<p>Powder bed fusion (PBF) process is a metal additive manufacturing process, which can build parts with any complexity from a wide range of metallic materials. Research in the PBF process predominantly focuses on the impact of a few parameters on the ultimate properties of the printed part. The lack of a systematic approach to optimizing the process parameters for a better performance of given material results in a sub-optimal process limiting the potentialof the application. This process needs a comprehensive study of all the influential parameters and their impact on the mechanical and microstructural properties of a fabricated part. Furthermore, there is a need to develop a quantitative system for mapping the material properties and process parameters with the ultimate quality of the fabricated part to achieve improvement in the manufacturing cycle as well as the quality of the final part produced by the PBF process. To address the aforementioned challenges, this research proposes a framework to optimize the process for 316L stainless steel material. This framework characterizes the influence of process parameters on the microstructure and mechanical properties of the fabricated part using a series of experiments. These experiments study the significance of process parameters and their variance as well as study the microstructure and mechanical properties of fabricated parts by conducting tensile, impact, hardness, surface roughness, and densification tests, and ultimately obtain the optimum range of parameters. This would result in a more complete understanding of the correlation between process parameters and part quality. Furthermore, the data acquired from the experimentsare employed to develop an intelligent parameter suggestion multi-layer feedforward (FF) backpropagation (BP) artificial neural network (ANN). This network estimates the fabrication time and suggests the parameter setting accordingly to the user/manufacturers desired characteristics of the end-product. Further, research is in progress to evaluate the framework for assemblies and complex part designs and incorporate the results in the network for achieving process repeatability and consistency.</p><br>

Additive manufacturing (AM) is the name given to the technology of building 3D parts by adding layer-by-layer of materials, including metals, plastics, concrete, etc. Of the different types of AM techniques, electron beam melting (EBM), as a powder bed fusion technology, has been used in this study. EBM is used to build parts by melting metallic powders by using a highly intense electron beam as the energy source. Compared to a conventional process, EBM offers enhanced efficiency for the production of customized and specific parts in aerospace, space, and medical fields. In addition, the EBM process is used to produce complex parts for which other technologies would be either expensive or difficult to apply. This thesis has been divided into three sections, starting from a wider window and proceeding to a smaller one. The first section reveals how the position-related parameters (distance between samples, height from build plate, and sample location on build plate) can affect the microstructural characteristics. It has been found that the gap between the samples and the height from the build plate can have significant effects on the defect content and niobium-rich phase fraction. In the second section, through a deeper investigation, the behavior of Alloy 718 during the EBM process as a function of different geometry-related parameters is examined by building single tracks adjacent to each other (track-by-track) andsingle-wall samples (single tracks on top of each other). In this section, the main focus is to understand the effect of successive thermal cycling on microstructural evolution. In the final section, the correlations between the main machine-related parameters (scanning speed, beam current, and focus offset) and the geometrical (melt pool width, track height, re-melted depth, and contact angle) and microstructural (grain structure, niobium-rich phase fraction, and primary dendrite arm spacing) characteristics of a single track of Alloy 718 have been investigated. It has been found that the most influential machine-related parameters are scanning speed and beam current, which have significant effects on the geometry and the microstructure of the single-melted tracks.

