This thesis deals with properties of austenitic stainless steel 304L processed by SLM technology and tested at room and cryogenics temperatures. Result is description of mechanical properties and microstructure. First step was to develop processing parameters to achieve porosity of prints fell below 0,01 %. Following tensile test showed higher yield and ultimate tensile strength than conventionally fabricated parts, even at temperature -80 °C, but at cost of reduced ductility. Due to deformation and low temperature austenite transformed into martensite. This transformation also occurred in Charpy toughness test, that resulted in ductile to brittle behaviour.

This study presents results of selective laser melting (SLM), powder metallurgy (PM), and casting technologies applied for producing Ti–TiB composites from Ti–TiB₂ powder. Diffraction patterns and microstructural investigations reveal that chemical reaction occurred between Ti and TiB₂ during all the three processes, leading to the formation of Ti–TiB composites. The ultimate compressive strength of SLM-processed and cast samples are 1421 and 1434 MPa, respectively, whereas the ultimate compressive strengths of PM-processed 25%, 29%, and 36% porous samples are 510, 414, and 310 MPa, respectively. The Young’s moduli of porous composite samples are 70, 45, and 23 GPa for 25%, 29%, and 36% porosity levels, respectively, and are lower than those of SLM-processed (145 GPa) and cast (142 GPa) samples. Fracture analysis of the SLM-processed and cast samples shows shear fracture and microcracks across the samples, whereas failure of porous samples occurs due to porosities and weak bonds among particles.

The use of Liquid Crystal (LC) materials, mainly in display applications, has contributed to major advancement in liquid crystal science and technology. New and more complex phases of liquid crystals were developed to compete with conventional nematic LC displays. The challenge now is to manufacture high birefringence liquid crystal materials with low viscosity. LC is also used in many other applications, such as temperature sensors and photonics beam shaping in the form of spatial light modulators (SLM) and q-plates. The first objective of this thesis is to investigate the magic mirror effect using a SLM following Sir Michael Berry’s theory. Here, we demonstrated a simple way of producing the magic mirror effect using LC devices and aimed to use a micron-sized device to shape the phase and polarization of light with gentle phase variation. We were able to generate the magic mirror image intensity pattern, both experimentally and theoretically. This was done by computing and generating the desired phase pattern of an image on the SLM, then aligning light propagation through this phase pattern. The experimental and theoretical results showed good agreement when comparing the produced intensity patterns. In the second part of this thesis, we experimentally investigated the use of structured photons, created using q-plates, which is a birefringent liquid crystal cell of OAM and SAM coupling, in quantum key distribution (QKD) using the BB84 protocol through orbital angular momentum (OAM) maintaining optical fibres. Here, we were successful in generating a secure key between two parties with a quantum bit error rate of 8.6% which is below the security threshold of 11%. This work demonstrates the feasibility of using structured light in QKD through fibres to boost key rates and security.

This thesis addresses the exponential growth of experimental data and the resulting computational complexity seen in two major scientific applications, which account for significant cycles consumed on today’s supercomputers. The first application concerns computation of the adaptive optics system in next-generation ground-based telescopes, which will expand our knowledge of the universe but confronts the astronomy community with daunting real-time computation requirements. The second application deals with emerging frequency-domain redatuming methods, e.g., Marchenko redatuming, which are game-changers in exploration geophysics. They are valuable to oil and gas applications and will soon be to geothermal exploration and carbon capture storage. However, they are impractical at industrial scale due to prohibitive computational complexity and memory footprint. We tackle the aforementioned challenges by designing high-performance algebraic and stochastic algorithms, which exploit the data sparsity structure of the matrix operator. We show that popular randomized algorithms from machine learning can also solve large covariance matrix problems that capture the correlations of wavefront sensors detecting the atmospheric turbulence for ground-based telescopes. Algebraic compression based on low-rank approximations that retains the most significant portion of the spectrum of the operator provides numerical solutions at the accuracy level required by the application. In addition, selective use of lower precisions can further reduce the data volume by trading off application accuracy for memory footprint. Reducing memory footprint has ancillary implications for reduced energy expenditure and reduced execution time because moving a word is more expensive than computing with it on today’s architectures. We exploit the data sparsity of matrices representative of these two scientific applications and propose four algorithms to accelerate the corresponding computational workload. In soft real-time control of an adaptive optics system, we design a stochastic Levenberg-Marquardt method and high-performance solver for Discrete-time Algebraic Riccati Equations. We create a tile low-rank matrix-vector multiplication algorithm used in both hard real-time control of ground-based telescopes and seismic redatuming. Finally, we leverage multiple precisions to further improve the performance of seismic redatuming applications We implement our algorithms on essentially all families of currently relevant HPC architectures and customized AI accelerators and demonstrate significant performance improvement and validated numerical solutions.

