Dissertations / Theses on the topic 'Laser directed energy deposition'
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Sreekanth, Suhas. "Laser-Directed Energy Deposition : Influence of Process Parameters and Heat-Treatments." Licentiate thesis, Högskolan Väst, Avdelningen för svetsteknologi (SV), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-15767.
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Laser-Directed Energy Deposition (L-DED), an Additive Manufacturing (AM) processused for the fabrication of parts in a layer-wise approach has displayed an immense potential over the last decade. The aerospace industry stands as the primary beneficiary due to the L-DED process capability to build near-net-shape components with minimal tooling and thereby producing minimum wastage because of reduced machining. The widespread use of Alloy 718 in the aero-engine application has prompted huge research interest in the development of L-DED processing of this superalloy. AM processes are hindered by low build rates and high cycle times which directly affects the process costs. To overcome these issues, the present work focusses on obtaining high deposition rates through a high material feed. Studying the influence of process parameters during the L-DED process is of prime importance as they determine the performance of in-service structures. In the present work, process parameters such as laser power, scanning speed, feed rate and stand-offdistances are varied and their influence on geometry and microstructure of Alloy 718 single-track deposits are analyzed. The geometry of deposits is measured in terms of height, width and depth; and the powder capture efficiency is determined by measuring areas of deposition and dilution. The microstructure of the deposits shows a column ardendritic structure in the middle and bottom region of the deposits and equiaxed grains in the top region. Nb-rich segregation involving laves and NbC phases, typical of Alloy718 is found in the interdendritic regions and grain boundaries. The segregation increases along the height of the deposit with the bottom region having the least and the top region showing the highest concentration of Nb-rich phases due to the variation in cooling rates. A high laser power (1600 W – 2000 W) and a high scanning speed (1100 mm/min) are found to be the preferable processing conditions for minimizing segregation. Another approach to minimize segregation is by performing post-build heat treatments. The solution treatment (954 °C/1 hr) and double aging (718 °C/8 hr + 621 °C/ 8 hr) standardized for the wrought form of Alloy 718 is applied to as-built deposits which showed a reduction in segregation due to the dissolution of Nb-rich phases. Upon solution treatment, this reduction is accompanied by precipitation of the delta phase, found predominantly in top and bottom regions and sparsely in the middle region of the deposit.
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Crisanti, Roberto. "Laser Direct Energy Deposition per la manifattura additiva: caratterizzazione del processo e prove sperimentali." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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Studio condotto presso il Dipartimento di Ingegneria Industriale dell’Università di Bologna su un processo di Laser Direct Energy Deposition, o Laser Cladding, e sulla sua caratterizzazione, avente come fine ultimo quello di realizzare pezzi massicci a base rettangolare dotati di una morfologia esterna regolare e al contempo privi di difetti macroscopici all’interno, quali porosità o zone con mancata fusione del materiale d’apporto. Nella prima parte dello studio sono stati presi in esame i principali parametri di processo, ovvero la potenza della sorgente laser e la portata di polvere, e l’influenza che essi hanno sulle caratteristiche geometriche del deposito (profondità di penetrazione, altezza, larghezza, grado di diluizione, area del deposito e del rinforzo, ampiezza media della ZTA, percentuale di porosità). Tale studio si è basato sull’osservazione ed analisi al microscopio di singoli cordoni di deposizione, realizzati variando la portata di polvere la potenza del laser, a parità di velocità di avanzamento. La seconda parte si basa sull’analisi dei risultati delle prove condotte con lo scopo di realizzare dei campioni massicci a base rettangolare: si sono studiati gli effetti che variazioni dei parametri di processo e della strategia di scansione hanno avuto sulla morfologia finale dei pezzi e sulle loro caratteristiche interne (porosità, zone con mancata fusione). Si sono confrontate due strategie di deposizione, la strategia con ritorno della testa a laser spento (laser OFF) e la strategia con ritorno della testa a laser acceso (laser ON). Tale studio ha permesso di concludere che la strategia con ritorno laser ON risulta essere preferibile in quanto non solo consente di ottenere un risparmio in termini energetici, di tempo e di quantità di polvere utilizzata, ma anche di realizzare dei pezzi massicci che rappresentano il miglior compromesso ottenuto tra una morfologia esterna uniforme e delle buone caratteristiche interne, con una densità prossima al 100%.
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Juhasz, Michael J. "In and Ex-Situ Process Development in Laser-Based Additive Manufacturing." Youngstown State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ysu15870552278358.
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Lindell, David. "Process Mapping for Laser Metal Deposition of Wire using Thermal Simulations : A prediction of material transfer stability." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-85474.
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Additive manufacturing (AM) is a quickly rising method of manufacturing due to its ability to increase design freedom. This allows the manufacturing of components not possible by traditional subtractive manufacturing. AM can greatly reduce lead time and material waste, therefore decreasing the cost and environmental impact. The adoption of AM in the aerospace industry requires strict control and predictability of the material deposition to ensure safe flights. The method of AM for this thesis is Laser Metal Deposition with wire (LMD-w). Using wire as a feedstock introduces a potential problem, the material transfer from the wire to the substrate. This requires all process parameters to be in balance to produce a stable deposition. The first sign of unbalanced process parameters are the material transfer stabilities; stubbing and dripping. Stubbing occurs when the energy to melt the wire is too low and the wire melts slower than required. Dripping occurs when too much energy is applied and the wire melts earlier than required. These two reduce the predictability and stability that is required for robust manufacturing. Therefore, the use of thermal simulations to predict the material transfer stability for LMD-w using Waspaloy as the deposition material has been studied. It has been shown that it is possible to predict the material transfer stability using thermal simulations and criterions based on preexisting experimental data. The criterion for stubbing checks if the completed simulation result produces a wire that ends below the melt pool. For dripping two criterions shows good results, the dilution ratio is a good predictor if the tool elevation remains constant. If there is a change in tool elevation the dimensionless slenderness number is a better predictor. Using these predictive criterions it is possible to qualitatively map the process window and better understand the influence of tool elevation and the cross-section of the deposited material.Additiv tillverkning (AT) är en kraftigt växande tillverkningsmetod på grund av sin flexibilitet kring design och möjligheten att skapa komponenter som inte är tillverkningsbara med traditionell avverkande bearbetning. AT kan kraftigt minska tid- och materialåtgång och på så sett minskas kostnader och miljöpåverkan. Införandet av AT i flyg- och rymdindustrin kräver strikt kontroll och förutsägbarhet av processen för att försäkra sig om säkra flygningar. Lasermetalldeponering av tråd är den AT metod som hanteras i denna uppsats. Användandet av tråd som tillsatsmaterial skapar ett potentiellt problem, materialöverföringen från tråden till substratet. Detta kräver att alla processparametrar är i balans för att få en jämn materialöverföring. Är processen inte balanserad syns detta genom materialöverföringsstabiliteterna stubbning och droppning. Stubbning uppkommer då energin som tillförs på tråden är för låg och droppning uppkommer då energin som tillförs är för hög jämfört med vad som krävs för en stabil process. Dessa två fenomen minskar möjligheterna för en kontrollerbar och stabil tillverkning. På grund av detta har användandet utav termiska simuleringar för att prediktera materialöverföringsstabiliteten för lasermetalldeponering av tråd med Waspaloy som deponeringsmaterial undersökts. Det har visat sig vara möjligt att prediktera materialöverföringsstabiliteten med användning av termiska simuleringar och kriterier baserat på tidigare experimentell data. Kriteriet för stubbning kontrolleras om en slutförd simulering resulterar i en tråd som når under smältan. För droppning finns två fungerande kriterier, förhållandet mellan svetshöjd och penetrationsdjup om verktygshöjden är konstant, sker förändringar i verktygshöjden är det dimensionslös ”slenderness” talet ett bättre kriterium. Genom att använda dessa kriterier är det möjligt att kvalitativt kartlägga processfönstret och skapa en bättre förståelse för förhållandet mellan verktygshöjden och den deponerade tvärsnittsarean.
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Kumara, Chamara. "Microstructure Modelling of Additive Manufacturing of Alloy 718." Licentiate thesis, Högskolan Väst, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-13197.
