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Towards Topography Characterization of Additive Manufacturing SurfacesVedantha Krishna, Amogh January 2020 (has links)
Additive Manufacturing (AM) is on the verge of causing a downfall to conventional manufacturing with its huge potential in part manufacture. With an increase in demand for customized product, on-demand production and sustainable manufacturing, AM is gaining a great deal of attention from different industries in recent years. AM is redefining product design by revolutionizing how products are made. AM is extensively utilized in automotive, aerospace, medical and dental applications for its ability to produce intricate and lightweight structures. Despite their popularity, AM has not fully replaced traditional methods with one of the many reasons being inferior surface quality. Surface texture plays a crucial role in the functionality of a component and can cause serious problems to the manufactured parts if left untreated. Therefore, it is necessary to fully understand the surface behavior concerning the factors affecting it to establish control over the surface quality. The challenge with AM is that it generates surfaces that are different compared to conventional manufacturing techniques and varies with respect to different materials, geometries and process parameters. Therefore, AM surfaces often require novel characterization approaches to fully explain the manufacturing process. Most of the previously published work has been broadly based on two-dimensional parametric measurements. Some researchers have already addressed the AM surfaces with areal surface texture parameters but mostly used average parameters for characterization which is still distant from a full surface and functional interpretation. There has been a continual effort in improving the characterization of AM surfaces using different methods and one such effort is presented in this thesis. The primary focus of this thesis is to get a better understanding of AM surfaces to facilitate process control and optimization. For this purpose, the surface texture of Fused Deposition Modeling (FDM) and Laser-based Powder Bed Fusion of Metals (PBF-LB/M) have been characterized using various tools such as Power Spectral Density (PSD), Scale-sensitive fractal analysis based on area-scale relations, feature-based characterization and quantitative characterization by both profile and areal surface texture parameters. A methodology was developed using a Linear multiple regression and a combination of the above-mentioned characterization techniques to identify the most significant parameters for discriminating different surfaces and also to understand the manufacturing process. The results suggest that the developed approaches can be used as a guideline for AM users who are looking to optimize the process for gaining better surface quality and component functionality, as it works effectively in finding the significant parameters representing the unique signatures of the manufacturing process. Future work involves improving the accuracy of the results by implementing improved statistical models and testing other characterization methods to enhance the quality and function of the parts produced by the AM process.
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Additive Manufacturing Applications for Suspension Systems : Part selection, concept development, and designWaagaard, Morgan, Persson, Johan January 2020 (has links)
This project was conducted as a case study at Öhlins Racing AB, a manufacturer of suspension systems for automotive applications. Öhlins usually manufacture their components by traditional methods such as forging, casting, and machining. The project aimed to investigate how applicable Additive Manufacturing (AM) is to manufacture products for suspension systems to add value to suspension system components. For this, a proof of concept was designed and manufactured. The thesis was conducted at Öhlins in Upplands Väsby via the consultant firm Combitech. A product catalog was searched, screened, and one part was selected. The selected part was used as a benchmark when a new part was designed for AM, using methods including Topology Optimization (TO) and Design for Additive Manufacturing (DfAM). Product requirements for the chosen part were to reduce weight, add functions, or add value in other ways. Methods used throughout the project were based on traditional product development and DfAM, and consisted of three steps: Product Screening, Concept Development, and Part Design. The re-designed part is ready to be manufactured in titanium by L-PBF at Amexci in Karlskoga. The thesis result shows that at least one of Öhlin's components in their product portfolio is suitable to be chosen, re-designed, and manufactured by AM. It is also shown that value can be added to the product by increased performance, in this case mainly by weight reduction. The finished product is a fork bottom, designed with hollow structures, and is ready to print by L-PBF in a titanium alloy.
