Introduction: Production systems go through changes over time and there are different factors driving the change. Metal Additive manufacturing (AM) could be a factor with industries that already havetaken interest in the manufacturing technique. Qualification and standards of manufacturing guide consistent product quality and could face challenges when implementing AM. However,most publications about metal AM are currently posted from a material point of view. This requires more publications with comprehensive overviews of metal AM and dive deeper into metal AMs industry applications, limitations and challenges. Purpose: The purpose of this thesis is to identify challenges that may arise in the implementation of AM. The intention is also to compare the conventional method of sand casting with AM for metal production targeted at excavators. This is accomplished by specifically highlighting the metallurgical benefits of AM. Research Questions: RQ1: What challenges arise when qualifying AM products for excavators? RQ2: What are the metallurgical benefits of an AM produced product in comparison to a Sand Casted product for excavator bucket teeth? Method: An inductive approach has been taken, with a literature, empirical and case study conducted.The construction of the theoretical framework used information from scientific articles and books. The findings of the empirical study arrived from information gathered through observations and experimentation, with help and interpretation from the case companies. The empirical findings will assist in answering the research questions. The case study consisted of metallurgical testing in form of porosity analysis, microstructure examination, hardness- and chemical composition test. Conclusion: Several challenges were discovered that will impact the qualification of AM products. These can affect the results derived from the case study, providing incorrect data. It can however be seen as beneficial as it provides knowledge of how to reduce or eliminate their impact withfuture analyses.The AM products tested, displayed positive metallurgical properties in comparison with sand casted products. A standout trait was the consistency in the dimension and density of the AM products, displaying how AM can create nearly identical products.

<p> The Selective Laser Melting (SLM) process is a manufacturing technique that facilitates the  production of metallic parts with complex geometries and reduces both materials waste and lead  time. The high tunability of the process parameters in SLM allows the design of the as-built part’s  characteristics, such as controlled microstructure formation, residual stresses, presence of pores,  and lack of fusion. The main parameter in the SLM process that influences these parts’  characteristics is the transient temperature field resulting from the laser-matter interaction.  Nanosecond pulsed lasers in SLM have the advantage of enabling rapid and localized heating and  cooling that make the formation of ultrafine grains possible. This work shows how different pulse  durations can change the near-surface microstructure and overall mechanical properties of metallic  parts. The nanosecond pulses can melt and resolidify aluminum parts’ near-surface region to form nanograined gradient structures with yield strengths as high as 250.8 MPa and indentation  strengths as high as 725 MPa, which are comparable to some steel's mechanical properties. Knowing that the nanosecond pulsed lasers cause microstructure refinement for high-purity metals,  the microstructure variations effects were also investigated for the cast iron alloy. Cast iron was  used alone and mixed with born or boron nitride powders to induce the precipitation of  strengthening phases only enabled under high cooling rates. Although producing parts with  superior mechanical properties and controlling the precipitation of strengthening phases, the SLM  process with nanosecond pulsed lasers is still accompanied by defects formation, mainly explained  by the large thermal gradients, keyhole effect, reduced melt pool depth, and rapid cooling rates.  Ideally, a smooth heating rate able to sinter powder grains, facilitating the heat flow through the  heat-affected zone, followed by a sharper heating rate that generates a fully molten region, but  minimizes ablation at the same time are targeted to reduce the porosity and lack of fusion. Then, a  sharp cooling rate that can increase the nucleation rate, consequently refining the final  microstructure is targeted in the production of strong materials in SLM with pulsed lasers. This  work is the pioneer in controlling the transient temperature field during the heating and cooling  stages in pulsed laser processing. The temperature field control capability by shaping a nanosecond  laser pulse in the time domain affecting defects formation, residual strains, and microstructure was  achieved, opening a wide research niche in the additive manufacturing field.  </p>

