@phdthesis{Abang2016, author = {Abang, Roger Atini}, title = {Thermodynamic modeling and experimental investigations of high temperature corrosion and oxidation due to increased power plant cycling}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-40032}, school = {BTU Cottbus - Senftenberg}, year = {2016}, abstract = {With the rapid growth of renewable energy sources (RES) in the power generation mix in accordance with the German energy transition policy ('Energiewende'), fewer baseload coal power plants will be required. Future power generation will be supplied through decentralized power utilities such as off-shore wind parks and also through high operational flexibility of existing conventional coal power units. High operational flexibility means conventional power plants have to increase cyclic operations to cope with feed-ins from variable-RES such as wind and solar. Unlike medium and peak load power plants that can react quickly to load changes and power ramps, baseload power plants are not suited for such operations. Important technical requirements for flexible operation include among others; frequent start-ups and shut-downs, a minimum downtime, shorter startup time and short operational periods. Baseload coal power plants however do not meet these requirements. This increased cyclic mode of operation can have severe impacts on vital power plant components such as superheater and reheater tubes resulting in high temperature cyclic oxidation/corrosion especially because these plants were not designed for frequent cyclic operations. To optimize plant operations, minimize material damage and reduce operational and maintenance cost, it is therefore important to understand the oxidation and corrosion risk to plants materials associated with this flexible mode of operation. In this context, thermochemical modeling in FactSage 6.4ᵀᴹ as well as experimental investigations were carried out. For the experimental investigations, five commercial coal boiler superheater and reheater materials, namely T91, VM12-SHC, TP347-HFG, DMV304 HCu and DMV310 N were exposed for 1000 hours under discontinuous isothermal oxidation conditions and 1000 hours thermo-cyclic oxidation conditions at a metal surface temperature of 650 °C. The synthetic corrosive flue gas consisted of a mixture of CO₂, O₂, SO₂, N₂ and H₂O. The test material samples were partly covered in fly ash to investigate the effect ash deposits on the corrosion and oxidation behavior of the test materials. After exposure metallographic analysis by means of light microscopy and scanning electron microscopy (LOM and SEM-EDS) were carried out to study the oxide morphology and micro-structural properties of the materials. The oxidation kinetics (weight change) results showed significant oxide growth rates (weight gain) under cyclic oxidation conditions especially in the martensitic alloys - T91, VM12-SHC. Furthermore, metallographic analysis revealed severe oxide spallation in the ash covered sections of these alloys. The austenitic materials (TP374-HFG, DMV310 N) with the exception of DMV304 HCu showed good oxidation behavior with minimal oxide growth both under isothermal and thermal cyclic conditions. However, severe grain boundary attack and internal sulphidation were found in these alloys. DMV310 N showed the best corrosion and oxidation performance. The thermochemical modeling calculations supported the experimental results.}, subject = {Thermo-chemical modeling; Oxidation; High temperature corrosion; Cycling; Flexible generation; Oxidation; Hochtemperaturkorrosion; Lastwechsel; Flexible Kraftwerke; Thermochemische Modellierung; Kraftwerk; Hochtemperaturkorrosion; Lastwechselverhalten; Oxidation; Thermodynamik; Modellierung}, language = {en} } @phdthesis{Roszak2023, author = {Roszak, Robert}, title = {Fluid structure interaction analysis considering the structural behavior}, doi = {10.26127/BTUOpen-6662}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-66629}, school = {BTU Cottbus - Senftenberg}, year = {2023}, abstract = {The development of computer technologies allows using numerical simulations in the early stages of aircraft design more and more often. The role of both wind tunnels and initial test flights used to validate of solutions seems to be diminishing. Big systems for three-dimensional simulations of Fluid-Structure Interactions (FSI) constitute highly specialized and costly software. Most of the codes are based on many simplifications. One of them is the assumption of linearity of the structural