There has been progress in the surface modification of low carbon steel in order to enhance its surface hardness. This study contributes to this by investigating the introduction of carbon nanotubes and amorphous carbon in the carburization of mild steel. In order to achieve the goal, carbon nanotubes were synthesized in a horizontal tubular reactor placed in a furnace also called the chemical vapor deposition process at a temperature of 700oC. Catalyst was produced from Iron nitrate Fe(NO3)3.9H2O and Cobalt nitrate Co(NO3)2.6H2O on CaCO3 support while acetylene C2H2 was used as the carbon source and nitrogen N2 was used as contaminant remover. The as-synthesized carbon nanotubes were purified using nitric acid HNO3 and characterized using scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA) and fourier transform infrared spectroscopy (FTIR). It was found that as-synthesized carbon nanotubes had varying lengths with diameters between 42-52 nm from the SEM and the TGA showed the as-synthesized CNTs with a mass loss of 78% while purified CNTs had 85% with no damage done to the structures after using the one step acid treatment. The as-synthesized and purified carbon nanotubes were used in carburizing low carbon steel (AISI 1018) at two austenitic temperatures of 750oC and 800oC and varying periods of 10-50 minutes while amorphous carbon obtained by pulverizing coal was also used as comparison. The mild steel samples were carburized with carbon nanotubes and amorphous carbon in a laboratory muffle furnace with a defined number of boost and diffusion steps. The carburizing atmosphere consisted of heating up to the varying temperatures at a speed of 10oC/minute, heating under this condition at varying periods, performing a defined number of boost and diffusion processes at the varying temperatures and cooling to room temperatures under the same condition. The carburized surfaces were observed with the Olympus SC50 optical microscope and the hardness distribution of the carburized layer was inspected with a Vickers FM 700 micro-hardness tester. The as-synthesized and purified CNT samples showed higher hardness on the surface of the mild steel than the amorphous carbon. In the same vein, the change in the microstructures of vi the steel samples indicated that good and improved surface hardness was obtained in this work with the reinforcements but with purified CNT having the highest peak surface hardness value of 191.64 ± 4.16 GPa at 800oC, as-synthesized CNT with 177.88 ± 2.35 GPa and amorphous carbon with 160.702 ± 5.79 GPa which are higher compared to the values obtained at 750oC and that of the original substrate which had a surface hardness of 145.188 ± 2.66 GPa. The percentage hardness obtained for the reinforcement with the amorphous carbon, the CNT and the pCNT showed an increase of 5.47%, 10.04% and 15.77% respectively at 750oC when compared to that of the normal substrate carburized without reinforcements. Furthermore, at 800oC, the reinforcement with the amorphous carbon, the CNT and the pCNT show a percentage hardness increase of 7.04%, 14.68% and 22.05% when compared to that of the normal substrate carburized without reinforcements. Comparing the reinforcement potential of the amorphous carbon, the CNT and the pCNT at 750oC, the percentage hardness reveal that using pCNT displayed an increase of 10.89% over that of amorphous carbon and of 6.37% over that of CNT. In addition, the use of CNT as reinforcement at 750oC displayed a percentage hardness increase of 4.83% over that of the amorphous carbon carburized at the same temperature / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)

Orientador: Luiz Carlos Barbosa / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-08T19:58:45Z (GMT). No. of bitstreams: 1 Osorio_SergioPauloAmaral_D.pdf: 8946065 bytes, checksum: 9771cf8636d67bee8eb1b92d030d0d13 (MD5) Previous issue date: 2007 / Resumo: Neste trabalho três tipos de vidro telurito são estudados, fabricados e caracterizados, tendo em vista a fabricação de fibras ópticas de cristal fotônico. Basicamente, dois processos de fabricação de fibras de cristal fotônico foram considerados: 1) Empilhamento e puxamento, e 2) Extrusão. Os vidros teluritos fabricados são: 0,77TeO2¿0,23WO3; 0,75TeO2¿0,20Li2O¿0,05TiO2 e 0,68TeO2¿0,155ZnO¿0,05Li2CO3¿0,015Bi2O3¿0,095CsCl (mol%), dos tipos binário, ternário e quinqüenário, respectivamente, os quais foram dopados com Er2O3. As caracterizações efetuadas foram: a) Medida do índice de refração, 2) Fotoluminescência, 3) Absorbância, 