Au cours du procédé de fusion laser sur lit de poudre, la température atteinte dans une zone locale est susceptible de générer des gradients thermiques importants. Ces gradients conduisent à leur tour à l'apparition de contraintes résiduelles qui ont un effet sur les caractéristiques mécaniques de la pièce, provoquent des déformations, ainsi que des micro et macro fissures. Dans ce contexte, les trajectoires de lasage jouent un rôle fondamental sur le niveau et la distribution de la température au cours de la fabrication. Il est ainsi nécessaire de valider la génération des trajectoires au regard du comportement thermique induit par ce procédé.Cette thèse propose d'exploiter une méthode analytique pour développer un modèle qui permette d'analyser d'une manière rapide et efficace le comportement thermique dans la pièce lors de la fabrication. En effet, à partir d'une trajectoire de lasage donnée, d'un ensemble de paramètres liés au matériau de la pièce à fabriquer et de paramètres liés au procédé, l'outil développé effectue une simulation de la température en chaque point de la pièce, au cours de temps et de manière rapide, comparée aux autres logiciels de simulation thermique. En effet, afin de réduire le temps de calcul et l'espace mémoire utilisé pour une telle simulation, un ensemble de techniques d'optimisation a été mis en place.Le modèle proposé a été validé dans le cas de l'alliage Ti6Al4V par comparaison avec une simulation thermique par éléments finis obtenue par un logiciel industriel. Ensuite, les résultats de ce modèle sont confrontés aux résultats expérimentaux. Une fois le modèle validé, il a été mis en œuvre pour analyser des trajectoires couramment utilisées dans la littérature et dans l'industrie.Afin de réduire les gradients thermiques et améliorer la qualité des pièces, la solution proposée consiste à contrôler la température et la taille du bain de fusion. Pour se faire, le modèle thermique développé a été exploité pour moduler les paramètres du procédé au cours de la fabrication d'une part et pour développer une stratégie de lasage à pas adaptatif d'autre part. / During manufacturing by Laser Powder Bed Fusion (LPBF), the achieved temperatures in local areas could generate significant thermal gradients. These gradients lead to the apparition of residual stresses which affect the mechanical characteristics of the part and may cause deformation, as well as micro and macro cracks. In this context, scanning paths play a fundamental role on temperature level and distribution during manufacturing. For that reason, it is necessary to validate the generation of trajectories considering the thermal behaviour induced by this process.The purpose of this PhD thesis is to use an analytical method in order to develop a model that allows a fast and efficient analysis of thermal behaviour, during part manufacturing. Indeed, with a given scanning path, material properties and process parameters, the developed tool performs a temperature simulation at each point of the part, over time and in a fast way, compared to other thermal simulation software. In order to reduce computation time and memory storage used for such a simulation, a set of optimization techniques has been proposed.The developed model has been validated in the case of the Ti6Al4V alloy through a comparison with a finite element thermal simulation obtained by industrial software. Then, the results of this model were compared to experimental results. Once validated, it has been implemented to analyze trajectories commonly used in the literature and industry.In order to reduce thermal gradients and improve part quality, the proposed solution consists in controlling the temperature and size of melt pool. For this purpose, the developed thermal model has been used to modulate the process parameters during manufacturing on the one hand and to develop an adaptive scanning strategy on the other hand.

No description available.

<p>This dissertation presents research work related to laser micro sintering, laser micro machining and laser-induced plasma. Firstly, we present extensive experimental studies of double-pulse laser micro sintering (DP-LMS), which typically utilizes the high pressure generated by laser-induced plasma over the powder bed surface to promote molten flow and enhance densification. Chapter 2 shows a single-track experimental study of the DP-LMS process using cobalt powder. The related fundamental mechanisms and effects of different laser parameters on the sintering results are analyzed with the help of <em>in-situ</em> time-resolved temperature measurements. Chapter 3 shows a multi-track experimental study of the DP-LMS process using iron powder. The sintered materials are characterized via the top surface porosity, elemental composition, grain microstructure, nanohardness and metal phase. Three strategic guidelines for laser parameter selection are summarized in the end. Chapter 4 shows time-resolved imaging and OES measurements for plasma induced during DP-LMS. The plasma temperature and free electron number density are deduced by its optical emission spectra (OES). These three chapters have clearly demonstrated DP-LMS can produce much more continuous and densified materials than LMS only using the sintering or pressing laser pulses.