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CRC871: Near net shape turbine blade repair using a joining- and coating hybrid process (Subproject B1)

Bild zum Projekt SFB871: Endkonturnahe Turbinenschaufelreparatur durch füge- und beschichtungstechnische Hybridprozesse (Teilprojekt B1)
Duration:01/2018 – 12/2021
Funded by:DFG
Brief description:Components of aircraft engines and stationary gas turbines like turbine- and compressor blades (airfoils and vanes) are subjected to extreme conditions. To increase the life time of such components, maintenance, repair and overhaul (MRO) play a paramount role. The subproject B1 of the CRC871 develops and investigates a near net shape joining and coating hybrid process which allows to shorten the state of the art process chain of turbine blade repair significantly. Since the turbine blades taken into consideration in this subproject are components of high pressure turbines, the focus of this work lies on nickel based alloys. The shortening of this process chain is achieved by applying the nickel based filler-metal together with the hot gas corrosion protective coating (e.g. NiCoCrAlY alloys) and the thermal barrier coating (TBC) with aluminium as a bond coat onto the substrate using the thermal spray technology. The following material combination results: substrate/nickel based filler-metal/NiCoCrAlY/Al/TBC. Subsequently this coating systems is subjected to a heat treatment which represents a common brazing- and aluminising process. The working hypothesis of this research project is that a thermal coating and joining process can be transferred to a hybrid technology and to achieve qualitative as well as economic advantages at the same time.
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Arc Welding of Titanium-Alloys

Bild zum Projekt Lichtbogenschweißen von Titanlegierungen
Duration:01.01.2018 bis 31.12.2021
Brief description:Focus of sub-project B6 is the development of repair methods for compressor blisks made from titanium alloys based on arc processes. Quality maintaining regeneration is achieved by the combination of flux effects and application of seeding agents as well as by controlled additive build-up of structures. To enhance the functional properties of blade regions that were regenerated and/or are subject to erosion, a localized surface nitriding using a plasma arc process is part of investigations. Besides practical welding tests, work programme includes structural analysis, measurement of hardness and residual stresses, fatigue evaluation and the implications of observed material properties on the expected service life of regenerated blisks.
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Precision forging of cast preforms

Bild zum Projekt Präzisionsschmieden gegossener Vorformen
Duration:01/2018 – 12/2020
Funded by:DFG
Brief description:The technology of forging cast preforms (casting/forging) represents an alternative to the conventional production of steel components with complex geometries. The main aim of the planned investigations is to obtain information on the development of the mechanical and microstructural properties of the structure of the casting preform during forming and the identification of suitable process parameters.
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Aluminiumlegierungen mit angepasstem Schmelzintervall für das prozessintegrierte Ausschäumen beim Strangpressen

Bild zum Projekt Aluminiumlegierungen mit angepasstem Schmelzintervall für das prozessintegrierte 
Ausschäumen beim Strangpressen
Duration:05/2017-05/2020
Funded by:DFG
Brief description:The aim of this project is to develop the basics for the direct foaming of hollow structures made of aluminum alloys by means of composite extrusion. The outer structural material of these components takes over force distribution, corrosion protection, as well as acting tensile forces, while the internal foam material increases the bending stiffness, damping properties, and energy absorption of the system. For instance, such extruded, foam-filled structures can advantageously be used in the automotive industry as crash profiles. Nevertheless, process-integrated foam-filled structures or foam structures with a dense cover layer are not yet used industrially in mass production, despite their superior property spectrum. This could be due to the limited freedom of design in the production of foam-filled components with dense cover layers, in addition to elaborate additional operations required during their manufacturing process, such as additional foaming, manipulation, and joining processes
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Mechanisms of action of nanoparticles as novel grain refiners for thermomechanically highly stressed cast aluminium components

Bild zum Projekt Wirkmechanismen von Nanopartikeln als neuartige Kornfeiner für thermomechanisch hoch beanspruchte Aluminiumgussbauteile
Duration:05/2017 – 04/2020
Funded by:DFG
Brief description:The aim of the research project is the targeted analysis of the use of nanoparticles of different size and composition as grain refiners in silicon-containing aluminium casting alloys, as well as the quantitative and qualitative evaluation of the effect of the grain refining effect on the microstructure and the thermomechanical properties.
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Selective thermally oxidated tool surfaces for dry deep drawing