4) Tempo de vida dos íons de Érbio, 5) Análise Térmica Diferencial, 6) Análise termogravimétrica e, 7) Viscosidade. Como dito anteriormente, pode-se fabricar fibras microestruturadas de telurito por extrusão, ou pelo método de empilhamento e puxamento. A extrusora disponível no laboratório de materiais vítreos foi feita para extrudar materiais polímeros. Nossa tentativa de utilizá-la para vidros telurito não foi bem sucedida. Porém, pudemos tirar algum proveito desta experiência para futuros projetos. Os tubos de vidro telurito utilizados no método de empilhamento e puxamento foram fabricados tanto por sucção vertical do vidro fundido, quanto por rotação horizontal dos tubos em chama. No primeiro método, o diâmetro interno dos tubos de revestimento diminuiu de baixo para cima, devido ao efeito da gravidade, fazendo com que o preenchimento dos mesmos com tubos capilares fosse inadequado, ou seja, a secção transversal da fibra apresentou espaços vazios não preenchidos pelos capilares. No segundo método, o diâmetro interno dos tubos de revestimento não apresentou variação significativa ao longo de seu comprimento, possibilitando, assim, um melhor preenchimento dos mesmos por tubos capilares. Embora as fibras fabricadas com tubos feitos por rotação horizontal em chama apresentem boa geometria de secção transversal, a contaminação do vidro pela chama acarreta um aumento nas perdas de potência óptica dos modos guiados. Este efeito foi eliminado pela utilização de centrifugação em um forno radiante. Verificamos, também, que as fibras microestruturadas com somente um anel de capilares ao redor do núcleo apresentam grandes perdas por confinamento. / Abstract: In this work, three types of tellurite glasses are synthesized and characterized, aiming the manufacturing of photonic crystal fibers or microstructured fibers. Basically, two types of manufacturing processes are considered: 1) Stacking and draw, and 2) Extrusion. The tellurite glasses are: 0,77TeO 2¿0,23WO3; 0,75TeO2¿0,20Li2O¿0,05TiO2 e 0,68TeO2¿ 0,155ZnO¿0,05Li2C3¿0,015Bi2O3¿0,095CsCl (mol%), composed by two, three and five types of oxides, respectively, and Erbium oxide. The glasses were characterized by: a) index of refraction, 2) photoluminescence, 3) absorbance, 4) Erbium ions lifetime, 5) Differential Thermal Analysis, 6) Thermo gravimetric Analysis, and 7) Viscosity. The extrusion machine of the laboratory was devised for polymers. Nevertheless, we tried with telluride glass but without success. The tellurite glass tubes used for the stack and draw process were manufactured by vertical suction of the melted glass as well as by horizontal rotation of the tubes in flame. For the vertical suction method, the tellurite tube inner diameter shows a taper feature from the bottom to the top of the tube, due to the gravity effect, that makes the jacket tube unsuitable for capillary filling, that is, the fiber transversal section shows empty spaces that could not be filled with capillaries. For the second method, the telluride jacket tube inner diameter do not shows a significant variation with length, so it was possible to better fill it with the capillaries. Although the fibers made with tubes manufactured by horizontal rotation in flame shows good transversal geometry, the contamination of the glass by the flame gases brought about great losses for optical guided modes. The burner was replaced by a radiant oven. We verified, also, that micro structured fibers with only one ring of capillaries around the nucleus shows great confinement loss arising from the leaky nature of the modes / Doutorado / Física da Matéria Condensada / Doutor em Física

In most casting applications, dendritic microstructure morphology is not desired because it leads to poor mechanical properties. Forced convection causing sufficient shearing in the mushy zone of the partially solidified melt is one of the means to suppress this dendritic growth. The dendrites formed at the solid-liquid interface are detached and carried away due to strong fluid flow to form slurry. This slurry, consisting of rosette or globular particles, provides less resistance to flow even at a high solid fraction and can easily fill the die-cavity. The stated principle is the basis of a new manufacturing technology called “semi-solid forming” (SSF), in which metal alloys are cast in the semi-solid state. This technique has numerous advantages over other existing commercial casting processes, such as reduction of macrosegregation, reduction of porosity and low forming efforts. Among