</p> <p><br></p> <p>Then, we present laser micro grooving of silicon carbide (SiC) in Chapter 5 by ultrasound-assisted water-confined laser micromachining (UWLM), in comparison with laser machining in water without ultrasound and laser machining in air. UWLM applies <em>in-situ</em> ultrasound to the water-immersed workpiece surface to improve the machining quality and/or productivity. Time-resolved water pressure measurements are carried out to help analyze relevant mechanisms. It has been demonstrated UWLM can be a competitive approach to produce high-quality micro grooves on SiC. The crack problem appears to be effectively solved using a high pulse repetition rate.</p> <p><br></p> <p>Finally, we report a double-front phenomenon for plasma induced by high-intensity nanosecond laser ablation of aluminum in Chapter 6. An additional plasma front is observed via an intensified CCD (ICCD) camera, which propagates very fast at the beginning but stops propagating soon after the laser pulse mostly ends. Its formation could be caused by the inverse bremsstrahlung absorption of laser energy by the ionized ambient gas. Three possible mechanisms on how the ambient gas breakdown is initiated are proposed. </p>

Electron beam powder bed fusion (PBF-EB) is an additivemanufacturing (AM) method based on layer-by-layer melting of apowder bed. The technology is industrialized in certain applicationsbut still considered as immature and is not as widely used as laserbeam-based systems (PBF-LB). PBF-EB can offer several benefits overPBF-LB such as process cleanliness, thermal efficiency, fast beam speed,higher power and energy transfer, low residual stresses in built partsand a good signal environment for process monitoring. This can beadded on top of the general benefits of AM such as geometricalfreedom, manufacturing efficiency, easy design revisions, short leadtimes and so on. This suggests that PBF-EB holds potential as atechnology for the sustainable production of materials andcomponents. This thesis investigates how PBF-EB can be furtherdeveloped to create new and unique materials features. This isachieved by introducing innovative methods for material processingand by further developing the PBF-EB process itself. The thesisintroduces a charge-free heating method for PBF-EB and the resultssuggest an enhanced processability of difficult-to-process materialsand powders. A method for building multi-materials in PBF-EB isintroduced and demonstrated by the manufacturing of direct andlamellar transitions between different alloys. Methods for processmonitoring and powder bed resistivity evaluation are proposed andxiidemonstrated. It is concluded that the results presented in this thesisenabled new PBF-EB processing modes, increased the knowledge ofthe process, and introduced a new material group by demonstratingthat ceramics can be processed at high temperatures (~1600C). / <p>Vid tidpunkten för framläggningen av avhandlingen var följande delarbeten opublicerade: delarbete 2 och delarbete 4 (inskickat).</p><p>At the time of the defence the following papers were unpublished: paper 2 and paper 4 (submitted).</p>

Traditional methods for increasing the energy absorption of a structure involve using a stronger material or increasing the volume of the structure, resulting in a higher cost or additional weight. Additive manufacturing (AM) can be used to maximize the energy absorption of materials with the ability to create complex geometries such as cellular structures. Previous work has shown that the energy absorption of additively manufactured parts can be improved through functionally graded cellular structures; however, this strategy has not been applied to ultra-high strength steel materials. This work characterizes the effect of multiple functional-grading strategies (e.g. uniform, rod-graded, size-graded) on the energy absorption to weight ratio of laser powder bed fusion (L-PBF) produced M300 maraging steel lattice structures. Each structure is designed with the same average relative density to analyze the structures on an equal mass basis, to evaluate manufacturability, mechanical response, and compare experimental results with numerical simulation.