model being in contradiction with real-life situations. The postdoctoral dissertation presents the results of simulations for complex, multi-scale objects and non-linear structure models and extended structure testing in relation to damage in macroscale analysis. What is crucial for carrying out the assumed analyses is to extend a numerical tool comprising a flow and a structural program and a space grid deformation model for a system allowing to take into consideration the non-linearity of the structure. The point of reference for testing the suggested approaches are the existing solutions of the aeroelastic linear problems. Results of the recent research might be applied for the construction of increasingly common unmanned aerial vehicle (UAV). Modern structure is a key element that affects the basic parameters as mass or range of these vehicles. Until now the research and development of the aeroelastic calculation algorithm for commonly used materials in the framework of linear geometry and linear-elastic material behavior was used. The current developments of materials for light-weight design common use of 3D printing technology causes the increasingly widespread use of new alternative materials in the aviation industry. This is particularly true for the design and construction of UAV, where the basic requirements are the lightness of the structure and the maximum range. Unfortunately, the fulfillment of the above criteria means that the materials used are often loaded not only in a elastic range but also more often above this limit. In case of analyzing aeroelastic phenomena for a loaded structure we should take a closer look at the behavior of the material outside the elastic range in which the damage occurs. The process of destroying in the face of such dangerous phenomena as flutter in aircraft constructions requires a deeper analysis of the mechanics of materials, in particular for new materials and their manufacturing techniques. As part of joint experiments and numerical simulations, detailed research was carried out to describe the behavior of printed materials, which will be increasingly used in the design of aircraft structures. Extending the postdoctoral dissertation with the research carried out at BTU will allow further development of the existing FSI algorithm, taking into account the structural behavior more accurately and the possibility of predicting damage processes.}, subject = {FSI; DMD; Material nonlinearity; Aeroelasticity; Materialnichtlinearit{\"a}t; Aeroelastizit{\"a}t; Dynamic mode decomposition; Fluid-structure interaction; Flugzeugbau; Aeroelastizit{\"a}t; Nichtlineares mathematisches Modell}, language = {en} } @phdthesis{Zhang2020, author = {Zhang, Haoyin}, title = {Novel type of biomedical titanium-manganese-niobium alloy fabricated by arc melting and metal injection moulding}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-51280}, school = {BTU Cottbus - Senftenberg}, year = {2020}, abstract = {Titanium and its alloys have been widely used as implant biomaterials due to their suitable combination of mechanical properties and biological compatibilities. At present, about 70-80\% of implants are made of metallic biomaterials. Compared with magnesium alloys, stainless steel and cobalt alloys, titanium alloys have a higher specific strength, high corrosion resistance, and excellent biocompatibility. With research, Ti-Nb biomedical titanium alloys have been constantly developed. In the Ti-Nb alloy, the amount of Nb is usually from 16\% to 42\% (wt.\%) which is about 10\% to 30\% (at.\%). As reported, Mn as a trace element to the human body has the potential to be used in bio-materials. Therefore, this study aims at the partial replacement of Nb by Mn to reduce the costs, without deteriorating the mechanical properties. Moreover, it must be ensured good biocompatibility and corrosion resistance. This is the first investigated on Ti-Mn-Nb ternary alloys. In this work, According to β single-phase field, Ti-xMn-yNb (x=4, 10, 16; y=2, 8, 14, at.\%) alloys (arc-melted) have been fabricated. The Ti-Mn-Nb alloys are investigated by optical microscopy (OM), X-ray diffraction (XRD), hardness test, transmission electron microscopy (TEM) and mechanical testing. By screening study on alloy, Ti-10Mn-14Nb (at.\%) (Ti-10Mn-23.7Nb (wt.\%)) is the optimal alloy with tensile strength (760 MPa) and elongation (10.5\%). After that, the Metal Injection Moulding (MIM) is used to prepare Ti-Mn-Nb alloys. The MIM method can greatly reduce the processing cost. MIM Ti-xMn-yNb (x=3, 4, 6; y=1, 2, 4, at.