This licentiate thesis has the main focus on evaluation of the wear of coated and uncoated polycrystalline cubic boron nitride cutting tool used in cutting operations against hardened steel. And to exam the surface finish and integrity of the work material used. Harder work material, higher cutting speed and cost reductions result in the development of harder and more wear resistance cutting tools. Although PCBN cutting tools have been used in over 30 years, little work have been done on PVD coated PCBN cutting tools. Therefore hard turning and hard milling experiments with PVD coated and uncoated cutting tools have been performed and evaluated. The coatings used in the present study are TiSiN and TiAlN. The wear scar and surface integrity have been examined with help of several different characterization techniques, for example scanning electron microscopy and Auger electron spectroscopy.   The results showed that the PCBN cutting tools used displayed crater wear, flank wear and edge micro chipping. While the influence of the coating on the crater and flank wear was very small and the coating showed a high tendency to spalling. Scratch testing of coated PCBN showed that, the TiAlN coating resulted in major adhesive fractures. This displays the importance of understanding the effect of different types of lapping/grinding processes in the pre-treatment of hard and super hard substrate materials and the amount and type of damage that they can create. For the cutting tools used in turning, patches of a adhered layer, mainly consisting of FexOy were shown at both the crater and flank. And for the cutting tools used in milling a tribofilm consisting of SixOy covered the crater. A combination of tribochemical reactions, adhesive wear and mild abrasive wear is believed to control the flank and crater wear of the PCBN cutting tools. On a microscopic scale the difference phases of the PCBN cutting tool used in turning showed different wear characteristics. The machined surface of the work material showed a smooth surface with a Ra-value in the range of 100-200 nm for the turned surface and 100-150 nm for the milled surface. With increasing crater and flank wear in combination with edge chipping the machined surface becomes rougher and showed a higher Ra-value. For the cutting tools used in milling the tendency to micro edge chipping was significant higher when milling the tools steels showing a higher hard phase content and a lower heat conductivity resulting in higher mechanical and thermal stresses at the cutting edge.

This work have served as a preliminary work for a more extensiveresearch on antimony- and nickel-doped tin dioxide electrodes used forozone generation in electrolytic reactions. The target has been to test themanufacturing process of Sb/Ni-doped SnO2 with spin-coating techniqueand succeed to make electrodes for anodic ozone evolution and tocharacterize them. Electrode manufacturing was made using sol-gelfrom chloride salts of tin, antimony and nickel, which were applied to atitanium substrate through spin-coating. The substrates were spun todifferent thickness followed by drying and baking of the substrate. A setof electrodes with three layers were made just with spin-coating, additionallya set of electrodes with twenty layers were made with bothspin-coating and dip-coating. To characterize physical properties of theelectrodes, x-ray diffraction, scanning electron microscopy and transmissionelectron microscopy were conducted. Electrochemical measurementswere made in open beakers with a platinum cathode andsulphuric acid electrolyte using a galvanostatic measurement with afixed current. To measure the ozone evolution the optical absorbancedifference from the electrolyte compared to a clean electrolyte wasmeasured, this however only measures the amount of aqueous ozonepresent. Assembling of SnO2 electrodes for ozone evolution was successful.For the three-layered electrodes the absorbance readings wereinconclusive but with the twenty-layered electrodes there was a smell ofozone present within the electrolyte and absorbance reading of the dipcoatedelectrode presented a clear peak for ozone.

The thin film technology is of great importance in modern society and is a key technology in wide spread applications from electronics and solar cells to hard protective coatings on cutting tools and diffusion barriers in food packaging. This thesis deals with various aspects of thin film processing and the aim of the work is twofold; firstly, to obtain a fundamental understanding of the sputter deposition and the reactive sputter deposition processes, and secondly, to evaluate sputter deposition of specific material systems with low friction properties and to improve their performance.From studies of the reactive sputtering process, two new methods of eliminating the problematic and undesirable hysteresis effect were found. In the first method it was demonstrated that an increased process pressure caused a reduction and, in some cases, even elimination of the hysteresis. In the second method it was shown that sufficiently high oxide content in the target will eliminate the hysteresis. Further studies of non-reactive magnetron sputtering of multi-element targets at different pressures resulted in huge pressure dependent compositional gradients over the chamber due to different gas phase scattering of the elements. This has been qualitatively known for a long time but the results presented here now enable a quantitative estimation of such effects. For example, by taking gas phase scattering into consideration during sputtering from a WS2 target it was possible to deposit WSx films with a sulphur content going from sub-stoichiometric to over-stoichiometric composition depending on the substrate position relative the target. By alloying tungsten disulphide (WS2) with carbon and titanium (W-S-C-Ti) its hardness was significantly increased due to the formation of a new titanium carbide phase (TiCxSy). The best sample increased its hardness to 18 GPa (compared to 4 GPa for the corresponding W-S-C coating) while still maintaining a low friction (µ=0.02) due to the formation of easily sheared WS2 planes in the wear track.