Bulk metallic glasses (BMGs) are known to have various advantageous chemical and physical properties. However, the condition of producing BMGs is critical. From a melt to congealing into a glass, the nucleation and growth of crystals has to be suppressed, which requires a fast removal of the heat. Such high cooling rates inevitably confine the casting dimensions (so-called critical casting thickness). To overcome this shortcoming, additive manufacturing proves to be an interesting method for fabricating metastable alloys, such as bulk metallic glasses. Selective laser melting (SLM), one widely used additive manufacturing technique, is based on locally melting powder deposited on the powder bed layer by layer. During the SLM process, the interaction between laser beam and alloys is completed with a high energy density (105 - 107 W/cm2) in very short duration (10-3 - 10-2 s), which results in a high cooling rate (103 - 108 K/s). Such high cooling rates favour vitrification and to date, various glass-forming alloys have been prepared. The approach to prepare bulk metallic glasses (BMGs) by SLM bears the indisputable advantage that the size of the additively manufactured glassy components can exceed the typical dimensions of cast bulk metallic glasses. Simultaneously, also delicate and complex geometries can be obtained, which are otherwise inaccessible to conventional melt quenching techniques. By using such advantages of SLM, Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2 (at.%) and Zr52.5Cu17.9Ni14.6Al10Ti5 (at.%) BMGs have been successfully fabricated via SLM in the current work. The SLM process yields material with very few and small defects (pores or cracks) while the conditions still have to render possible vitrification of the molten pool. This confines the processing window of the fully amorphous SLM samples. By additively manufacturing different BMG systems, it is revealed that the non-linear interrelation is differently pronounced for varied compositions. The only way to obtain glassy and dense products is optimizing all the process parameters. However, it is difficult to obtain fully dense sample (100%). The relative density of the additively manufactured BMGs can reach 98.5% (Archimedean method) in current work. The residual porosity acts as structural heterogeneities in the additively manufactured BMGs. The structures of BMGs are sensitive to the thermal history, i.e. to the cooling rate and to the thermal treatment. During SLM process, the laser beam not only melts the topmost powder, but also the adjacent already solidified parts. Such complicated thermal history may lead to locally more/less relaxed structure of the additively manufactured BMGs. Thus, systematic and extensive calorimetric measurements and nanoindentation tests were carried out to detect these structural heterogeneities. The relaxation enthalpies, which can reveal the free volume content and average atomic packing density in the additively manufactured BMGs are much higher than that in the as-cast samples, indicating an insufficient duration for structural relaxation. The nanoindentation tests indicate that the structure of additively manufactured BMG is more heterogeneous than that of as-cast sample. Nevertheless, no obvious heat-affected zone which corresponds to the more/less relaxed structure is visible in the hardness map. In order to reveal the origin of such heterogeneity, the thermal field of the additively manufactured BMGs was simulated via finite volume method (FVM). Owing to the different process parameters and varied thermophysical properties of Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2 and Zr52.5Cu17.9Ni14.6Al10Ti5 BMGs, the heat-affected zone (HAZ) is differently pronounced, resulting in the varied heterogeneities of both additively manufactured BMGs. Afterwards, the physical and chemical properties of the additively manufactured BMGs were systematically studied. The additively manufactured BMGs tend to fail in a premature manner. The heterogeneities (defects, crystalline phases and relaxed/rejuvenated regions) can determine the mechanical and chemical properties of the BMGs. In the current work, the additively manufactured BMGs are fully amorphous. Thus, the effects of crystalline phases can be ruled out. The effect of residual porosity and more/less relaxed state on the deformation of additively manufactured and as-cast BMGs has been studied. The analysis of the observed