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Innovative Tessellation Algorithm for Generating More Uniform Temperature Distribution in the Powder-bed Fusion ProcessMaleki Pour, Ehsan 12 1900 (has links)
Purdue School of Engineering and Technology, Indianapolis / Powder Bed Fusion Additive Manufacturing enables the fabrication of metal parts with complex geometry and elaborates internal features, the simplification of the assembly process, and the reduction of development time. However, the lack of consistent quality hinders its tremendous potential for widespread application in industry. This limits its ability as a viable manufacturing process particularly in the aerospace and medical industries where high quality and repeatability are critical. A variety of defects, which may be initiated during the powder-bed fusion additive manufacturing process, compromise the repeatability, precision, and resulting mechanical properties of the final part. The literature review shows that a non-uniform temperature distribution throughout fabricated layers is a significant source of the majority of thermal defects. Therefore, the work introduces an online thermography methodology to study temperature distribution, thermal evolution, and thermal specifications of the fabricated layers in powder-bed fusion process or any other thermal inherent AM process. This methodology utilizes infrared technique and segmentation image processing to extract the required data about temperature distribution and HAZs of the layer under fabrication. We conducted some primary experiments in the FDM process to leverage the thermography technique and achieve a certain insight to be able to propose a technique to generate a more uniform temperature distribution. These experiments lead to proposing an innovative chessboard scanning strategy called tessellation algorithm, which can generate more uniform temperature distribution and diminish the layer warpage consequently especially throughout the layers with either geometry that is more complex or poses relatively longer dimensions. In the next step, this work develops a new technique in ABAQUS to verify the proposed scanning strategy. This technique simulates temperature distribution throughout a layer printed by chessboard printing patterns in powder-bed fusion process in a fraction of the time taken by current methods in the literature. This technique compares the temperature distribution throughout a designed layer printed by three presented chessboard-scanning patterns, namely, rastering pattern, helical pattern, and tessellation pattern. The results confirm that the tessellation pattern generates more uniform temperature distribution compared with the other two patterns. Further research is in progress to leverage the thermography methodology to verify the simulation technique. It is also pursuing a hybrid closed-loop online monitoring and control methodology, which bases on the introduced tessellation algorithm and online thermography in this work and Artificial Neural Networking (ANN) to generate the most possible uniform temperature distribution within a safe temperature range layer-by-layer.
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Powder Rheology within AM production : Evaluating Compressibility, Permability, & Aeration for 316L Powders Within SLM Processes / Pulver Reologi Inom AM Production : Utvärdering av Kompressibilitet, Permeabilitet, och Luftning för 316L pulver inom SLM processerLeo, André January 2022 (has links)
Additive manufacturing with the use of metals have been a steadily increasing field, being able to create products with a higher degree of complexity than traditional processing techniques. SLM is a popular AM process that uses metal powder as feedstock, and one of the key components of this process is the powder rheology. In recent years the use of a powder rheometer has been shown to be a good way of evaluating powder rheology of metal powders used within AM processes, but there is a clear lack of standardised tests and methods. In this study the Compressibility, Permeability, and Aeration test for 316L powders used within SLM processes was evaluated with a FT4 powder rheometer. 15 powders that had undergone printing in SLM processes were studied. This showed that the compressibility test had the best results in differentiating the bad preforming powders, thereafter the Aeration test. The Permeability test wasn’t able to differentiate the bad preforming powders with the settings used. This study demonstrates that some tests with a powder rheometer can evaluate the powder performance in SLM processes, but further research to evaluate the tests and standardise the settings are needed for clearer test results. / Additiv tillverkning med metall är ett område som stadigt ökat i intresse, främst på grund av möjligheten att producera produkter med en mycket högre grad av komplexitet i jämförelse med traditionella processmetoder. SLM är en populär AM process som använder metallpulver som råmaterial, och en av huvudkomponenterna för processen är pulvrets reologi. Under senare år har användningen av en pulver-reometer visat sig ett bra sätt att utvärdera pulver-reologi för metallpulver som används inom AM, men det finns en klar avsaknad av standardiserade test och metoder. I denna studie utvärderas Kompressabilitet, Permeabilitet, och Aerabilitet testen för 316L pulver producerade för SLM processer med en FT4 pulver-reometer. 15 pulver som genomgått SLM printing studerades. Studien visar att kompressabilitets testets utfall bäst överensstämde med det som setts under SLM processen, och bäst urskilde pulvren som fungerat dåligt att printa med, därefter Aerations testet. Permeabilitets testet kunde inte urskilja de sämre pulvren med de inställningarna som användes. Studien demonstrerar att vissa test och index samlade med ett pulver reometer är mer tillförlitliga än andra när det gäller för att utvärdera pulvrets prestanda inom SLM processer, men vidare forskning och studier krävs för att utvärdera testen och standardisera inställningar baserat på pulvret som testas.