Over time science has provided us with new materials and fabrication techniques making it possible to design and create more complex engineering components for service. If we are to include these materials in damage tolerant design efforts, engineers need to understand when/where degradation will occur in the engineering component. To do so it is imperative that micromechanical studies be conducted to understand the material behavior of the microstructural features including phases, build pattern features, and microstructural imperfections including cracks of new materials to validate any future modeling efforts. This dissertation will discuss the experimental and computational micromechanics of extruded and cast aluminum cerium alloys and selective laser melted 316L stainless steel. In Chapters 2 and 3, micromechanical experiments and computational efforts are carried out on extruded 52:1 Al-8Ce-10Mg alloy. Using in-situ scanning electron microscopy tensile testing microcracking is observed in Al11Ce3 intermetallic after yield in the bulk alloy. In-situ digital image correlation tests observe the load sharing characteristics between the Al(Mg) matrix and the Al11Ce3 intermetallic before and after microcracking. Finally, that failure process is determined to be coalesce of microvoids leading to ductile damage failure. These results are used to create an experimental-computational framework to develop a crystal plasticity finite element model for extruded Al-8Ce-10Mg alloys. The calibrated model is used to perform multiple simulations evaluate the possible effect changes intermetallic content and grain orientation texture have on the mechanical strength of the alloy. The experimental and computational framework are expandable to other material systems not just Al-Ce alloys. In Chapter 4, in-situ scanning electron microscopy tensile testing is used to investigate how the matrix and intermetallic phases contribute to the failure behavior alloy of cast Al-11Ce- 0.4Mg alloy. The in-situ tests shows that after multiple points of crack nucleation, crack coalescence causes the subsequent failure to occur in the Al(Mg) matrix phase of the alloy, as seen by tortuous behavior. The cause of this crack behavior is determined to be due to the high strength match between the matrix and intermetallic phase, strong metallurgical bond between the two phases, and the size effect created by large eutectic colonies created during casting. The results of the experimental work are used to propose a 3D multiscale computational model of cast Al-Ce alloys. In Chapter 5, micromechanical experiments are carried out on SLM 316L Stainless Steel with four different sets of varied processing parameters. Discontinuous yielding is observed in the lowest energy density sample caused by the strong [110] texture, optimal for dislocation slip, in the loading direction. The in-situ loading experiments are also able to capture the melt pool track deformation and crack formation that leads to the failure of these samples. This highlights the importance of micromechanical experiments for additive manufactured materials. / Doctor of Philosophy / As time has progressed new materials have been discovered that make it possible to design more complex parts for engineering design. To ensure the safety and reliability of these materials, engineers need to understand when/where damage will occur in a design. Micromechanical studies conducted at magnifications higher than human visible range allow engineers to explore where damage in materials initiates which would otherwise not be detected until after failure. The results of these studies can be used to build and test models of these materials. This dissertation will discuss the micromechanical studies of extruded and cast aluminum cerium alloys and selective laser melted 316L stainless steel. In Chapters 2 and 3, micromechanical experiments and computational techniques are performed on extruded Al-Ce alloys. In Chapter 4, the failure behavior of cast Al-Ce alloys is examined in active tension using scanning electron microscopy. Finally, in Chapter 5, selective laser melted 316L stainless steel is studied and the results highlight the importance of micromechanical experiments for the new age of metal 3D printing.