serrations during compressive loading implies that the shear-band dynamics in the additively manufactured samples distinctly differ from those of the as-cast glass. This phenomenon appears to originate from the presence of uniformly dispersed spherical pores as well as from the more pronounced heterogeneity of the glass itself as revealed by instrumented indentation. Despite these heterogeneities, the shear bands are straight and form in the plane of maximum shear stress. Additive manufacturing, hence, might not only allow for producing large BMG samples with complex geometries but also to manipulate their deformation behaviour through tailoring porosity and microstructural heterogeneity. Different from the compressive tests, the heterogeneities of additively manufactured BMGs have no significant effect on the tribological and corrosion properties. The similar specific wear rate and the worn surfaces demonstrate that similar wear mechanisms are active in the additively manufactured and the as-cast samples. The same holds for the corrosion tests. The anodic polarization curves of SLM samples and as-cast samples illustrate a similar corrosion behaviour. However, the SLM samples have a slightly reduced susceptibility to pitting corrosion and reveal an improved surface healing ability, which might be attributed to an improved chemical homogeneity of the additively manufactured BMGs. In order to improve plasticity, bulk metallic glasses composites (BMGCs) have been developed, in which crystals precipitate in a glassy matrix. The crystalline phases can alter the local stress state under loading, thereby, impacting the initiation and propagation of the shear bands. However, it is difficult to control the crystalline volume fraction as well as the size and spacing between the crystals by using the traditional melt-quenching method. One approach is to mix glass-forming powder with conventional alloy powder. In this way, a large degree of freedom for designing the microstructure can be gained. Thus, SLM was chosen to prepare such “ideal” BMGCs in the present work. The β-phase stabilizer Nb powder was mixed with Zr52.5Cu17.9Ni14.6Al10Ti5 powder. After SLM processing, the irregular-shaped Nb particles are distributed uniformly within the glassy matrix and bond well to it. At the higher Nb content, diffusion of Nb during processing locally deteriorates the glass-forming ability of the matrix and results in the formation of several brittle intermetallic phases around the Nb particles. The size of these precipitates covers a wide range from nanometres to micrometres. Despite the fact that the soft Nb particles increase the heterogeneity of the glassy matrix, none of the samples deforms plastically. This is attributed to the network-like distribution of the intermetallic phases, which strongly affects the fracture process. Besides the ex-situ method of mixing powders, designing in-situ ductile phases and controlling the fraction of the crystalline phases by altering process parameters can also prepare optimized BMGCs. Cu46Zr46Al8 (at.%) was processed via SLM to produce in-situ BMGCs. It is revealed that the microstructure of the nearly fully dense additively manufactured BMGs is strongly affected by the energy input. By increasing the energy input, the amount of the crystalline phases was raised. By optimizing the energy input, the B2 CuZr phase was particularly deliberately introduced. Due to the residual porosity and brittle phases, no plasticity is visible in the additively manufactured samples. Generally, selective laser melting opens a gateway to design the microstructure of the BMG matrix composites.:Abstract I Kurzfassung IV Symbols and abbreviations VIII Aims and objectives VIII CHAPTER 1 Metallic glasses and selective laser melting 1 1.1 Formation of metallic glasses from the melt 1 1.2 Mechanical properties of BMGs and their composites 4 1.2.1 Shear banding in metallic glasses 4 1.2.2 Effect of structural heterogeneities on plastic deformation 7 1.2.2.1 Nanoscale heterogeneities 8 1.2.2.2 Microscale heterogeneities 11 1.2.3 Shear band dynamics 13 1.2.4 Tribological properties of BMGs 15 1.3 Corrosion behaviour of bulk metallic glasses 16 1.4 Selective laser melting (SLM) 20 1.4.1 The SLM process 20 1.4.1.1 Powder properties 21 1.4.1.2 Process parameters 22 1.4.2 Solidification and thermal history 25 1.5 Selectively laser-melted glass formers 28 1.5.1 Selective laser melting of a single alloy powder 28 1.5.2 Heterogeneities and mechanical properties of additively manufactured BMGs 32 CHAPTER 2 Experimental 36 2.1 Sample preparation 36 2.1.1 Arc melting 36 2.1.2 Suction casting 36 2.1.3 Gas atomization 37 2.1.4 Powder mixtures 37 2.1.5 Selective laser melting (SLM) 