\%), Ti-4Mn-14Nb and Ti-10Mn-14Nb alloys are fabricated. Among them, a very good combination of mechanical properties is achieved for MIM processed Ti-4Mn-2Nb (at.\%) (Ti-4.5Mn-3.8Nb (wt.\%)), namely a YS of 642 MPa, UTS of 725 MPa and high ductility of 16\% elongation to fracture. With further investigations, when the yttrium content is 0.1\% (at.\%), the tensile strength of Ti-4Mn-2Nb-0.1Y (at.\%) (Ti-4.5Mn-3.8Nb-0.18Y (wt.\%)) is increased to 785 MPa while elongation of 12.9\%. These mechanical properties already exceed Ti-6Al-4V (ASTM F2885 Grade 5 undensified). In the in vitro evaluation, in comparison with MIM pure titanium, human osteoblasts MG63 adhered as well and proliferated on the surface of MIM Ti-Mn-Nb specimens. In the supernatant after cell culture, the Ti-Mn-Nb alloy shows similar osmolality and pH value results as MIM pure titanium. By LDH assay and DNA isolation, the MIM Ti-Mn-Nb alloys are not found to be toxic to MG63 cells. In the study of corrosion resistance in Hanks' balanced salt solution (HBSS) at 37 °C, the corrosion current densities as well as the impedance of MIM Ti-Mn-Nb alloys are all better than those of MIM pure titanium and even better than those of MIM Ti-6Al-4V alloy.}, subject = {Titanium; Metal injection moulding; Niobium; Mangane; Biomedical; Titan; Mangan; Niob; Metallspritzguss; Biomedizin; Biomedizin; Lichtbogen; Metallspritzguss; Nioblegierung; Schmelzen; Manganlegierung; Titanlegierung}, language = {en} } @phdthesis{Berding2016, author = {Berding, Jens}, title = {Entwicklung eines wandlungsf{\"a}higen Pressensystems mit Servospindelantrieb}, publisher = {Winter-Industries GmbH}, address = {Berlin}, isbn = {978-3-86624-633-1}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-41227}, school = {BTU Cottbus - Senftenberg}, year = {2016}, abstract = {Unternehmen der Umformtechnik sehen sich vermehrt steigenden Anforderungen bei schwankenden Einflussfaktoren ausgesetzt. F{\"u}r eine wirtschaftliche Fertigung sind Pressen erforderlich, die sich den steigenden Anforderungen und schwankenden Einflussfaktoren anpassen und mit m{\"o}glichst hoher Produktivit{\"a}t, Qualit{\"a}t und Wirtschaftlichkeit eine breite Produktpalette fertigen k{\"o}nnen. Unter diesen Voraussetzungen bietet sich der Einsatz von kraftgebundenen Servospindelpressen an. Diese erm{\"o}glichen frei programmierbare St{\"o}ßelbewegungsprofile und stellen die Nennkraft {\"u}ber den gesamten St{\"o}ßelhub zur Verf{\"u}gung. Allerdings erf{\"u}llen die bekannten Servospindelpressen die Forderung nach wandlungsf{\"a}higen Pressen, welche an unterschiedliche Anforderungen angepasst werden, besonders die {\"A}nderung der Abfolge von Teilprozessen und der Austausch von Maschinenkomponenten, nur sehr eingeschr{\"a}nkt. Aus diesem Grund wird ein neuartiges wandelbares Pressensystem entwickelt. Dieses soll dem Anwender weitreichende Vorteile bringen: Die Nennkraft des Pressensystems wird auf mehrere, in Durchlaufrichtung der Teile frei positionierbare und miteinander koppelbare Pressenmodule mit eigenen Pressenantrieben und -st{\"o}ßeln aufgeteilt. Durch Servospindelantriebe werden prozessangepasste St{\"o}ßelbewegungsprofile f{\"u}r einzelne Teilprozesse erm{\"o}glicht. Dies erlaubt eine wandelbare Anordnung von Teilprozessen, wodurch die Prozesskette skaliert werden kann. Unterst{\"u}tzt wird die Wandlungsf{\"a}higkeit des Pressensystems, indem es durch den Anwender erweitert werden kann und sich weitere Prozesse wie Schweißen, L{\"o}ten oder Kleben integrieren lassen. Ziel der Arbeit ist die Entwicklung des beschriebenen wandlungsf{\"a}higen Pressensystems mit Servospindelantrieb f{\"u}r die Komplettbearbeitung von kleinen Bauteilen. Grundlage bildet die Untersuchung des Standes der Pressentechnik und der Methoden der Produktentwicklung. Der Entwicklungsprozess wird in die Phasen Anforderungsfindung, Konzeptfindung und Entwurfsfindung gegliedert. Zur {\"U}berpr{\"u}fung wird aus dem Entwurf ein Prototyp ausgearbeitet. Im Anschluss werden Maßnahmen zur Produktstrukturierung durchgef{\"u}hrt, aus denen die Weiterentwicklung des Entwurfes zu einer Typengruppe und einem Baukastensystem resultiert. Zum Abschluss wird das Pressensystem bewertet, sein Einsatzspektrum beschrieben und das Pressensystem innerhalb bestehender Pressen eingeordnet.