Bild zum Projekt Selektiv thermisch oxidierte Werkzeugoberflächen im Einsatz beim trockenen Tiefziehen
Duration:01.01.2014 – 01.01.2020
Funded by:DFG
Brief description:Friction and wear have significant influence on tool life in sheet metal forming. In this regard, ‎lubricants are generally used to extend the tool life. Since the use of these ‎lubricants does not correspond with the target of sustainable production, methods for ‎dry forming are investigated in the priority program 1676. Within the scope of this project, the production and the use of tool coatings, which ‎are produced by selective thermal oxidation, are investigated.‎ The oxidative heat treatments of the tool surfaces take place at a defined oxygen residual. Therefore the treatments are carried out under a protective gas atmosphere (nitrogen) and monosilane doped nitrogen, respectively. So it is possible to generate ‎oxide coatings with a defined chemical composition and thickness.‎ The investigation results from the first project period show that oxide layers ‎produced under certain process conditions have friction coefficients, that are ‎comparable to those measured on the tool surfaces after applying lubricants.‎ In the second phase of this subproject, an innovative heat treatment method has been ‎developed. Conventionally, a continuance heating process was used to create the oxide layers. This manufacturing method requires an increased processing time and an increased amount of process gases. In ‎comparison, the new heat treatment method deploys a tube furnace, which ‎allows the production of oxidised-coated specimens with reduced protective gas ‎consumption. ‎In addition, an inductive heating unit was installed in the heating system to decrease ‎process time d. Moreover, various surface modifications were ‎investigated in the second phase of the project including friction and wear ‎experiments. These, and further results from the numerical investigations carried out ‎in the first and second project phases are necessary to understand the approach of ‎dry metal forming researched and thus to ensure the industrial application of this forming ‎technology. This point, applying the gathered experience in ‎dry metal forming in industrial processeswill be the core of the research project in ‎its third phase, whereby a modular deep-drawing tool is going tobe built, which will be ‎equipped with oxidised mold inserts. By manufacturing different components with various geometries using the planned ‎tool system it is possible to increase the load collective on the generated oxide layers ‎successively and thus investigating the behaviour of the layer system in a ‎conventional deep-drawing process.‎ At the same time, the heat treatment process to produce the oxide layers will ‎be continually optimised. Furthermore, the developed numerical model, which was validated on test ‎specimens, will be deployed on the geometries investigated in this phase as well. ‎Finally, the recreating process of the layer system will be investigated, so that more ‎information about the tool life can be determined.‎
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Dynamic magnetic-data storage on thermal sprayed layers

 
Duration:01/2017-12/2019
Funded by:DFG
Brief description:The aim of the project is the manufacturing and characterisation of thermal sprayed layers with magnetic properties to store data dynamically on the component’s surface. It will be examined if the field of application of established coating systems, such as hard coatings or corrosion protection (e.g. WCCo(Cr)), can be extended to magnetically store data. Additionally, the ferrimagnetic maghemite (ɣ-Fe2O3), which is not used as a spray material yet, should be examined as an alternative for thermal spray coatings. Based on these results, the next step of the project is the understanding and quantification of the magnetic properties of the manufactured thermal spray coatings.
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In-situ investigations of the physicochemical mechanisms of surface activation of stainless steels during heat treatment applying brazing-process-like conditions in reducing process gases

Bild zum Projekt Forschungsvorhaben MA 1175/48-1: In-Situ Untersuchungen der physikalisch-chemischen Mechanismen der Oberflächenaktivierung von Edelstählen bei Wärmebehandlungen unter lötprozessähnlichen Bedingungen im reduzierendem Schutzgas
Duration:01.04.2014-31.12.2019
Funded by:DFG
Brief description:The deoxidation of work piece surfaces in a furnace brazing process using reducing process gases is the precondition for its wettability with braze metal and determines the success and the quality of the resulting brazed joints. While the necessary thermodynamic conditions e.g. for the reduction of native oxidized stainless steel surfaces with hydrogen or monosilane are known, the kinetics of such reactions is not investigated up to now on the atomic scale. However, the latter is essential for a general understanding of the process and is the precondition for further developments in brazing technology. In this context, the use of monosilane doped nitrogen as cost efficient and resource saving alternative to hydrogen, which is state of the art in furnace brazing, is of mayor scientific and technologic interest. Scope of this project is the investigation of the physicochemical mechanism of surface deoxidation, when brazing stainless steels in a conveyor belt furnace using hydrogen and monosilane containing process gases. The experiments planned are expected to provide detailed information of the chemical reactions and surface conditions during brazing, which are essential for the advancement of fluxless brazing processes with regard to lower process temperatures, robust processes and demanding stainless steel specifications. Starting point of the project are thermodynamic calculations of possible reactions, for which analytical transport models of oxide layer formation are specified and adjusted for the actual problem. These theoretical considerations are tested by in situ analysis of surface reactions - also time resolved - covering typical process conditions in a conveyor belt furnace, in order to get kinetic information about changes in the surface region of stainless steels with respect to crystal structure, atomic coordination (bond distances, coordination numbers), chemical bonding and atomic diffusion. For this purpose TR-XRD (Time Resolved X-ray Diffraction) and time resolved EXAFS/XANES (Extended X-ray Absorption Fine Structure/ X-ray Absorption Near Edge Structure) measurements using synchrotron radiation are performed. The simulation of realistic furnace conditions during this measurements are carried out in a high temperature cell for X-ray experiments, which is manufactured specially for the requirements to be simulated. The mentioned X-ray measurements are performed at the DELTA synchrotron light source in Dortmund and at the Deutsche Elektronen-Synchrotron (DESY, Hamburg) On the basis of the performed measurements and complementary brazing experiments in a conveyor belt furnace with ex-situ analysis of the heat treated specimen a physical model will be developed, which takes into account all physicochemical aspects of surface changes observed in the simulation of the brazing processes.
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Cu-Al-composite braze metals

