Chair of

High Temperature Materials

The interdisciplinary research initiative SmartProSys (Smart Process Systems for a Green Carbon-based Chemical Production in a Sustainable Society) aims to transform chemical and biotechnological production processes in a sustainable way. The aim is to transform energy-intensive, linear process chains based on fossil raw materials and energy sources into sustainable, completely closed, energy-saving cycles. The core question relates to plastic waste as well as biogenic residues and waste materials, which are to be systematically and efficiently converted into valuable molecules for new products. The sub-project relates to mechanical comminution processes using high-energy mechanical impact processes and their optimization. In addition, research is being conducted into how powdered plastics can be processed into new products.
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The aim of the project is to develop and qualify dispersoid-reinforced high-temperature resistant alloys for use as potential structural materials in the aerospace industry. Increased efficiency through increased operating temperatures and reduced weight lead to improved efficiency of turbines.
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Scientific goals
The idea of co-evolution at the human-technology interface is based on the fact that both the biological side and the technical side of an interface are not only dynamic and adaptive, but also take account of the other side in their adaptivity. Investigating this mutual influence leads to a deeper understanding of the causes of undesired processes, such as the maladaptation of inflammatory responses to unwanted changes in implant surfaces. This understanding then opens up new strategies to support desired processes in the sense of co-evolution. These include the possibilities of adaptive technologies and sensor approaches that can adjust to individual dynamics in the biological system, or the development of process-aware technologies that can bring about desired dynamics in the biological system.

Intended strategic goals
The modules of the TACTIC graduate school are designed to enhance translational expertise in the fields of medical technology, sensor technology, and artificial intelligence (AI). The goal is to strengthen research, development, and innovation activities on site. The aim is to closely interlink life sciences and engineering across all modules in order to facilitate future collaborative projects in this area. In addition, the integration of AI is intended to strengthen the profile area of medical technology. By internationalizing the research focus areas, TACTIC enables networking with EU partners, which is an important prerequisite for the alignment of consortia in order to strengthen science in Saxony-Anhalt.

Work program
The graduate school comprises three modules with a total of 9 doctoral students. A thematic network is established through doctoral topics, where at least two thematic modules are assigned concurrently. Each of the three thematic modules - Interaction, AI and Interface - is endowed with three doctoral positions (100%). The aim is to qualify our doctoral students for both the academic and private sector job markets. Interdisciplinary skills are to be imparted through doctoral seminars. Annual thesis committee meetings and TACTIC symposia support the development of doctoral students. An international network is to be established through presentations at international conferences and self-organized symposia.

