quantum dots can overcome the large difference in size between the two nanoparticles, thus displacing the cobalt nanoparticles from the interface. Finally, preliminary results using amphiphilic graft copolymers instead of nanoparticles for interfacial stabilization of liquids are discussed. The resulting capsules are used for encapsulation and release of nanoparticles. In a technique termed repair-and-go, these nanoparticle-filled capsules are used for repairing cracked surfaces by passing the capsules over hydrophilic substrates containing hydrophobic cracks.