all currently available methods available for large scale production of semisolid slurry, the cooling slope is considered to be a simple but effective method because of its simple design and easy control of process parameters, low equipment and running costs, high production efficiency and reduced inhomogeneity. With this perspective, the primary objective of the present research is to investigate, both experimentally and numerically, convective heat transfer and solidification on a cooling slope, in addition to the study of final microstructure of the cast billets. Some key process parameters are identified, namely pouring temperature, slope angle, slope length, and slope cooling rate. A systematic scaling analysis is performed in order to understand the relative importance of the parameters in influencing the final properties of the slurry and microstructure after solidification. A major part of the present work deals with the development of an experimental set up with careful consideration of the range of process parameters involved by treating the cooling slope as a heat exchanger. Subsequently, a comprehensive numerical model is developed to predict the flow, heat transfer, species concentration solid fraction distribution of aluminum alloy melt while flowing down the cooling slope. The model uses a variable viscosity relation for slurry. The metal-air interface at the top during the melt flow is tracked using a volume of fluid (VOF) method. Solidification is modeled using an enthalpy based approach and a volume averaged technique. The mushy region is modeled as a multi-layered porous medium consisting of fixed columnar dendrites and mobile equiaxed or fragmented grains. In addition, the solidification model also incorporates a fragmentation criterion and solid phase movement. The effects of key process parameters on flow behavior involving velocity distribution, temperature distribution, solid fractions at the slope exit, and macrosegregation, are studied numerically and experimentally for aluminium alloy A356. The resulting microstructures of the cast billets obtained from the experiments are studied and characterized. Finally the experimental results are linked to the model predictions for establishing the relations involving interdependence of the stated key process parameters in determining the quality of the final cast products. This study is aimed towards providing the necessary guidelines for designing a cooling slope and optimizing the process parameters for desirable quality of the solidified product.

Le travail s’intéresse aux effets d’un pré-écrouissage cyclique axial ou en torsion sur le comportement cyclique et la durée de vie en fatigue sous sollicitation axiale à température ambiante d’un acier inoxydable austénitique 304L. Les essais cycliques séquentiels à amplitude de déformation croissante ou décroissante montrent que la courbe cyclique du 304L est non-unique. Cette caractéristique est liée à la persistance de l’état microstructural généré pendant les cycles d’amplitude de déformation maximale de la première séquence. En augmentant le nombre des séquences, l’acier 304L montre une tendance vers une courbe cyclique asymptotique, l’écrouissage semble se stabiliser. Des essais de fatigue sous chargement axial ont été réalisés sur des éprouvettes vierges ou pré-écrouies en traction-compression ou en torsion. Les durées de vie ont été sensiblement réduites pour les éprouvettes pré-écrouies. Ce phénomène est lié à la formation de structures de dislocations denses héritées de la phase de pré-écrouissage. Cependant, l’augmentation de l’amplitude de déformation en fatigue réduit l’effet du pré-écrouissage. / This study investigates the effects of loading history on the cyclic stress-strain curve and fatigue behavior of 304L stainless steel at room temperature. Tension-compression tests were performed ont the same specimen under controlled strain, using several loading sequences of increasing or decreasing amplitude. The results showed that fatigue life is significantly reduced by the previous loading history. A previously developed method for determining the effect of prehardening was evaluated. Microstructural analyses were also performed; the microstructures after preloading and their evolution during the fatigue cycles were characterized by TEM. The results of these analyses improve our understanding of the macroscopic properties of 304L stainless steel and can help us identify the causes of failure and lifetime reduction.

No description available.