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Topology Optimized Unit Cells for Laser Powder Bed FusionBoos, Eugen, Ihlenfeldt, Steffen, Milaev, Nikolaus, Thielsch, Juliane, Drossel, Welf-Guntram, Bruns, Marco, Elsner, Beatrix A. M. 22 February 2024 (has links)
The rise of additive manufacturing has enabled new degrees of freedom in terms of design and functionality. In this context, this contribution addresses the design and characterization of structural unit cells that are intended as building blocks of highly porous lattice structures with tailored properties. While typical lattice structures are often composed of gyroid or diamond lattices, this study presents stackable unit cells of different sizes created by a generative design approach tomeet boundary conditions such as printability and homogeneous stress distributions under a given mechanical load. Suitable laser powder bed fusion (LPBF) parameterswere determined forAlSi10Mg to ensure high resolution and process reproducibility for all considered unit cells. Stacks of unit cells were integrated into tensile and pressure test specimens for which the mechanical performance of the cells was evaluated. Experimentally measured material properties, applied process parameters, and mechanical test results were employed for calibration and validation of finite element (FE) simulations of both the LPBF process as well as the subsequent mechanical characterization. The obtained data therefore provides the basis to combine the different unit cells into tailored lattice structures and to numerically investigate the local variation of properties in the resulting structures. / Durch die Einführung der Additiven Fertigung können neue Freiheitsgrade in Bezug auf Gestaltungsfreiheit und Funktionalität erreicht werden. In diesem Zusammenhang adressiert dieser Beitrag das Design und die Charakterisierung struktureller Einheitszellen als Bausteine für hochgradig poröse Gitterstrukturen mit maßgeschneiderten Eigenschaften. Während typische Gitterstrukturen oft auf Gyroid- oder Diamantstrukturen basieren, präsentiert dieser Beitrag stapelbare Einheitszellen unterschiedlicher Größe, die durch einen generativen Designansatz erstellt wurden. Hierdurch sollen verschiedene Randbedingungen wie eine gute Druckbarkeit und homogene Spannungsverteilung unter gegebenen mechanischen Lasten erreicht werden. Um eine hohe Auflösung und Reproduzierbarkeit der Einheitszellen zu erreichen, wurden für den verwendeten Werkstoff AlSi10Mg geeignete Druckparameter für das Laserstrahlschmelzen (LPBF) ermittelt. Stapel von Einheitszellen wurden in Zug- und Druckproben integriert, anhand derer die mechanische Stabilität der Zellen ermittelt wurde. Experimentell bestimmte Materialeigenschaften, die verwendeten Prozessparameter und die Ergebnisse der mechanischen Untersuchungen wurden anschließend für die Kalibrierung und Validierung Finiter Elemente (FE) Simulationen herangezogen, wobei simulationsseitig sowohl der Prozess des Laserstrahlschmelzens als auch die nachgelagerte mechanische Charakterisierung berücksichtigt wurden. Die hier präsentierten Ergebnisse sollen als Basis sowohl für eine gezielte Anordnung der Einheitszellen zu maßgeschneiderten Gitterstrukturen dienen als auch für die numerische Auswertung der lokal variierenden Eigenschaften der somit resultierenden Strukturen.