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In recent years, additive manufacturing (AM) of Alloy 718 has received increasing interest in the field of manufacturing engineering owing to its attractive features compared to those of conventional manufacturing methods. The ability to produce complicated geometries, low cost of retooling, and control of the microstructure are some of the advantages of the AM process over traditional manufacturing methods. Nevertheless, during the building process, the build material undergoes complex thermal conditions owing to the inherent nature of the process. This results in phase transformation from liquid to solid and solid state. Thus, it creates microstructural gradients in the built objects, and as a result,heterogeneous material properties. The manufacturing process, including the following heat treatment that is used to minimise the heterogeneity, will cause the additively manufactured material to behave differently when compared to components produced by conventional manufacturing methods. Therefore, understanding the microstructure formation during the building and subsequent post-heat treatment is important, which is the objective of this work. Alloy 718 is a nickel-iron based super alloy that is widely used in the aerospace industry and in the gas turbine power plants for making components subjected tohigh temperatures. Good weldability, good mechanical properties at high temperatures, and high corrosion resistance make this alloy particularly suitablefor these applications. Nevertheless, the manufacturing of Alloy 718 components through traditional manufacturing methods is time-consuming and expensive. For example, machining of Alloy 718 to obtain the desired shape is difficult and resource-consuming, owing to significant material waste. Therefore, the application of novel non-conventional processing methods, such as AM, seems to be a promising technique for manufacturing near-net-shape complex components.In this work, microstructure modelling was carried out by using multiphase-field modelling to model the microstructure evolution in electron beam melting (EBM) and laser metal powder directed energy deposition (LMPDED) of Alloy 718 and x subsequent heat treatments. The thermal conditions that are generated during the building process were used as input to the models to predict the as-built microstructure. This as-built microstructure was then used as an input for the heat treatment simulations to predict the microstructural evolution during heat treatments. The results showed smaller dendrite arm spacing (one order of magnitude smaller than the casting material) in these additive manufactured microstructures, which creates a shorter diffusion length for the elements compared to the cast material. In EBM Alloy 718, this caused the material to have a faster homogenisation during in-situ heat treatment that resulting from the elevated powder bed temperature (> 1000 °C). In addition, the compositional segregation that occurs during solidification was shown to alter the local thermodynamic and kinetic properties of the alloy. This was observed in the predicted TTT and CCT diagrams using the JMat Pro software based on the predicted local segregated compositions from the multiphase-field models. In the LMPDED Alloy 718 samples, this resulted in the formation of δ phase in the interdendritic region during the solution heat treatment. Moreover, this resulted in different-size precipitation of γ'/γ'' in the inter-dendritic region and in the dendrite core. Themicro structure modelling predictions agreed well with the experimental observations. The proposed methodology used in this thesis work can be an appropriate tool to understand how the thermal conditions in AM affect themicro structure formation during the building process and how these as-built microstructures behave under different heat treatments.
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Pinchuk, A., and K. Jiang. "Laser-Directed Deposition of Mannan-Functionalized Silver Nanostructures." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42504.
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Mannan is a polymannose isolated from the cell wall of Saccaromyces cerevisiae and has strong binding affinity to mannose receptors on antigen presenting cells (APCs), such as dendritic cells and macrophages. Mannan-functionalized nanomaterials or nanostructures are thus of high interests in studying immune responses towards fungi. In this work, we investigated the fabrication of mannan-coated silver nanostructures using a laser-deposition technique. Specifically, two different starting materials were applied for laser-deposition. One is a mixture solution of AgNO3 and mannan, and the other one is the suspension of silver nanoparticles synthesized with mannan as the sole reducing and capping agent. Using 405 nm diode laser in a confocal microscope, we successfully fabricated mannan-covered micropatterns by laser-induced photoreduction of silver ions or aggregation of mannan-capped AgNPs. The results show that both starting materials can be applied to deposit micro- or nanoscaled structures that are covered with mannan, which was confirmed by fluorescence microscopy. These silver nanostructure-supported mannan patterns are promising candidates to mimic the fungal membrane and beneficial for immune cell studies.
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McGinnis, Roger D. "Free Electron Laser development for directed energy." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/ADA387898.
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Dissertation (Ph.D. in Physics) Naval Postgraduate School, Dec. 2000.Dissertation advisor, Colson, William B. "December 2000." Includes bibliographical references (p. 131-133). Also available in print.
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Waller, Gordon Henry. "Template Directed Growth of Nb doped SrTiO3 using Pulsed Laser Deposition." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/32723.
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Oxide materials display a wide range of physical properties. Recently, doped complex
oxides have drawn considerable attention for various applications including thermoelectrics.
Doped complex oxide materials have high Seebeck coefficients (S) and electrical conductivities
(o) comparable to other doped semiconductors but low thermoelectric figure of merit ZT values
due to their poor thermal conductivities. For example, niobium doped strontium titanate
(SrNbxTi1-xO3 or simply Nb:STO) has a power factor comparable to that of bismuth telluride.
Semiconductor nanostructures have demonstrated a decrease in thermal conductivity () resulting in an increase in the thermoelectric figure of merit (ZT). Nanostructures of doped oxides like niobium doped strontium titanate, may also lead to decreased and a corresponding increase in ZT. The major impediment to nanostructured oxide thermoelectric materials is the lack of suitable fabrication techniques for testing and eventual use. Electron Beam Lithography(EBL) was used to pattern poly-methyl-methacrylate (PMMA) resists on undoped single crystalline SrTiO3 (STO) substrates which were then filled with Nb:STO using Pulsed Laser Deposition (PLD) at room temperature. This technique produced nanowires and nanodots with critical dimensions below 100 nm, and a yield of approximately 95%. In addition to scanning electron microscopy and atomic force microscopy morphological studies of the patterned oxide, thin film analogues were used to study composition, crystallinity and electrical conductivity of the material in response to a post deposition heat treatment. Since the thin films were grown under similar experimental parameters as the oxide nanostructres, the patterned oxides are believed to be stoichiometric and highly crystalline. The study found that using a combination of EBL and PLD, it is possible to produce highly crystalline, doped complex oxide nanostructures with excellent control over morphology. Furthermore, the technique is applicable to nearly all materials and provides the capability of patterning doped oxide materials without the requirement of etching or multiple lithography steps makes this approach especially interesting for future fundamental materials research and novel device fabrication.Master of Science
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Williams, Robert E. "Naval electric weapons : the electromagnetic railgun and free electron laser /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FWilliams.pdf.
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Kundrapu, Madhusudhan, Michael Keidar, and Charles Jones. "Electrostatic Approach for Mitigation of Communication Attenuation During Directed Energy Testing." International Foundation for Telemetering, 2009. http://hdl.handle.net/10150/606128.
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ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, NevadaElectrostatic approach is considered for mitigation of communication attenuation during the testing of laser powered directed energy weapon. Mitigation analysis is carried out for two target materials Al and Ti. Plasma parameters are obtained using one dimensional coupled analysis of laser-target interaction. Influence of laser beam frequency on plasma parameters is addressed. Sheath thickness is obtained using transient sheath calculations. It is found that uninterrupted telemetry can be achieved | using a maximum bias voltage of 10 kV, through Al plasma for fluences below 5 J/cm² and through Ti plasma for fluences below 2 J/cm².
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Rajendran, Saravanakanthan, Michael Keidar, Iain D. Boyd, Charles H. Jones, and Brian Mork. "MODELING OF THE PLASMA FORMATION DUE TO LASER IRRADIENCE DURING DIRECTED-ENERGY TESTING." International Foundation for Telemetering, 2007. http://hdl.handle.net/10150/604489.
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ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, NevadaReal-time transmission of airborne images to a ground station is highly desirable in many telemetering applications. Such transmission is often through an error prone, time varying wireless channel, possibly under jamming conditions. Hence, a fast, efficient, scalable, and error resilient image compression scheme is vital to realize the full potential of airborne reconnaisance. JPEG2000, the current international standard for image compression, offers most of these features. However, the computational complexity of JPEG2000 limits its use in some applications. Thus, we present a scalable low complexity coder (SLCC) that possesses many desirable features of JPEG2000, yet having high throughput. Continuous radio-wave telemetry is required during planned tests of directed-energy weapons systems in order to characterize in situ the effects of laser irradiation on different target materials. Unfortunately, the incident radiation can cause disruption of the radio signal during the directed-energy testing. Several phenomena associated with directed-energy impact can lead to communication path losses, such as ablation, charged particle emission, charring, and chemical changes in the target materials. Directed-energy impact on the target material leads to target heating and consequent ablation. In this paper, a numerical model has been developed to describe the laser induced ablation of metal surfaces. The model describes the absorption of the laser energy by the metal and the resulting temperature rise in the surface. This temperature rise then induces ablation of the target material. Results for an aluminum target irradiated with a KrF laser were obtained. Temperature profiles in the target material and surface temperature changes are presented along with the ablation rate as a function of time as the aluminum target is irradiated. This report presents results for cases when laser energy absorption by the plasma plume created above the surface is not significant.
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Balit, Yanis. "Mechanical properties of additively manufactured or repaired single-track thickness structures by Directed Energy Deposition." Thesis, Institut polytechnique de Paris, 2019. http://www.theses.fr/2019IPPAX014.