This thesis focuses on the topic of PBF-LB applied to titanium alloys. Of allalloys, an α + β is chosen, named Ti-6Al-4V. The selection of this particular alloy is driven by its current widespread use in many industrial applications where high strength coupled with low density are both desirable properties. For the last 50 years, parts made with this alloy have been cast or forged and then machined to achieve the final geometry. There is now an opportunity totransform this process chain by additive manufacturing, hence reducing material waste and achieving near net shape from powder feedstock. The process is summarised as follows: a laser selectively melts areas on a build plate where powder is pre-placed. Then a successive powder layer is spread and the process is repeated until completion. Upon removal of the part from the build plate, loose powder in the chamber is collected and recycled whenever possible. The design freedom provided by powder bed fusion methods enables production of intricate geometries and added functionality, despite the need for post-build consolidation and/or microstructural adjustments. Today’s fine and narrow powder cuts (e.g., 15-50μm) are designed to be coupled with low layer thicknesses (i.e., 30μm) to achieve smooth surfaces and high resolutions of small features e.g., internal cooling channels. However, costs associated with production of fine and narrow powder cuts are substantial as refinement of batches requires multiple sieving steps. In addition, resulting building times are considerably long (i.e., days), therefore a beneficial alternative could be that of exploring higher layer thicknesses together with wider and coarser powder cuts. The main idea of this work is to investigate the effects of employing a powder with a wider size distribution 15-90μm. The aim is to reduce the sievingrequired and consequently decrease the costs of developing and building parts made by PBF-LB. An extensive microstructural investigation is conducted on single tracks and cubes built with 27 different process parameter combinations, which also attempts to establish correlations between characteristics of tracks and responses measured in cubes. As a second step, the amount of residual porosity of asbuilt cubes is chosen as the discriminant for further mechanical testing of sub and super-β transus high-pressure heat treated material. / Den här avhandlingen fokuserar på additiv tillverkning av titanlegeringar med laser pulverbädd metoden. Den legering som främst är i fokus är Ti-6Al-4Vsom är en α+β legering. Anledningen till valet av denna titanlegering är att det är den vanligast förekommande titanlegeringen och att den används i ett antal olika industriella tillämpningar där hög styrka i kombination med låg vikt är önskvärda egenskaper. Under de senaste 50 åren har komponenter utav denna legering tillverkats med gjutning eller smide, följt av bearbetning till slutlig geometri. Med hjälp av additiv tillverkning finns nu en möjlighet att förändra tillverkningskedjan i vilket minskat materialspill och en mer nära-slutgeometri kan erhållas direkt genom användning av metallpulver som utgångsmaterial. Processen kan summeras enligt följande: en laser smälter ett förbestämt område på en byggplatta som täckts mer pulver. Därefter adderas ytterligare ett lager med metallpulver ovanpå, på vilket samma process sker igen, och igen osv, tills hela detaljen är färdigtillverkad. När detaljen ska tas loss ifrån byggplattan samlas det kvarvarande icke-smälta pulvret upp och återanvänds i så stor utsträckning som möjligt. Frihetsgraderna vid design i processen möjliggör tillverkning av komplexa geometrier och adderade funktionaliteter, även fast efterbehandling och/eller justeringar av mikrostrukturen kan behövas. Dagens smala pulverstorleksfördelning (tex 15-50μm) är avsedd att ge tunna lagertjocklekar (tex 30μm) för att åstadkomma en fin yta och hög upplösning av små geometrier, såsom exempelvis interna kylkanaler. Men kostnaderna som det innebär att framställa och sortera ut fina och smala kornstorleksfördelningarär avsevärd eftersom det innebär flera steg med silning. Vidare leder de tunnalagertjocklekarna till långa byggtider (typiskt dagar). Ett alternativ, som därför vore fördelaktigt, är att undersöka möjligheten med att bygga tjockare lager med en bredare och större pulverstorleksfördelning. Huvudfokuset i detta arbete fokuserar på att undersöka effekterna av att använda en bredare pulverpartikelstorleksfördelning 15-90μm, med syfte at minska silningsbehovet och därmed reducera kostnaden för att utveckla och tillverka detaljer med laser pulverbädd additiv tillverkning. En omfattande mikrostrukturundersökning har gjorts på enkelsträngar och kuber byggda med 27 olika processparameter-kombinationer, vilket samtidigt försöker identifiera korrelationer mellan enkelsträngarnas karaktäristik med resultaten uppmätta hos kuberna. I ett nästa steg har material, som tillverkats med processparametrar som renderade i minst/mest porer hos kuberna, mekaniskt provats efter att det högtrycksvärmebehandlats över- respektive under β-transus. / <p>Paper A is not included due to the copyright.</p><p>Paper B and C are to be submitted.</p>

When skeletal fractures are too extensive for fixation with plates and screws, autografts are the most used technique for treating this. Within the biomedical field the interest in biodegradable implants made from additive manufacturing have increased. Magnesium alloys has also gained interest because of its favorable mechanical properties.. The objective of this project is to report on new knowledge, possibilities and limitations of powder bed fusion-laser beam (PBF-LB) printed magnesium-based alloys for biomedical applications, specifically the mechanical properties of WE43. Before the practical work was carried through, a gathering of literature from scientific papers was put together to a background with information regarding Magnesium, additive manufacturing, microscopic observation methods and mechanical testing.  The practical elements were divided into 4 different categories: printing, sample preparation for observation and testing, microscopic observation, and mechanical testing. All the collected data was observed and discussed, and lastly compiled in to a result with microscopic images, stress-strain curves and data tables. It was discovered that the mechanical properties differed between the two build orientations. The specimen most appropriate for load bearing implants was the horizontal build direction. The differences between 67° and 90° scan strategy were that the 90° scan strategy with horizontal build orientation showed the lowest Young´s modulus which is favorable, whereas the 67° scan strategy showed higher tensile strength and ductility which also is favorable. Thereby no conclusion could be drawn on whether a 67° or 90° scan strategy was preferable. The conclusion was made that a horizontal build orientation had the most optimal mechanical properties, and that more research needs to be conducted on this topic before it can be used for biomedical applications.

