The focus of this literary study was additive manufacturing (AM) and the purpose was to find general trends for selected materials that have been additively manufactured and compare them to results from other reviews. The raw materials studied were stainless steels 316L, 17-4 PH, 15-5 PH and 420, as well as tool steel H13 and nickel alloys 625, 718 and Hastelloy X. The AM techniques studied were selective laser melting (SLM), electron beam melting (EBM) and binder jetting (BJG).  A total of 69 articles have been studied to fulfill the purpose above. The articles were used to write a summary of the techniques, compare them to each other and to conventional methods. They were also used to create a database to compile information on mechanical properties, microstructure and process parameters. Based on the database mechanical properties for SLM tend to be higher compared to EBM. This however varied somewhat depending on the processed material. Furthermore the yield and tensile strength obtained from the database for SLM seemed to be higher compared to the values in review articles for almost all materials. Unfortunately not enough values were found for BJG to compare it to SLM and EBM.AM seems to produce weaker, equal and superior products compared to conventional methods. However due to the limited nature of the project and the research found no conclusions can be drawn about any trends, how to achieve the different results or how parameters affect the finished product. To be able to say anything with more certainty more research has to be done. Not only in general concerning the AM techniques, but more studying of existing articles is needed. Finally a standardization on how to reference properties and process parameters is necessary. Currently it is very difficult to compare results or draw conclusions due to different designations, units and a lot of missing essential information.

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Binder jetting (BJT) is a powder bed based additive manufacturing (AM) process where the interaction of inkjetted droplets of a binder and particles in the powder bed create 3D geometries in a layerwise fashion. The fabricated green parts are usually thermally post-processed for densification and strengthening. BJT holds distinct advantages over other AM processes as it can fabricate parts with virtually any materials (metals, ceramics, and polymers) in a fast and cost-effective way, while achieving isotropic material properties in the parts. However, broad adoption of this process for production is still lagging, partially due to the lack of repeatable part quality, which largely stems from the limited understanding of the process physics, namely binder-powder (B/P) interaction. To bridge this knowledge gap, it is necessary to understand the implications of B/P interaction on process-structure-property relationships and discover ways to achieve new functionalities for enhanced properties. Thus, this research is broadly focused in establishing understanding in (i) binder-powder interaction and (ii) the impact of binder on part densification. Prior studies have focused on the effects of powder interaction with micro/meso-scale binder droplets, despite commercial BJT systems featuring picoliter-scale droplets. These studies have explored the effects of B/P interaction on printed primitive formation, but it's implication on final part properties have not been studied. In this work, the effects of particle size distribution and droplet size variation on final part properties are explored. Additionally, the effects of B/P interaction on accuracy and the resolution of the printed parts are investigated. Densification of parts is a primary focus of many BJT studies as it dictates the final part properties and is influenced by factors from both the printing process and post-processing treatments. Binder plays an integral role in the shaping of parts and maintaining part integrity until densification through sintering. Prior studies on the effects of binder content on densification are inclusive. In this work, a new approach termed as "shell printing" is introduced to vary the binder content in the parts. The process-structure-properties influenced by this approach are investigated. It was found that binder hinders densification, and through the selective variation of binder content throughout the part volume, this new approach is introduced as a means for enhancing part properties. Finally, the insights from the impact of binder on densification are leveraged to create an anti-counterfeiting tagging strategy by controlling the pores and grain microstructures inside a part. In this novel approach, binder concentration is controlled in a manner that the stochastically formed pores are clustered to create a designed domain that represents a secret 'tag' within the part volume. The created tagging domains, and the feature resolvability of this approach are investigated through metallographic characterization and non-destructively evaluated through micro-computed tomography. / Doctor of Philosophy / Binder jetting (BJT) is an additive manufacturing (AM) process to create 3D geometries from powder particles. Liquid droplets of binder from an inkjet printhead are jetted on a bed of packed powders, binding the particles. The as-printed parts, known as green parts, are generally fragile and require thermal post-processing (through sintering) for densification and strengthening. BJT holds distinct advantages over other AM processes as it can fabricate parts with virtually any powdered materials (metals, ceramics, and polymers) in a fast and cost-effective way. However, broad adoption of this process for production is still lagging, partially due to the lack of repeatable part quality, which largely stems from the limited understanding of the process physics, namely binder-powder (B/P) interaction. In this study the implications of B/P interaction on part quality (e.g., density, strength) and dimensional accuracy are studied. Additionally, the impact of binder on sintering densification is studied. Specifically, the effects of varying amount of binder on sintered part density, strength and internal pore and grain microstructures are empirically investigated. Finally, a novel anti-counterfeiting method for BJT printed parts is introduced based on the insights gained from the study of the impact of binder on densification. Through control over binder placement throughout the part, porous regions can be generated selectively throughout the part volume, which can be detected through x-ray computed tomography. Overall, an improved understanding of BJT processing conditions is achieved through this research, which can guide future designers to fabricate BJT parts with enhanced part properties and functionality.