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This project is a joint project within the framework of the DFG SPP 2419 "A contribution to the realization of the energy transition: Optimization of thermochemical energy conversion processes for the flexible use of hydrogen-based renewable fuels through additive manufacturing processes".
In this project, an additively manufactured bluff-body burner for the fuel-flexible, stable and safe combustion of NH3/H2 mixtures is considered. Accurate numerical simulations and detailed experiments are carried out to investigate the combustion characteristics and pollutant emissions. The burner design is then optimized (in terms of shape, size and position of the flame holder) to achieve efficient combustion behavior. Open and closed burner geometries are considered. The side of the flame holder in contact with the flame and other high temperature parts are produced by additive manufacturing using initially Ni-based alloys and later ultra-high temperature resistant refractory metal alloys to allow rapid geometry variations. The dynamics of the turbulent flame, the interactions between flame and wall, the limit of stable combustion, flashback and heat release are investigated. Finally, an optimal bluff-body burner design is developed for stable, safe, fuel-flexible and clean combustion of NH3/H2 as a mixed fuel.
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V-Si-B alloys have been the focus of scientific material development for several years. Due to their outstanding specific mechanical properties, these alloys represent a promising alternative to Ni and Mo-based materials in the field of high-temperature alloys. In terms of its microstructure, the V-Si-B alloy system has some interesting similarities with the well-studied Mo-Si-B sister system. Both alloy systems form a ternary eutectic in the metal-rich region (e.g. vanadium) from a solid solution, V(Mk), and the two intermetallic phases V3Si and V5SiB2. Directional solidification allows the eutectic to be "grown" along the direction of solidification, which results in a strong directional dependence of the resulting mechanical properties (strength, creep resistance). Similar to Ni-based superalloys, these could be specifically adjusted for an application-relevant load case. The proposed project investigates the microstructure formation and the resulting properties (direction-dependent strength and creep properties) of directionally solidified, novel eutectic V-Si-B alloys. For this purpose, the zone melting process will be investigated and analyzed both ex-situ and the direct transition from the liquid to the solid phase at the moment of directional solidification in-situ.
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As part of the scientific and technical collaboration, the aim is to produce high-performance metal-matrix composites based on multi-component materials for high-temperature applications. In particular, the production of multicomponent materials is simplified by a combination of classic powder metallurgy and spark plasma sintering processes and should guarantee significantly improved (mechanical) properties. This method makes it possible to implement a material design tailored to specific applications and at the same time represents a scientific and technological challenge. In addition, the addition of ceramic particles makes it possible to increase the strength of the alloys. The technology to be tested could be applied on an industrial scale in the future.
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Metallic materials for applications as structural materials, e.g. in corrosive environments at different temperatures, must have a wide range of properties. By adding alloying elements, the properties can be influenced over a wide range. For example, the strength of molybdenum materials can be significantly increased by adding even small amounts of silicon. Other properties, such as tribological abrasion, the oxidation or corrosion rate and cyclic strength, are also heavily dependent on the selection, concentration and combination of alloying elements. In addition, the heat treatment condition of the alloys plays a major role in adjusting the range of properties to suit the application. For materials in the medical sector, e.g. implant materials, properties under varying stress conditions (cyclic loading) also play a decisive role. The aim of this project is to modify materials in such a way that hardness and wear resistance are increased and static and cyclic stress resistance is improved without reducing oxidation and corrosion resistance. The microstructure-property relationships are specifically influenced in order to create optimum conditions for the subsequent application.
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This project brings together the expertise of the chair "High Temperature Materials" at OVGU with the groups of Prof. H. Stone and Prof. N. Jones at the Department of Materials Science and Metallurgy of the University of Cambridge, UK.
The project focuses on materials development and understanding of microstructure-property-relations between the microstructure of multi-component metallic materials and their mechanical properties. Selected materials are examples from the class of biocompatible Ti-Nb-Ta alloys.