Pt-aluminide (PtAl) coatings form an integral part of thermal barrier coating (TBC) systems that are applied on Ni-based superalloy components operating in the hot sections of gas turbine engines. These coatings serve as a bond coat between the superalloy substrate and the ceramic yttrium stabilized zirconia (YSZ) coating in the TBC system and provide oxidation resistance to the superalloy component during service at high temperatures. The PtAl coatings are formed by the diffusion aluminizing process and form an integral part of the superalloy substrate. The microstructure of the PtAl coatings is heavily graded in composition as well as phase constitution. The matrix phase of the coating is constituted of the B2-NiAl phase. Pt, in the coating, is present as a separate PtAl2 phase as well as in solid solution in B2-NiAl. The oxidation resistance of the PtAl bond coat is derived from the B2-NiAl phase. At high temperatures, Al from the B2-NiAl phase forms a regenerative layer of alumina on the coating surface which, thereby, lowers the overall oxidation rate of the superalloy substrate. The presence of Pt is beneficial in improving the adherence of the alumina scale to the surface and thereby enhancing the oxidation resistance of the coating. However, despite its excellent oxidation resistance, the B2-NiAl being an intermetallic phase, renders the PtAl coating brittle and imparts it with a high brittle-to-ductile-transition-temperature (BDTT). The PtAl coating, therefore, remains prone to cracking during service. The penetration of these cracks into the substrate is known to degrade the strain tolerance of the components. Evaluation of the mechanical behavior of these coatings, therefore, becomes important from the point of views of scientific understanding as well as application of these coatings in gas turbine engine components. Studies on the mechanical behavior of coatings have been mostly carried on coated bulk superalloy specimens. However, since the coating is brittle and the superalloy substrate more ductile when compared to the coating, the results obtained from these studies may not be representative of the coating. Therefore, it is imperative that the mechanical behavior of the coating in stand-alone condition, i.e. the free-standing coating specimen without any substrate attached to it, be evaluated for ascertaining the true mechanical response of the coating. Study of stand-alone bond coats involves complex specimen preparation techniques and challenging testing procedures. Therefore, reports on the evaluation of mechanical properties of stand-alone coatings are limited in open literature. Further, no systematic effort has so far been made to examine important aspects such as the effect of temperature and strain rate on the tensile behavior of these coatings. The deformation mechanisms associated with these bond coats have also not been reported in the literature. In light of the above, the present research study aims at evaluating the tensile behavior of free-standing PtAl coatings by the micro-tensile testing technique. The micro-tensile testing method was chosen for property evaluation because of its inherent ability to generate uniform strain in the specimen while testing, which makes the results easy to interpret. Further, since the technique offers the feasibility to test the entire graded PtAl coating in-situ, the results remain representative of the coating. Using the above testing technique, the tensile behavior of the PtAl coating has been evaluated at various temperatures and strain rates. The effect of strain rate on the BDTT of the coating has been ascertained. Further, the effect of Pt content on the tensile behavior of these coatings has also been evaluated. Attempts have been made to identify the mechanisms associated with tensile deformation and fracture in these coatings. The thesis is divided into nine chapters. Chapter 1 presents a brief introduction on the operating environment in gas turbine engines and the materials that are used in the hot sections of gas turbine engines. The degradation mechanisms taking place in the superalloy in gas turbine environments and the need for application of coatings has also been highlighted. The basic architecture of a typical thermal barrier coating (TBC) system applied on gas turbine engine components has been presented. The constituents of the TBC system, i.e. the ceramic YSZ coating, MCrAlY overlay as well as diffusion aluminide bond coats and, the various techniques adopted for the deposition of these coatings have been described in brief. Chapter 2 presents an overview of the literature relevant to this study. This chapter is divided into four sub-chapters. The formation of diffusion aluminide coatings on Ni-based superalloys has been described in the first sub-chapter. Emphasis has been laid on pack cementation process for the formation of the coatings. The fundamentals of pack aluminizing process, including the thermodynamic and kinetic aspects, have been mentioned in brief. The microstructural aspects of high activity and low activity plain aluminide and Pt-aluminide coatings have also been illustrated. The techniques applied for the mechanical testing of bond coats have been discussed in the second sub-chapter. The macro-scale testing techniques have been mentioned in brief. The small scale testing methods such as indentation, bend tests and micro-tensile testing have also been discussed in the context of evaluation of mechanical properties of bond coats. Since the matrix in the aluminide bond coats is constituted of the B2-NiAl phase, a description of the crystal structure and deformation characteristics of this phase including the flow behavior, ductility and fracture behavior has been mentioned in the third sub-chapter. In the