The self-assembly of magnesium aluminate spinel as a result of dewetting an overlaid thin film of (chiefly) gold was investigated. Thin films of gold were deposited on single-crystalline spinel substrates and were heat-treated to dewet gold film which led to self-assembly of intricate structures consisting of faceted spherical particles atop of frustums. The current work was conducted in continuation of previous studies which reported formation of such intricate structures. The most recent studies had evidently overruled a pure gold self-assembly scenario as was pointed out in preliminary investigations. It was in fact proven that these structures consist of three distinct parts: (i) a single or polycrystalline gold faceted sphere, (ii) quasi-phase interfacial bilayer, and (iii) a crystalline MgAl2O4 necking structure spontaneously risen from spinel substrate. In the current work, samples were produced through different film deposition methods of sputter, thermal evaporation, and e-beam evaporation coating which underwent thermal annealing to induce dewetting of gold film and subsequent self-assembly of intricate structures. Several characterization methods such as electron microscopy, X-ray energy dispersive spectroscopy, electron energy loss spectroscopy, and atom probe tomography were utilized to survey the different features of the intricate structures with focus on chemical analysis of the gold-spinel interface. The results rejected the previous findings about formation of interface complexion at the boundary of gold-spinel. It was found out that gold-spinel interface is in fact an ordinary metal-oxide boundary with sharp atomic distinction and no inter-diffusion or formation of interfacial complexion. It was further discovered that dewetting pure gold thin films does not result in formation of spinel self-assembly and existence of elemental impurities of copper (Cu) in the initial film is vital in development of such structures. Finally, it was concluded that chemical composition of metallic overlayer and the heat treatment parameters most fundamentally influence formation and physical characteristics of those self-assembled structures. / Thesis / Master of Applied Science (MASc)

No description available.

Heat treatment is a way to significantly change materials properties. When presented with materials that lack certain mechanical properties, it is possible to change its chemical properties and microstructures by applying heat. This can help achieve better yield strength, ductility and toughness. This project discusses the effects of multiple distinct heat treatment methods for several materials in order to improve ductility and elongation without diminishing strength. The materials in question are High Aluminum Steel and Strenx 700MC steel, the first being under development and the second being a commercially available steel. These steels show promise to be used as high ductility, high strength, and 3rd generation steels. The heat treatments can change the mechanical proprieties of the base materials in order to optimize these steels for applications in vertical access solutions. The heat treatments in this project were Quenching and Partitioning (QP), Quenching and Tempering (QT), Austempering (AUST), Intercritical Heat Treatment (IHT) and other usual heat treatments such as Double normalizing (D-Norm). First, the most beneficial type of the above mentioned heat treatments was selected for each steel and series of heat treatments were performed in order to identify and optimize the best method for each steel. Then, heat treated samples underwent a series of tests to numerically quantify their properties and compare them to the existing steels in Alimak’s applications. The results show that Quenching and Partitioning is the most promising heat treatment for optimizing strength and ductility in High Aluminum Steel, with elongation values up to 19% together with yield strengths of 700 MPa. For Strenx 700MC a combination of temperature and time was found that gave an elongation of above 25% with a yield strength of 450 MPa. The explanation for the good properties was partly grain refinement and phase transformations during heat treatments.

As the world becomes more focused on sustainability, there is increasing pressure on steel-bearing companies to improve their energy efficiency and reduce their carbon footprint. The heat treatment process accounts for about 25% of SKF's energy consumption, and it aims to achieve decarbonized operations by 2030 and the supply chain by 2050. Therefore, improving the energy efficiency of the heat treatment process can have significant economic and environmental benefits for the company. This thesis project aimed to conduct an energy mapping of different heat treatment processes at SKF to develop a methodology and standard key performance indicator for establishing energy performance and ensuring comparability between installations and processes. Three heat treatment processes were studied: through hardening, location A; case carburizing, location B; and surface induction hardening, location C. A detailed methodology and guidelines for carrying out energy mapping were developed. A standard key performance indicator known as Specific Energy consumption in kWh/kg at a particular utilization in % was set for comparisons among different heat treatment processes. Regression analysis was used to normalize the results. On the same utilization level, case carburizing, location B consumes more energy than through hardening, location A. Surface induction hardening, location C consumes 90% less than others and is less dependent on utilization. The carbon intensity in g CO2-eq/kg for greenhouse gas scopes 1, 2 and 3 were also studied. Case carburizing, location B had the highest climate impact due to the coal-based electricity mix of the country. Hence, the future availability of renewable electricity is critical when switching from gas to electricity across factories in SKF.