Bild zum Projekt Forschungsvorhaben 07.088 (AiF-Nr. 19.839 N): Cu-Al-Verbundlote
Duration:01.01.2018-31.12.2019
Funded by:AiF-DVS
Brief description:With the aluminum bronzes copper alloys are known, which have a good temperature strength and a high corrosion and oxidation resistance. However, these alloys cannot be used as braze metals in furnace processes e.g. for brazing CrNi steels, since the high oxygen affinity of the aluminum leads to a passivation of the braze metal preventing it from wetting the steel surface. To solve this problem braze metal composites consisting of an aluminum core and a copper capping layer are used, wherein the braze alloy composition is adjusted by the ratio of the material thicknesses used. The desired copper-aluminum braze alloy is formed then "in situ" during the melting process of the composite. The composite geometry and the temperature control during furnace brazing then determine within wide limits the braze metallurgy and thus the technological properties of the resulting brazed joint. Objective of the project is to investigate these dependencies and to develop suitable aluminum-copper composite brazes and appropriate furnace brazing processes. The braze metal composites can be produced both as wires and as sheets, making them suitable for a variety of brazing applications. Both suppliers of braze materials and producer of brazed assemblies made of CrNi steels, which are required in automotive construction, in heating and air-conditioning technology or in apparatus construction in a wide variety of shapes and designs, can benefit from this.
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Research project VP 1249 (AiF-IGF 19602N): intelligent materials II

Bild zum Projekt Forschungsvorhaben VP 1249 (AiF-IGF 19602N): Intelligente Werkstoffe II
Duration:10/2017 – 09/2019
Funded by:AiF-FOSTA
Brief description:Cyclically occurring stresses on forging tools lead to a constant damage of the tool surface and ultimately to wear-related failure of tools. In context of this research wear resistance shall be improved by a combination of intelligent steels and a material-specific adapted nitriding. With an additional mass fraction of 2 % manganese and 1.5 % nickel, the austenite start temperature (Ac1b temperature) is deliberately lowered for the hot-work steel 1.2365, resulting in recurring cyclic surface hardening during forging process as a result of thermomechanical conditions (see Figure 1). At thermomechanically lower loaded areas where no re-hardening occurs due to insufficient stress, the nitride layer contributes to the wear protection of the forging tool.
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Investigation and use of thermo physicochemical mechanism of surface deoxidation using silane-doped argon in low vacuum brazing processes

Bild zum Projekt Forschungsvorhaben MO881/22-1: Aufklärung und Nutzung thermophysikalisch-chemischer Mechanismen der Oberflächendesoxidation zum Löten von Edelstählen unter silandotiertem Argon-Grobvakuum
Duration:01.12.2014-30.07.2019
Funded by:DFG
Brief description:The objective of the proposed project is the investigation and clarification of deoxidation mechanism of natural passivated steel surfaces in vacuum brazing processes, in order to understand and then optimize vacuum brazing of stainless steels. Firstly, analytical methods will be developed, which allow a surface-sensitive “in situ” analysis of metal surfaces during annealing of metal specimens using vacuum-furnace-like process conditions. The methods must tolerate variations of the heating conditions as well as a variation of the gas atmosphere concerning its composition and its pressure up to 1 mbar. Particularly the use of silane-doped Argon for realizing defined deoxidizing conditions is a major aspect of the investigations planned, since significant improvements for the brazing of stainless steels are expected from this gas mixture in a low vacuum process. The “in situ” investigations will be confirmed by vacuum brazing tests using similar process conditions. A vacuum furnace, which is equipped with a gassing system that allows for defined silane-argon-compositions up to 1 mbar within the furnace recipient, is used for tempering and brazing steel specimens with appropriate braze metals. From an analysis of the brazed specimen a correlation between the “in situ” investigations of surface deoxidation and the wetting behavior of brazes on the steel surfaces as function of the performed process conditions will be worked out. Furthermore the experimental data from „in situ“-measurements will be used to clarify the deoxidation mechanism and quantify the kinetics of the detected surface reactions. These data are the base for a physical model to be developed, which describes the thermodynamic and kinetic aspects of the observed surface reactions and shall allow for a prediction of optimal process conditions for vacuum brazing of particular difficult-to-braze stainless steels.
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Innovative Mischbauweisen mit dünnwandigen Aluminiumdruckguss-Strukturen mittels Bolzensetzen und fließlochformenden Schrauben

Bild zum Projekt Innovative Mischbauweisen mit dünnwandigen Aluminiumdruckguss-Strukturen mittels Bolzensetzen und fließlochformenden Schrauben
Duration:01.01.2017 - 30.06.2019
Funded by:AiF
Brief description:Aluminum casting components are becoming increasingly popular due to their specific weight, high stiffness, and individual geometries. A prerequisite for the use of these cast components in mixed structures with aluminum or steel sheets is the application of a suitable joining technique. Due to the design individuality of these components, there is often only a one-sided access to the joint area. Joining methods which allow one-sided joining of casted aluminum components are, for example, flow-drilling screwing or tack-setting. For these methods, the local joint stiffness is of decisive importance. However, for cast components, local joint stiffness can be very variable. For example, hollow areas present low stiffness, while joint areas between ribs often show increased values. Reduced joint stiffness complicate the joining process and lead to component deformation, gaps between the joining partners, and in hybrid joining, to a poorer adhesive bond. This is due to the joining forces introduced statically or abruptly during the joining process. To solve the described problem, a holistic approach to the component and joining areas design is pursued. This will allow, in an early stage of designing and production planning, to select the according joining processes for components with one-sided accessibility, and therefore, improve manufacturing planning. The project results can be used in the design of cast components in order to optimize them for one-sided joining processes. The sample component to be developed can be used by SMEs and OEMs in the early stages of product development to sample component stiffness and to investigate the influence of production related disturbances. Project partner: Universität Paderborn, Laboratorium für Werkstoff- und Fügetechnik (LWF)
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Production of areas with reduced strength in press-hardened components by means of a tempering station