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Microstructural and Micro-Mechanical Characterization of As-built and Heat-treated samples of HASTELLOY X produced by Laser Powder Bed Fusion ProcessSanni, Onimisi January 2022 (has links)
Microstructure and micro-mechanical characterization of as-built and heat-treated samples of Hastelloy X produced by laser powder bed fusion (LPBF) process has been carried out in this study. As-built LPBF blocks were solution heat-treated at 1177°C and 1220°C followed by fast cooling. The microstructure of as-built and heat-treated samples were studied by light optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Instrumented indentation micro Vickers testing was performed to obtain microhardness and elastic modulus of asbuilt and heat-treated samples. Microtensile samples from as-built and heat-treated blocks were prepared and polished for mechanical characterization. Microtensile testing inside the scanning electron microscope was performed to evaluate the mechanical properties and to get information about the microstructural changes during plastic deformation. Microstructure characterization revealed disrupted epitaxial grain growth for the as-built samples whereas the two heated-treated Hastelloy X samples exhibited equiaxed grains with varying twin fractions. As-built Hastelloy X samples exhibited higher mean hardness than heat-treated samples. The yield strength of as-built samples reveals higher values as compared to conventional wrought Hastelloy X samples, whereas lower yield strength and higher elongation were observed for heat-treated samples as compared to as-built samples. Higher elongation and lower yield strength values were observed for the samples solution heat-treated at 1220°C compared to the solution heat-treated at 1177°C. Microstructural evaluation at different plastic strains during in-situ microtensile testing reveals a clear difference in dislocation density for as-built and heat-treated samples.
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Influence of Two-Step Heat Treatments on Microstructure and Mechanical Properties of a β-Solidifying Titanium Aluminide Alloy Fabricated via Electron Beam Powder Bed FusionMoritz, Juliane, Teschke, Mirko, Marquardt, Axel, Heinze, Stefan, Heckert, Mirko, Stepien, Lukas, López, Elena, Brueckner, Frank, Walther, Frank, Leyens, Christoph 27 February 2024 (has links)
Additive manufacturing technologies, particularly electron beam powder bed fusion (PBF-EB/M), are becoming increasingly important for the processing of intermetallic titanium aluminides. This study presents the effects of hot isostatic pressing (HIP) and subsequent two-step heat treatments on the microstructure and mechanical properties of the TNM-B1 alloy (Ti–43.5Al–4Nb–1Mo–0.1B) fabricated via PBF-EB/M. Adequate solution heat treatment temperatures allow the adjustment of fully lamellar (FL) and nearly lamellar (NL-β) microstructures. The specimens are characterized by optical microscopy and scanning electron microscopy (SEM), X-ray computed tomography (CT), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). The mechanical properties at ambient temperatures are evaluated via tensile testing and subsequent fractography. While lack-of-fusion defects are the main causes of failure in the as-built condition, the mechanical properties in the heat-treated conditions are predominantly controlled by the microstructure. The highest ultimate tensile strength is achieved after HIP due to the elimination of lack-of-fusion defects. The results reveal challenges originating from the PBF-EB/M process, for example, local variations in chemical composition due to aluminum evaporation, which in turn affect the microstructures after heat treatment. For designing suitable heat treatment strategies, particular attention should therefore be paid to the microstructural characteristics associated with additive manufacturing.
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Locally adapted microstructures in an additively manufactured titanium aluminide alloy through process parameter variation and heat treatmentMoritz, Juliane, Teschke, Mirko, Marquardt, Axel, Stepien, Lukas, López, Elena, Brueckner, Frank, Walther, Frank, Leyens, Christoph 27 February 2024 (has links)
Electron beam powder bed fusion (PBF-EB/M) has been attracting great research interest as a promising technology for additive manufacturing of titanium aluminide alloys. However, challenges often arise from the process-induced evaporation of aluminum, which is linked to the PBF-EB/M process parameters. This study applies different volumetric energy densities during PBF-EB/M processing to deliberately adjust the aluminum contents in additively manufactured Ti–43.5Al–4Nb–1Mo–0.1B (TNM-B1) samples. The specimens are subsequently subjected to hot isostatic pressing (HIP) and a two-step heat treatment. The influence of process parameter variation and heat treatments on microstructure and defect distribution are investigated using optical and scanning electron microscopy, as well as X-ray computed tomography (CT). Depending on the aluminum content, shifts in the phase transition temperatures can be identified via differential scanning calorimetry (DSC). It is confirmed that the microstructure after heat treatment is strongly linked to the PBF-EB/M parameters and the associated aluminum evaporation. The feasibility of producing locally adapted microstructures within one component through process parameter variation and subsequent heat treatment can be demonstrated. Thus, fully lamellar and nearly lamellar microstructures in two adjacent component areas can be adjusted, respectively.