Die Implementierung von Laser Powder Bed Fusion bei Aluminiumoxidkeramiken ist aufgrund einer geringen Temperaturwechselbeständigkeit, Bauteilverdichtung, Pulverfließfähigkeit und Lichtabsorption eine große Herausforderung. In dieser Arbeit wurden diese Prob-leme mit unterschiedlichen Ansätzen adressiert. Sprühgetrocknete Aluminiumoxid Granulate wurde zur Verbesserung der Laserabsorption (über 80 % Verbesserung) mit farbigen Nano-Oxidpartikeln dotiert. Es wurden verschiedene Partikelpackungstheorien und Pulverbehand-lungen getestet, um die Pulverbettdichte und damit die Dichte des endgültigen Bauteils (Dichten bis zu 98,6 %) zu erhöhen. Die Pulverqualität wurde durch Schütt und Rütteldichte, Feuchtigkeitsgehalt, Partikelgrößenverteilung, Hausner-Verhältnis, Lawinenwinkel und Oberflächenfraktal charakterisiert. Des Weiteren wurde der Zusatz geeigneter Stoffe zur Verringerung der Rissbildung durch thermische Spannungen getestet. Die In-situ-Bildung von Phasen mit geringer und negativer Wärmeausdehnung reduzierte die Rissbildung in den lasergefertigten Oxidkeramiken stark.:1 Introduction 1 1.1 Motivation 1 1.2 State of the art . 2 1.3 Aim of the project 2 2 Literature review 5 2.1 Additive manufacturing by laser powder bed fusion 5 2.1.1 Classification and process description 5 2.1.2 Advantages against other AM processes 9 2.1.3 Challenges of laser powder bed fusion 12 2.1.4 State of the art of laser powder bed fusion of aluminum oxide based ceramics 13 2.1.4.1 Powder bed preparation and impact on the process 13 2.1.4.2 Critical rating of the powder bed preparation techniques 17 2.1.4.3 Processing methods and properties 19 2.1.4.4 Part properties 26 2.2 Theoretical and experimental considerations for powder bed preparation 35 2.2.1 Spray granulation 35 2.2.2 Particle packing theories 39 2.3 Mechanisms for particle dispersing 41 2.3.1 DLVO-theory 41 2.3.2 Surface charge and electrical double layer 43 2.4 Conceptualization of new ideas for laser powder bed fusion of aluminum oxide 45 2.4.1 Densification, powder flowability and absorption issue 46 2.4.2 Reduction of crack formation 47 3 Doped spray-dried granules to solve densification and absorption issue in laser powder bed fusion of alumina 55 3.1 Dispersing of aluminum oxide, iron oxide and manganese oxide 55 3.1.1 Experimental 55 3.1.2 Particle characterization 57 3.1.3 Saturation amount evaluation of dispersant 59 3.1.4 Particle size distributions after dispersing 62 3.1.4.1 Particle size distributions of alumina powders 62 3.1.4.2 Particle size distribution of dopant 67 3.2 Packing density increase of spray-dried granules 76 3.2.1 Experimental 77 3.2.2 Influence of solid load and particle ratio on granules 83 3.2.3 Influence of dopant shape and multimodal distributions on granules 84 3.2.4 Evolution of pH-value during slurry preparation and slurry stability after mixing of all components 85 3.2.5 Influence of slurry viscosity on yield of granules 88 3.2.6 Addition of coarse alumina to spray-dried granules 89 3.2.7 Application of Andreasen model on mixtures of ceramic particles with spray-dried granules 94 3.2.8 Thermal pre-treatment of granules 98 3.2.9 Influence of surface tension of slurry on granule size and density 110 3.3 Investigation of laser manufactured parts 114 3.3.1 Experimental 115 3.3.2 Influence of different iron oxide dopants and multimodal particle distributions within granules 118 3.3.3 Influence of coarse alumina variation 121 3.3.4 Influence of thermal pre-treatment of powders 127 3.3.5 Grain structure of laser additive manufactured parts 135 3.3.6 Thermal