Bild zum Projekt Erzeugung von Bereichen mit reduzierter Festigkeit an formgehärteten Bauteilen mittels einer Temperierungsstation
Duration:01/07/2017 – 30/06/2019
Funded by:DFG
Brief description:The transfer project should adapt the methodology of a local temperature control of austenitized materials before or between individual forming steps for the specific setting of a desired microstructure in a practical application using the example of press hardening. Graded material properties are obtained in the press-hardened components based on locally adapted microstructures by employing the technology of a two-phase spray cooling process in collaboration with the project partner, Volkswagen AG. Press-hardened components that have regions with locally reduced strength show an increased ability to join and facilitate trimming. In the proposed transfer project, the microstructural adjustment should take place through a targeted pre-cooling on localized component areas before the actual press hardening process. A suitable heat control unit must be developed to design such a pre-cooling by means of two-phase spray and simultaneous temperature control of component regions, which should not cool down and must be kept at a temperature above Ac3. For this purpose, numerical simulation models and experiences from the ongoing project can be used. In the pre-cooled areas first a temperature in the range of bainite or pearlite transformation should be adjusted to achieve a bainitic microstructural transformation during the subsequent and uniform cooling in the press-hardening tool. Areas quenched from a temperature level above Ac3 undergo a martensitic transformation due to cooling in the press-hardening tool. As an example, possible difference in hardness due to different temperature control is shown in Fig. 1. The advantage of this procedure is that no locally tempered press-hardening tools are required and short holding times during hot stamping can be used. Ultimately, it should be verified whether the tempering station is practically useful for the local formation of different microstructures by means of local cooling and maintaining the local austenitized state of the sheets at the same time. At Leibniz Universität Hannover, the design of the tempering station and the hot stamping is carried out at the Institute of Forming Technology and Machines, and the development of the pre-cooling device and the microstructure characterization is carried out at the Institut für Werkstoffkunde (Materials Science).
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Herstellung und Applikation thermoplastumhüllter Lotpartikel für die löttechnische Fertigung mit pulverförmigen Hartloten AiF-Projekt

Bild zum Projekt Herstellung und Applikation thermoplastumhüllter Lotpartikel für die löttechnische Fertigung mit pulverförmigen Hartloten
Duration:01.02.2017-31.01.2019
Funded by:AiF
Brief description:Within the scope of this project, brazing powders coated with a thermoplastic sheath are examined. The purpose of the coating is to fulfill two tasks: On the one hand, the metallic particles are electrically insulated by their coating, so that it is possible to aplly them by means of electrostatic powder coating processes prior to brazing, which is a new method to aplly brazing powders. From a scientific-technical point of view, suitable thermoplastics have to be found and a simple and economical coating process for the brazing powder has to be developed. Substantial technical, economic and ecological advantages can be achieved compared to solvent based brazing pastes. Users of this technology include both brazin powder products manufacturers who are expanding their portfolio and users of brazing technology who are enabled to use the product for new economical solder application processes.
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Residual stresses in brazed hybrid steel joints

Bild zum Projekt Forschungsvorhaben P 1197 (AiF-Nr. 18157N): Eigenspannungen gelöteter Stahlmischverbindungen
Duration:01.11.2016-31.10.2018
Funded by:AiF-FOSTA
Brief description:In many cases, e. g. in vehicle or plant construction, heating or energy technology, manufacturing processes based on brazing technique are applied. In this context many components made of high-alloy steels are produced which are brazed in vacuum or protective gas furnaces at temperatures above 900°C. Often joining of ferritic and austenitic steels is desiderable or even necessary. Due to different thermo-mechanical properties of the materials and the solder used, high amounts of residual stresses can occur, which considerably reduce strength in comparison with joints made of similar steel types. In this project residual stress states are analyzed and assessed in detail depending on material combinations, geometries of the joints and the process parameters applied furnace brazing operations. From the results, strategies will be derived and validated to achieve minimum residual stress amounts in brazed dissimilar joints. The main objective of the project is to develop appropriate constructions and brazing processes adapted to the steel combinations used for dissimilar joints to achieve minimum residual stress amounts. As a result, manufacturers should be able to produce reliable high-strength hybrid components made of different stainless steel qualities by appropriate brazing processes applying reliable and process routes.One can expect that especially ferritic stainless steel qualities, which up to now are hardly used in practice will gain increasing importance as construction materials.
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Influence of nitrogen in the brazing atmosphere on the creep resistance of corrosive loaded CrNi-steel joints brazed with nickel based filler metals

