Master's thesis deals with the experimental determination of process parameters reaching densities >99 % for scandium modified aluminium alloy (Scalmalloy®) processed by SLM. The alloy achieves higher mechanical properties than the AlSi10Mg aluminum alloy commonly used. The theoretical part deals mainly with the results of Scalmalloy® alloys. Experimental bodies, testing methodology and evaluation method were designed on the basis of the theoretical parts,. The practical part is divided into four main stages: experimental determination of process parameters, a description of the effect of the parameters used on the relative density achieved, examination of the influence of process parameters on surface quality and mechanical testing. The mechanical properties were determined for the best parameters.

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Additive Manufacturing (AM), commonly known as 3D Printing, is a disruptive modern manufacturing process, in which parts are manufactured in a layer-wise fashion. Among the metal AM processes, Powder Bed Fusion (PBF) technology has opened up a design space that was not formerly accessible with conventional manufacturing processes. It is, now, possible to manufacture complex geometries, such as topology-optimized structures, lattice structures and intricate internal channels, with relative ease. PBF is comprised of Electron Beam Melting (EBM) and Selective Laser Melting (SLM) processes. Though AM processes offer several advantages, the suitability of these processes to replace conventional manufacturing processes must be studied in detail; for instance, the capability to produce components of consistent quality. Therefore, understanding the relationship between the AM process together with the post treatment used and the resulting microstructure and its influence on the mechanical properties is crucial, to enable manufacturing of high-performance components. In this regard, for AM built Alloy 718, only a limited amount of work has been performed compared to conventional processes such as casting and forging. The aim of this work, therefore, is to understand how the fatigue properties of EBM and SLM built Alloy 718, subjected to different thermal post-treatments, is affected by the microstructure. In addition, the effect of as-built surface roughness is also studied. Defects can have a detrimental effect on fatigue life. Numerous factors such as the defect type, size, shape, location, distribution and nature determine the effect of defects on properties. Hot Isostatic Pressing (HIP) improves fatigue life as it leads to closure of most defects. Presence of oxides in the defects, however, hinders complete closure by HIP. Machining the as-built surface improves fatiguelife; however, for EBM manufactured material, the extent of improvement is dependent on the amount of material removed. The as-built surface roughness, which has numerous crack initiation sites, leads to lower scatter in fatigue life. In both SLM and EBM manufactured material, fatigue crack propagation is transgranular. Crack propagation is affected by grain size and texture of the material.

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Laser-based additive manufacturing offers a high degree of thermokinetic flexibility that has implications on the structure and properties of the fabricated component. However, to exploit the flexibility of this process, it is imperative to understand the process-inherent thermokinetic evolution and its effect on the material characteristics. In view of this, the present work establishes a fundamental understanding of the spatiotemporal variation of thermokinetics during the fabrication of the non-ferrous alloys using the laser powder bed fusion process. Due to existing limitations of experimental techniques to probe such thermokinetics, a finite element method-based computational model is developed to predict the thermokinetic variations during the process. With the computational approach coupled with experimental techniques, the current work presents the solidification behavior influenced by spatially varying thermokinetics. In addition, it uniquely predicts the process-inherent multi-track multi-layer evolution of thermal cycles as well as thermal stress cycles and identifies their influence on the post-solidification microstructural evolution involving solid-state phase transformation. Lastly, the response of the material with a unique microstructure is recorded under various conditions (static and dynamic), which is again compared with the same set properties obtained for the same material processed via conventional routes.