expansion of laser processed parts 137 3.3.7 Influence of thermal pre-treatment and laser processing on manganese amount within granules and laser additive manufactured parts 138 4 Additives to reduce crack formation in selective laser melting and sintering of alumina 143 4.1 Experimental 144 4.2 Additives to reduce thermal stresses 150 4.2.1 Selective laser melting with mullite additives 150 4.2.2 Amorphous alumina formation by rare earth oxide doping 160 4.2.3 Formation of aluminum titanate by use of reduced titanium oxide 169 4.2.3.1 Dispersing of titanium oxide nanoparticles in water 170 4.2.3.2 Thermal treatment of Al2O3/TiO2 granules under argon/hydrogen atmosphere 172 4.2.3.3 Laser manufacturing of parts 178 4.2.4 In-situ formation of negative thermal expansion materials 187 4.2.4.1 Dispersing of zirconia and tungsten oxide nanoparticles 187 4.2.4.2 Influence of spray drying process parameters 191 4.2.4.3 Preparation of final powders for laser powder bed fusion 197 4.2.4.4 Laser manufacturing of layers and parts 200 4.3 Mechanical properties of laser processed parts 205 5 Flowability and inner structure of customized granules 209 5.1 Experimental 209 5.2 Comparison of flowability in terms of Hausner ratio, Avalanche angle and surface fractal measurements 211 5.2.1 Influence of coarse alumina AA18 variation 211 5.2.2 Influence of thermal pre-treatment of powders 213 5.2.3 Influence of dopant content within granules 216 5.2.4 Flowability of zirconia-tungsten oxide granules and alumina granules with mullite or rare earth oxide addition 219 5.2.5 Flowability of titanium oxide doped alumina powders 221 5.3 Cross sections of customized granules to image inner structure 224 6 Summary, conclusions and outlook 233 6.1 Summary and conclusions 233 6.2 Outlook 241 References 245 List of Figures 260 List of Tables 269 / The implementation of laser powder bed fusion of aluminum oxide ceramics is challenging due to a low thermal shock resistance, part densification, powder flowability and light absorptance. In this work, these challenges have been addressed by different approaches. Spray-dried alumina granules were doped with colored oxide nanoparticles to improve the laser absorption (improvement by over 80%). Different particle packing theories and powder treatments were tested to increase the powder bed density and therefore, the final part density (densities up to 98.6%). The powder quality was characterized by apparent and tapped density, moisture content, particle size distribution, Hausner ratio, avalanche angle and sur-face fractal. Furthermore, the addition of suitable was tested to reduce crack formation caused by thermal stresses. The in-situ formation of low and negative thermal expansion phases strongly reduced the crack formation in the laser manufactured oxide ceramic parts.:1 Introduction 1 1.1 Motivation 1 1.2 State of the art . 2 1.3 Aim of the project 2 2 Literature review 5 2.1 Additive manufacturing by laser powder bed fusion 5 2.1.1 Classification and process description 5 2.1.2 Advantages against other AM processes 9 2.1.3 Challenges of laser powder bed fusion 12 2.1.4 State of the art of laser powder bed fusion of aluminum oxide based ceramics 13 2.1.4.1 Powder bed preparation and impact on the process 13 2.1.4.2 Critical rating of the powder bed preparation techniques 17 2.1.4.3 Processing methods and properties 19 2.1.4.4 Part properties 26 2.2 Theoretical and experimental considerations for powder bed preparation 35 2.2.1 Spray granulation 35 2.2.2 Particle packing theories 39 2.3 Mechanisms for particle