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Vanadium silicide materials represent a potential alternative to currently used high-temperature materials, in particular due to their excellent specific mechanical properties. For example, V-Si-B alloys from the vanadium-rich region of the three-material system consist of a ductile vanadium solid solution (V-Mk) and the two intermetallic phases V₃Si and V₅SiB₂. However, this alloy system, which has been little researched to date, has some surprising similarities to its well-studied neighboring system Mo-Si-B in terms of microstructure. In initial preliminary tests on V-Si-B alloys, significantly better specific compressive strengths were achieved in the temperature range from 600 °C to 900 °C compared to Ni-based alloys. However, the mechanism of phase formation and the correlation of the microstructure-property relationships are still completely unexplored. The primary objective of this project is the development of novel V-Si-B alloys for high temperature applications. The aim is to develop ternary-eutectic alloys. In a series of V-rich binary and ternary test alloys, the phase formation and stability from the melt to the homogenized microstructure will be investigated. In the 2nd funding phase, research will focus on the significance of the newly discovered phase V8SiB4.
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The overarching aim of the ME-MAT project is to establish a network between cooperation partners from Germany, Poland, Bulgaria and Hungary.
The scientific focus is on adapting powder production for additive manufacturing processes. As the envisaged multiphase material from the group of refractory metals has an extremely high melting temperature and is also very reactive under environmental conditions, challenging research questions arise.
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The complex oxidation behavior of vanadium is the reason why vanadium-based alloys cannot be considered for use at high temperatures, despite their high strength and low density. In addition, vanadate changes very easily between different oxidation states and thus extremely accelerates the high-temperature corrosion of Ni, Co or Fe-based materials, especially when it is present in molten form. This also rules out the use of current vanadium alloys in the environment of these materials.
In order to make vanadium alloys usable at high temperatures, a completely new and innovative approach to oxidation protection with simultaneous oxide particle reinforcement is therefore to be pursued: The development of Mg- and Ca-containing oxide particles for the production of oxidation-resistant ODS vanadium-silicon alloys. The ODS particles introduced in sufficient concentration should prevent liquid phase formation at high temperatures. At the same time, the ODS particles are expected to have a strength-enhancing effect, which is to be quantified in the potential application area of such alloys from room temperature to 1050 °C.
The project aims to clarify (1) up to what volume fraction of MgO, CaO or magnesium orthosilicate particles homogeneous microstructures can be achieved in vanadium materials, (2) how high the necessary MgO, CaO or magnesium orthosilicate concentration is in order to prevent liquid phase formation or to provoke a self-protecting mechanism, (3) how great the strength-enhancing effect of the addition of oxide dispersoids is and how the ODS particles affect creep formation. to provoke a self-protecting mechanism, (3) how great the strength-enhancing effect is through the addition of oxide dispersoids and how the ODS particles affect the creep behavior of vanadium alloys.
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The efficiency of gas and aircraft turbines could be increased considerably by a slightly higher gas inlet temperature, which would result in a significant improvement in the environmental balance and use of resources. The nickel-based superalloys currently in use are very limited in this context due to their comparatively low melting temperature, which is why hardly any improvements can be achieved with this class of materials. The most promising candidates for replacing nickel-based superalloys are the refractory metal-based Mo-Si-B alloys that have been under discussion for some time and whose range of properties is most balanced both at room temperature and at higher temperatures. In addition, earlier studies have shown that the addition of vanadium within these high-temperature alloys leads to a significant reduction in density, which would predestine them for possible use in aerospace technology.
The biggest challenge for these alloys is still their oxidation resistance, which needs to be improved in this respect. In particular, the range between 600 °C and 800 °C must be regarded as extremely critical, as this is where so-called "pesting", a catastrophic oxidation failure, occurs. From a temperature of 1000 °C, however, a protective borosilicate layer begins to form on the surface after a certain time, which protects the material from further oxidation.
The main focus of this project is the development and optimization of Mo-40V-9Si-8B materials, which are additionally provided with a coating [MoSi₂/RHEA Mo-Ta-Ti- (Cr, Al)] in order to meet the requirements of the aerospace industry in terms of mechanical properties and oxidation resistance. To this end, a suitable alloying strategy must first be developed for both the substrate and the coating material. Subsequently, a corresponding powder metallurgical production route is to be established via mechanical alloying. The base material is to be produced via a corresponding sintering process, while the oxidation protection layer is to be applied by means of high-performance cathode sputtering or pack cementing. In the final step, various tests (microstructure analysis, mechanical properties, oxidation resistance, etc.) will be carried out on both the uncoated and coated material in order to test the applicability of the developed material system as a structural material.
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Since the CCAs are being actively explored for next-generation structural materials for high-temperature applications and therefore, they should have a high creep resistance besides that a comprehensive understanding of their creep and fracture behaviors is also indispensable.
Among the several anomalies existing in the creep behavior of HEAs, the foremost important is the stress exponent, n, calculated from the Berkovich nanoindentation creep tests turns out to be much larger than that calculated based on the uniaxial stress relaxation and spherical nanoindentation creep tests, and this could not be explained using classical creep theory for crystalline metals. It is still uncertain whether the classical creep theory for conventional metals are applicable for the HEAs.
The Fe32.3Al29.3Cu11.7Ni10.8Ti15.9 CCA, developed by OVGU-HT Materials group – whose compression behavior was studied under a constant displacement test with quasi static strain rate between room temperature (RT) and 1100°C revealed a stable single phase bcc microstructure with precipitates at the grain boundaries. The high temperature deformation and creep behavior of this material will be studied during a 3 months visit of Prof. Puspendu Sahu, Professor of Physics), Jadavpur University, Kolkata, India. In addition, TEM analyses are planned to perform at Jadavpur University with the deformed materials to get insights into the deformation mechanisms.