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Les travaux de cette thèse ont été dédiés à l’étude de pièces minces en acier inoxydable 316L fabriquées ou réparées par Directed Energy Deposition (DED). La nouveauté principale est l’observation de la déformation à l’échelle de la microstructure. Pour ce faire, une expérience associant un essai de traction in situ dans un microscope électronique à balayage, de la corrélation d’images à haute résolution et une carte EBSD de la microstructure ont été réalisés. Les résultats obtenus permettent alors de mieux appréhender les différentes propriétés en traction ainsi que les comportements d’autoéchauffement lors d’essais cycliques. Le premier objectif a été de qualifier et quantifier les mécanismes de déformation à l’échelle de la microstructure pour expliquer le comportent anisotrope révélé lors d’essais de traction. Par conséquent, deux orientations de sollicitation permettant d’effectuer un chargement perpendiculaire ou parallèle à la direction d’impression ont été définies. Dans le premier cas, la localisation de déformation s’effectue au niveau de certaines intercouches. Pour le second, une localisation dans certaines régions correspondant à de gros grains particuliers a été observée. Le deuxième objectif a été d’évaluer la capacité du DED à réparer. Pour ce faire, des éprouvettes moitié tôle / moitié imprimées ont été fabriquées afin de solliciter l’interface en traction. Une grande différence de microstructure a été observée entre les deux matériaux. Néanmoins, l’interface n’a jamais été la zone de rupture lors d’essais de traction. De plus, une déformation homogène a été observée dans la partie tôle alors qu’une déformation hétérogène avec des pics de concentration au niveau de certaines intercouches a été remarquée dans la partie imprimée lors d’essais in situ. Enfin, une zone de faible déformation a été constatée de part et d’autre de l’interface, zone dans laquelle une plus grande dureté a été mesurée. Le dernier objectif a été d’évaluer les propriétés en fatigue par des essais d’autoéchauffement. Il a été montré que les difficultés liées à la faible épaisseur de nos éprouvettes pouvaient être surmontées en maitrisant le protocole expérimental. Un comportement anisotrope a été observé durant ces essais cycliques avec des éprouvettes perpendiculaires au sens d’impression montrant une plus grande limite d’endurance par rapport aux éprouvettes sollicitées parallèlement. Pour ces dernières, des analyses post-mortem ont montré un scénario de fatigue classique avec une fissure dominante et donc une source de dissipation de chaleur localisée. A l’inverse, une multitude de fissures aux intercouches créant de nombreux sites de dissipation a été constatée pour les éprouvettes testées perpendiculairementThis thesis was dedicated to the study of 316L stainless steel additively manufactured or repaired specimens by Directed Energy Deposition (DED). Different configurations were manufactured under optimal process parameters. The novelty of this work is the observation of the microstructural strain localization. This experiment combined an in situ tensile test inside a scanning electron microscope with high resolution digital image correlation and an electron backscatter diffraction map. These results allowed for a fresh interpretation of monotonic tensile tests as well as of self-heating experiments under cyclic loading and the failure patterns observed at the surface of specimens. The first objective was to understand the deformation mechanisms at the grain scale which could explain the observed macroscopic anisotropy of the tensile properties as reported in literature. Two loading directions, along and perpendicular, were considered with respect to the printing direction for fully printed specimens. We observed that for a tensile load perpendicular to the printing direction, the strain localization is mainly situated at some interlayers. For a tensile load along the printing direction, the strain localization was observed in some particular regions of large grains. The second objective was the assessment of DED as a repair technology. Dog bone shaped repaired specimens (half hot rolled sheet and half printed) were designed and they exhibited an important hierarchical microstructural gradient. We noticed that the interface is not a weak area during a monotonic tensile test. Moreover, while homogeneous strain was observed in the substrate half, the printed half showed a strain heterogeneity, with the highest localization found at some interlayers. An unstrained zone was observed at both sides of the interface and was associated with higher hardness. The last objective was to evaluate the fatigue properties by self-heating tests. The experiment has proven that the difficulties due to the small dimensions of the single-track thickness specimens can be overcome by careful construction of the experimental set-up. The results revealed a certain correlation between the pattern of the microstructure, the deformation pattern at this scale and the self-heating results. Anisotropy was highlighted during these cyclic tests where specimens tested perpendicularly to the printing direction showed higher fatigue limits in comparison to the ones tested along the printing direction. Post mortem analysis revealed a multitude of cracks at interlayers for the specimens tested perpendicularly to the printing direction creating several sites of heat diffusion. For the specimens tested along the printing direction, a more classical fatigue scenario was observed with one dominating crack and thus a localized heat dissipation
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Snyder, Ryan Daniel. "Combinatorial Analysis of Thermoelectric Materials using Pulsed Laser Deposition." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1460037906.
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Mantzouris, Georgios. "Thermomechanical effects of ground-based directed energy weapons on satellites and Intercontinental Ballistic Missiles." Thesis, Monterey, California. Naval Postgraduate School, 2006. http://hdl.handle.net/10945/2570.
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Approved for public release; distribution is unlimitedThermo mechanical modeling and simulation of a satellite and intercontinental ballistic missile assumes importance due to the increased interest in assessing the potential of such attacks. Effective and innovative methods are sought in assessing the structural integrity of such structural components. In this study, we present modeling and simulation aspects of two generic models loaded by high energy laser beam. We present an application of MSC software in modeling thermo-mechanical behavior, both steady state and transient behavior of satellite and missile structures. Thermal energies used for simulation correspond to high energy laser flux available at low earth orbits as reported in literature. A brief review of the concepts involved is outlined. The analysis is performed under several scenarios that include thermal failures due to steady state as well as transient thermal exposures. The thermal exposure times and locations are varied to assess typical failure modes of the structure. Analysis is done in order to define suitable material thicknesses that will make a satellite or a ballistic missile hardened enough to withstand these specific amounts of energy. Other parameters of interest pertaining to this study are the pulse width, and resulting transient phenomena affecting the behavior. Temperature gradients as well as resulting thermal stresses and thermal deformations are reported in this study.
Outstanding Thesis
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Guevenoux, Camille. "Réparation de pièces métalliques par Directed Energy Deposition : gradient microstructural, comportement mécanique et tenue en fatigue." Thesis, Institut polytechnique de Paris, 2021. http://www.theses.fr/2021IPPAX006.
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Le Directed Energy Deposition (DED) est un procédé de fabrication additive utilisant une buse constituée d’un faisceau laser et d’un jet de poudre coaxiaux. Le laser crée un bain liquide dans lequel la poudre est projetée, elle fond puis se solidifie formant un cordon de matière lorsque la buse se déplace. Ce procédé présente en particulier un fort potentiel pour réparer des pièces métalliques à haute valeur ajoutée. Néanmoins, le faible diamètre et les mouvements rapides du faisceau laser entraînent des gradients thermiques et des vitesses de refroidissement élevés et cette évolution thermique spécifique est responsable de la formation de microstructures différentes de celles des composants traditionnels mis en forme par forge ou fonderie. Ainsi, les composants réparés présentent une interface qui sépare le matériau de base (souvent forgé) et la région reconstruite par DED. Ce gradient microstructural conduit à un gradient de propriété et donc à des phénomènes de localisation qui affectent la durée de vie des composants réparés. Cette thèse propose une méthode de caractérisation de la zone d'interface des composants réparés. Un outil semi-analytique de modélisation des champs de température pendant le procédé de rechargement a été mis au point pour concevoir des éprouvettes représentatives géométriquement et thermiquement de la réparation sur la pièce réelle. Le gradient de microstructure à travers l'interface est d'abord caractérisé par imagerie MEB et par analyse EBSD. Des éprouvettes de traction sont ensuite prélevées à l'interface et sollicitées lors d’essais conduits sous MEB. La déformation est suivie à l'échelle micrométrique par corrélation d'images, ce qui permet d'étudier les phénomènes de localisation. Par la suite, ces cartes expérimentales sont utilisées pour identifier le comportement local du matériau dans la région de l’interface, en minimisant l’erreur entre les champs de déformation expérimental et numérique. Le gradient de propriété ainsi déterminé permet de calculer la répartition de contraintes dans des éprouvettes soumises à des essais de fatigue. La limite d'endurance des structures réparées est ensuite calculée à partir des résultats expérimentaux d'une campagne de fatigue et comparée à celle de la pièce d'origine pour déterminer l'abattement causé par le rechargementDirected Energy Deposition (DED) process is a powder-jet additive manufacturing process involving a nozzle composed of coaxial laser beam and powder stream. The laser generates a melt pool in which the powder is projected, it melts and then solidifies creating a deposit as the nozzle moves. However, this process is particularly appealing to repair valuable metallic components. The small spot size and fast motions of the laser causes strong thermal gradient and important cooling rates and this specific thermal evolution is responsible for the formation of microstructures different from traditional processes like forge or foundry. Consequently, the repaired components exhibits an interface between the base material (generally wrought) and the region reconstructed with DED. This microstructural gradient leads to a mechanical gradient and therefore to localization phenomena which can affect the lifetime of repaired components. This thesis proposes a method to characterize the interface region of repaired components. A semi-analytic tool has been developed to model the thermal evolution during the repair process in order to design representative specimens, in terms of geometry but also in terms of thermal history. The microstructural gradient through the interface is first characterized with a SEM and EBSD analyses. Tensile specimen are then taken in the interface region and loaded during SEM in-situ tests. The strain is followed at the micrometric scale with Digital Image Correlation, what provides the information regarding localization phenomena. Those experimental data are then injected into a numerical method to identify the local parameters of the mechanical behavior by minimizing the error between the experimental and numerical fields. Using this mechanical gradient, the stress in fatigue specimens is derived. A fatigue limit is then derived from the experimental results of the fatigue tests and it is compared to the endurance of the original part to estimate the reduction of resistance caused by the repair
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Collins, Peter Chancellor. "A combinatorial approach to the development of composition-microstructure-property relationships in titanium alloys using directed laser deposition." Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1078949851.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xxxi, 307 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Hamish L. Fraser, Dept. of Materials Science and Engineering. Includes bibliographical references (p. 302-316).