Bild zum Projekt Forschungsvorhaben 07.084 (AiF-Nr. 19.056 BG): 
Untersuchungen zum Einfluss von Stickstoff in der Lötatmosphäre auf die Lebensdauerfestigkeit Ni-Basis-gelöteter CrNi-Stahl-Verbindungen unter korrosiver Belastung
Duration:01.04.2016-30.09.2018
Funded by:AiF-DVS
Brief description:The widespread use of nitrogen as a process or cooling gas sometimes leads to massive problems in the brazing of CrNi steels with nickel-base braze metals. A reduction of the corrosion resistance of the brazed joints are observed then, which is apparently related to the nitriding of the materials in the area of the joining zone. Within the scope of the research project, it is therefore intended to clarify to what extent and under which brazing process conditions nitrogen enrichment takes place in the brazed seam area and how this influences the corrosion behavior and also the lifetime of the brazed joints. Specifically, it is investigated which correlation exists between the degree of nitrogen enrichment and the selected process conditions during brazing, how the different nitriding degrees affect the electrochemical corrosion behavior of the brazed joints and what consequences the degree of nitriding and the resulting corrosion damage have on the durability of the brazed joints. The results are used to derive process conditions for furnace brazing, in which the consequences of nitrogenification can be avoided without having to forego nitrogen, which is very cost-effective and easy to handle in terms of safety compared to alternative process gases (argon, hydrogen).
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SFB TR73 - Subproject C6: Fatigue Behavior of Sheet-Bulk Metal Formed Parts

Bild zum Projekt SFB TR73 - Teilprojekt C6: Ermüdungsverhalten von blechmassivumgeformten Bauteilen
Duration:07/2013 - 12/2020
Funded by:DFG
Brief description:Objective of subproject C6 - "Fatigue behavior" is the analysis of fatigue mechanisms due to cyclic loads for components produced by sheet-bulk metal forming. Defects in the microstructure, which are formed or grow due to the high degree of deformation in these forming processes, act as possible crack initiators and have an as yet unexplored influence on the components fatigue life.
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SFB TR73 - Teilprojekt C4: Analyse der belastungspfadabhängigen Schädigungs- und Mikrostrukturentwicklung zur numerischen Auslegung von Blech-Massiv-Umformprozessen

Bild zum Projekt SFB TR73 - Teilprojekt C4: Analyse der belastungspfadabhängigen Schädigungs- und Mikrostrukturentwicklung zur numerischen Auslegung von Blech-Massiv-Umformprozessen
Contact:Projekteiw.uni-hannover.de
Duration:01/2013 - 12/2020
Funded by:DFG
Brief description:Der Prozess der Blech‐Massiv‐Umformung soll die Herstellung von Bauteilen mit Funktionselemente aus Feinblech‐Halbzeugen ermöglichen. Aufgrund komplexer Belastungspfade und Umformsequenzen muss in diesem Projekt ein neuer Ansatz zur Vorhersage der Werkstoffschädigung und Restbelastbarkeit entwickelt werden.
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SPP 2006 CCA-HEA - Subproject 5: Investigation of the correlation between microstructure and functional fatigue in high entropy shape memory alloys

Bild zum Projekt SPP 2006 CCA-HEA – Teilprojekt 5: Untersuchung des Zusammenhangs zwischen Mikrostruktur und funktionaler Ermüdung in Hochentropie-Formgedächtnislegierungen
Duration:10/2017 – 09/2020
Funded by:DFG
Brief description:High entropy shape memory alloys (HESMA) have special mechanical properties and are used for many challenging applications. For example, they show a reversible martensitic transformation at temperatures well above 100°C. However, the evolution of the functional properties comprising of five or more alloy components are still fully unexplored. Thus, the objective of the present study is to analyze the basic functional and mechanical properties as well as functional fatigue under complex thermo-mechanical loading conditions of these novel metallic alloys. Particular attention will be placed on the local microstructural phenomena and the macroscopic behavior.
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Induktionswärmetechnik als praxisrelevantes Vor- und Nachbehandlungsverfahren zur Verbesserung der Schweißnahtqualität beim Unterwasserschweißen von Feinkornstählen mit erhöhtem Kohlenstoffäquivalent

Bild zum Projekt Induktionswärmetechnik als praxisrelevantes Vor- und Nachbehandlungsverfahren zur Verbesserung der Schweißnahtqualität beim Unterwasserschweißen von Feinkornstählen mit erhöhtem Kohlenstoffäquivalent
Duration:01.07.2018 - 30.06.2020
Funded by:AiF
Brief description:Ziel des Forschungsprojektes ist die Erarbeitung einer effektiven Alternative zur aufwändigen Temper-Bead-Technik, um höherfeste Stähle und Feinkornbaustähle mit einem Kohlenstoffäquivalent von CEV > 0,4 hyperbar nass schweißbar zu machen. Dabei sollen der Wasserstoffgehalt und das Gefüge kontrollierbar werden.
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SPP 1640 – Teilprojekt A4: Elektrochemisch unterstütztes Fügen blechförmiger Werkstoffe