fourth sub-chapter, reported literature on the tensile behavior and brittle-to-ductile-transition-temperature (BDTT) of diffusion aluminide bond coats has been discussed. In Chapter 3, details on experiments carried out for the formation of various coatings used in the present study and, their microstructural characterization, are provided. The method for extraction of stand-alone coating specimens and their testing is discussed. The microstructure and composition of the various coatings used in the present study are discussed in detail in Chapter 4. Unlike in case of bulk tensile testing, for which standards on the design of specimens exist, there are no standards available for the design of micro-tensile specimens. Therefore, as part of the present research work, a finite element method (FEM)-based study was carried out for ascertaining the dimensions of the specimens. The simulation studies predicted that failure of the specimens within the gage length can be ensured only when certain correlations between the dimensional parameters are satisfied. Further, the predictions from the simulation study were validated experimentally by carrying out actual testing of specimens of various dimensions. Details on the above mentioned aspects of specimen design are provided in Chapter 5. The PtAl coatings undergo brittle fracture at lower temperatures while ductile fracture occurs at higher temperatures. Further, the coatings exhibit a scatter in the yielding behavior at temperatures in the vicinity of BDTT. Therefore, the BDTT, determined as the temperature at which yielding is first observed in the stress-strain curves, may not be representative of the PtAl coatings. In Chapter 6, a method for the precise determination of BDTT of aluminide bond coats, based on the variation in the plastic strain to fracture with temperature, has been demonstrated. The BDTT determined by the above method correlated well with the variation in fracture surface features of the coating and was found representative of these coatings. In Chapter 7, the effect of temperature and strain rate on the tensile properties of a PtAl bond coat has been evaluated. The temperature and strain rate was varied between room temperature (RT)-1100°C and 10-5 s-1-10-1 s-1, respectively. The effect of strain rate on the BDTT of the PtAl bond coat has been examined. Further, the variation in fracture surface features and mechanism of fracture with temperature and strain rate are illustrated. The micro-mechanisms of deformation and fracture in the coating at different temperature regimes have also been discussed. The coating exhibited brittle-to-ductile transition with increase in temperature at all strain rates. The BDTT was strain rate sensitive and increased significantly at higher strain rates. Above BDTT, YS and UTS of the coating decreased and its ductility increased with increase in the test temperature at all strain rates. Brittle behavior occurring in the coating at temperatures below the BDTT has been attributed to the lack of operative slip systems in the B2-NiAl phase of the coating. The onset of ductility in the coating in the vicinity of BDTT has been ascribed to generation of additional slip systems caused by climb of dislocations onto high index planes. The coating exhibited two distinct mechanisms for plastic deformation as the temperature was increased from BDTT to 1100°C. For temperatures in the range BDTT to about 100°C above it, deformation was controlled by dislocations overcoming the Peierls-Nabarro barrier. Above this temperature range, non-conservative motion of jogs by jog dragging mechanism controlled the deformation. The transition temperature for change of deformation mechanism also increased with increase in strain rate. For all strain rates, fracture in the coating at test temperatures below the BDTT, occurred by initiation of cracks in the intermediate single phase B2-NiAl layer of the coating and subsequent inside-out propagation of the cracks across the coating thickness. Ductile fracture in the coating above the BDTT was associated with micro-void formation throughout the coating. The effect of Pt content on the tensile behavior of PtAl coating, evaluated at various temperatures ranging from room temperature (RT) to 1100°C and at a nominal strain rate of 10-3 s-1, is presented in Chapter 8. Irrespective of Pt content in the coating, the variation in tensile behavior of the coating with temperature remained similar. At temperatures below BDTT, the coatings exhibited linear stress-strain response (brittle behavior) while yielding (ductile behavior) was observed at temperatures above BDTT. At any given temperature, the elastic modulus decreased while the strength increased with increase in Pt content in the coating. On the other hand, the ductility of the coating remained unaffected with Pt content. The BDTT of the coating also increased with increase in Pt content in the coating. Addition of Pt did not affect the fracture mechanism in the coating. Fracture at temperatures below BDTT was caused by nucleation of cracks at the intermediate layer and their subsequent inside-out propagation. At high temperatures, fracture occurred in a ductile manner comprising void formation, void linkage and subsequent joining with cracks. The deformation sub-structure of the coating did not get affected with Pt incorporation. Short straight dislocations were observed at temperatures below BDTT, while, curved dislocations marked by jog formation were observed at temperatures above BDTT. The factors controlling fracture stress and strength in the PtAl coatings at various temperatures have also been assessed. The overall summary of the present research study and recommendations for future studies are presented in the last chapter, i.e. Chapter 9.