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Multi-component materials are known as alloys which are based on a variety of elements in equiatomic or highly concentrated fractions, instead of the concept of alloys based on one mayor element. Materials classes like High-Entropy alloys (HEAs), Medium-Entropy alloys (MEAs) and Compositionally Complex Alloys (CCAs) belong to these systems. The special feature of multicomponent alloys is due to the physical and thermodynamic conditions (high entropy effect, cocktail effect, sluggish diffusion effect, etc.), which lead to outstanding mechanical and physical material properties. Especially refractory elements such as Mo, Nb, Ta and Ti have emerged as essential components regarding the development of high-temperature materials. However, an additional aspect has rather moved into the background: the biocompatibility of many refractory metals. This property is considered as a key aspect in the development of multicomponent alloys for biomedical applications. In the course of this research project, materials conception and alloy development is carried out at the chair of high-temperature materials of Otto-von-Guericke University Magdeburg, whilst biocompatibility experiments and validation are conducted in cooperation with the chair of experimental orthopedics under supervision of Prof. Dr. rer. nat. Jessica Bertrand. The aim of this project is to develop a novel multi-component alloying system with outstanding mechanical properties, combined with optimized biocompatibility with respect to different biological cells and tissue for the use in biomedical applications.

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As part of the DFG joint project launched in 2020, complex, multifunctional oxidation protection coating systems were developed for the material protection of molybdenum (Mo)-containing refractory metal alloys. Such alloys exhibit higher thermal stability than the nickel-based superalloys previously used as turbine materials. With sufficient long-term stability, they could therefore be operated in turbine applications at temperatures 150 K higher, which would result in an increase in turbine efficiency. However, the oxidation of Mo and the evaporation as Mo oxide are proving to be a problem, which inevitably leads to the mechanical disintegration of a corresponding component and requires protective coatings of a few tens to a few hundred micrometers thick, preferably with a self-healing function to prevent cracking in the coating.
Such a coating system, consisting of a so-called preceramic polymer - an oligomeric chemical compound that can be converted into a ceramic by heat treatment -, particulate fillers such as silicon, boron and hexagonal boron nitride, was tested in long-term oxidation experiments and shows promising properties on selected Mo-containing alloys.
As the layer thicknesses cannot be extended indefinitely, a supplementary application was submitted to the above-mentioned application in order to combine the coating process based on filled preceramic polymers with the so-called pack cementation process - a coating process in which protective components such as boron and silicon are applied from the powder bed using transport agents via diffusion processes in the gas phase - and thus a) to further increase the layer thicknesses and b) the effectiveness of the protective layers obtained. Initial results are promising and show that it is possible to combine both processes to produce oxidation protection coatings with thicknesses of more than one hundred micrometers. The work on combining both processes is being systematically investigated as part of a Walter Benjamin Research Fellowship funded by the DFG.
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The International Graduate Program at Tohoku University in Sendai, Japan, was opened in 2018 with the participation of numerous colleagues from Asia, Europe and the USA. Prof. Manja Krüger and Dr. Georg Hasemann from Otto von Guericke University Magdeburg are involved in the program (see photo). Together with our Japanese colleagues Prof. Kyosuke Yoshimi and Ass. Prof. Shuntaro Ida and use the unique equipment in the laboratories of Tohoku University in Sendai and Otto von Guericke University Magdeburg.
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The recycling of plastics is an important issue in terms of environmental sustainability, recyclability and of waste management. The development of proper technologies for plastic recycling is generally recognized as a priority. To achieve this aim, the technologies that have been developed and applied in mineral processing can be adapted to recycling systems. In particular, the improvement of comminution technologies is one of the main actions to improve the quality of recycled plastics. The aim of this work is to study the comminution processes in milling for different types of plastic materials.

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This project is sponsored as part of the Philipp Schwartz Initiative of the Alexander von Humboldt Foundation.

The optimization of the microstructure is essential for a balanced property profile of metallic materials in the low and high temperature range. The generation of a matrix-reinforcement phase structure is the focus of this project. To achieve this goal, the method of mechanical high-energy grinding or mechanical alloying is to be used. This method is used, for example, for oxide-dispersion strengthened alloys. For the synthesis of high-performance high-temperature materials, a particulate hard phase (boride, silicide or oxide) is first to be enclosed with a ductile metallic phase in order to produce core-shell particles that are compacted in a subsequent sintering process.
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Mo-Hf-B and Mo-Zr-B alloys as a new class of refractory alloys are potential candidates in stationary and mobile turbine applications. Due to the high melting points of the constituents high-temperature strength and creep strength are expected up to 1,400 °C. Those high service temperatures, in turn, may result in higher turbine efficiencies and may reduce primary energy consumption.