38 2.1.5 Heat treatment 39 2.2 Sample characterization methods 39 2.2.1 Composition analysis 40 2.2.2 X-ray diffraction 40 2.2.3 Calorimetry 40 2.2.4 Density measurements (Archimedean method) 41 2.2.5 µ-CT 41 2.2.6 Scanning electron microscopy (SEM) 41 2.2.7 Transmission electron microscopy (TEM) 42 2.2.8 Hardness measurements 42 2.2.9 Compression tests 43 2.2.10 Sliding wear tests 43 2.2.11 Corrosion tests 44 2.2.12 Finite volume method modelling 45 CHAPTER 3 Selective laser melting of glass-forming alloys 46 3.1 Selective laser melting of a Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2 BMG 46 3.1.1 Powder analysis 47 3.1.2 Parameter optimization and microstructural characterization 48 3.1.3 Mechanical properties 55 3.1.3.1 Compression tests 55 3.1.3.2 Microhardness and structural relaxation 57 3.1.3.3 Nanoindentation 59 3.1.4 Corrosion properties 61 3.2 Selective laser melting of a Zr52.5Cu17.9Ni14.6Al10Ti5 BMG 62 3.2.1 Powder analysis 62 3.2.2 Microstructural characterization 63 3.2.3 Mechanical properties 66 3.2.3.1 Compression tests 66 3.2.3.2 Microhardness and structural relaxation 68 3.2.3.3 Nanoindentation 71 3.2.4 Shear band dynamics and shear band propagation 74 3.2.5 Tribological and corrosion properties 80 3.3 Structural heterogeneities of BMGs produced by SLM 87 CHAPTER 4 Selective laser melting of ex-situ Zr-based BMG matrix composites 97 4.1 Phase formation 97 4.2 Microstructures 101 4.3 Mechanical properties 110 CHAPTER 5 Selective laser melting of in-situ CuZr-based BMG matrix composites 115 5.1 Powder analysis 115 5.2 Parameter optimization 116 5.3 Microstructure 120 5.4 Mechanical properties 124 5.4.1 Compression tests 124 5.4.2 Microhardness and structural relaxation 127 5.4.3 Nanoindentation 129 CHAPTER 6 Summary 132 CHAPTER 7 Outlook 132 Acknowledgements 137 Bibliography 139 Publications 163 Eidesstattliche Erklärung 164

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<p>The electric arc furnace (EAF) is a critical steelmaking facility that melts the scrap by the heat produced from electrodes and burners. The migration to EAF steelmaking has accelerated in the steel industry over the past decade owing to the consistent growth of the scrap market and the goal of "green" steel production. The EAF production already hit a new high in 2018, contributing to 67% of total short tons of U.S. crude steel produced. The EAF steelmaking process involves dynamic complex multi-physics, in which electric arc plasma and coherent jets coexist resulting in an environment with local high temperature and velocity. Different heat transfer mechanisms are closely coupled and the phase change caused by melting and re-solidification is accompanied by in-bath chemical reactions and freeboard post-combustion, which further creates a complicated gas-liquid-solid three-phase system in the furnace. Therefore, not all conditions and phenomena within the EAF are well-understood. The traditional experimental approach to study the EAF is expensive, dangerous, and labor-intense. Most of the time, direct measurements and observations are impossible due to the high temperature within the furnace. To this fact, the numerical model has aroused great interest worldwide, which can help to gain fundamental insights and improve product quality and production efficiency, greatly benefiting the steel industry. However, due to the complexity of the entire EAF steelmaking process, the relevant computational fluid dynamics (CFD) modeling and investigations of the whole process have not been reported so far. </p> <p><br></p> <p>The present study was undertaken with the aim of developing the modeling methodologies and the corresponding comprehensive EAF CFD models to simulate the entire EAF steelmaking process. Two state-of-the-art comprehensive EAF CFD models have been established and validated for both the lab-scale direct current (DC) EAF and the industry-scale alternating current (AC) EAF, which were utilized to understand the physical principles, improve the furnace design, optimize the process, and perform the trouble-shootings.</p> <p><br></p> <p>For the lab-scale DC EAF, a direct-coupling methodology was developed for its comprehensive EAF CFD model which includes the solid steel melting model based on the enthalpy-porosity method and the electric arc model (for lab-scale DC arc) based on the Magneto Hydrodynamics (MHD) theory, so that the dynamic simulation of the steel ingot melting by DC arc in the lab-scale furnace can be achieved, which considered the continuous phase changing of solid steel, the ingot surface deformation, and the phase-to-phase interaction. Both stationary DC arc and the arc-solid steel interface heat transfer and force interaction were validated respectively against the experimental data in published literature. For the given lab-scale furnace, the DC arc behavioral characteristics with varying arc lengths generated by the moving electrode were analyzed, and the effects of both the initial arc length and the dynamic electrode movement on the steel ingot melting efficiency were revealed.