Nowadays, manufacturing technologies become more and more aware of efficiency and sustainability. One of them is the so called 3D printing. While 3D printing is often linked to plastic, the truth is there are many other materials that are being tested which could have several improvements over plastics.One of these options is stone or concrete, which is more suitable the architecture and artistic fields. However, due to its nature, this new technology involves the use of new techniques when compared to the more commonly used 3D printers. This implies that it could interesting to know how much energy efficient these techniques are and how can they be improved in future revisions.This thesis is an attempt to disclose and analyze the different devices that make up one of these printers and with this information, build a model that accurately describes its behavior.For this purpose, the power is measured at many points and later it is analyzed and fitted to a predefined function. After the fitting has been done, an error is calculated to show how accurate the model is when compared to the original data.It was found that many of these devices produce power spikes due to its nonlinear behavior. This behavior is usually related to switching, and can avoided with different devices.Finally, some advice is given focused on future research and revisions, which could be helpful for safety, efficiency and quality. / Numera blir tillverkningstekniken alltmer medveten om effektivitet och hållbarhet. En av dem är den så kallade 3D­utskriften. Medan 3D­utskrift ofta är kopplad till plast, är verkligheten att det finns många andra material som testas, vilket kan ha flera förbättringar över plast.Ett av dessa alternativ är sten eller betong, vilket är mer lämpligt inom arkitektur och konstnärliga fält. På grund av sin natur inbegriper denna nya teknik användningen av nya tekniker jämfört med de vanligare 3D­skrivarna. Detta innebär att det kan vara intressant att veta hur mycket mer energieffektiva dessa tekniker är och hur de kan förbättras i framtida revisioner.Denna avhandling är ett försök att studera och analysera de olika enheter som utgör en av dessa skrivare och med denna information, bygga en modell som exakt beskriver dess beteende.För detta ändamål mäts effekten på många punkter och senare analyseras och anpassas den till en fördefinierad funktion. Efter anpassning har gjorts beräknas felet för att visa hur exakt modellen är jämfört med originaldata.Det visade sig att många av dessa enheter producerar spännings­spikar på grund av dess olinjära beteende. Detta beteende är vanligtvis relaterat till omkoppling och kan undvikas med olika enheter.Slutligen ges några råd om framtida forskning och revideringar, vilket kan vara till hjälp för säkerhet, effektivitet och kvalitet.

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This doctoral work was developed in the frame of bone tissue engineering, dealing with the fabrication of scaffolds for the regeneration of bones. At this purpose, calcium phosphates derived from natural sources are very interesting because they are more similar to the bone mineral and possess better bioactivity. Indeed, the bone mineral is different from synthetic hydroxyapatite as it is non-stoichiometric, nanosized, it presents a high degree of disorder and contains many additional ions and impurities such as CO32-, Mg2+, Sr2+, Na+, etc. These characteristics can be easily obtained by synthesizing hydroxyapatite from natural sources, such as corals, starfishes, seashells, animal bones, bird eggshells etc. The natural sources used in the present work are three types of biogenic calcium carbonate, i.e. calcium carbonate that is produced by living organisms in the form of aragonite or calcite. Among the different sources, three biogenic calcium carbonates were chosen: cuttlefish (Sepia Officinalis) bones, mussel (Mytilus Galloprovincialis) shells and chicken eggshells. Besides their abundance and availability, they were selected because of their different composition: aragonite in cuttlebones, calcite in eggshells and a mixture of aragonite and calcite in mussel shells. After the first chapter, which is a theoretical introduction, this thesis is divided into other five chapters. Chapter 2 contains a careful characterization of the three biogenic raw materials while Chapter 3 deals with the synthesis of hydroxyapatite starting from these natural sources. The process developed here takes place entirely at nearly room temperature, which allows the organic part of the biological materials to be preserved. This synthesis process is basically a wet mechanosynthesis followed by a mild heat treatment (up to 150°C). The study focuses on the influence of several process parameters on the synthesis efficiency: temperature, milling time, pH and raw material. The temperature used to dry the slurry after the wet ball-milling was found to be the most important parameter, the higher the temperature the faster the conversion of CaCO3 into hydroxyapatite. Moreover, aragonite was found to transform more easily into hydroxyapatite with respect to calcite, and also to follow a different reaction path. The synthesis process described in Chapter 3 allowed to produce different bio-derived powders that were found to be non-stoichiometric, nanosized, carbonated hydroxyapatites, containing also additional ions, especially Mg2+ in the eggshell-derived material and Sr2+ in the cuttlebone-derived one. These powders were then used as a starting point for the studies presented in the next three chapters. Chapter 4 shows a very preliminary evaluation of the interaction with human cells in