As a manufacturing route, directional solidification via zone melting as a new processing approach for Mo-Hf-B and Mo-Zr-B results in low oxygen (< 50 ppm) impurities, which is essential to avoid embrittlement of these alloys; moreover the materials possess an anisotropic lamellae-reinforced microstructure.

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The demand for new high temperature alloys increases due to economic reasons and stricter climate protection and resource conservation requirements. For applications in the field of energy conversion, new Mo-Si-B materials are in the focus of current research. There is a specific interest in alloys with a continuous Mo matrix phase and silicide particles, which provide an acceptable fracture toughness and high creep resistance at the same time.
A drawback of potential applications of Mo-Si-B alloys, e.g. as rotating turbine blades, is the density of > 9 g/cm³. Therefore, this project aims into a density reduction of this alloy type, meeting values of < 8 g/cm³. This is challenging because significant losses in the fracture toughness and the creep resistance should be avoided.

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The work focuses on the development and characterization of novel multiphase high-temperature materials based on a Mo solid solution phase (Moss) reinforced with intermetallic Mo2ZrB2 and Mo2HfB2 phases with high melting points. Mo-Hf-B and Mo-Zr-B are a class of high-temperature materials that can find various applications, e.g. in the aircraft industry due to their high creep resistance at the targeted application temperatures, which is superior to modern nickel-based superalloys. However, the material behaviour in the medium temperature range is critical; here the molybdenum oxidizes, which makes material protection necessary.
As part of a sub-project, self-healing coating systems are being developed, characterized and tested in an application-oriented manner. These coating systems consist of an oxygen-free preceramic polymer and oxygen-binding filler particles such as Si and B. The conversion into a closed ceramic protective layer takes place in an inert atmosphere in the temperature range between 800 °C and 1200 °C.
Cyclic oxidation tests prove a protective effect (still to be improved) of the coating in the temperature range between 800 °C and 1000 °C; the effect at higher temperatures is currently being investigated.
Initial results of radiographic investigations show that a zirconium molybdate phase is formed by adding ZrO2 as an additional filler, i.e. the alloy components Mo react to form stable phases and remain in the sample; the evaporation of Mo oxides is largely prevented. The role of the protective layer in this process has not yet been fully clarified and is the subject of further investigations.
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The overall objective of the present project is to expand the existing collaboration between the research groups of Prof. Krüger at Otto-von-Guericke-University Magdeburg and Priv.-Doz. Bogomol from the National Technical University of Ukraine "Igor Sikorsky KPI” (Ukraine). Additionally, a new cooperation with the research group of Prof. Smyrnov from the same Ukrainian University will be established. The planned activities should enable a multilateral consortium on the basis of joint research on innovative materials.
The aim of the scientific and technical cooperation is to produce a novel Mo-based alloy for structural applications in a high-temperature gas turbine using an optimized powder metallurgical manufacturing process. The optimum combination of properties of Mo-based alloys can be achieved when the alloy has a fine-grained microstructure with a ductile Mo solid solution matrix and high temperature resistant intermetallic inclusions.

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The so-called High Entropy Alloys (HEAs) or Compositionally Complex Alloys (CCAs) represent a new and attractive class of materials with promising mechanical, physical and chemical properties. In contrast to conventional alloys based on a specific metal, they consist of at least 5 different elements in approximately equal atomic proportions. Such alloys have remarkable property profiles that differ significantly from those of the respective base components. Refractory metal-based HEAs appear to be particularly interesting; they typically consist of components with melting temperatures above 2000°C. These refractory metal-based HEAs are promising new material candidates for high-temperature structural materials in various areas of energy technology, e.g. as gas turbine blades or solar receivers. In addition, potential applications in medical technology are also conceivable due to their good biocompatibility.
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With the aid of density functional theory it is possible to adress many questions regarding metals and intermetallics likewise. Not only it is possible to predict the crystal structure of a solid, but also the ability to investigate and explain site preferences within intermetallics like borides and silicides comes in handy. It is also very important to determine the stability of metals and intermetallics and, in doing so, the electronic and phononic properties is investigated. The phase stability of matrix, side phases and precipitations depends on the temperature and the pressure and therefore one uses first principles calculations to investigate the thermodynamic properties of these metals and intermetallic phases at least qualitatively. The elastic properties of the metals and intermetallics can also be predicted to a very good precision.
Density functional theory is therefore the ideal ansatz to investigate metals and intermetallics as it is accurate and fast.