</p> <p><br></p> <p>For the industry-scale AC EAF, an innovative integration methodology was proposed for its comprehensive EAF CFD model, which relies on the stage-by-stage approach to simulate the entire steelmaking process. Six simulators were developed for simulating sub-processes in the industry-scale AC EAF, and five models were developed for the above four simulators, including the scrap melting model, the electric arc model (for industry-scale AC arc), the coherent jet model, the oxidation model, and the slag foaming model, which can be partially integrated according to the mass, energy, and momentum balance. Specifically, the dual-cell approach and the stack approach were proposed for the scrap melting model to treat the scrap pile as the porous medium and simulate the scrap melting together with its dynamic collapse process. The statistical sampling method, the CFD-compatible Monte Carlo method, and the electrode regulation algorithm were proposed for the electric arc model to estimate the total AC arc power delivery, the arc radiative heat dissipation, and the instantaneous electrode movement. The energetic approach was proposed to determine the penetration of the top-blown jet in the molten bath based on the results from the coherent jet model. The source term approach was proposed in the oxidation model to simulate the in-bath decarburization process, where the oxidation of carbon, iron, and manganese as well as the effect of those exothermic reactions on bath temperature rising was considered. Moreover, corresponding experiments were performed in the industry-scale EAF to validate the proposed simulators. The quantitative investigations and analyses were conducted afterward to explore and understand the coherent jet performance, the AC arc heat dissipation, the burner preheating characteristics, the scrap melting behavior, the in-bath decarburization efficiency, and the freeboard post-combustion status.</p> <p><br></p>

Metal  additive  manufacturing  technologies  are  widely  employed  in  the aerospace, automotive  and  medical  industries. Selective  laser  melting  is  a type  of  metal additive manufacturing process in which powders are consolidated layer by layer in a predefined pattern with the help of a laser beam to create a component.   Powder characteristics are critical in influencing the quality of the printed component.  Metal powders must be within a specific size range and have spherical morphology to exhibit good  flow  and  spread behaviour  during  the  additive  manufacturing  process.   It  is necessary to understand the flow behaviour to comprehend the powder’s performance during the  process.   The  study  investigates  the  effect  of  powder  characteristics like particle  shape,  particle  size  and  size  distribution  on  the  flow behaviour  of  steel powders.   Powder  characterisation  techniques  relevant  to the  powders  for  additive manufacturing application is identified and performed. Sieve analysis fails to incorporate the particle shape during the particle size estimation. Optical microscopy is not a robust method for determining the particle shape.  Flow behaviour of the powders was studied using flowmeter test, rheometric analysis and static angle of repose test.  Rheometric analysis is more sensitive to minor variations in the flow behaviour compared to flowmeter tests. The static angle of repose test fails to incorporate the stresses experienced by the powder during the process and can be used to get a rough estimate for the powder flow behaviour in terms of cohesion.  Of the seven steel powders examined, the same powder with flow time 12 [s/(50 g)] kept being ranked in the top three for all the flow tests. So this powder is recommended for use in additive manufacturing. In addition, one other powder that failed in flowmetertests was consistently placed towards the bottom of all tests. / Metalladditiv tillverkningsteknik används i stor utsträckning inom flyg­, fordons­, och medicinsk industri. Selektiv lasersmältning är en typ av metalladditiv tillverknings­ process där pulver konsolideras lager för lager i ett fördefinierat mönster med hjälp av en laserstråle för att skapa en komponent. Pulveregenskaper är avgörande för att påverka kvaliteten på den tryckta komponenten. Metallpulver måste ligga inom ett visst storleksintervall och ha en sfärisk