vitro. First, the as-synthesized powders were consolidated by uniaxial pressing and sintering at temperatures between 900°C and 1100°C and their crystallographic composition was analyzed. Then, after having established the non-cytotoxicity of the sintered pellets, osteoblasts from human osteosarcoma cell line were seeded on the pellets and their behavior after 1, 3 and 5 days of culture was observed by confocal microscopy. In general, all materials promoted good cell adhesion and proliferation, especially the eggshell-derived one. At this point, the bio-derived materials were found to induce a good cellular response but, in order to foster the regeneration of bones, a scaffold must also contain a large amount of interconnected porosity. Among the numerous methods to fabricate porous structures, additive manufacturing is surely very attractive due many advantages, such as the possibility of customizing the shape based on tomography images from the patients, the fact that no mold is needed and the freedom of fully designing the porosity. Indeed, not only the size and the amount of porosity are important, but also the shape of the pores and their position and orientation have a deep effect on the interaction with the cells. Therefore, Chapter 5 and Chapter 6 deal with the fabrication of scaffolds by 3D printing, following two different approaches. In the study presented in Chapter 5, the powders synthesized from cuttlebones, mussel shells and eggshells were used in combination with a thermoplastic polymer (PCL, polycaprolactone) to obtain bioactive composites. Composite materials made of 85 wt% PCL and 15 wt% bio-derived hydroxyapatite were used to fabricate porous scaffolds by extrusion 3D printing. The biological in vitro tests showed that the composite scaffolds possess better bioactivity than the pure PCL ones, especially those containing mussel shell- and cuttlebone-derived powders, which promoted the best cell adhesion, proliferation and metabolic activity of human osteosarcoma cells after 7 days of culture. In addition, the elastic compressive modulus, which was found to be between 177-316 MPa, thus in the range of that of trabecular bone, was found to increase of about ∼50% with the addition of the bio-derived nanopowders. Finally, in Chapter 6, the cuttlebone-derived powder was used to fabricate porous bioceramic scaffolds by binder jetting 3D printing. Due to serious technical issues related to the printing of a nanosized powder, 10 wt% of bio-derived powder was mixed with a glass-ceramic powder with bigger particle size. Moreover, the organic part of the cuttlebone had to be previously eliminated by a heat treatment at 800°C. Thanks to the great freedom of design that is allowed by the binder jetting process, scaffolds with two different pore geometries were fabricated: with pores of uniform size and with a size-gradient. Indeed, natural bone possesses a gradient in porosity from the core to the surface, from porous trabecular bone to dense cortical bone. The sintered scaffolds showed a total porosity of ∼60% for the pure glass-ceramic and ∼70% for the glass-ceramic with 10 wt% of cuttlebone-derived nanoparticles, which most probably slowed down the densification by limiting the contact between the glassy particles. All the bioceramic scaffolds promoted good adhesion and proliferation of human bone marrow-derived mesenchymal stem cells in vitro, without any significant difference between the different samples. However, the scaffolds with the cuttlebone-derived powder and with gradient porosity showed the greatest decrease of metabolic activity after 10 days of culture, which could be accounted as a sign of differentiation of stem cells.

Additive manufacturing (AM) has experienced significant growth and development in recent years, owing to the ability to produce complex parts using a wide range of materials with relative ease. Powder bed-based metal AM has been at the forefront of this growth, even reaching the point where parts can be manufactured for end-use applications. Binder jetting (BJ) is one such technique where a liquid binder is selectively deposited on powder layers to create a green body which is then densified using sintering. The aim of this work was to use binder jetting to produce parts using Vanadis 4 Extra, a highly alloyed cold-work tool steel produced by Uddeholm AB for applications involving high demand on abrasive wear. Optimization of the densification parameters, which included debinding atmosphere, debinding temperature, sintering atmosphere, sintering temperature, and sintering time, to achieve full density parts was carried out as the first phase. It was found that the sintering atmosphere and time had the most significant impact on the density of the samples while the debinding atmosphere heavily impacted the C residue from the binder. In the second phase, samples were produced using the optimized parameters for mechanical analysis, which included analyses of the surface roughness and the wear resistance of the binder jetted samples against the conventionally produced samples. The surface roughness was in line with the data presented in literature for binder jetted samples. The binder jetted samples produced during this work exhibited better wear resistance than the conventionally produced samples, with the samples post-processed using hot isostatic pressing showing even better wear resistance. One possible explanation is the diffusion of N from the sintering atmosphere into the samples, leading to the conversion of carbides to carbonitrides and even nitrides. However, further investigation is needed in order to confirm this theory.