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In cooperation with Prof. K. Yoshimi from Tohoku University in Sendai, Japan, vanadium-based high-temperature materials are being produced and investigated. The materials are selected on the basis of thermodynamic phase equilibria. They are produced using a melting metallurgical process with subsequent heat treatment. Results are discussed and alloy development is further optimized during reciprocal visits.
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Artificial prostheses can be successfully implanted in the human body for many years and improve the mobility, vitality and quality of life of patients. A variety of different ceramic and metallic implant materials, such as alumina-hardened zirconia and the alloys Ti-Al-V and Co-Cr-Mo, are already in clinical use. However, there is a constant need and scientific interest in improving the properties and longevity of implants in terms of wear resistance, corrosion and, in particular, biocompatibility and tissue compatibility, e.g. to prevent inflammatory reactions. The innovative material class of bio-refractory metal materials(bio-MEAs) and bio-high entropy alloys (bio-HEAs) represent a unique design approach for the development of new biomedical materials. In addition to attractive mechanical properties and excellent wear and corrosion resistance, this class of materials offers potential for improved biocompatibility compared to previously used materials.
In addition to the development of new alloy concepts, the focus is also on the production of biocompatible materials. In recent years, demand for additive manufacturing - known as 3D printing - has risen sharply in the industrial sector, but especially in the field of medical implants. Due to the layered structure, highly complex geometries in anatomical shapes and delicate lightweight structures can be realized, which can hardly be produced using conventional methods. Another advantage of additive manufacturing is that the required patient-specific implants can be made available in a very short time. This results in very specific advantages for the additive manufacturing of implants that bring both economic and patient welfare benefits, as waiting times and therefore inpatient stays and the resulting complications can be massively reduced. The project, which is funded by the Innovation Fund of Otto von Guericke University (OVGU) Magdeburg, aims to intensify the interdisciplinary collaboration between the Chair of High Temperature Materials at the OVGU's Faculty of Mechanical Engineering and the Experimental Orthopaedics research department at the Orthopaedic University Hospital Magdeburg. New findings on the development of biocompatible HEAs/MEAs, innovative manufacturing strategies and important mechanical properties of the new materials are to be investigated.
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The sub-project is related to Engineering Materials to be used in a wide temperature range and under complex mechanical loading. The project will focus on the microstructure/properties relationship of single and multi-phase metallic materials. Theoretical considerations of microstructure evolution or phase stability/transition will be done by Phase-Field Simulation and/or DFT, MD, or other nanoscale-related numerical methods. Mechanical properties will be determined from (micro and nano) indentation, bending, compression as well as creep tests.

A simulation-supported approach shall be used to develop further these materials.

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High-temperature resistant Mo-Si-B materials are being intensively investigated as suitable substitutes for nickel-based materials. One problem with these materials that has not yet been solved is their oxidation behavior. The Mo solid solution phase in particular oxidizes catastrophically depending on the temperature, forming a volatile Mo oxide. Previously known protective coating systems have not been able to solve this problem satisfactorily. The aim of the project is therefore to develop a novel, active protective system based on preceramic polymers containing fillers with a high oxygen absorption capacity in combination with the inhibition of oxygen diffusion in cooperation with Prof. M. Scheffler (Chair of Non-Metallic Materials).

Prof. Krüger's department is producing suitable active filler particles for this purpose, which are then applied to the substrate materials via a slurry using a dip coating process. Oxidation tests at different temperatures with subsequent analysis of the coating and the coating-substrate interface are intended to show the extent to which the oxidation behavior of the substrate is influenced by the new coating systems.

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High-temperature resistant Mo-Si-B materials are being intensively investigated as suitable substitutes for nickel-based materials. A known problem with these materials is their oxidation behavior. The Mo solid solution phase in particular oxidizes catastrophically depending on the temperature, forming a volatile Mo oxide. Previously known protective coating systems have not been able to solve this problem satisfactorily. The aim of the project is to develop a new protective system based on preceramic polymers containing fillers with high oxidation resistance.