morfologi för att uppvisa ett bra flödes­, och dispersionsbeteende under den additiva tillverkningsprocessen. Det är nödvändigt att förstå flödesbeteendet för att förstå pulvrets prestanda under processen. Studien undersöker effekten av pulveregenskaper som partikelform, partikelstorlek och storleksfördelning på flödesbeteendet hos stålpulver. Pulverkarakteriseringstekniker som är relevanta för pulvren för tillsatstillverkning identifieras och utförs. Siktanalysen misslyckas med att införliva partikelformen under partikelstorleksupp­ skattningen. Optisk mikroskopi är inte en robust metod för att bestämma partikelformen. Pulvrets flödesbeteende studerades med hjälp av flödesmätartest, reometrisk analys och statisk vinkel på vilotest. Reometrisk analys är mer känslig för mindre variationer i flödesbeteendet jämfört med flödesmätartester. Det statiska vilovinkeltestet misslyckas med att införliva de påfrestningar som pulvret upplever under processen och kan användas för att få en grov uppskattning av pulverflödesbeteendet i termer av kohesion. Av de sju stålpulver som undersöktes rankades samma pulver med flödestiden 12 [s/(50 g)] i topp tre för alla flödestester. Så detta pulver rekommenderas för användning i additiv tillverkning. Dessutom placerades ett annat pulver som misslyckades i flödesmätartester konsekvent mot botten av alla tester.

Pure copper (Cu) has the properties of high optical reflectivity and surface tarnishing as well as excellent thermal and electrical conductivity. Accordingly, laser-based additive manufacturing (AM) techniques confront various difficulties to produce thismaterial. In contrast, the electron beam melting (EBM) process is paving to become an excellent method to manufacture AM parts from such materials. This is since theelectron beam is not influenced by the optical reflectivity of the material. Furthermore, EBM works under vacuum that can protect the powder material from oxidization. In addition, the high working temperature and preheating process for each layer canensure a uniform heat input and a much lower cooling rate. Hence, the EBM processcan significantly prevent the parts from delamination failure caused by residual stress. Accordingly, this research work is intended to investigate the EBM processability and geometrical freedom/accuracy of EBM made copper components. The 99.95% pure Cu powder with a particle size range of 45-100μm are used to produce samples. All the samples are built with a certain layer thickness of 50μm with altering parameters, including the processing temperature, line offset, focus offset, beamspeed, and beam current. It is found that the processing temperature of 500°C leadsto low density and severe lateral melting/sintering. Accordingly, the temperature is lowered to 450°C, 400°C, 350°C, and 310°C to control the excessive lateral melting. Since dense parts could only be produced above 400°C, this work focuses on developing 400°C processing temperature with different line offset, focus offset, beamspeed, and beam current. However, it is observed that the processing window of the EBM process is rather narrow, too high or too low energy input could both result in a porous part with severe distortion. After many experimental optimizations runs, the combination of the optimum parameters is reached which can deliver parts with over 99% density and a good geometrical stability. After optimization, the benchmark partsare designed and manufactured according to electrical and thermal applications (using the optimum parameters). Afterwards, the corresponding geometrical freedomand accuracy of the copper components made by EBM is assessed and discussed. / Ren koppar (Cu) har egenskaper som hög optisk reflektivitet och ytans anlöning samt utmärkt termisk och elektrisk ledningsförmåga. Följaktligen möter laserbaserad additiv tillverkning (additive manufacturing, AM) olika svårigheter när det gäller att producera detta material. Däremot är elektronstrålesmältning ("electron beam melting", EBM) på väg att bli en utmärktmetod för att tillverka AM-delar av sådana material. Detta beror på att elektronstrålen inte påverkas av materialets optiska reflektivitet. Dessutom arbetar EBM under vakuum som kan skydda pulvermaterialet från oxidering. Dessutom kan den höga arbetstemperaturen och förvärmningsprocessen för varje lager säkerställa en jämn värmetillförsel och en mycket lägre kylningshastighet. EBM-processen kan därför i hög grad förhindra att delamineringsfel orsakade av restspänningar uppstår. Syftet med detta forskningsarbete är därför att undersöka EBM-processbarheten och den geometriska friheten/precisionen hos EBM tillverkade kopparkomponenter. Det 99,95 % rena Cu-pulvret med ett partikelstorleksområde