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Electron beam powder bed fusion manufacturing of a Ti-5Al-5Mo-5V-3Cr alloy: a microstructure and mechanical properties’ correlation studyHendl, Julius, Marquardt, Axel, Leyens, Christoph 26 February 2024 (has links)
Electron beam powder bed fusion (EB-PBF) is a powder-bed fusion additive manufacturing process, which is suitable for fabricating high-performance parts for a wide range of industrial applications, such as medical and aerospace. Due to its deep curing capabilities, the metastable β-alloy Ti-5Al-5Mo-5V-3Cr (Ti-5553) is currently mostly used in the landing gear of airplanes. However, its great mechanical properties make it also attractive for small, complex, and load-bearing components. In this study, nine melting parameter sets, combining different scanning speeds and beam currents, were used in the EB-PBF ARCAM A2X system. Furthermore, the correlation between the microstructure and the mechanical properties was investigated and analyzed by applying µ-focus computer tomography and microscopic methods (optical, SEM/EDS). A significant influence of the different melting parameters on the microstructure as well as on the mechanical performance was found. In a subsequent step, three melting parameters were selected and the specimens were heat-treated (BASCA, STA) for further investigation. The experimental results of this work indicate that Ti-5553 parts can be manufactured successfully with high quality (ρ > 99.60%), and post-processing heat-treatments can be used to modify the microstructure in such a way that the parts are suitable for a large variety of possible applications.
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Design of High Mn Fe-Mn-Al-C Low Density Steels for Additive ManufacturingSánchez Poncela, Manuel 13 June 2024 (has links)
[ES] La fabricación aditiva, de sus siglas en inglés AM (Additive Manufacturing) es un proceso que construye objetos sólidos tridimensionales mediante la superposicióon de materiales basados en un modelo de diseño asistido por ordenador. La AM está llamada a convertirse en la próxima revolución industrial, transformando el panorama del desarrollo y la producción. La AM ofrece numerosas ventajas, como posibilidades de diseño complejas y flexibles, la eliminación de procesos intermedios como el mecanizado, la independencia de los costes de producción del tamaño de los lotes, la reducción de los residuos de material, las estructuras ligeras, las reparaciones personalizadas de las máquinas y la capacidad de desarrollar nuevos materiales, entre otras ventajas. En las tecnologías de fabricación aditiva que emplean un rayo láser como fuente de energía, la materia prima inicial (en forma de polvo o cable) es fundida por la fuente de calor láser de forma controlada, capa a capa, hasta crear un componente con dimensiones finales o casi finales. Estas tecnologías implican someter el material impreso a un proceso térmico único, en el que el material se funde en un área muy específica y luego se enfría rápidamente a velocidades extremadamente altas de hasta 10^6 K/s. Por lo tanto, las microestructuras que surgen de los procesos de fabricación en AM difieren significativamente de las que se consiguen en los procesos tradicionales. Además, los materiales que se emplean principalmente en la AM no se han diseñado explícitamente para estas tecnologías. Las características específicas de los procesos de AM pueden utilizarse para lograr microestructuras y propiedades distintas en aceros que han sido adaptados para aprovechar las rápidas velocidades de enfriamiento y la historia térmica del proceso, entre otros factores.