}, subject = {Umformtechnik; Pressensystem; Wandlungsf{\"a}higkeit; Servopresse; Spindelpresse; Forming technology; Press system; Adaptability; Servo press; Spindle press; Presse ; Spindel ; Servomotor}, language = {de} } @phdthesis{Xu2020, author = {Xu, Peng}, title = {Enhancement of tensile fracture resistance of metal-injection-molded β titanium alloys biomaterials via diverse sintering pathways}, doi = {10.26127/BTUOpen-5512}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-55126}, school = {BTU Cottbus - Senftenberg}, year = {2020}, abstract = {The powder metallurgically produced beta titanium alloys (traditional PM beta Ti-alloys) have long been plagued by high impurities contamination. For binder-based powder technologies, they originate from the sintering atmosphere, the debinding processes and the starting powders. In general, a normal carbon residual of binder-based powder technologies is capable of incurring the formation of aligned TiCx particles along beta grain boundaries (GB-TiCx) in most classes of beta Ti-alloys. Whereas, oxygen atoms are likely to deteriorate the ductility of PM Ti alloys by promoting the formation of diverse brittle phases and/or altering the deformation modes. Such materials exhibiting rather low toughness to strain ratios are not an option for critical structural applications, where catastrophic damage is completely unacceptable. In this study, biotolerant metastable beta Ti-20Nb-10Zr alloys, containing a certain amount of carbon, oxygen residuals originated from materials processing and consequently 0.5 vol.\% in situ synthesized TiCx particles, were fabricated via metal-injection-molding (MIM). With varying yttrium (Y) addition, the effects of Y-induced oxygen scavenging, beta-grain refinement and porosity increment on tensile properties were systematically investigated. To scavenge oxygen from the beta Ti-matrix, the Y elemental powder with a maximum particle size of 15 µm (e.g. <12 µm or 1200 mesh) is more appropriate than the commonly used <45 µm (i.e. 325 mesh) sized powder or larger ones and without significant detrimental effect on the as-sintered density of beta Ti-alloys. A novel toughening strategy was proposed by regulating TiCx precipitation evolution and resultantly adjusting particles distribution pattern. Synchrotron radiation identified that two separate TiCx precipitation-type reactions occurred at the beta phase region and the alpha/beta region. In a narrow temperature range between these two precipitation reactions, dissolution of carbides was observed just below alpha/beta transus. Y addition can postpone TiCx precipitation. On the basis of those mechanisms, adjusting TiCx particle distribution was proposed for the first time, specifically a combination of yttrium addition (Y) and carbide spheroidization reprecipitation annealing (CSRA). As a result, aligned GB-TiCx particles were adjusted to dispersed intragranular TiCx particles. An apparent toughening effect (≈ 113\% increment reaching elongation = 8.3\%) was achieved after TiCx redistribution, while non-optimally aligned TiCx pattern seriously limited tensile toughness of materials. Here, the mechanisms of TiCx redistribution behavior and its toughening are elucidated systematically.}, subject = {Metal-Injection-Molding; Titanium; Carbide; Fracture; Oxygen; Metallspritzguss; Titan; Karbid; Fraktur; Sauerstoff; Biomaterial; Metallspritzguss; Titanlegierung; Carbide; Sauerstoff; Bruchverhalten}, language = {en} } @phdthesis{Eisentraut2024, author = {Eisentraut, Mark}, title = {Beschleunigung des Isothermschmiedens von Titanaluminiden durch gezielte Mikrostrukturentwicklung}, doi = {10.26127/BTUOpen-7000}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-70000}, school = {BTU Cottbus - Senftenberg}, year = {2024}, abstract = {Titanaluminide (TiAl) sind vielversprechende Hochtemperaturwerkstoffe, die aufgrund ihrer geringen Dichte und hohen spezifischen Festigkeit insbesondere in der Luft- und Raumfahrtindustrie Anwendung finden. Die Mikrostruktur von TiAl-Legierungen spielt eine entscheidende Rolle f{\"u}r deren mechanische Eigenschaften und Bearbeitbarkeit. Durch gezielte Mikrostrukturentwicklung kann die Umformbarkeit und damit die Effizienz der Bearbeitungsprozesse verbessert werden. Deshalb wurde in der vorliegenden Arbeit eine neue Prozesskette f{\"u}r das Schmieden von Titanaluminiden entwickelt und erprobt, um die Prozesszeiten zu reduzieren und die Wirtschaftlichkeit des Werkstoffs zu erh{\"o}hen. Die Prozesskette umfasst drei Schritte: eine Vorw{\"a}rmebehandlung, eine beschleunigte Umformung und eine eigenschaftsbestimmende Nachw{\"a}rmebehandlung. Die spezifische Vorw{\"a}rmebehandlung zur Verbesserung der Umformbarkeit f{\"u}hrt