Bild zum Projekt SPP 1640 – Teilprojekt A4: Elektrochemisch unterstütztes Fügen blechförmiger Werkstoffe
Duration:bis 31/12/18
Funded by:DFG
Brief description:This research project investigates the cold pressure welding of similar and dissimilar metals by incremental forming and inline electrochemical surface activation. The project intends to identify and analyse the mechanisms of cold pressure welding in order to improve current cold welding processes in terms of process flexibility and joint strength. The joining with electrochemical support (EUCF) is a new process that intends to cold pressure weld a broad range of metal pairs. Major innovations include the determined modification of the micro and macroscopic surface structure e.g. by the inline activation of metallic surfaces using electrochemical reactions (like oxide reduction and metal layer deposition). The course and result of the following pressure welding process is supported by a special tool set-up and an adapted incremental process control to ensure a sufficient bonding process with locally restricted high deformation ratios. The pressure welding process will be realized with support of robotic actuators and an incremental process control to allow both partial and fully joining of hybrid products/assemblies made from various semi-finished parts.
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FOR1766 – Teilprojekt TP4: Hochtemperatur-Formgedächtnislegierungen – Von den Grundlagen zur Anwendung

Bild zum Projekt FOR1766 – Teilprojekt TP4: Hochtemperatur-Formgedächtnislegierungen – Von den Grundlagen zur Anwendung
Duration:bis 10.2018
Funded by:DFG
Brief description:The research unit FOR1766 combines partners from Ruhr University Bochum, University Kassel, Ludwig-Maximilians-University München and Leibniz University Hanover. For many of the envisaged applications, damage evolution under cyclic thermal and/or mechanical load will govern the fatigue life of high-temperature shape memory alloys (HTSMAs). Thus, the focus of the project in Hanover is the functional and structural thermomechanical fatigue of HTSMAs. To analyse the mechanisms that lead to functional degradation, this subproject concentrates on the functional fatigue tests of Ti-Ta HTSMAs in isostress thermal cycling tests under tensile load conditions and also on the In-situ thermo-mechanical cycling experiments. To understand the structural fatigue processes, within this project, structural fatigue test under high cycle thermomechanical loading conditions and crack propagation test will be carried out. To gain a fundamental understanding of the dominating microstructural processes, both post-mortem and in-situ fatigue experiments in the neutron source will be conducted.
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Influence of local microstructure on the formability of extruded composite profiles

Bild zum Projekt SFB 1153 – Teilprojekt A1: Einfluss der lokalen Mikrostruktur auf die Umformbarkeit stranggepresster Werkstoffverbunde
Duration:07/2015 - 06/2019
Funded by:DFG
Brief description:Subproject A1 focuses on the development of a compound extrusion process which enables the continuous production of hollow profiles consisting of aluminum alloys and steel. The extruded profiles serve as a semi-finished product used in a subsequent forging process to produce bearing bushes (subproject B2), and therefore, they demand special properties. Besides the challenging process development, special focus is laid on sufficient weld seam properties and on the formation of continuous material bonding between aluminum and steel. The case-hardened steel (20MnCr5) acts as the wear-resistant functional surface of the bearing bushes. As seen in figure 1, the steel is inserted laterally as a tube into the modular extrusion die, especially designed so that the tube does not undergo deformation. The aluminum wrought alloy EN AW-6082 is then extruded onto the entire circumference of the steel profile via Lateral Angular Co-Extrusion (LACE). The quality of the metal bonding is determined first by the character of the bonding surface such as the presence of oxide layers and the creation of juvenile metallic surfaces during deformation, and second, by the intermetallic phases formed in the diffusion zone. The aim of this project is to investigate the influence of the interphase properties on the subsequent forging process and whether the bonding strength can be improved by process-dependent structural properties e.g. texture of the aluminum components, or the mechanical properties of the weld seam. The influence of the process parameters such as temperature, pressure, and time on the diffusion process in the bonding area will be examined accordingly in a deformation dilatometer. The results will be used for a numerical simulation of the process in a macroscopic model. The design of the extrusion process will be determined by means of numerical simulation, aiming at the formation of compound profiles with an adequate thin interphase suitable for the subsequent forming process. The joining zone of the extruded compounds will be analyzed using light and scanning electron microscopy techniques. The gained insights will be applied for the benefit of the process design and for the validation of the model.
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SFB 1153 – Teilprojekt A2: Wärmebehandlung für belastungsangepasste Werkstoffeigenschaften von Tailored Forming-Komponenten

Bild zum Projekt SFB 1153 – Teilprojekt A2: Wärmebehandlung für belastungsangepasste Werkstoffeigenschaften von Tailored Forming-Komponenten
Duration:07/2015 - 06/2019
Funded by:DFG
Brief description:Within the framework of the Collaborative Research Centre 1153 "Tailored Forming", heat treatment strategies for tailored forming components are developed in the subproject A2. The aim is a local adaptation of the material properties. In addition to this local adaptation, the heating and cooling processes over the entire process chain are also to be considered, thereby resolving conflicts of interest between forming and heat treatment parameters. Since the bond zone of the joining partners represents the main challenge, the analysis of their development (layer thickness, microstructural composition) is of particular importance in all process steps. In order to perform the heat treatment, a tempering arrangement based on induction heating and air-water spray cooling is developed (see Fig. 1). Following the hardening of the steel functional surfaces, a simultaneous heat treatment of the steel-aluminium compounds can be developed and analyzed using different process routes (Fig. 2)
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Grenzflächeneffekte und Einwachsverhalten von Magnesiumschwämmen als bioresorierbares Knochenersatzmaterial