dispersing 41 2.3.1 DLVO-theory 41 2.3.2 Surface charge and electrical double layer 43 2.4 Conceptualization of new ideas for laser powder bed fusion of aluminum oxide 45 2.4.1 Densification, powder flowability and absorption issue 46 2.4.2 Reduction of crack formation 47 3 Doped spray-dried granules to solve densification and absorption issue in laser powder bed fusion of alumina 55 3.1 Dispersing of aluminum oxide, iron oxide and manganese oxide 55 3.1.1 Experimental 55 3.1.2 Particle characterization 57 3.1.3 Saturation amount evaluation of dispersant 59 3.1.4 Particle size distributions after dispersing 62 3.1.4.1 Particle size distributions of alumina powders 62 3.1.4.2 Particle size distribution of dopant 67 3.2 Packing density increase of spray-dried granules 76 3.2.1 Experimental 77 3.2.2 Influence of solid load and particle ratio on granules 83 3.2.3 Influence of dopant shape and multimodal distributions on granules 84 3.2.4 Evolution of pH-value during slurry preparation and slurry stability after mixing of all components 85 3.2.5 Influence of slurry viscosity on yield of granules 88 3.2.6 Addition of coarse alumina to spray-dried granules 89 3.2.7 Application of Andreasen model on mixtures of ceramic particles with spray-dried granules 94 3.2.8 Thermal pre-treatment of granules 98 3.2.9 Influence of surface tension of slurry on granule size and density 110 3.3 Investigation of laser manufactured parts 114 3.3.1 Experimental 115 3.3.2 Influence of different iron oxide dopants and multimodal particle distributions within granules 118 3.3.3 Influence of coarse alumina variation 121 3.3.4 Influence of thermal pre-treatment of powders 127 3.3.5 Grain structure of laser additive manufactured parts 135 3.3.6 Thermal expansion of laser processed parts 137 3.3.7 Influence of thermal pre-treatment and laser processing on manganese amount within granules and laser additive manufactured parts 138 4 Additives to reduce crack formation in selective laser melting and sintering of alumina 143 4.1 Experimental 144 4.2 Additives to reduce thermal stresses 150 4.2.1 Selective laser melting with mullite additives 150 4.2.2 Amorphous alumina formation by rare earth oxide doping 160 4.2.3 Formation of aluminum titanate by use of reduced titanium oxide 169 4.2.3.1 Dispersing of titanium oxide nanoparticles in water 170 4.2.3.2 Thermal treatment of Al2O3/TiO2 granules under argon/hydrogen atmosphere 172 4.2.3.3 Laser manufacturing of parts 178 4.2.4 In-situ formation of negative thermal expansion materials 187 4.2.4.1 Dispersing of zirconia and tungsten oxide nanoparticles 187 4.2.4.2 Influence of spray drying process parameters 191 4.2.4.3 Preparation of final powders for laser powder bed fusion 197 4.2.4.4 Laser manufacturing of layers and parts 200 4.3 Mechanical properties of laser processed parts 205 5 Flowability and inner structure of customized granules 209 5.1 Experimental 209 5.2 Comparison of flowability in terms of Hausner ratio, Avalanche angle and surface fractal measurements 211 5.2.1 Influence of coarse alumina AA18 variation 211 5.2.2 Influence of thermal pre-treatment of powders 213 5.2.3 Influence of dopant content within granules 216 5.2.4 Flowability of zirconia-tungsten oxide granules and alumina granules with mullite or rare earth oxide addition 219 5.2.5 Flowability of titanium oxide doped alumina powders 221 5.3 Cross sections of customized granules to image inner structure 224 6 Summary, conclusions and outlook 233 6.1 Summary and conclusions 233 6.2 Outlook 241 References 245 List of Figures 260 List of Tables 269