No description available.

Laser metal deposition (LMD) offers a unique combination of process flexibility, time savings, and reduced cost in producing titanium alloy components. The current challenge in processing titanium alloys using LMD methods is understanding the complex microstructure evolution as a part is fabricated layer by layer. The current work focuses on the characterization, thermal, and microstructural modeling of multilayered Ti-6Al-4V deposits. A thermal model has been developed using finite difference techniques to predict the thermal history of LMD processes. A microstructure model that predicts the alpha phase fraction and morphology evolution was constructed to quantify the effect of thermal cycling on the as-deposited microstructure evolution. Alpha dissolution and growth are modeled assuming one-dimensional plate dissolution according to a parabolic rate law, and a Johnson-Mehl-Avrami-Kolmorgorov (JMAK) nucleation and growth model, respectively. Alpha morphology (colony-alpha and basketweave-alpha) evolution is tracked using a simplistic approach. Characterization of the deposit has shown that a complex microstructure evolves consisting of a two distinct regions: a transient region of undeveloped microstructure and a characteristic layer that is periodically repeated throughout the deposit. The transient region contains a fine basketweave and colony-alpha morphology. The characteristic layer contains a two phase mixture of alpha+beta, with the alpha phase exhibits regions of colony-alpha (layer band) and basketweave-alpha morphology. The different regions of microstructural contrast in the deposit are associated with thermal cycling. The thermal model results show that a heat affected zone defined by the beta transus extends approximately 3 layers into the deposit. The phase fraction model predicts the greatest variation in microstructural evolution to occur in a layer n after the deposition of layer n+3. The results of the morphology model show that increased amounts of colony-alpha form near the top of a characteristic layer. It follows that a layer band (colony-alpha region) forms as a result of heating a region of material to a peak temperature just below the beta transus, where a large amount of primary-alpha dissolves. Upon cooling, colony-alpha forms intragranularly. The coupled thermal and microstructure models offer a way to quantitatively map microstructure during LMD processing of Ti-6Al-4V. / Ph. D.

A glucose glycine liquid model system fortified with 24 ppm of iron as either ferrous sulfate, ferric orthophosphate or ferric orthophosphate + 110 ppm ascorbic acid was thermally processed as 240, 250 and 260°F for 3, 6, 9, 12 and 15 minutes. Levels of elemental, nonelemental, soluble, total ionic and ferrous iron were measured for the model systems at each processing parameter. Data from the iron profiles were evaluated for the effect of iron salt; ascorbic acid; glucose and glycine, and processing temperature and time on changes in the iron chemistry during processing. The ferrous sulfate model system resulted in significantly higher levels of soluble and ferrous iron. Soluble iron from the ferric orthophosphate model system increased significantly with the addition of ascorbic acid. The presence of glucose and glycine prevented formation of insoluble iron hydroxides during processing of the ferrous sulfate system, promoted solubilization and ionization of iron for the ferric orthophosphate system and restricted the enhancing effect of ascorbic acid on the ferric orthophosphate profile. The interaction of the iron salt with the model system was stimulated by the application of heat. The insignificant correlation between process lethality values and the iron profile for each iron salt indicated that changes in the iron profile were time and temperature dependent. Kinetic parameters were calculated for all three model systems. The ferric orthophosphate iron profile was less sensitive to temperature change than either of the other two model systems. Evaluation of samples at sequential time intervals during the processing treatment allowed for a better understanding of the reaction mechanisms that occurred during processing which brought about a change in the iron profile of each model system. / Master of Science