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Mansfield, Robb P. "High energy solid state and free electron laser systems in tactical aviation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Jun%5FMansfield.pdf.
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Sena, S. P. "An investigation of some magnetic oxides grown by pulsed laser deposition." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287655.
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Shrestha, Sulochana. "MECHANICAL CHARACTERIZATION OF Ti-6AL-4V REPAIRED BY DIRECTED ENERGY DEPOSITION IN COMPARISON WITH THE CONVENTIONAL Ti-6AL-4V." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1619700926536015.
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Gvozdich, Grant Gregory. "Modeling the Transient Effects of High Energy Subsystems on High-Performance Aerospace Systems." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/35704.
Full textAbstract:
As directed energy technology continues to evolve and become a viable weapon alternative, a need exists to investigate the impacts of these applications without a â plug-and-checkâ method, but rather with an analysis governed by fundamental principles. This thesis examines the transient thermal loads that a high-energy weapon system introduces into a high performance aircraft using fundamental thermodynamic and heat transfer analyses.The high-energy weapon system employed in this research contains power storage, power conditioning equipment, optics, and a solid-state laser. The high-energy weapon system is integrated into the aircraft by a dedicated thermal management system connected to the onboard air and fuel fluid networks. The dedicated thermal management system includes heat exchangers, thermal storage, microchannel coolers, valves, and pumps. Governing equations for the electric directed energy weapon subsystem and thermal management system are formulated for each system component and modeled in Mathworkâ s SimulinkTM. System models are integrated into a generic, high-performance aircraft model created as part of the Air Force Research Laboratoryâ s Integrated Vehicle Energy Technology Demonstration (INVENT) program. The aircraft model performs a defined mission profile, firing the directed energy weapon during the high-altitude, transonic cruise segment.
When firing a 100-kilowatt directed energy weapon system operating at 16.9% efficiency, large thermal transients quickly heat downstream onboard systems. Real-time heat rejection causes temperature spikes in avionic and environment systems that exceed allowable operation constraints. The addition of thermal storage to the thermal management system mitigates thermal impacts downstream of the directed energy weapon by delaying the time thermal loads are rejected to aircraft, thereby reducing peak and average loads. Although thermal storage is shown to mitigate peak loads in downstream onboard systems, thermal closure is yet to be achieved.
This research presents a general and fundamental approach to investigating the thermal impacts of a directed energy weapon system on a high-performance aircraft. Although specific
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cases are analyzed, this general approach to model development and simulation is conducive to component and system customization for many other cases. Additionally, the supplementation of models with analytical, semi-empirical, and empirical data further tailors model development to each userâ s need while increasing the potential to enhance accuracy and efficacy. Without the material expenses of a â plug-and-checkâ method, component and system level modeling of the directed energy weapon system and high-performance aircraft provides valuable insight into the thermal responses of highly-coupled systems.
Master of Science
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Allgaier, Gregory G. "The shipboard employment of a free electron laser weapon system." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FAllgaier.pdf.
Full textAbstract:
Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003.Thesis advisor(s): William Colson, Robert Armstead. Includes bibliographical references (p. 67-68). Also available online.
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Chanal, Margaux. "Space-time study of energy deposition with intense infrared laser pulses for controlled modification inside silicon." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0488/document.
Full textAbstract:
La modification du silicium dans son volume est possible aujourd’hui avec des lasers infrarouges nanosecondes. Néanmoins, le régime d’intérêt pour la modification contrôlée en volume des matériaux transparents correspond aux impulsions femtosecondes. Cependant, aujourd’hui aucune démonstration de modification permanente du volume du Si n’a été réalisée avec une impulsion ultra-brève (100 fs). Pour infirmer ce résultat, nous avons développé des méthodes de microscopie infrarouge ultra-rapides. Tout d’abord, nous étudions le microplasma confiné dans le volume, caractérisé par la génération de porteurs libres par ionisation nonlinéaire du silicium, suivie de la relaxation totale du matériau. Ces observations, couplées à la reconstruction de la propagation du faisceau dans le matériau, démontrent un dépôt d’énergie d’amplitude fortement limitée par des effets nonlinéaires d’absorption et de propagation. Cette analyse a été confirmée par un modèle numérique simulant la propagation nonlinéaire du faisceau femtoseconde. La compréhension de cette limitation a permis de développer de nouvelles configurations expérimentales grâce auxquelles l’endommagement local et permanent du volume du silicium a pu être initié en régime d’impulsions courtesThe modification of bulk-silicon is realized today with infrared nanosecond lasers. However, the interest regime for controlled modifications inside transparent materials is femtosecond pulses. Today, there is no demonstration of a permanent modification in bulk-Si with ultra-short laser pulses (100 fs). To increase our knowledge on the interaction between femtosecond lasers and silicon, we have developedultra-fast infrared microscopy experiments. First, we characterize the microplasma confined inside the bulk, being the generation of free-carriers under nonlinear ionization processes, followed by the complete relaxation of the material. These results, combined with the reconstruction of the beam propagation inside silicon, demonstrate that the energy deposition is strongly limited by nonlinear absorption andpropagation effects. This analysis has been confirmed by a numerical model simulating the nonlinear propagation of the femtosecond pulse. The understanding of this clamping has allowed us the development of new experimental arrangements, leading to the modification of the bulk of Si with short pulses
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Point, Guillaume. "Energy deposition in air from femtosecond laser filamentation for the control of high voltage spark discharges." Palaiseau, Ecole polytechnique, 2015. https://tel.archives-ouvertes.fr/tel-01202982/document.