Por el momento, el número de calidades de acero comerciales disponibles en el mercado de la AM es limitado. Diversas industrias demandan nuevos grados de acero con menor densidad para disminuir el peso sin comprometer las propiedades mecánicas. Los aceros con alto contenido en manganeso se consideran materiales muy prometedores para aplicaciones estructurales debido a su excepcional combinación de resistencia y ductilidad, con una baja densidad. Sin embargo, a pesar de sus excepcionales propiedades, los aceros con alto contenido en manganeso se enfrentan a diversas limitaciones o retos durante las técnicas de procesado convencionales. Afortunadamente, la solidificación rápida puede resolver estos problemas. En este sentido, las tecnologías de AM basadas en láser proporcionan velocidades de enfriamiento rápidas, así como flexibilidad en términos de diseño geométrico. Los nuevos retos de estas tecnologías implicarán la microsegregación y el agrietamiento en caliente o hot cracking en inglés, que se producen durante la solidificación.
Esta tesis está dedicada a explotar el método CALPHAD para realizar cálculos termodinámicos con el fin de diseñar varios aceros con alto contenido en manganeso que puedan prevenir eficazmente los problemas de solidificación rápida en AM. Las composiciones de acero diseñadas se produjeron en forma de polvo para AM mediante atomización con gas. Se analizaron los polvos para determinar su microestructura en relación con la química y la velocidad de enfriamiento. Ajustando adecuadamente los parámetros de impresión, estos polvos de acero con alto contenido en manganeso se imprimieron con éxito en AM, dando lugar a densidades relativas superiores al 99.9%. Se analizó la microestructura de estas muestras totalmente densas y se comparó con sus respectivos polvos, con el fin de identificar cualquier diferencia resultante de las variaciones en la velocidad de enfriamiento y los ciclos térmicos. Por último, tras definir el mejor conjunto de condiciones de impresión para cada composición de polvo, se produjeron varias muestras para evaluar las propiedades mecánicas. / [CA] La fabricació additiva, de les seues sigles en anglés AM (Additive Manufacturing) és un procés que construïx objectes sòlids tridimensionals mitjançant la superposició de materials basats en un model de disseny assistit per ordinador. L'AM està cridada a convertir-se en la pròxima revolució industrial, transformant el panorama del desenvolupament i la producció. L'AM oferix nombrosos avantatges, com a possibilitats de disseny complexes i flexibles, l'eliminació de processos intermedis com el mecanitzat, la independència dels costos de producció de la grandària dels lots, la reducció dels residus de material, les estructures lleugeres, les reparacions personalitzades de les màquines i la capacitat de desenvolupar nous materials, entre altres avantatges. En les tecnologies de fabricació additiva que empren un raig làser com a font d'energia, la matèria primera inicial (en forma de pols o filferro) és fosa per la font de calor làser de manera controlada, capa a capa, fins a crear un component amb dimensions finals o quasi finals. Estes tecnologies impliquen sotmetre el material imprés a un procés tèrmic únic, en el qual el material es funde en una àrea molt específica i després es refreda ràpidament a velocitats extremadament altes de fins a 10^6 K/s. Per tant, les microestructures que sorgixen dels processos de fabricació en AM diferixen significativament de les que s'aconseguixen en els processos tradicionals. A més, els materials que s'empren principalment en l'AM no s'han dissenyat explícitament per a estes tecnologies. Les característiques específiques dels processos d'AM poden utilitzar-se per a aconseguir microestructures i propietats diferents en acers que han sigut adaptats per a aprofitar les ràpides velocitats de refredament i la història tèrmica del procés, entre altres factors.
De moment, el nombre de qualitats d'acer comercials disponibles en el mercat de l'AM és limitat. Diverses indústries demanden nous graus d'acer amb menor densitat per a disminuir el pes sense comprometre les propietats mecàniques. Els acers amb alt contingut en manganés es consideren materials molt prometedors per a aplicacions estructurals a causa de la seua excepcional combinació de resistència i ductilitat, amb una baixa densitat. No obstant això, malgrat les seues excepcionals propietats, els acers amb alt contingut en manganés s'enfronten a diverses limitacions o reptes durant les tècniques de processament convencionals. Afortunadament, la solidificació ràpida pot resoldre estos problemes. En este sentit, les tecnologies d'AM basades en làser proporcionen velocitats de refredament ràpides, així com flexibilitat en termes de disseny geomètric. Els nous reptes d'estes tecnologies implicaran la microsegregació i l'esquerdament en calent, o hot cracking en anglés, que es produïxen durant la solidificació.