In recent years, there has been growing interests on II-VI semiconductor nanostructures, which are suitable for applications in electronics and optoelectronic devices such as solar cells, UV lasers, sensors, light emitting diodes and field emission displays. II-VI semiconductor nanostructures with different morphologies such as wires, belts, rods, tubes, needles, springs, tetrapods, plates, hierarchical structures and so on, have been widely grown by vapor transport methods. However the process conditions used for the growth of nanostructures still remains incompatible for device fabrication. The realization of practical nanoscale devices using nanostructured film depends mainly on the availability of low cost and lower processing temperatures to manufacture high purity nanostructures on a variety of substrates including glass and polymer. In this thesis work, studies have been made on the growth and characterization of II-VI semiconductor nanostructures prepared at room temperature, under high vacuum, without employing catalysts or templates. (i) ZnO nanostructured films with different morphology such as flowers, needles and shrubs were deposited at room temperature on glass and polymer substrates by plasma assisted reactive process. (ii) Zn/ZnO core/shell nanowires were grown on Si substrates under optimized oxygen partial pressure. Annealing of this core shell nanowire in high vacuum resulted in the formation of ZnO nanocanals. (iii) ZnS and ZnSe nano and microstructures were grown on Si substrates under high vacuum by thermal evaporation. The morphology, structural, optical properties and composition of these nano and microstructures were investigated by XRD, SEM, TEM, Raman, PL and XPS. The growth mechanism behind the formation of the different nanostructures has been explained on the basis of vapour-solid (VS) mechanism.

Το αντικείμενο της παρούσας Διδακτορικής Διατριβής είναι η ανάπτυξη νέων υλικών για σύγχρονες τεχνολογικές εφαρμογές. Για αυτό τον λόγο, επιλέχτηκε κατ’ αρχήν να αναπτυχθεί μια καινούρια και ταυτόχρονα πρωτότυπη διαδικασία παρασκευής νανοσωματιδίων. Για το σκοπό αυτό σχεδιάστηκε και ανακατασκευάστηκε εξ’ αρχής μια υπάρχουσα συσκευή sputtering, εφαρμόζοντας νέες τεχνικές και διατάξεις για την εναπόθεση των λεπτών και υπέρλεπτων υμενίων χρυσού σε διαφορετικές θερμοκρασίες υποστρώματος. Παρασκευάστηκαν δείγματα σε κρυογενικές θερμοκρασίες εναπόθεσης (-195 oC) έως και σε υψηλές Θερμοκρασίες των 450 oC. Παράλληλα πραγματοποιήθηκε και σύγκριση με μια σειρά δειγμάτων λεπτών υμενίου χρυσού με θερμική ανόπτηση μετά την εναπόθεση έως τους 800 oC. Αφού μελετήθηκε ο τρόπος ανάπτυξης των υμενίων του χρυσού με αυτές τις τεχνικές, και χαρακτηρίστηκαν τα λεπτά υμένια με διαφόρους τρόπους, επιλέχθηκε η πιο αποδοτική από μορφολογικής άποψης μέθοδος, για την παρασκευή νανοσωματιδίων χρυσού. Έτσι παρασκευάστηκαν υπέρλεπτα υμένια χρυσού, κάτω από συγκεκριμένες συνθήκες. Αυτά τα δείγματα έδωσαν νανοσωματίδια χρυσού της τάξεως των μερικών νανομέτρων, ικανά να δώσουν βάση των φασμάτων απορρόφησης, επιφανειακούς πλασμονικούς συντονισμούς σε διάφορα μήκη κύματος από τα 2 - 2,5 eV ανάλογα με το μέγεθος των νανοσωματιδίων που καθορίζουμε από τις συνθήκες του πειράματος. Στην συνέχεια παρασκευάστηκαν αντίστοιχα δείγματα από ένα νέο σύγχρονο υλικό, που αποτελείται από χρυσό, γερμάνιο και άργυρο. Χρησιμοποιώντας την ίδια διάταξη παρασκευάστηκαν αντίστοιχα υπέρλεπτα υμένια, στα οποία ανιχνεύτηκαν υβριδικά νανοσωματίδια χρυσού – αργύρου σε αναλογίες 1:1, προστατευμένα από μια άμορφη υαλώδη μήτρα οξειδίου του γερμανίου. Τέλος, κατά τον οπτικό χαρακτηρισμό των δειγμάτων αυτών και διαπιστώθηκε από τα φάσματα απορρόφησης συνδυασμένος επιφανειακός πλασμονικός συντονισμός. Τέλος, τα μεταλλικά και τα ημιαγώγιμα υπέρλεπτα υμένια έχουν τεράστια σημασία σε διάφορους τομείς της επιστήμης των υλικών και της νανοτεχνολογίας. Έτσι, η πρωτότυπη πειραματική διάταξη που αναπτύχτηκε είναι ενδιαφέρουσα για την παρασκευή μιας πληθώρας νάνο-ηλεκτρομηχανικών και οπτοηλεκτρονικών συστημάτων βασισμένα σε διάφορα σύγχρονα υλικά. / The objective of this Thesis is to develop new high – Tech materials for modern technological applications. For this reason, we have chosen in principle