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La filamentation laser est un régime de propagation optique spectaculaire atteint pour des impulsions dont la puissance crête excède quelques gigawatts dans l’air. Le filament se forme sous l’action de l’effet Kerr optique du milieu traversé qui tend à auto-focaliser le faisceau jusqu’à ce que l’intensité résultante atteigne le seuil d’ionisation du milieu par absorption multiphotonique. Une compétition dynamique complexe s’établit alors entre l’effet Kerr, d’une part, et la diffraction, l’absorption non-linéaire de l’énergie laser et l’effet défocalisant du plasma d’autre part. Il en résulte une réorganisation du profil du faisceau, caractérisée par un coeur mince (100 µm) et intense (10^18 W/m²) pouvant se maintenir sur une distance égale à plusieurs longueurs de Rayleigh. Lorsque la puissance initiale de l’impulsion dépasse largement le seuil de filamentation, on assiste à la formation de plusieurs filaments co-propagatifs au sein du même faisceau, chacun de ces multifilaments possédant des caractéristiques physiques proches de monofilaments isolés. Au cours de sa propagation dans l’air, le filament transfère une partie de l’énergie laser au milieu, principalement via l’excitation rotationnelle Raman des molécules d’air, l’ionisation de l’air et l’effet de Bremsstrahlung inverse au sein du plasma. Cette énergie est redistribuée au cours de la nanoseconde suivant le passage du laser, principalement sous forme d’énergie translationnelle des molécules d’air, c’est-à-dire de chaleur. Le milieu réagit à ce chauffage rapide par la formation d’une onde de pression cylindrique, qui ramène le système à l’équilibre de pression en éjectant de la matière du centre. Il en résulte la formation d’un canal d’air sous-dense et chaud, qui se résorbe par diffusion à des échelles de temps supérieures à la milliseconde. Ma thèse s’est en premier lieu focalisée sur l’étude et l’optimisation du dépôt d’énergie dans l’air par filamentation. J’ai ainsi étudié l’influence des différents paramètres laser, comme l’énergie de l’impulsion, la focalisation employée et la durée d’impulsion sur la densité d’énergie déposée. Pour ce faire, j’ai employé plusieurs diagnostics complémentaires : mesure des ondes de pression à l’aide de microphones, analyse du plasma de filament par spectroscopie et mesure résolue en temps des canaux sous-dense par interférométrie. J’ai ainsi montré en régime de monofilamentation qu’au-delà d’une certaine énergie laser initiale, le dépôt d’énergie devient si important qu’une onde de choc est générée en lieu et place d’une onde sonore, et que les canaux sous-denses résultant ont des durées de vie de l’ordre de 100 ms. J’ai également étudié et caractérisé le régime de multifilamentation à haute énergie, montrant qu’en focalisant modérément l’impulsion, les filaments se réorganisent dans la zone focale pour former des structures plus larges générant un plasma dix fois plus dense que les filaments. Les effets hydrodynamiques engendrés par filamentation entraînent un abaissement transitoire du seuil de claquage électrique de l’air le long du trajet de l’impulsion laser, permettant ainsi de déclencher et de guider des décharges électriques. La seconde partie de ma thèse avait pour objet l’étude et l’optimisation de telles décharges guidées pour la mise au point d’une antenne plasma radio-fréquence, de commutateurs haute tension sans contact ou encore d’un paratonnerre laser. Pour ce faire, j’ai développé et construit un diagnostic plasma interférométrique à deux couleurs permettant de caractériser la durée de vie des plasmas générés. J’ai également participé à une expérience de principe démontrant la possibilité de réaliser une antenne plasma RF à partir d’un filament laser. Enfin, j’ai participé à diverses études expérimentales prospectives dans l’optique du développement d’un paratonnerre laserLaser filamentation is a spectacular optical propagation regime appearing for pulses of which peak power exceeds a few GW in air. Filament forms due to the optical Kerr effect, which tends to self-focus the beam until intensity reaches the medium ionization threshold by multiphoton absorption. A complex dynamic competition is then established between the Kerr effect on the one hand, and diffraction, nonlinear absorption and plasma defocusing effect on the other hand. This results in a reorganization of the beam profile, characterized by a thin (100 µm) and intense (10^18 W/m²) core able to propagate over a distance much longer than the Rayleigh length. When the initial pulse peak power largely exceeds filamentation threshold, several co-propagating filaments are formed in the same beam, with each of these multifilaments sharing physical properties of isolated single filaments. While propagating in air, filaments transfer a portion of the laser energy to the medium, mainly through Raman rotational excitation of air molecules, ionization and inverse Bremsstrahlung in the plasma. This energy is redistributed in one nanosecond and almost entirely converted into air molecule translational energy, that is heat. The medium reacts to this rapid heating by launching a cylindrical pressure wave that brings the system back to pressure equilibrium by ejecting matter from the center. This results in the formation of a hot underdense air channel, which slowly resorbs by diffusion at timescales > 1 ms. My work as a Ph. D. Student first focused on the study and the optimization of laser energy deposition in air by filamentation. Thus, I investigated the influence of laser parameters such as pulse energy, focusing strength or pulse duration on deposited energy. To this purpose, I used several complementary diagnostics: study of pressure waves using microphones, characterization of the filamentation plasma by means of spectroscopy and time resolved study of underdense air channels using interferometry. I demonstrated in the single filamentation regime that above a given pulse energy, energy deposition becomes so important that the medium generates a shock wave instead of a sound wave, and that underdense channels can last for more than 100 ms. I also studied and characterized the high energy multifilamentation regime, showing that moderately focusing the pulse leads to a reorganization of filaments in the focal zone, generating large structures with a resulting plasma ten times denser than filaments. Filamentation-induced hydrodynamic effects lead to a transient reduction of the air breakdown voltage along the path of the laser pulse, enabling one to trigger and guide electric discharges. The second part of my thesis focused on the study and the optimization of such guided discharges for the design of a radio-frequency plasma antenna, contactless high-voltage switches or a laser lightning rod. To this purpose I developed and built an interferometric plasma diagnostic, allowing to measure the lifetime of generated plasmas. I also contributed to the proof of principle for a filament induced plasma antenna emitting RF signal. Finally, I took part to prospective experimental studies for the development of a laser lightning rod
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Kawwam, Mohammad. "Pulsed Laser Deposition and Structural Analysis of Crystalline CuO and GaN Thin Films." Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10007.
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Cette thèse présente les résultats expérimentaux relatifs à l'étude des couches de GaN et de CuO déposées par la technique PLD (dépôt par laser à impulsions) sur des substrats de saphir, SrTiO3, quartz et MgO. Nous avons étudié les effets de plusieurs paramètres qui jouent sur la cristallisation et la morphologie des surfaces des films déposés, à savoir, la température du substrat, la pression au fond, la distance entre le substrat et la cible, la densité d'énergie du laser et la position du substrat. Les couches ont été caractérisées par XRD, microscopie à force atomique et Le microscope électronique à balayage, RHEED et RAMAN. Les résultats montrent que la rugosité et la qualité de la surface des films déposés par PLD dépendent de l'énergie cinétique de déposition des espèces chimiques. L'épaisseur du film, la cristallinité, l'homogénéité et la rugosité sont étroitement liés aux conditions de dépôtThe thesis presents experimental results related to the Pulsed Laser Deposition (PLD) of GaN and CuO thin films using sapphire, SrTiO3, quartz and MgO substrates. The evolution of crystallization and surface morphology of the as-deposited films were studied to investigate the influence of the process conditions such as: substrate heating, background pressure, target-substrate distance, laser energy density, and substrate location, which were systematically varied. The as-deposited films were characterized by X-ray diffraction, atomic force microscopy and scanning electron microscopy, X-ray photoelectron spectroscopy, RHEED and RAMAN techniques. The results convincingly demonstrate that the enhancement in film growth quality - the reduction in roughness and the delay of epitaxial breakdown - is related to the control of PLD species kinetics. The films thickness, crystallinity, homogeneity and surface roughness are strongly dependent on deposition conditions
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Limbach, Christopher M. "Characterization of nanosecond, femtosecond and dual pulse laser energy deposition in air for flow control and diagnostic applications." Thesis, Princeton University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3737448.
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The non-resonant heating of gases by laser irradiation and plasma formation has been under investigation since the development of 100 megawatt peak power, Q-switched, nanosecond pulse duration lasers and the commensurate discovery of laser air sparks. More recently, advances in mode-locking and chirped pulse amplification have led to commercially available 100 gigawatt peak power, femtosecond pulse duration lasers with a rapidly increasing number of applications including remote sensing, laser spectroscopy, aerodynamic flow control, and molecular tagging velocimetry and thermometry diagnostics. This work investigates local energy deposition and gas heating produced by focused, non-resonant, nanosecond and femtosecond laser pulses in the context of flow control and laser diagnostic applications.
Three types of pulse configurations were examined: single nanosecond pulses, single femtosecond pulses and a dual pulse approach whereby a femtosecond pre-ionizing pulse is followed by a nanosecond pulse. For each pulse configuration, optical and laser diagnostic techniques were applied in order to qualitatively and quantitatively measure the plasmadynamic and hydrodynamic processes accompanying laser energy deposition. Time resolved imaging of optical emission from the plasma and excited species was used to qualitatively examine the morphology and decay of the excited gas. Additionally, Thomson scattering and Rayleigh scattering diagnostics were applied towards measurements of electron temperature, electron density, gas temperature and gas density.
Gas heating by nanosecond and dual pulse laser plasmas was found to be considerably more intense than femtosecond plasmas, irrespective of pressure, while the dual pulse approach provided substantially more controllability than nanosecond pulses alone. In comparison, measurements of femtosecond laser heating showed a strong and nonlinearly dependence on focusing strength. With comparable pulse energy, measurements of maximum temperature rise ranged from 50K to 2000K for 500mm and 175mm focal length lenses, respectively. Experiments with various lens and pulse energy combinations indicated an important connection between gas heating and the phenomena of intensity clamping and self-guiding. The long-term behavior of the heated region varied considerably among pulse configurations. However, in each case, the formation of a toroidal vortex could be suppressed or enhanced depending on the variables of pressure, focusing and pulse energy.
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Bernhard, John Michael. "Work Function Study of Iridium Oxide and Molybdenum Using UPS and Simultaneous Fowler-Nordheim I-V Plots with Field Emission Energy Distributions." Thesis, University of North Texas, 1999. https://digital.library.unt.edu/ark:/67531/metadc2211/.
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The characterization of work functions and field emission stability for molybdenum and iridium oxide coatings was examined. Single emission tips and flat samples of molybdenum and iridium oxide were prepared for characterization. The flat samples were characterized using X-ray Photoelectron Spectroscopy and X-ray diffraction to determine elemental composition, chemical shift, and crystal structure. Flat coatings of iridium oxide were also scanned by Atomic Force Microscopy to examine topography. Work functions were characterized by Ultraviolet Photoelectron Spectroscopy from the flat samples and by Field Emission Electron Distributions from the field emission tips. Field emission characterization was conducted in a custom build analytical chamber capable of measuring Field Emission Electron Distribution and Fowler-Nordheim I-V plots simultaneously to independently evaluate geometric and work function changes. Scanning Electron Microscope pictures were taken of the emission tips before and after field emission characterization to confirm geometric changes. Measurement of emission stability and work functions were the emphasis of this research. In addition, use of iridium oxide coatings to enhance emission stability was evaluated.