The potentially most important challenges today are related to energy and the environment. New materials and methods are needed in order to, in a sustainable way, convert and store energy, reduce pollution, and clean the air and water from contaminations. In this, nanomaterials and nanocomposites play a key role, and hence knowledge about the relation between synthesis, structure, and properties of nanosystems is paramount. This thesis demonstrates that solution-chemical synthesis, using amine-modified acetates and nitrates, can be used to prepare widely different nanostructured films. By adjusting the synthesis parameters, metals, oxides, and metal–oxide or oxide–oxide nanocomposites were prepared for two systems based on Co and Zn:Fe, respectively, and the films were characterised using diffraction, spectroscopy, and microscopy techniques, and SQUID magnetometry. A variety of crystalline cobalt films—Co metal, CoO, Co3O4, and composites with different metal:oxide ratios—were synthesised. Heat-treatment parameters and control of the film thickness enabled tuning of the phase ratios. Random and layered Co–CoO composites were prepared by utilising different heating rates and gas flow rates together with a morphology effect associated with the furnace tube. The Co–CoO films exhibited exchange bias due to the ferromagnetic–antiferromagnetic interaction between the Co and CoO, whereas variations in e.g. coercivity and exchange bias field were attributed to differences in the structure and phase distribution. Ordered structures of wurtzite ZnO surrounded by amorphous ZnxFeyO were prepared through controlled phase segregation during the heating, which after multiple coating and heating cycles yielded ZnO–ZnxFeyO superlattices. The amorphous ZnxFeyO was a prerequisite for superlattice formation, and it profoundly affected the ZnO phase, inhibiting grain growth and texture, already from 1% Fe. In addition, ZnO–ZnxFeyO exhibited a photocatalytic activity for the oxidation of water that was higher than results reported for pure ZnO, and comparable to recent results reported for graphene-modified ZnO.

Selective Laser Melting (SLM) of Additive Manufacturing is an attractive fabrication method that employs CAD data to selectively melt the metal powder layer by layer via a laser beam and produce a 3D part. This method not only opens a new window in overcoming traditional NiTi fabrication problems but also for producing porous or complex shaped structures. The combination of SLM fabrication advantages with the unique properties of NiTi alloys, such as shape memory effect, superelasticity, high ductility, work output, corrosion, biocompatibility, etc. makes SLM NiTi alloys extremely promising for numerous applications. The SLM process parameters such as laser power, scanning speed, spacing, and strategy used during the fabrication are determinant factors in composition, microstructural features and functional properties of the SLM NiTi alloy. Therefore, a comprehensive and systematic study has been conducted over Ni50.8 Ti49.2 (at%) alloy to understand the influence of each parameter individually. It was found that a sharp [001] texture is formed as a result of SLM fabrication which leads to improvements in the superelastic response of the alloy. It was perceived that transformation temperatures, microstructure, hardness, the intensity of formed texture and the correlated thermo-mechanical response are changed substantially with alteration of each parameter. The provided knowledge will allow choosing optimized parameters for tailoring the functional features of SLM fabricated NiTi alloys. Without going through any heat treatments, 5.77% superelasticity with more than 95% recovery ratio was obtained in as-fabricated condition only with the selection of right process parameters. Additionally, thermal treatments can be utilized to form precipitates in Ni-rich SLM NiTi alloys fabricated by low energy density. Precipitation could significantly alter the matrix composition, transformation temperatures and strain, critical stress for transformation, and shape memory response of the alloy. Therefore, a systematic aging study has been performed to reveal the effects of aging time and temperature. It was found that although SLM fabricated samples show lower strength than the initial ingot, heat treatments can be employed to make significant improvements in shape memory response of SLM NiTi. Up to 5.5% superelastic response and perfect shape memory effect at stress levels up to 500 MPa was observed in solutionized Ni-rich SLM NiTi after 18h aging at 350ºC. For practical application, transformation temperatures were even adjusted without solution annealing and superelastic response of 5.5% was achieved at room temperature for 600C-1.5hr aged Ni-rich SLM NiTi. The effect of porosity on strength and cyclic response of porous SLM Ni50.1 Ti49.9 (at%) were investigated for potential bone implant applications. It is shown that mechanical properties of samples such as elastic modulus, yield strength, and ductility of samples are highly porosity level and pore structure dependent. It is shown that it is feasible to decrease Young’s modulus of the SLM NiTi up to 86% by adding porosity to reduce the mismatch with that of a bone and still retain the shape memory response of SLM fabricated NiTi. The shape memory effect, as well as superelastic response of porous SLM Ni50.8Ti49.2,were also investigated at body temperature. 32 and 45% porous samples with similar behaviors, recovered 3.5% of 4% deformation at first cycle. The stabilized superelastic response was obtained after clicking experiments.