to develop a new prototype manufacturing process for growth of nanoparticles. For this purpose we designed and rebuilt from the beginning an existing D.C. sputtering apparatus to apply new techniques and devices for the deposition of thin and ultrathin films of gold at various substrate temperatures. We prepared samples at cryogenic temperatures deposition (-195 oC) up to a high temperature of 450 oC. The results were compared with a series of samples of thin gold films post annealed up to 800 oC. After studying the growth modes of thin gold films with these techniques, and characterize thin films in different ways, we chose the most efficient method from morphological point of view, for the optimum preparation of gold nanoparticles. So we proceeded to the deposition of ultrathin gold films, under certain conditions. These samples gave us gold nanoparticles in the range of a few nanometers, able to give us surface plasmon resonances at different wavelengths from 2 - 2,5 eV depending on the size of nanoparticles. Then samples were prepared respectively from a modern new target material consisting of gold, germanium and silver. Using the same configuration we were able to prepare ultrathin films. These films were found to consist of Au-Ag nanoparticles self-organized in an amorphous GeOx matrix. Finally, we proceeded to the optical characterization of these samples and found on the absorption spectra combined surface plasmon resonances. Finally, the metal and the semiconductor ultrathin films are crucial in various fields of materials science and nanotechnology. Thus, the original experimental setup which was developed is useful in order to prepare a multitude of nano - electromechanical and optoelectronic systems based on various modern materials.

The dissertation thesis is focused on research and development in the field of microfabrication by the technology of electron beam lithography. In the first part of this work, the extensive study is conducted in the field of technology of electron beam lithography in terms of physical principles, writing strategies and resist materials. This is followed with description of physical principles of etching for the transfer of relief structures into substrates. The thesis describes innovative techniques in modelling, simulation, data preparation and optimization of manufacturing technology. It brings new possibilities to record deep binary or multilevel microstructures using electron beam lithography, plasma and reactive ion etching technology. Experience and knowledge in the large area of microlithography, plasma and anisotropic wet-etching of silicon have been capitalized to the design process of manufacturing of nano-patterned membranes. It was followed with practical verification and optimization of the microfabrication process.

Electron beam powder bed fusion (PBF-EB/M) has been attracting great research interest as a promising technology for additive manufacturing of titanium aluminide alloys. However, challenges often arise from the process-induced evaporation of aluminum, which is linked to the PBF-EB/M process parameters. This study applies different volumetric energy densities during PBF-EB/M processing to deliberately adjust the aluminum contents in additively manufactured Ti–43.5Al–4Nb–1Mo–0.1B (TNM-B1) samples. The specimens are subsequently subjected to hot isostatic pressing (HIP) and a two-step heat treatment. The influence of process parameter variation and heat treatments on microstructure and defect distribution are investigated using optical and scanning electron microscopy, as well as X-ray computed tomography (CT). Depending on the aluminum content, shifts in the phase transition temperatures can be identified via differential scanning calorimetry (DSC). It is confirmed that the microstructure after heat treatment is strongly linked to the PBF-EB/M parameters and the associated aluminum evaporation. The feasibility of producing locally adapted microstructures within one component through process parameter variation and subsequent heat treatment can be demonstrated. Thus, fully lamellar and nearly lamellar microstructures in two adjacent component areas can be adjusted, respectively.