Esta tesi està dedicada a explotar el mètode CALPHAD per a realitzar càlculs termodinàmics amb la finalitat de dissenyar diversos acers amb alt contingut en manganés que puguen previndre eficaçment els problemes de solidificació ràpida en AM. Les composicions d'acer dissenyades es van produir en forma de pols per a AM mitjançant atomització amb gas. Es van analitzar les pólvores per a determinar la seua microestructura en relació amb la química i la velocitat de refredament. Ajustant adequadament els paràmetres d'impressió, estes pólvores d'acer amb alt contingut en manganés es van imprimir amb èxit en AM, donant lloc a densitats relatives superiors al 99.9%. Es va analitzar la microestructura d'estes mostres totalment denses i es va comparar amb les seues respectives pólvores, amb la finalitat d'identificar qualsevol diferència resultant de les variacions en la velocitat de refredament i els cicles tèrmics. Finalment, desprès de definir el millor conjunt de condicions d'impressió per a cada composició de pols, es van produir diverses mostres per a avaluar les propietats mecàniques. / [EN] Additive manufacturing (AM) is a process that builds three-dimensional solid objects by layering materials based on a computer-aided design model. AM is set to become the next industrial revolution, transforming the landscape of development and production. AM provides numerous benefits, including complex and flexible design possibilities, the elimination of intermediate processes like machining, production cost independence from batch size, reduced material waste, lightweight structures, customized machine repairs, and the ability to develop new materials, among other advantages. In additive manufacturing technologies that employ a laser beam as an energy source, the initial raw material (in the form of powder or wire) is melted by the laser heat source in a controlled manner, layer by layer, until a component with final or nearly final dimensions is created. These technologies involve subjecting the printed material to a unique thermal process, where the material is melted in a very specific area and then rapidly cooled at extremely high rates of up to 10^6 K/s. Hence, the microstructures that arise from the manufacturing processes in AM differ significantly from those achieved in traditional processes. Moreover, the materials predominantly employed in AM have not been explicitly designed for these technologies. The specific characteristics of AM processes can be utilized to achieve distinct microstructures and properties in steels that have been tailored to take advantage of the rapid cooling rates and thermal history of the process, among other factors.
For the moment, the number of commercial steel grades available in the AM market is limited. Various industries are demanding new steel grades with lower density to decrease weight without compromising mechanical properties. High manganese steels are regarded as highly promising materials for structural applications due to their exceptional combination of strength and ductility, with low density. Nevertheless, despite the exceptional properties of high manganese steels, they encounter various limitations or challenges during conventional processing techniques. Fortunately, rapid solidification may solve these issues. In this sense, laser-based AM technologies provide rapid cooling rates, as well as flexibility in terms of geometric design. The new challenges of these technologies will involve micro-segregation and hot cracking occurring during solidification.
This thesis is dedicated to exploiting the CALPHAD method to perform thermodynamic calculations in order to design various high manganese steels that can effectively prevent fast solidification issues in AM. The steel compositions designed were produced in the form of powder for AM using gas atomization. Powders were analyzed to determine their microstructure in relation to the chemistry and cooling rate. By adjusting properly, the printing parameters, these high manganese steel powders were successfully printed in AM, resulting in relative densities exceeding 99.9%. The microstructure of these fully dense samples was analyzed and compared to their respective powders, in order to identify any difference resulting from variations in cooling rate and thermal cycling. Lastly, after defining the best set of printing conditions for each powder composition, various samples were produced to evaluate the mechanical properties, to determine the correlation between the composition, microstructure and properties of these steels. In addition, lattice structures that are close to final part geometries were constructed to quantify the energy absorbed during compression by one of these high manganese steels. The results were then compared to those of 316L, revealing that the high manganese steel absorbs roughly twice as much the specific energy in compression. This finding demonstrates the potential of these novel AM steels for use in industrial applications. / Sánchez Poncela, M. (2024). Design of High Mn Fe-Mn-Al-C Low Density Steels for Additive Manufacturing [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/205174
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