<p>Glavni cilj doktorske disertacije bio je ispitivanje op&scaron;tih odlika industrijski proizvedenih, fermentisanih suvih kobasica u Srbiji i mogućnost dodatnog unapređenja njihove mikrobiolo&scaron;ke bezbednosti. Ispitivani su mikrobiolo&scaron;ki i fizičko-hemiijski pokazatelji u industrijskom proizvodnom lancu sremske kobasice i sudžuka, tipičnih fermentisanih suvih kobasica od svinjskog i goveđeg mesa. U sremskoj kobasici praćeno je prisustvo Salmonella а Escherichia coli O157 u sudžuku. Ispitane su i promene glavnih grupa mikrobiota, pH i aw vrednosti i hemijski sastav proizvoda. Mikrobiolo&scaron;ka kontaminacija u početnim koracima proizvodnje bila je uglavnom visoka. Salmonela je ustanovljena u fazi pripreme nadeva u dva od tri proizvodna pogona, dok je E. coli O157 potvrđena u jednom uzorku usitnjenog mesa i masnog tkiva jednog proizvodnog pogona. Rezultati ispitivanja proizvodnje kobasica slični su rezultatima istraživanja u drugim zemljama. Svi uzorci gotovih sremskih kobasica bili su zadovoljavajućeg nivoa mikrobiolo&scaron;kog kvaliteta, dok većina uzoraka sudžuka nije bila zadovoljavajuća. Početno prisustvo alimentarnih patogena može se smatrati bezbednosnim rizikom.<br />Preživljavanje Salmonella Тyphimurium, Escherichia coli O157 i Listeria monocytogenes tokom proizvodnje i skladi&scaron;tenja inokulisane, sremske kobasice i sudžuka, praćeno je u drugoj fazi istraživanja. Smanjenje brojnosti sva tri patogena u skladu je sa literaturnim podacima i može se zaključiti da postupci uobičajeno primenjeni u industrijskoj proizvodnji sremske kobasice i sudžuka ne osiguravaju uvek, u dovoljnoj meri, mikrobiolo&scaron;ku bezbednost proizvoda. Ispitiana je i mogućnost pasterizacije u cilju redukcije navedenih patogena u kobasicama od svinjskog, odnosno, goveđeg mesa, uz ocenu senzorskog kvaliteta proizvoda. Rezultati su pokazali da Salmonella Typhimurium i E. coli O157 mogu da budu uklonjene pasterizacijom gotovih fermentisanih suvih kobasica а dа senzorske odlike proizvoda i dalje оstanu prihvatljive. L. monoctogenes se pokazala kao patogen koji je značajno otporniji na zagrevanje, u oba tipa kobasica, zbog čega su potrebna dalja istraživanja radi redukcije dо prihvatljivog nivoa.</p> / <p>Glavni cilj doktorske disertacije bio je ispitivanje op&scaron;tih odlika industrijski proizvedenih, fermentisanih suvih kobasica u Srbiji i mogućnost dodatnog unapređenja njihove mikrobiolo&scaron;ke bezbednosti. Ispitivani su mikrobiolo&scaron;ki i fizičko-hemiijski pokazatelji u industrijskom proizvodnom lancu sremske kobasice i sudžuka, tipičnih fermentisanih suvih kobasica od svinjskog i goveđeg mesa. U sremskoj kobasici praćeno je prisustvo Salmonella a Escherichia coli O157 u sudžuku. Ispitane su i promene glavnih grupa mikrobiota, pH i aw vrednosti i hemijski sastav proizvoda. Mikrobiolo&scaron;ka kontaminacija u početnim koracima proizvodnje bila je uglavnom visoka. Salmonela je ustanovljena u fazi pripreme nadeva u dva od tri proizvodna pogona, dok je E. coli O157 potvrđena u jednom uzorku usitnjenog mesa i masnog tkiva jednog proizvodnog pogona. Rezultati ispitivanja proizvodnje kobasica slični su rezultatima istraživanja u drugim zemljama. Svi uzorci gotovih sremskih kobasica bili su zadovoljavajućeg nivoa mikrobiolo&scaron;kog kvaliteta, dok većina uzoraka sudžuka nije bila zadovoljavajuća. Početno prisustvo alimentarnih patogena može se smatrati bezbednosnim rizikom.