Molybdenum and iridium oxide, IrO2, were characterized and found to have a work function of 4.6 eV and 4.2 eV by both characterization techniques, with the molybdenum value in agreement with previous research. The analytic chamber used in the field emission analysis demonstrated the ability to independently determine the value and changes in work function and emitter geometry by simultaneous measurement of the Field Emission Energy Distribution and Fowler-Nordheim I-V plots from single emitters.
Iridium oxide coating was found to enhance the stability of molybdenum emission tips with a relatively low work function of 4.2 eV and inhibited the formation of high work function molybdenum oxides. However, the method of deposition of iridium and annealing in oxygen to form iridium oxide on molybdenum emitters left rather severe cracking in the protective oxide coating exposing the molybdenum substrate.
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Acharya, Krishna Prasad. "Photocurrent Spectroscopy of CdS/Plastic, CdS/Glass, and ZnTe/GaAs Hetero-pairs Formed with Pulsed-laser Deposition." Bowling Green State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1245089031.
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Mitchell, Ethan D. "Multiple beam directors for naval free electron laser weapons." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Mar%5FMitchell.pdf.
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Daugherty, Timothy J. "Assessment of the ballistic performance of compositional and mesostructural functionally graded materials produced by additive manufacturing." Youngstown State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1596474811965998.
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Tai-YuChiu and 邱泰育. "Effect of Laser Power on Mechanical Properties and Microstructure of 316L Stainless Steel Deposited by Direct Energy Deposition(DED)." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/djmpx4.
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碩士國立成功大學
材料科學及工程學系
107
Laser power is the most directly relevant process parameter affecting the quality in Direct Energy Deposition (DED) process. In this study, we investigated laser power effect on mechanical properties and microstructure of multi-layer products after vertical deposition of 40 layers using 316L stainless steel powder. The mechanical properties were analyzed by three-point bending test combined with digital image correlation (DIC) to obtain strain distribution. The microstructure under tensile, compressive stress and neutral regions were analyzed by EBSD. Considering laser power from 800 W to 2000 W, 800 W has the highest yield stress of 476 MPa and 1600 W the lowest yield stress of 407 MPa due to coarsening effect. By analyzing strain distribution and Schmid factor, 2000 W shows low strain value and low value of Schmid factor resulting in increasing yield stress of 454 MPa.
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Hsin-WeiHuang and 黃信瑋. "Numerical Modeling on Multi-layer Scanning of Directed Energy Deposition Using Stainless Steel 316L and Thermal Analysis for the Effects and Optimization of Process Parameters." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/anqc4m.
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碩士國立成功大學
機械工程學系
106
In this research, a numerical model for multi-layer scanning of Directed Energy Deposition (DED) process for SS316L is constructed to study transient thermal phenomenon under primary process parameters. The geometrical sizes and cooling rate of multi-layer metal thin layers are investigated under various combination of laser power and scanning speed. It is discovered that the layer height will increase with layer number when maintaining the same process parameters. Moreover, judged from the view of time-saving, energy-saving and reducing cooling rate, the optimal combination of process parameters is determined. Furthermore, in order to obtain superior deposition appearance, the trends of reducing laser power for each layer are proposed. It is found that laser power of 1800 W and scanning speed of 8 mm/s are the optimal combination of process parameters, which is most beneficial for time saving, energy saving, promoting the growth of columnar grains and reducing cracking possibility. To further improve the manufacturing problems induced by thermal field, the effects of idle time, substrate preheating and scanning direction are studied. Results indicate that idle time has no obvious effects on process. Substrate preheating could increase geometrical sizes of metal thin layers, and obviously reduce cooling rate and temperature gradient. The single scanning direction is helpful for maintaining the conformity of deposition appearance.
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Min-XuanJiang and 蔣旻軒. "Numerical Modeling on Multi-layer Scanning of Directed Energy Deposition Using Inconel 718 Superalloy and Thermal Analysis for the Effects and Optimization of Process Parameters." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/hk548g.
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Loureiro, Maria João Grilo. "Off-line robot programming for metal additive manufacturing using robot external axis." Master's thesis, 2020. http://hdl.handle.net/10316/92243.
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Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e TecnologiaRobotics is destined to become the supporting technology that promotes the connection between the digital and the physical world. In an extremely competitive industrial environment, automated manufacturing is a key factor for any operation that seeks maximum efficiency, safety, and competitiveness. Despite its convenience, for certain functions, a robot is limited by its own axis system. The introduction of a coordinated system, with the external axis, allows flexibility and expansion of the robot's work zone in companies production lines.This thesis comprises the manipulation of external axes of a robotic cell applied to additive manufacturing. Offline programming methods are used in a virtual environment to assist the construction of an aircraft engine part using one of the direct energy deposition methods. The work carried out was focused on the production of a particular feature of an aircraft engine part, denominated here as Rim Part, which was initially tested on the RoboDK simulation software. During the tests, it was possible to conclude that the proposed impositions presented strong barriers to their production and for these reasons, it was necessary to change the approach, using macro programming, in C# language, to improve the coordinated movements between robots. With this method, simultaneously with the generated graphic interface, the production of the requested part was visualized, thus obtaining a very satisfactory result and without collisions between the two robots.
A robótica está destinada em tornar-se a tecnologia de suporte que promove a ligação entre o mundo digital e o físico. No meio industrial extremamente competitivo, a manufatura automatizada é um fator chave para qualquer operação que procure máxima eficiência, segurança e competitividade. Apesar da sua conveniência, para certas funções, um robô por si só é limitado pelo seu próprio sistema de eixos. A introdução de um sistema coordenado, com eixos externos, permite flexibilizar e expandir a zona de trabalho do robô nas linhas de produção das empresas. Esta tese compreende a aplicação de eixos externos num robô em manufatura aditiva e diferentes métodos de programação off-line num ambiente virtual, com o objetivo de auxiliar a construção de uma peça de um motor de avião utilizando um dos métodos de deposição direta de energia apresentados. O trabalho realizado foi focado na produção de uma feature em particular, designada por Rim Part, que inicialmente foi testado no software de simulação RoboDK. No decorrer dos ensaios, permitiu-se concluir que as imposições propostas apresentavam fortes barreiras à sua produção e por estes motivos, foi necessário mudar de abordagem recorrendo-se à programação de macros, em linguagem C#, para permitir os movimentos coordenados entre robôs. Com este método, juntamente com a interface gráfica gerada, foi possível a visualização da produção da parte requerida obtendo-se assim, um resultado bastante satisfatório e sem colisões entre os dois robôs.
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Maciel, Duarte de Araújo. "Fatigue behaviour of Inconel 625 produced by Directed Energy Deposition." Master's thesis, 2021. https://hdl.handle.net/10216/134949.
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Maciel, Duarte de Araújo. "Fatigue behaviour of Inconel 625 produced by Directed Energy Deposition." Dissertação, 2021. https://hdl.handle.net/10216/134949.
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Chang, Hung-Yu, and 張弘諭. "Finite Element Analysis of Thermal Effect on Directed Energy Deposition." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/vffw77.
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碩士國立高雄科技大學
機械工程系
107
In this study, the displacement behavior of SUS316L stainless steel under five-layer continuous direct energy deposition was investigated by using experiment and commercial finite element method software ANSYS, and the displacement effects of five-layer deposit were discussed after cooling. In addition, the relationship between laser power and laser feed rate under different curvatures is discussed. First, the full-section morphology was obtained by experimental method and the parameters of laser power 300W, 400W, 500W and laser feed rates of 3mm/s, 5mm/s, 7mm/s were used to simulate using thermal-structure interaction mode. The results show that the optimal preheating temperature during the deposition process is about 150 °C, and the displacement gap will be relatively stable. The effect of curvature on displacement is indistinguishable on the neutral axis, the displacement of the height can be predicted by the straight path. However, the inner and outer circles need additional experiments or finite element analysis to predict. The results show that low laser power and high feed rate in the deposition are preferable in consideration of displacement.
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Rodrigues, Rui Pedro Teixeira. "Teste e Caracterização de Peças Metálicas Produzidas por Directed Energy Deposition." Master's thesis, 2018. https://hdl.handle.net/10216/116520.
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Rodrigues, Rui Pedro Teixeira. "Teste e Caracterização de Peças Metálicas Produzidas por Directed Energy Deposition." Dissertação, 2018. https://repositorio-aberto.up.pt/handle/10216/116520.
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Duarte, Valdemar Rebelo. "Developments in Directed Energy Deposition Additive Manufacturing: In-situ Hot Forging and Indirect Cooling." Doctoral thesis, 2022. http://hdl.handle.net/10362/134198.
Full textAbstract:
Additive Manufacturing (AM) by Directed Energy Deposition-arc (DED-arc) is competing
with other AM technologies due to its high deposition rate, ability to produce large parts
with medium/high geometric complexity and low capital and running costs. However,
residual stresses, coarse microstructures, and defects on parts, such as cracks and
pores, may compromise in-service industrial applications and need to be overcome.