Bild zum Projekt Grenzflächeneffekte und Einwachsverhalten von Magnesiumschwämmen als bioresorierbares Knochenersatzmaterial
Duration:09/2015-08/2018
Funded by:DFG
Brief description:Im Rahmen dieses Teilprojektes werden schwammartige Strukturen aus diversen Magnesiumlegierungen mittels Feinguss hergestellt. Durch Variation der Legierungselemente und Beschichtungen werden die Grenzflächeneffekte, wie die Degradation und das Anwachsen von Zellen, und die Biokompatibilität eingestellt. Die fertigen Implantate (gegossen und z.T. beschichtet) werden sowohl in einer Körperersatzflüssigkeit, als auch in Zusammenarbeit mit der Chirurgischen und Gynäkologischen Kleintierklinik der Ludwig-Maximilians-Universität München in vivo analysiert. Dabei können sich die Eigenschaften, vor allem die mechanischen Kennwerte, mit der Degradation stark verändern. Diese werden im Laufe der Degradation, wie auch das Korrosionsverhalten und die Biokompatibilität, analysiert. Ziel dieses Projektes ist die Herstellung von Knochenimplantaten auf Magnesiumbasis. Der Vorteil von Magnesium ist, dass es nicht toxisch und bioabsorbierbar ist, das heißt es wird vom Körper ohne eine schädliche Wirkung vom Körper abgebaut, während der Knochen in die poröse Schwammstruktur eindringen kann. In diesem Fall wird eine zweite Operation eingespart und die Gefahr für Komplikationen und mögliche Schäden im Körper reduziert.
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Investigation of combined influence of skin pass rolling and roller straightening of a thin sheet made of materials with different crystal lattice on microstructure, texture, static and fatigue strength

Bild zum Projekt Untersuchung des kombinierten Einflusses des Dressierens und Rollenrichtens von Dünnblechen aus Materialien mit unterschiedlichem Kristallgitter
Duration:01.10.2016-30.09.2019
Funded by:DFG
Brief description:Skin pass rolling and roller straightening represent the final operations in sheet production and decisively determine the resulting microstructural and mechanical properties of the products. In preliminary investigations, it was shown that the intensity of the influence of these forming operations depends inter alia on material lattice structure. Further investigation is required on the combined influence on sheet properties as a result of monotonous forming by skin pass rolling which induces material work hardening and cyclical forming by roller straightening, which could induce either work hardening or work softening. Since sheet metal parts are subject to not only static but also cyclical mechanical stresses in later operations the residual stress state is of essential significance in addition to work hardening or softening. Thus, a comprehensive material characterization is required concerning mechanical properties during static and cyclical stresses. The work programme of the planned project includes the analysis of changes in mechanical properties during static and cyclical stresses as well as the investigation of microstructure and texture of sheets during various skin pass rolling and roller straightening conditions including the s-shape enclosing the rolls. The scientific aim of the planned research project is the investigation of combined influence of monotonous forming during skin pass rolling and cyclical forming during roller straightening of sheets made of materials with different crystal lattices (DC01, Cu, α-Ti) on microstructure, texture, the level and sign of residual stresses, and the mechanical properties within the framework of static and cyclical experiments. The practical aim of the project is the development of an appropriate technology for production of sheets with load-adjusted microstructure, texture, and a high static and fatigue strength by a suitable combination of monotonous forming by skin pass rolling and cyclical forming by roller straightening conditions.
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Research project P1125 (AiF-IGF 19289N): Cryogenic treatment of tool steels to improve technological properties (Nanocarbide)

Bild zum Projekt Forschungsvorhaben P1125 Steigerung technologischer Eigenschaften durch 
Kryobehandlung von Werkzeugstählen (Nanocarbide)
Duration:01/2017 – 12/2019
Funded by:AiF
Brief description:Cryogenic treatment of tool steels increases toughness and wear resistance. The aim is to change the microstructure by precipitation of nanocarbides throughout the whole cross section (Figure 1). Integrating the cryogenic treatment in the heat treatment chain provides a substantial cost reduction as an alternative to coating and surface layer methods. This project will lead to a basic understanding of the efficiency of cryogenic treatment by investigating submicroscopic processes. These include microstructural investigations by means of scanning and transmission electron microscopy and mechanical tests.
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Extending the process limits for further processing of rolled semi-finished products by analysing the cause-effect relationships during roller straightening