Production by Additive Manufacturing creates opportunities to make customized products in small batches with less material than in traditional manufacturing. It is more sustainable and suitable for niche products, but entails new production demands to ensure quality. The goal of this study is to define the most crucial parameters when creating Additive Manufactured products in metal and suggest tools for quality improvement. This is done by analysing earlier studies and evaluating the standard production procedures for manufacturing by Selective Laser Melting. The results from this study stated that porosity and insufficiencies in shape are the most common factors leading to deviation in quality. To avoid it, the most crucial parameters to consider are; The laser freeform fabrication-system related parameters, hatch distance, laser power, layer thickness, fscanning pattern, scan speed and flowability of the powder. Concluded is also that crucial parameters within additive manufacturing are very dependent on the definition of quality for a certain product and can therefore vary. By continuous collection and analysis of data, the task of improving quality will be simplified. / Produktion genom Additiv Tillverkning möjliggör tillverkande av skräddarsydda produkter i små batcher och med mindre material än vid traditionell tillverkning. Det är ett mer hållbart tillverkningssätt och mer passande för nischprodukter, men innebär nya produktionskrav för att säkerhetsställa bra kvalitet. Målet med denna studie är att definiera de viktigaste parametrarna vid Additiv Tillverkning av produkter i metall och föreslå verktyg för att förbättra dem. Detta genom analys av tidigare studier och utvärdering av klassiska produktionsrutiner för Selective Laser Melting. Resultaten från denna studie visar att porositet och formfel är de vanligaste faktorerna som leder till bristande kvalitet. För att undvika detta är de viktigaste parametrarna att ta i beaktande; parametrar kopplade till "laser freeform fabrication"-system, distans mellan laserstrålar, kraft på lasern, lagertjocklek, skanningsmönster, fart på skanningen och flytbarhet på pulvret. Slutsatsen pekar även på att avgörande parametrar inom Additiv Tillverkning beror på definitionen av kvalitet för en speciell produkt och kan därför variera. Genom kontinuerlig insamling och analys av data kommer förbättringen av kvalitet förenklas markant.

Metallic biomaterials have an essential portion of uses in biomedical applications. Their properties can be tuned by many factors resulting in their process tuneability. Among metallic biomaterials for biomedical and specifically orthopedic applications, titanium and its alloys exhibit the most suitable characteristics as compared to stainless steels and Co-Cr alloys because of their high biocompatibility, specific strength (strength to density ratio), and corrosion resistance. According to their phase constitution, Ti-alloys are classified into three main groups, namely alpha, beta, and alpha+beta alloys. Depending on the degree of alloying and thermomechanical processing path, it is possible to tune the balance of α and β phases, which permits to tailor properties like strength, toughness, and fatigue resistance. (alpha+beta) Ti alloys, especially Ti-6Al-4V, are widely used alloys in biomedical applications; however, they have some drawbacks like the presence of toxic elements i.e., V and relatively high elastic modulus to that of bones. In view of the lower elastic modulus of body center cubic beta phase (50GPa<100GPa) compared to the alpha+beta, as well as due to their good mechanical properties, excellent corrosion resistance, and biocompatibility, beta-Ti alloys have been recently proposed as a valid alternative to alpha+beta ones. The growing interest in additive manufacturing (AM) techniques opens new and very interesting perspectives to the production of biomedical prosthetic implants. AM will prospectively allow implant customization to the patient and produce it on demand, with large savings on times and costs. Moreover, AM is gaining increasing interest due to the possibility of producing orthopedic implants with functionally graded open-cell porous metals. The main advantages of porous materials are the reduction of the elastic modulus mismatch between bone and implant alloy reducing the stress shielding effect and improving implant morphology providing biological anchorage for tissue in-growth. In this scenario, the first goal of the present PhD thesis work was to identify a high-performance β-Ti alloy formulation suitable to Laser-Powder Bed Fusion (L-PBF) additive manufacturing. In particular, it explores the potential use of a β-metastable Ti alloy, namely Ti-15Mo-2.7Nb-3Al-0.2Si (Beta Ti21S, 21 wt.% of alloying additions, including Silicon) for biomedical applications. Through microstructural, mechanical, and cytotoxicity analyses, it could be shown that this alloy grade exhibits i) an unprecedented ultra-low elastic modulus, ii) improved cytocompatibility due to the lack of Vanadium, and iii) no martensitic transformation responsible for hard and brittle solidification structures. A second goal was to assess the manufacturability of metamaterials made of β-Ti21S via L-PBF. For this purpose, cubic cellular lattice structures of different unit cell sizes (and therefore different strut thickness) have been fabricated and characterized through microstructural analysis using different techniques, and computed tomography combined with linear elastic finite element simulations to identify the minimum cell size that can be printed with adequate dimensional and geometrical accuracy. Samples of the selected unit cell size were also tested to determine their static and fatigue properties. The main results show that i) the suitable manufacturing quality is obtained for strut thickness above 0.5 mm, ii) the mechanical tests place the present cellular structures among the best stretching dominated cellular lattice materials investigated to date in the literature, and iii) the fatigue tests showed a normalized fatigue strength at 107 cycles of close to 0.8, similar to cubic lattices made of Ti-6Al-4V, and higher than most cellular structures in the literature. In the last part of the thesis, a more complex octet truss structure was fabricated in the manufacturable cell size, and its mechanical properties were investigated. The octet truss topology can be beneficial both in terms of mechanical properties and biocompatibility by providing the different types of porosity suitable for bone in-growth.