<br />Preživljavanje Salmonella Typhimurium, Escherichia coli O157 i Listeria monocytogenes tokom proizvodnje i skladi&scaron;tenja inokulisane, sremske kobasice i sudžuka, praćeno je u drugoj fazi istraživanja. Smanjenje brojnosti sva tri patogena u skladu je sa literaturnim podacima i može se zaključiti da postupci uobičajeno primenjeni u industrijskoj proizvodnji sremske kobasice i sudžuka ne osiguravaju uvek, u dovoljnoj meri, mikrobiolo&scaron;ku bezbednost proizvoda. Ispitiana je i mogućnost pasterizacije u cilju redukcije navedenih patogena u kobasicama od svinjskog, odnosno, goveđeg mesa, uz ocenu senzorskog kvaliteta proizvoda. Rezultati su pokazali da Salmonella Typhimurium i E. coli O157 mogu da budu uklonjene pasterizacijom gotovih fermentisanih suvih kobasica a da senzorske odlike proizvoda i dalje ostanu prihvatljive. L. monoctogenes se pokazala kao patogen koji je značajno otporniji na zagrevanje, u oba tipa kobasica, zbog čega su potrebna dalja istraživanja radi redukcije do prihvatljivog nivoa.</p> / <p>The main aim of this doctoral thesis was to investigate the general characteristics of industrially-produced Serbian dry fermented sausages and the possibility of further improving their microbiological safety. Microbiological and physicochemical indicators were studied along the industrial production chains producing Sremska and Sudzuk sausage, typical of dry, fermented sausage prepared from pork or beef, respectively. The occurrences of Salmonella in pork sausages, and of Escherichia coli O157 in beef sausages were determined. Changes in the main groups of microbiota, pH, aw values and the chemical composition of the products were evaluated. Microbiological contamination in the initial stages of production was generally high. Salmonella was confirmed from the batter-preparation phase in two of three production lines, while E. coli O157 was confirmed in one sample of meat and fatty tissue from one production line. The results of this investigation of sausage production were similar to results obtained in other countries. All samples of finished pork sausage were of acceptable microbiological quality, while the majority of beef sausage samples were not microbiologically acceptable. The initial presence of foodborne pathogens can be considered a food safety risk.<br />The survival of Salmonella Тyphimurium, Escherichia coli O157 and Listeria monocytogenes during production and storage of inoculated pork and beef sausages was determined in the second phase of the investigation. All three pathogens declined in numbers in accordance with data from the literature, and it can be concluded that normal measures for pork and beef sausage preparation in industrial production do not always ensure, to a suitable level, the microbiological safety of the products. The possibility of pasteurising finished pork and beef sausages, with the aim of reducing Salmonella Typhimurium and E. coli O157, respectively, was investigated, and at the same time, sensory evaluation of product quality was performed. The results showed that pasteurisation eliminated Salmonella Typhimurium and E. coli O157 from finished dry fermented sausages, while sensory qualities of the products remained acceptable. L. monoctogenes proved to be a significantly more heat-resistant pathogen in both types of sausage, and therefore, further research is required to determine how to reduce numbers of this pathogen to acceptable levels.</p>