på 45-100 μm används för att producera prover. Alla prover är byggda med en viss tjocklek på 50 μm med ändrade parametrar, inklusive bearbetningstemperatur, linjeförskjutning, fokusförskjutning, strålhastighet och strålström. Det har visat sig att bearbetningstemperaturen på 500°C leder till låg densitet och allvarlig lateral smältning/sintring. Följaktligen sänks temperaturen till 450°C, 400°C, 350°C och 310°C för att kontrollera den överdrivna laterala smältningen. Eftersom täta delar endast kunde produceras över 400°C, fokuserar detta arbete på att utveckla 400°C bearbetningstemperatur med olika linjeförskjutning, fokusförskjutning, strålhastighet och strålström. Det observeras dock att bearbetningsfönstret för EBMprocessen är ganska smalt, för hög eller för låg energitillförsel kan båda resultera i en porösdel med allvarlig förvrängning. Efter många experimentella optimeringskörningar uppnås kombinationen av de optimala parametrarna som kan leverera delar med över 99% densitet och en god geometrisk stabilitet. Efter optimering designas och tillverkas benchmarkdelarna i enlighet med elektriska och termiska applikationer (med optimala parametrar). Därefter bedöms och diskuteras motsvarande geometriska frihet och noggrannhet hos kopparkomponenterna tillverkade av EBM.

Additive manufacturing methods for steel are competing against commercial production in an increasing pace. The geometry freedom together with the high strength and toughness due to extreme cooling rates make this method viable to use for high-performance components. The desirable material properties originate from the ultrafine grain structures. The production is often followed by a post hardening heat treatment to induce precipitation of other phases. The printing process does however bring several challenges such as cracking, pore formation, inclusions, residual stresses and distortions. It is therefore important to be able to predict the properties such as temperature evolution and residual stresses of the resulting part in order to avoid time consuming trial-and-error and unnecessary material waste. In order to link different parts and length scales of the process, the integrated computational materials engineering framework can be used where linkage tools couples results of different length scales. 18Ni300 maraging steel is a material that has been used extensively to produce parts by additive manufacturing, but there is still a wide scope for optimising the process and properties. In this thesis, the integrated computational materials engineering inspired framework is applied to link the process to the microstructure, which dictates the properties. Temperature evolution strongly influences the material properties, residual stresses and distortion in additive manufacturing. Therefore, simulations of temperature evolution for a selective laser melted 18Ni300 maraging steel have been performed by Simufact Additive and linked with the microstructure prediction tools in Thermo-Calc and DICTRA. Various printing parameters have been examined and resulting temperatures, cooling rates, segregations and martensitic start temperatures compared for different locations of the build part. Additionally, residual stresses and distortions were investigated in Simufact. It was found that higher laser energy density caused increased temperatures and cooling rates which generally created larger segregations of alloying elements and lower martensitic start temperatures at the intercellular region. There is however an impact from cooling rate and temperature independent of the energy density which makes energy density not an individual defining parameter for the segregations. By decreasing the baseplate temperature, lower temperatures below the martensitic start temperature were reached, enhancing martensite transformation. Primary dendrite arm spacing calculations were used to validate the cooling rates. The cell size corresponded well to literature of &lt;1 μm. Distortions and residual stresses were very small. The calibration was based according to literature and need experimental values to be validated. The integrated framework demonstrated in this thesis provides an insight into the expected properties of the additively manufactured part which can decrease and replace trial-and-error methods. / dditiva tillverkningsmetoder för stål tävlar mot kommersiell produktion i en ökande takt. Geometrifriheten tillsammans med hög styrka och slagseghet på grund av extrema kylhastigheter gör den här metoden intressant att använda för högpresterande komponenter. De önskvärda materialegenskaperna härstammar från den ultrafina mikrostrukturen. Processen följs ofta av en värmebehandlande härdning för att inducera utskiljningar av andra faser. Printing processen innebär dock flertalet utmaningar som exempelvis sprickbildning, porer, inneslutningar, restspänningar och förvrängningar. Det är därför intressant och viktigt att förutspå egenskaper såsom temperaturutveckling och restspänningar av den slutgiltiga komponenten för att minska tidskrävande ”trial-and-error” och onödigt materialsvin. För att länka ihop olika delar och längdskalor av processen kan ”the integrated computational materials engineering” strukturen användas där länkverktyg kopplar ihop resultat av olika längdskalor. 