This work aimed to develop and validate two innovative process variants: one based on
in-situ hot forging; and the other on temperature control, that is, indirect cooling of
deposited material and hot forging.
The hot forging variant consisted of locally forging the deposited layer at high
temperatures using low forces. The goal is to create an uniform plastic deformation zone
along the layer, to promote grain refinement, reduce material anisotropy and collapse
defects.
The variant based on temperature control consisted of cooling the hammer components
and the shielding gas used to protect the molten pool, to increase the solidification rate
and thus, prevent grain coalescence.
For this, dedicated DED-arc equipment was designed and manufactured with specific
features for research. The effect of hot forging was analysed in detail on 316LSi stainless
steel, and the feasibility of its application was verified in other relevant industrial
materials. It was concluded that hot forging can induce dynamic recrystallization,
increase nucleation sites and prevent epitaxial grain growth. Thus, it contributes to an
overall refined and homogeneous microstructure with improved mechanical properties.
The developed cooling system lowered the average temperature of the nozzle and
hammer during consecutive depositions. Cooling of the shielding gas had no major effect
on the cooling rates and microstructure of the materials, however, it was observed that
the hot forging changes the heat flow conditions of the part, promoting higher cooling
rates.A tecnologia de deposição direta de energia por arco (DED-arc) tem competido com outras tecnologias de fabrico aditivo devido à sua elevada taxa de deposição, capacidade de produzir componentes de grandes dimensões com média/alta complexidade geométrica e baixos custos de implementação e funcionamento. Contudo, as elevadas tensões residuais, as microestruturas grosseiras, ou os defeitos do tipo poros, podem comprometer algumas aplicações industriais e necessitam de ser superados. Este trabalho visou desenvolver e validar duas variantes inovadoras de processo DED- arc: uma baseada no forjamento a quente; e outra no controlo de temperatura. A variante baseada no forjamento, consistiu em forjar o material depositado imediatamente após a deposição, utilizando baixas forças. O objetivo foi a produção de uma zona de deformação plástica uniforme ao longo de cada camada, para promover alterações microestruturais, nomeadamente o refinamento dos grãos e a redução da anisotropia. A variante baseada no trabalho termodinâmico consistiu em arrefecer os componentes do martelo e o gás utilizado para proteger o banho de fusão, com o objetivo de aumentar a taxa de arrefecimento e assim evitar a coalescência dos grãos. Neste sentido, foi concebido e fabricado um equipamento de DED-arc, com características específicas para investigação. O efeito do forjamento a quente foi estudado detalhadamente no aço inoxidável 316LSi, e foi verificada a viabilidade da sua aplicação noutros materiais relevantes industrialmente. Concluiu-se que o forjamento induz recristalização dinâmica, aumenta os pontos de nucleação e impede o crescimento de grãos epitaxiais, contribuindo para uma microestrutura globalmente mais fina, homogénea e com melhores propriedades mecânicas. O sistema de arrefecimento desenvolvido baixou a temperatura do bocal e do martelo durante as deposições consecutivas. O arrefecimento do gás de proteção não teve efeito nas taxas de arrefecimento nem na microestrutura do material, contudo, observou-se que o forjamento altera as condições de fluxo de calor, promovendo taxas de arrefecimento maiores.
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Cooke, Shaun. "Numerical modelling and metallurgical characterization of Cr-Mo steels processed by directed energy deposition." Thesis, 2021. http://hdl.handle.net/1828/13103.
Full textAbstract:
Additive manufacturing (AM) provides unique opportunities to push the boundaries of material properties and free form fabrication. However with this novel manufacturing technique a number of defects not commonly found in conventional processes such as machining or casting can arise. Both experimental and numerical studies can help better understand the printed material on a more fundamental level in order to optimize the process and mitigate these defects. Electron microscopy can provide essential information about the as-built microstructure and characteristic defects while numerical modelling can help determine a correlation between process parameters and the resulting properties. First, an initial investigation of directed energy deposition (DED) processed 4140 steel was conducted using various microscopy methods to better understand the defects and microstructure of the printed alloy. A martensite dominate microstructure within a bainitic matrix with increasing degrees of tempering further down the build was revealed. Additional sample preparation was conducted with a focused ion beam and analyzed with the transmission electron microscope to investigate features such as grain boundaries, mechanical twins and interplanar spacing. This interplanar spacing was measured for a number of different diffraction images and compared with the theoretical values. The deviation between the measured and theoretical values can be attributed to defects such as residual stress which causes lattice strain and consequently a smaller or larger spacing between atomic planes. Lastly, diffraction images were characterized and compared with the literature to determine the Miller indices and the specific zone axis orientations. A thermo-mechanical-metallurgical finite element model for 42CrMo4 steel was then developed in ABAQUS to identify the correlation between processing parameters and resulting properties by predicting the temperature history, and resulting residual stresses and metallurgical phase fractions for the DED process. A pre-processing framework was implemented in order to allow the modelling of complex geometries and laser trajectories while experiments were conducted to validate the fidelity of the model. Four separate cases were fabricated with varying processing parameters and geometries. In addition to in-situ temperature measurements, post-build residual stress and substrate distortion data was also collected. Furthermore, metallurgical analysis was performed for each case and compared with the simulated phase fractions. The accuracy of the distortion profile increased with increasing dwell time while the accuracy in predicting the metallurgical phase fractions and residual stresses demonstrated the opposite trend.Graduate
2022-07-05
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Abutaha, Anas I. "Nanostructured Thermoelectric Oxides for Energy Harvesting Applications." Diss., 2015. http://hdl.handle.net/10754/583286.
Full textAbstract:
As the world strives to adapt to the increasing demand for electrical power, sustainable energy sources are attracting significant interest. Around 60% of energy utilized in the world is wasted as heat. Different industrial processes, home heating, and exhausts in cars, all generate a huge amount of unused waste heat. With such a huge potential, there is also significant interest in discovering inexpensive technologies for power generation from waste heat. As a result, thermoelectric materials have become important for many renewable energy research programs. While significant advancements have been done in improving the thermoelectric properties of the conventional heavy-element based materials (such as Bi2Te3 and PbTe), high-temperature applications of thermoelectrics are still limited to one materials system, namely SiGe, since the traditional thermoelectric materials degrade and oxidize at high temperature. Therefore, oxide thermoelectrics emerge as a promising class of materials since they can operate athigher temperatures and in harsher environments compared to non-oxide thermoelectrics. Furthermore, oxides are abundant and friendly to the environment. Among oxides, crystalline SrTiO3 and ZnO are promising thermoelectric materials.
The main objective of this work is therefore to pursue focused investigations of SrTiO3 and ZnO thin films and superlattices grown by pulsed laser deposition (PLD), with the goal of optimizing their thermoelectric properties by following different strategies. First, the effect of laser fluence on the thermoelectric properties of La doped epitaxial SrTiO3 films is discussed. Films grown at higher laser fluences exhibit better thermoelectric performance. Second, the role of crystal orientation in determining the thermoelectric properties of epitaxial Al doped ZnO (AZO) films is explained. Vertically aligned (c-axis) AZO films have superior thermoelectric properties compared to other films with different crystal orientations. Third, additional B-site doping of A-site doped SrTiO3 films leads to a prominent reduction in the lattice thermal conductivity without limiting the electrical transport, and hence an improvement in the figure of merit is noticed. Fourth and last, the enhancement of thermoelectric properties of thermally robust, high quality SrTiO3-based superlattices is discussed. Beside the randomly distributed oxygen vacancies and extrinsic dopants, the structure of SrTiO3-based superlattices increases the scattering of phonons at the interfaces between the alternative layers, and hence reducing the thermal conductivity, which leads to a notable enhancement in the figure of merit.
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Cheng-HungChu and 居正宏. "Numerical Modeling on Directed Energy Deposition for Stainless Steel 316L and Thermal Analysis of the Effects of Process Parameter." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/fw2m2d.
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Seca, Ricardo João Martins. "Desenvolvimento de técnicas de reparação de peças por fabrico aditivo através da tecnologia de Directed Energy Deposition (DED) - Aços Maraging." Master's thesis, 2021. https://hdl.handle.net/10216/136750.
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"Pulsed Laser Deposition of Highly Conductive Transparent Ga-doped ZnO for Optoelectronic Device Applications." Doctoral diss., 2011. http://hdl.handle.net/2286/R.I.8868.