Bild zum Projekt Erweiterung der Prozessgrenzen bei der Weiterverarbeitung von gewalztem Halbzeug durch Analyse der Ursache-Wirkungs-Beziehungen beim Planrichten
Duration:04/2017 – 03/2019
Funded by:AiF
Brief description:The aim of this research project is to develop a prognosis model for the description of relevant cause-effect relationships in the straightening process of steel and aluminium semi-finished products. The further processing of rolled strips in forming or cutting processes requires a flat running-in state with controlled and homogeneous properties. These required properties are usually not given due to imperfections that occur during the manufacture of semi-finished products and transportation as coils. The straightening process makes it possible to flatten the incoming material and influence the sheet properties in a controlled manner by utilizing alternating bending operations. Since process-related inhomogeneities of the infeed material affect the material properties after the straightening process, a specific correction of the straightening process over the unwound semi-finished product length is necessary. By identifying all relevant cause-effect relationships, guidelines are to be derived within a forecasting model for plan straightening, which allow a maximization of the process limits in the respective subsequent production stage.
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SFB871: Endkonturnahe Turbinenschaufelreparatur durch füge- und beschichtungstechnische Hybridprozesse (Teilprojekt B1)

Bild zum Projekt SFB871: Endkonturnahe Turbinenschaufelreparatur durch füge- und beschichtungstechnische Hybridprozesse (Teilprojekt B1)
Brief description:Ziel des Forschungsvorhabens ist die Kombination des Reparaturlötens mit der Heißgaskorrosionsschutzbeschichtung in einem gemeinsam integrierten Prozess, um die dem Stand der Technik entsprechende Prozesskette zur Turbinenschaufelreparatur zu verkürzen. Sowohl die Lotapplikation als auch die Heißgaskorrosionsschutzbeschichtung erfolgt durch thermisches Spritzen. Der Werkstoffaufbau soll dadurch weitestgehend endkonturnah realisiert werden. Die thermischen Spritzprozesse sollen so geführt werden, dass der Lötprozess im CVD-Diffusionsglühprozess (Chemical Vapor Depostition) als TLP-Bonding-Prozess (Transient Liquid Phase) integriert und somit als eigenständiger Prozess entfallen kann. Somit ist die Arbeitshypothese des Forschungsvorhabens, einen thermischen Beschichtungs- und einen Fügeprozess in einen gemeinsamen integrierten Hybridprozess überführen zu können und dabei sowohl qualitative als auch wirtschaftliche Vorteile zu erzielen. Die Bedeutung dieser Verfahrenskombination liegt in der Reduzierung an Schleifaufwand sowie in der Einsparung des bisher eigenständigen Vakuumlötprozesses und somit in verringerten Fertigungskosten.
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SPP 1959 Teilprojekt: Untersuchung der Mikromechanismen des elektroplastischen Effekts in Magnesiumlegierungen mittels Elektronenmikroskopie

Bild zum Projekt SPP 1959 Teilprojekt: Untersuchung der Mikromechanismen des elektroplastischen Effekts in Magnesiumlegierungen mittels Elektronenmikroskopie
Duration:31.12.2019
Funded by:DFG
Brief description:Der elektroplastische Effekt (EPE) umfasst all jene Änderungen mechanischer Eigenschaften von Werkstoffen, die durch Impulse hoher Stromdichten (> 1kA/mm²) hervorgerufen werden und nicht auf der Temperaturerhöhung auf Grund des elektrischen Wiederstands beruhen (Abb. 1 zeigt die durch einen Stromimpuls hervorgerufene Entfestigung in Mg). Im Fokus dieses Projektes stehen die Magnesiumlegierungen AZ31 (96% Mg, 3% Al, 1% Zn), WE43 (92,6% Mg, 4% Y, 3% Seltene Erden, 0,4% Zr) sowie poly- und einkristallines Magnesium als Referenz. Diese Legierungen vereinen eine geringe Dichte (etwa ein Viertel von Stahl) mit hoher Festigkeit, was sie für Anwendungen im Leichtbau interessant macht. Darüber hinaus finden sie aufgrund ihrer Biokompatibilität Einsatz in der Biomedizintechnik. Nachteilig ist die schlechte Umformbarkeit dieser Werkstoffe. Umformung unter Ausnutzung des EPE ist für diese Materialien vielversprechend. Um die zur Untersuchung dieses Effektes notwendigen, hohen Stromdichten zu erreichen, wird am Institut eine eigens konstruierte Hochstromimpulsanlage betrieben (siehe Abb. 2: a) Hochstromimpulsanlage, b) Universalprüfmaschine, c) Probe zwischen Kontaktplatten). Ziel dieses Projektes ist es, den Einfluss elektrischer Impulse auf das Verhalten während der Umformung zu untersuchen. Weiterhin sollen grundlegende Erkenntnisse über die zugrundeliegenden Mechanismen des EPE, die noch nicht vollständig verstanden sind, gewonnen werden.
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IRTG 1627 – Teilprojekt C5: Virtuelle Gestaltung und Herstellung von belastungsangepassten Rohren

Bild zum Projekt IRTG 1627 – Teilprojekt C5: Virtuelle Gestaltung und Herstellung von belastungsangepassten Rohren
Duration:01/10/2016 – 30/09/2019
Funded by:DFG
Brief description:Steel tubes featuring lengthwise tailored properties are promising for applications where a subsequent deformation requires locally adapted mechanical properties. Within this project suited models to predict both microstructure and mechanical properties due to a new manufacturing process consisting of tube forming, inductive heating and adapted quenching shall be developed. Locally adapted microstructures shall be realized by an intercritical annealing. The models shall be validated at the example of steel tubes manufactured in the workshop.
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