@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{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{Naveed2015, author = {Naveed, Muhammad}, title = {Study of crystallography and erosion behavior of single and multilayer coatings used for applications in aero engines}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-35620}, school = {BTU Cottbus - Senftenberg}, year = {2015}, abstract = {Erosion of aero-engine components has been identified as a serious problem since the World War II. During this time various attempts have been made to study this phenomenon in order to improve the life and performance of the used components. Flights in particulate environments led to the drastic degradation of the performance due to blunting of blade edges, reduction of chord and increase of tip clearance. Measures like coating of blades and high efficiency filters have been introduced in order to protect the aero-engine components from wear in dusty environments. In the present work an effort has been made in order to deposit various single and multilayer coatings for the erosion protection of Inconel718 alloy used as the substrate material. Inconel718 finds its applications in high pressure compressors within gas turbines. To deposit the various coatings onto the substrate material the Direct Current (DC) Method has been used as a Physical Vaporization Deposition technique. The architecture of the investigated coatings is on one side a single layer TiN coating and on the other side multilayer Cr/CrN, Ti/CrN and TiN/CrN coatings as well. The experimental results show that bilayer Cr/CrN multilayer coatings possess a variation in mechanical properties with the change in bilayer period. Additional adhesion tests show various spallation mechanisms which are related to the coating architecture. Process parameters used during the coating process had an influence on the coating growth. The growth of coatings as in form of a V-structure results in low adhesion between the coating and the substrate or the previous coating layer. Another change in the coating structure is obtained by changing metallic or ceramic layer between CrN layers. The presence of coating defects, like droplets, on the coating surface acts as voids within the coating structure decreasing the structural integrity of the coatings. The conduction of a phase analysis of Cr/CrN multilayer developed the presence of a mixture of fcc-CrN, hcp-Cr2N and bcc-Cr phases. A variation in the phase formation is found to be dependent on the bilayer period of the coatings. A complex XPS analysis and a related thermodynamic study indicate that the variation in the binding energies and thermodynamic stability of the CrN and Cr2N phases are responsible for their stable formation during the coating deposition. TiN single layer coatings showed the formation of a single phase fcc-TiN. The presence of Cr2N, Cr2Ti, TixNy phases is found during the deposition of Ti/CrN and TiN/CrN coatings. An additional Scherrer analysis to evaluate the determination of crystal size pointed out the presence of nano-crystals of various phases within the coatings. Stress analysis of the tested Cr/CrN coatings showed compressive stresses within the coatings, respectively. In this case only slight differences in stress values are observed for Cr1/CrN3 and Cr0.25/CrN3.75 coatings. Erosion tests of Cr/CrN coatings showed erosion protection at shallow incidence angles (30°) as compared to uncoated Inconel718 alloy. In contrast, no erosion protection is obtained during the erosion at oblique angles. Crack deflection at the metal-ceramic interface, shearing of columns, internal distortion of CrN layer, radial and cone cracking, step shear, inter- and intra-columnar crack propagation are reported as some of the processes occurring during the erosion process. The presence of micro droplets is reported to be one of the major causes of low adhesion between the coating and substrate or structural weakness of coating, which provokes a rapid removal of the coating. Within the last section of the present thesis the correlation between various models (proposed through contact mechanics) and erosion rate is studied. It is found that for the single layer and multilayer coatings a low correlation between H3/E2 and erosion rate exists. A study of the ratio between elastic modulus of coating to elastic modulus of substrate (Ef/Es) in order to describe the erosion mechanism in a coating show non-conformance of the results as proposed by contact mechanic theories. A difference in the elastic modulus of consecutive coating layers (E1-E2) showed that no correlation can be found for the coatings during erosion at 30° and 90°.}, subject = {Multilayer Coatings; Solid Particle Erosion; Multilagenschichten; Erosionsschutzschichten}, 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{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} } @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{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} }