Full textAbstract:
abstract: Transparent conductive oxides (TCOs) are used as electrodes for a number of optoelectronic devices including solar cells. Because of its superior transparent and conductive properties, indium (In) tin (Sn) oxide (ITO) has long been at the forefront for TCO research activities and high-volume product applications. However, given the limited supply of In and potential toxicity of Sn-based compounds, attention has shifted to alternative TCOs like ZnO doped with group-III elements such as Ga and Al. Employing a variety of deposition techniques, many research groups are striving to achieve resistivities below 1E-4 ohm-cm with transmittance approaching the theoretical limit over a wide spectral range. In this work, Ga-doped ZnO is deposited using pulsed laser deposition (PLD). Material properties of the films are characterized using a number of techniques. For deposition in oxygen at pressures >1 mTorr, post-deposition annealing in forming gas (FG) is required to improve conductivity. At these higher oxygen pressures, thermodynamic analysis coupled with a study using the Hall effect measurements and photoluminescence spectroscopy suggest that conductivity is limited by oxygen-related acceptor-like defects in the grains that compensate donors, effectively reducing the net carrier concentration and creating scattering centers that reduce electron mobility. Oxygen is also responsible for further suppression of conductivity by forming insulative metal oxide regions at the grain edges and oxygen-related electron traps at the grain boundaries. The hydrogen component in the FG is thought to passivate the intra-grain acceptor-like defects and improve carrier transport across these grain boundaries. Given this deleterious effect of oxygen on conductivity, depositions are performed in pure argon (Ar), i.e., the only oxygen species in the growth ambient are those ejected directly from the PLD solid source target. Ga-doped ZnO deposited in Ar at 200 °C and 10 mTorr have resistivities of 1.8E-4 ohm-cm without the need for post deposition annealing. Average transmittance of the Ga-doped films is 93% over the visible and near infrared (IR) spectral regions, but free carrier absorption is a limiting factor further into the IR. After annealing in FG at 500 °C, a 300 nm Ar film has a Haacke figure of merit of 6.61E-2 sq. ohm.Dissertation/Thesis
Ph.D. Materials Science and Engineering 2011
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Höfer, Kevin. "Qualifizierung des Plasma-Pulver-Auftragschweißprozesses für die generative Herstellung von Bauteilen der Legierung 1.4404." 2020. https://monarch.qucosa.de/id/qucosa%3A74064.
Full textAbstract:
Die generative Fertigung stellt eine Schlüsseltechnologie der Zukunft für weite Teile der Wirtschaft dar. Der Prozess des Plasma-Pulver-Auftragschweißens soll eine Lücke im bestehenden Portfolio an generativen Prozessen schließen. Zunächst wurde der klassische Beschichtungsprozess an die Erfordernisse der generativen Fertigung angepasst. Im Ergebnis konnten Bauteile, welche aus bis zu vier verschiedenen Materialen bestehen können, prozesssicher generiert werden. Die anschließende Betrachtung des Einflusses der Systemparameter auf das Bauteil ergab, dass die Haupteinflussgrößen auf die Bauteilgeometrie die Schweißstromstärke, die Schweißgeschwindigkeit, der Pulvermassestrom sowie die Plasmagasmenge sind. Die Bauteildichte sowie der Pulverausnutzungsgrad zeigen keine signifikanten Änderungen innerhalb des hier betrachteten Bereiches. Im Mittel konnte eine relative Bauteildichte von 98,7 % und ein Materialausnutzungsgrad von 77 % bestimmt werden. In Summe ist der Prozess durch eine stabile Auftragscharakteristik mit mindestens vergleichbaren Eigenschaften zu bestehenden Systemen zu bewerten und sehr gut als generativer Prozess, insbesondere für die Herstellung von mehrkomponentigen Bauteilen, geeignet.Additive manufacturing is one of the key technologies of the future for large parts of the economy. The process of plasma powder deposition welding is intended to close a gap in the existing portfolio of generative processes. First, the classical cladding process was adapted to the requirements of additive manufacturing. As a result, components, which can consist of up to four different materials, could be reliably generated. The subsequent consideration of the influence of the system parameters on the component showed that the main influencing variables on the part geometry are the welding current, the welding speed, the powder flow rate and the plasma gas volume. The component density as well as the powder utilization rate show no significant changes within the range considered here. On average, a relative component density of 98.7 % and a material utilization rate of 77 % could be determined. In sum, the process can be characterized by a stable application characteristic with at least comparable properties to existing systems and is very well suitable as an additive manufacturing process, especially for the production of multi material components.
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Sunil, Maligi Anantha. "Studies on AgInS2 Films as Absorber Layer for Heterojunction Solar Cells." Thesis, 2016. http://etd.iisc.ernet.in/handle/2005/2818.
Full textAbstract:
Currently conventional sources like coal, petroleum and natural gas meet the energy requirements of developing and undeveloped countries. Over a period of time there is high risk of these energy sources getting depleted. Hence an alternate source of energy i.e. renewable energy is the need of the hour. The advantages of renewable energy like higher sustainability, lesser maintenance, low cost of operation, and minimal impact on the environment make the role of renewable energy sources significant. Out of the various renewable energy sources like solar energy, wind energy, hydropower, biogas, tidal and geothermal, usage of solar energy is gradually increasing. Among various solar energy sources, Photovoltaics has dominated over the past two decades since it is free clean energy and availability of abundant sunlight on earth.
Over the past few decades, thin film solar cells (TFSC) have gained considerable interest as an economically feasible alternative to conventional silicon (Si) photovoltaic devices. TFSCs have the potential to be as efficient as Si solar cells both in terms of conversion efficiency as well as cost. The advantages of TFSC are that they are easy to prepare, lesser thickness, requires lesser materials, light weight, low cost and opto-electronic properties can be tuned by varying the process parameters. The present study is focused on the fabrication of AgInS2/ZnS heterojunction thin film solar cell. AgInS2 absorber layer is deposited using both vacuum (sputtering/sulfurization) and non-vacuum (ultrasonic spray pyrolysis) techniques. ZnS window layer is prepared using thermal evaporation technique, detailed experimental investigation has been conducted and the results have been reported in this work. The thesis is divided into 6 chapters.
Chapter 1 gives general introduction about solar cells and working principle of solar cell. It also discusses thin film solar cell technology and its advantages. Layers of thin film solar cell structure, Significance of each layers and possible materials to be used are emphasized. A detailed overview of the available literature on both AgInS2 absorber layer and ZnS window layer has been presented. Based on the literature review, objectives of the present work are defined.
Chapter 2 explains the theory and experimental details of deposition techniques used for the growth of AgInS2 and ZnS films. Details of characterization techniques to study film properties are described in detail.
Chapter 3 presents a systematic study of AgInS2 thin films deposited by sulfurization of sputtered Ag-In metallic precursors. Initially, AgInS2 films are deposited by varying the substrate temperature and properties of as-deposited films are characterized. Structural, morphological, electrical and optical properties of AgInS2 films are explained. From these studies, samples with better properties at particular substrate temperature are optimized. By fixing the substrate temperature, deposition time of silver is varied by keeping other deposition conditions same and the properties of films are discussed. It was observed that deposition time of silver doesn’t have much impact on structural properties of AgInS2 films. However, opto-electric properties of AgInS2 films are enhanced. Based on characterization studies, deposition time of silver is optimized. Deposition time of indium is varied by keeping substrate temperature and silver deposition to optimized value. The properties of as-deposited films are discussed. Based on the above studies, the optimized p type films have a band gap of 1.64 eV, carrier concentration of 1013 ions/cm3 and Resistivity of order 103 Ω-cm.
Chapter 4 presents a systematic study of AgInS2 thin films deposited by ultrasonic spray pyrolysis. AgInS2 films are deposited by varying the substrate temperature and properties of as deposited films are characterized. Structural, morphological, electrical and optical properties of AgInS2 films are explained. From these studies, samples with better properties at particular substrate temperature are optimized. By fixing the substrate temperature, concentration of silver molarity in the precursor solution is varied by keeping other deposition conditions same and the properties of films are discussed. Structural, optical and electrical properties of AgInS2 films are
enhanced with the increase in silver concentration. Based on characterization studies, concentration of silver is optimized. Similarly concentration of indium molarity in the precursor solution is varied and the properties of as-deposited films are discussed. Finally, sulfur molarity in the precursor solution is varied and properties of films are discussed. It was observed that increasing sulfur after certain limit does not have any effect on the properties of the films. Based
on the above studies, this method resulted in the films with resistivity of 103 Ω-cm and band gap of 1.64 eV. These films showed a carrier concentration of 1013 ions/cm3.
Chapter 5 describes the growth of ZnS films using thermal evaporation technique. Influence of thickness on the properties of ZnS films is explained. Samples with good crystallinity, high transmission, and wider gap are selected for device fabrication. This p type layer showed a band gap of 3.52 eV. Solar cells have been fabricated using the AgInS2 films developed by both sputtering and ultrasonic spray pyrolysis techniques. A maximum cell efficiency of 0.92 percent has been achieved for the cell with 0.950 µm thick sputtered AgInS2 layer and thermally evaporated 42 nm thick ZnS layer. In comparison, the ultrasonic spray pyrolysis deposited films gave an efficiency of 0.54 percent. These values are comparable to those mentioned in a couple of reports earlier.
Chapter 6 summarizes the conclusions drawn from the present investigations and scope of future work is suggested.