L'incertitude de l'énergie mondiale avec l'augmentation constante de la demande d'énergie déclenche la recherche de technologies de conversion d'énergie à haut rendement. Les dispositifs thermoélectriques (TE) peuvent jouer un rôle très important dans la collecte et la valorisation de l'énergie car ils peuvent être employés pour récupérer la chaleur résiduelle. Par exemple, la quantité de chaleur émise sous forme de déchets par les différents moteurs thermiques est évaluée en centaines de millions de MWh /an.Cette thèse vise à démontrer la faisabilité de fabrication des systèmes de récupération de la chaleur issue des déchets à l'échelle industrielle en utilisant des générateurs thermoélectriques (TE). Les techniques de fabrication proposées sont basées sur l'utilisation de technologies avancées comme le frittage par spark plasma, le broyage, la fusion laser sélective et la technologie de projection thermique. Ces techniques rendent possible l'élaboration de revêtements de matériau thermoélectrique avec des performances thermoélectriques supérieures et une flexibilité forte liées aux choix multiples de tailles, de formes et de matériaux.Nous nous sommes intéressés à l'étude du matériau semi-conducteur ß-FeSi2 car il présente un coefficient de mérite fort dans une plage de température de 300-800oC qui est la température des gaz en sortie de moteur voiture.Les techniques de SLM (Selective Laser Melting), de broyage, de frittage et de frittage flash (SPS) ont été successivement utilisées pour aboutir à l'élaboration de l'alliage ¿-FeSi2. Les revêtements ont ensuite été obtenus par la technique de projection plasma sous basse pression.Concernant le revêtement formé à partir de l'alliage par procédé LPPS, la transformation de phase de la phase cubique -ferrosilicium et de la phase quadratique ¿-Fe2Si5 en phase orthorhombique ß-FeSi2 se produit en obéissant aux réactions péritectique et eutectique. Après recuit sous température et temps appropriés, les revêtements présentent une phase complète ß-FeSi2 sur le substrat céramique.En outre pour une application à grande échelle, il est nécessaire de déposer ce type de revêtement sur un substrat en acier inoxydable et il convient dans ce cas d'utiliser un masque approprié pour fabriquer le dispositif thermoélectrique. / The uncertainty in the global energy with the constant increase in energy demand triggers the search for energyconversion technologies with high efficiency. The thermoeletrical devices (TE) can play a relevant role in thecollection and recovery of energy because they can be used to recover waste heat. For example, the amount of heatemitted as waste by different ombustion engines is evaluated hundreds of millions of MWh / year.This thesis aims to demonstrate the feasibility of anufacturing heat recovery systems from waste on an industrialscale using thermoelectric generators (TE). The proposed manufacturing techniques are based on the use ofadvanced technologies such as spark plasma sintering, crushing, selective laser melting and thermal spraytechnology. These techniques make possible the development of thermoelectric material coatings with superiorthermoelectric performance and high flexibility related to multiple choices of sizes, shapes and materials.The study of semiconductor ß-FeSi2 material was conducted in this goal because it has a strong merit coefficient(ZT) in the temperature range of 300-800°C which is the temperature of the output gas of the cars.Selective Laser Melting, sintering and spark plasma sintering (SPS) were successively used to lead to themanufacture of ¿-FeSi2 alloy. The coatings were then obtained by low pressure plasma spraying.Concerning the coating formed from the alloy, the phase transformation of the cubic phase ¿-ferro-silicon and thetetragonal phase ¿-Fe2Si5 in the orthorhombic phase ß-FeSi2 is produced by obeying the eritectic and eutecticreactions. After annealing under suitable temperature and time, the coatings sprayed on the ceramic bstratepresent a complete phase ß-FeSi2.In view of a large-scale application, it is necessary to spray this type of coating on a stainless steel substrate and inthis case to use a suitable mask for making the appropriate thermoelectric device.

The master's thesis deals with properties of aluminium alloys prepared by SLM process. The teoretical part of thesis is focused on decribtion of selective laser melting technology, metallurgical defects and mechanical properties of aluminium alloys processed by this technology. The experimental part of this thesis deals with selections of the SLM process parameters suitable for samples preparation in bulk. Tensile testing at room temperature was used for evaluation of basic mechanical properties. Metallographic and fractographic analyses were performed for evaluation of the microstructure and fracture mechanisms. The materials characteristics obtained on SLM samples were compared with the properties of the same materials grade produced by conventional technologies.

The thesis deals with the design, construction and testing of two different metal powder coating equipment, which is able to work with SLM 280HL metal 3D printer. Since the field of multimaterial metal printing by selective laser melting (SLM) has not been significantly investigated yet, an overview of existing patents and possible approaches to the solution has been developed. The device has been successfully designed and a series of tests was carried out defining the issue of applying an improved head that uses a nozzle and an eccentric vibration motor. Based on the experiments performed, the coating parameters of the multimaterial layer of FeAm and 316L materials were defined. A control system for the partial process automation was created for the proposed device. The device was implemented in a printer that demonstrated both the ability to apply a single multimaterial layer of at least 50 m thickness, and the ability to produce a 3D multimaterial component comprised of up to 200 layers and containing material change across all axes.

The final thesis determined the properties of alloys formed from mixtures of powders processed by the SLM method. Powders of alloy AlSi12 and EN AW 2618 were fused in the proportion 75 wt. % AlSi12 + 25 wt. % 2618, 50 wt. % AlSi12 + 50 wt. % 2618 and 25 wt. % AlSi12 + 75 wt. % 2618. Metallographic analysis, EBSD analysis and line EDS microanalysis were made on the samples. Tensile test at room temperature and hardness were carried out to determine the mechanical properties. Fractographic analysis was performed after tensile test.

The diploma thesis deals with the development of process parameters of SLM technology for the material IN718. The main goal is an experimental development of a set of parameters for the production of thin-walled parts with regard to material density, surface roughness and tightness. The essence of the development of parameters is an experimental explanation of the influence of laser power and scanning speed on the morphology of single tracks, which are used for the production of a thin wall. Together with walls of larger widths and volume samples, it is possible to create an intersection of parameters by which is possible to create components formed by a combination of thin-walled and volume geometry. The performed research created a material set, where the parameters of thin walls are used for the area of contours of bulk samples. We managed to produce a wall with an average width of 0.15 mm and roughness of 6 m, which meets the requirement for the tightness. The meander scanning pattern achieved a relative material density of 99.92%, which is more than with the supplier's parameters. Based on the acquired knowledge, it was possible to apply a set of parameters to components combining both geometries.