18Ni300 maraging stål är ett material som har använts till additivt tillverkade produkter i hög utsträckning men det finns fortfarande mycket utrymme för optimering av processen och egenskaperna. I den här avhandlingen, den ”integrated computational materials engineering” inspirerade tillvägagångssättet används för att länka processen med mikrostrukturen, vilken bestämmer egenskaperna. Temperaturutveckling påverkar kraftigt materialegenskaper, restspänningar och deformation vid additiv tillverkning. Förutsägelse av temperatur för ett selektivt lasersmält 18Ni300 stål har därför genomförts i Simufact Additive och länkats med mikrostruktursförutsägande redskapen Thermo-Calc och DICTRA. Olika maskinparametrar har undersökts och efterföljande temperaturer, kylhastigheter, segregeringar och martensitiska starttemperaturer jämförts för olika delar av geometrin. Tilläggningsvis var även restspänningar och deformationer undersökta i Simufact. Det konstaterades att högre energidensitet för lasern orsakade högre temperaturer och kylhastighet vilket generellt skapade mer segregeringar av legeringsämnen och lägre martensitisk starttemperatur i de intercellulära områdena. Det är däremot en gemensam påverkan av kylhastighet och temperatur vilket gör att energidensitet inte är den enskilda bestämmande parametern över segregeringarna. Genom att sänka temperaturen på basplattan uppnåddes lägre temperaturer under den martensitiska starttemperaturen vilket förenklar den martensistiska omvandlingen. Beräkningar av primär dendritisk armlängd användes för att validera kylhastigheterna. Cellstorleken överensstämde bra med litteraturen på &lt;1 μm. Deformationer och restspänningar var väldigt små. Kalibreringarna baserades på litteraturvärden och kräver experimentella värden för att valideras. Den integrerade strukturen  som demonstreras i den här avhandlingen förser en insikt i de förväntade egenskaperna av en additivt tillverkad del vilket kan minska och ersätta ”trial-and-error” metoder.

Metal additive manufacturing can be used for producing complex and functional components in the aerospace industry. This thesis deals with the process-structure-property relationships in selective laser melting of three aerospace alloys: Invar 36, stainless steel 316L, and Ti-6Al-4V. These alloys are weldable but hard to machine, which make them good candidates for the selective laser melting process. Invar 36 has a very low coefficient of thermal expansion because of its nickel concentration of 36% and stainless steel 316L contains 16-18% chromium that gives the alloy a corrosion resistance property. Ti-6Al-4V offers high strength-to-weight ratio, high biocompatibility, and outstanding corrosion resistance. Any changes in the chemical composition of these materials could affect their performance during application. In this thesis, a full factorial design of experiments is formulated to study a wide range of laser process parameters. The bulk density, tensile mechanical properties, fractography, microstructure, material composition, material phases, coefficient of thermal expansion, magnetic dipole moments, and residual stresses of the parts produced are experimentally investigated. An optimum process window has been suggested for each material based on experimental work. The thermal cycle, residual stresses, and part distortions are examined using a thermo-mechanical finite element model. The model predicts the residual stress and part distortion after build plate removal. The thesis introduces two laser energy densities for each material: brittle-ductile transition energy density, ET, and critical laser energy density, EC. Below the brittle-ductile transition energy density, the parts exhibited void formation, low density, and brittle fracture. Above the critical energy density, the parts showed vaporization of some alloying elements that have low boiling temperatures. Additionally, real-time measurements were taken using a pyrometer and a high-speed camera during the selective laser melting process. The trends found in the numerical results agree with those found experimentally. / Thesis / Doctor of Philosophy (PhD)