zu einer Mikrostruktur mit einem geringen lamellaren Anteil, einem hohen β/β0-Gehalt und einem hohen Anteil an zellularen Reaktionen. Dadurch konnte die maximale Fließspannung im Vergleich zum geHIPten Zustand um ca. 20 \% gesenkt werden. Es wurde ein Prozessfenster definiert, in dem der w{\"a}rmebehandelte Zustand eine geringere Fließspannung und eine verbesserte Schadenstoleranz im Vergleich zum geHIPten Ausgangsmaterial aufweist. Basierend auf den Ergebnissen von Stauchversuchen mit konstanter Dehnrate wurden Dehnratenprofile mit variablen Dehnraten entwickelt, um den Umformprozess zu beschleunigen. Diese Umformung mit variabler Dehnrate wurde sowohl an zylindrischen Proben als auch an Gussrohlingen durchgef{\"u}hrt. Die Ergebnisse zeigten, dass die Prozesszeiten im Vergleich zur Umformung mit konstanter Dehnrate um 50 bis 70 \% reduziert werden konnten, ohne eine erh{\"o}hte Materialsch{\"a}digung zu verursachen. Zudem wurde festgestellt, dass die f{\"u}r diese Legierung entwickelten Dehnratenprofile auf andere TiAl-Legierungen {\"u}bertragbar sind. Abschließend wurde eine eigenschaftsbestimmende Nachw{\"a}rmebehandlung eingesetzt, die zu einer Mikrostruktur mit verbesserten Eigenschaften f{\"u}hrte. Die mechanischen Eigenschaften der mit der neuen Fertigungskette erzeugten Proben sind dabei mit denen der konventionellen Fertigungskette vergleichbar.}, subject = {Mechanische Eigenschaften; Mechanical properties; Titanaluminide; Titanium aluminides; TNM-B1; Umformung; Forming; Titanaluminide; Mikrostruktur; Schmieden; Umformen; Prozesskette; Optimierung}, language = {de} } @phdthesis{SanthanakrishnanBalakrishnan2020, author = {Santhanakrishnan Balakrishnan, Venkateswaran}, title = {Near-net-shape semi-finished products for the local reinforcement and repair of fibre reinforced plastics}, doi = {10.26127/BTUOpen-5266}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-52667}, school = {BTU Cottbus - Senftenberg}, year = {2020}, abstract = {The European Parliament and Council has defined a mandatory specific emission target of 95 g CO2/km by 2020 for passenger cars. Vehicle weight is a significant factor contributing to fuel consumption. Reducing the weight of the vehicle can be one promising option for decreasing CO2 emissions, which becomes a top priority for the automotive industry. In this research, two approaches were used to address the need. One involved developing structural parts using fibre reinforced plastics (FRP), and the other involved designing and developing FRP-metal hybrid laminates, which were constructed by reinforcing FRP locally to the metal surface. Existing joining techniques such as riveting, bolting, adhesive joining, ultrasonic welding, and flow drill joining techniques require additional processing steps to perform the joining, which could considerably increase processing time, cost, and energy expenditure. The present work describes a method to join FRP and metals using the adhesion strength of the investigated polymers. The developed FRP-metal hybrid laminates combine the advantages of metal and FRP together. Steel hot-stamping is known to yield very high strength. Fibre reinforced plastic-metal hybrid laminates were developed using hot stamped steels to transfer their superior mechanical properties to the final structure. To utilize the complete lightweight potential of thermoset and thermoplastic polymers, FRPs and FRP-metal hybrid laminates were developed using both the polymers. Along with this increased demand for FRP structures, there is growing interest in a repair technique in the automotive industry. The second objective of this thesis consists of designing and developing a new repair technique, which regains the strength and stiffness properties of the damaged part. The existing scarf repair technique is not suitable for thin laminates, which have limited access to the damaged area. Perforation damages were introduced into the FRP structures using a low-velocity impact load. A modified injection repair technique is used to repair these damaged FRP structures. Non-destructive techniques were utilized to understand the damage and the effectiveness of the repair.}, subject = {Fibre metal laminates (FML); Lightweight construction; Composite/metal hybrids; Joining technology; Injection repair; Faser-Metall-Laminate (FML); Leichtbaukonstruktion; Komposite/Metall-Hybride; F{\"u}getechnologie; Injektionsreparatur; Faserverst{\"a}rkter Kunststoff; Metallischer Werkstoff; Schichtverbundwerkstoff; Laminat; F{\"u}gen}, language = {en} }