A cathode structure was demonstrated that utilizes aligned carbon nanotubes (CNTs) to improve the thermionic electron emission by increasing the field enhancement of the cathode surface. Aligned CNTs were grown on the surface of a tungsten substrate by plasma enhanced chemical vapor deposition. The tungsten-CNT structure was further coated with a thin film of low work function emissive materials by magnetron sputtering. Numerous cathodes with varying CNT morphology and oxide layer thickness were created. The field and thermionic emission of the cathodes were tested in order to study the effects of the surface properties on the emission characteristics. It was observed that the introduction of CNTs into an oxide cathode structure improves both the thermionic and field emission, even in cathodes with relatively low field enhancement factors. Because of the high field enhancement factors that are available for CNTs, there remains a potential for dramatically improved electron emission. / Department of Physics and Astronomy

Microstructural comparison of the isothermal oxidation performance of an experimental Ni-5Cr-15Al overlay coating applied to CMSX-4 and CMSX-486 was performed at 1100 ℃. High temperature oxidation was carried out in a box furnace for a maximum duration of 192 hrs. Samples were periodically removed and the oxide, coating and substrates microstructurally analyzed using SEM, EDS and XRD equipment. Uncoated CMSX-4 and CMSX-486 were also oxidized using the same conditions in an attempt to understand how the coating affected oxidation performance based on microstructural changes. Results show that both CMSX-4 and CMSX-486 have unacceptable oxidation characteristics in the un-coated condition, where CMSX-486 had significantly better performance than CMSX-4. However, in the coated condition, both CMSX-4 and CMSX-486 had no significant difference in oxidation performance. It was found, in the un-coated and coated conditions, that the role of Hf in CMSX-486 played a significant role in determining oxidation performance of the material.

The growing interest in increasing the wear resistance and hardness of surfaces that are in contact with abrasives or corrosive materials has inspired the development of several processes for creating protective coatings. In-situ laser cladding is one of the most promising of these processes. It enables the formation of a uniform coating by melting powder to form the desired composition from a pure powder component. In this research, pure Ti, graphite, and Fe are used for in-situ laser cladding on a steel substrate to form an Fe-TiC metal matrix composite (MMC). The effect of laser parameters on both the quality of the bonding and morphology of the in-situ-formed TiC iron-based composite clad are investigated. Results show that laser parameters play a crucial role in determining the clad quality and clad microstructure. Two combined parameters, effective energy and powder deposition density, are used to study the effect of laser parameters (i.e., laser power, scan speed and powder feed rate) on the clad properties. While results indicate that combined parameters help to determine the quality limit, laser process parameters need to be taken into account in order to study the clad microstructure. To increase the clad hardness and TiC volume fraction, C:Ti atomic ratio should increase from 45:55 to 55:45, and Fe percentages in the powder composition should decrease from 70 wt% to the 10 wt%. By varying the powder composition, a change in TiC morphology, clad microstructure and clad hardness occurs. The dilution effect is also considered in the interpretation of results. In order to estimate wear resistance, the ASTM G65-A procedure was selected to perform tests on various clad compositions. An increased wear resistance is seen when the volume fraction of TiC is increased.

Wrought magnesium alloys are considered attractive candidates for structural members in automotive and aerospace industries due to their high specific strength. Although new processes have helped to produce high purity magnesium alloys with higher resistance to corrosion, these alloys still need protection against corrosion when they are used in aggressive environments. Cold spray coating is one of the protective methods that are employed for this purpose. The similarity between cold spray coating and shot peening process poses the question whether cold spray coating can improve the fatigue strength in addition to providing corrosion protection. The objective of this research is to answer this question for the specific case of the coating of wrought magnesium alloy AZ31B with aluminum powder. This study comprises two parts. The first part characterises the residual stress induced by cold spray coating. This investigation employs both numerical and experimental methods. For the numerical study, the cold spray coating process has been simulated via ANSYS software classic package. The numerical results have been compared to experimental results from X-Ray Diffraction (XRD) stress measurement of a coated sample. For the second part of this research, the fatigue strength of as received, stress relieved, and stress relieved/coated specimens have been compared. Three groups of AZ31B specimens have been prepared and tested by rotating bending machine and their S-N curves have been prepared. Comparison of the results reveals that there is a considerable loss in fatigue strength of as received specimens after stress relief. This is due to the removal of compressive residual stress in the raw material induced by the extrusion process. Also, comparison of S-N curves of stress relieved and stress relieved/coated specimens shows fatigue life improvement after cold spray coating. The maximum improvement is 49 percent in the load of 120 MPa and the endurance limit has improved 9 percent.

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Fresh-cut watermelon is appreciated for its taste, flavor, and juiciness. However, there are challenges in maintaining the freshness since fresh-cut processing of fruits promotes faster deterioration. Our objective was to determine the effectiveness of multilayered antimicrobial edible coating on the shelf-life of fresh-cut watermelon while keeping its original attributes for longer, without affecting its sensory properties. A set of solutions containing sodium alginate (0.5, 1, 2% w/w), beta-cyclodextrin, trans-cinnamaldehyde (antimicrobial agent), pectin, and calcium lactate were used as coating systems for fresh-cut watermelon cylinders. The samples were coated by the layer-by-layer dipping technique and stored at 4 degrees C for 15 days. Results were analyzed individually for each quality attribute evaluated, and the best concentration among the solutions to improve each attribute was found. Watermelon quality was measured in terms of texture, color, juice leakage (weight loss), oBrix, and pH. Microbiological analysis consisted of total coliforms, yeasts and molds, aerobics, and psychrotrophs. A consumer test was carried out (~ 40 panelists) to support the objective quality data. Panelists scored the samples using a 9-point hedonic scale. Uncoated samples served as controls. Quality tests were conducted at days 1, 3, 7, 12, and 15 of storage. Sensory tests showed high acceptance (P < 0.05) of the coated samples when compared to the controls. Quality attributes, particularly texture (firmness) and juice leakage (weight loss) were enhanced (P < 0.05) by the coating. Microbiological analysis demonstrated that alginate-based edible coating has a huge effect against microbial growth. 1% sodium alginate coating provided better preservation in terms of quality parameters, microbiological growth, and sensory acceptance. These results indicate that different ratios between solutions present a significant variation for each quality attribute measured in this study; and the thickness of the coating as well as the amount of antimicrobial are critical for shelf-life extension of fresh-cut watermelon. Hence, application of an alginate based multilayered edible coating has tremendous potential to enhance microbial quality and extend the shelf-life of fresh-cut watermelon.