As part of the sub-project, oxidation protection coating systems based on preceramic polymers of the polysilazane type with oxygen-absorbing filler particles (Si, B, silicides) are being developed and tested in application-oriented oxidation tests with regard to their protective effect. In addition to a perhydropolysilazane, promising compositions contain 25 % silicon and 15 % boron by volume; both fillers form a low-viscosity glass under oxygen absorption, which is able to close microcracks in the coating system and on the material surface to be protected. Modifications of the protective coatings are currently being carried out with the filler boron nitride. Oxidation tests of the coated refractory metal alloys pyrolyzed at 1000 °C in nitrogen show very good oxidation protection at 800 °C, which showed no further changes in mass over the test period of 100 hours after an initial increase in mass, thus indicating a high protective effect.
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The requirements placed on medical devices and medical technology components are heavily dependent on their use. For a long time, biocompatible materials were regarded as chemically and biologically inert within the human body, but this has since been revised, as there is always a response from the body.
Nanostructured biomaterials, including those based on refractory metals, may be of great interest for the future of the biomedical industry and are therefore increasingly the focus of current research. Their fundamentally good compatibility in the human body together with excellent mechanical properties are decisive factors here. The use of titanium and titanium alloys in surgery has steadily increased due to their good combination of properties compared to other metallic implant materials such as stainless steel and cobalt-chromium alloys. Biocompatible titanium and titanium-based alloys are characterized by good fatigue strength, corrosion resistance and low density, resulting in a high specific strength-to-weight ratio that allows for lighter and stronger structures. One of the most popular titanium alloys used in medicine today is Ti-6Al-4V. However, even approved medical materials can still be optimized for acceptance in the human body.
In this project, the first cell population experiments are being carried out on new, innovative materials with mesenchymal stem cells and osteoblasts. They are a perfect indicator of biocompatibility and cell ingrowth behavior for potential implant materials or other medical materials.
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Nickel-based superalloys are currently the material class of choice for high-temperature applications in turbine construction. Vanadium silicide materials represent a potential alternative, particularly due to their excellent specific mechanical properties. For example, V-Si-B alloys from the vanadium-rich region of the three-material system consist of a ductile vanadium solid solution (V-Mk) and the two intermetallic phases V₃Si and V₅SiB₂. However, this alloy system, which has been little researched to date, has some surprising similarities to its well-studied neighboring system Mo-Si-B in terms of microstructure. In initial preliminary tests on V-Si-B alloys, significantly better specific compressive strengths were achieved in the temperature range from 600 °C to 900 °C compared to Ni-based alloys. However, the mechanism of phase formation and the correlation of the microstructure-property relationships are still completely unexplored. The primary objective of this project is the development of novel V-Si-B alloys for high temperature applications. The aim is to develop ternary-eutectic alloys. In a series of V-rich binary and ternary test alloys, the phase formation and stability from the melt to the homogenized microstructure will be investigated.
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Background
Due to the low density in combination with a high melting point, vanadium demonstrates a great lightweight potential for turbines in aircrafts or energy industry. Since vanadium as a structural material is in focus of research only recently, the effects of several alloying elements on the materials properties are not or insufficiently examined yet.

Objective
The investigation of the microstructure-property relationship in binary, ternary and quaternary V-based alloys in order to use the findings to improve high-temperature alloys based on V-Si-B.

Methods
By means of ingot metallurgy (arc-melting process), vanadium samples with different concentrations of alloying elements were manufactured. Resulting from this, single phase vanadium solid solutions (Vss), two-phase and three-phase alloys were produced. Microhardness measurements and compression tests were carried out to determine the mechanical properties in dependence on the alloying components. SEM (Scanning Electron Microscopy) and XRD (X-ray Diffraction) methods were used to examine the microstructure, to identify phases and to measure elements concentration in the respective phases.

Results
The combination between mechanical characteristics and microstructural investigations enables conclusions concerning the materials behavior and the efficiency of solid solution strengthening and second phase strengthening.

Conclusions
The elements Cr, Mo and Nb have a high potential for improving the microstructure property relationship in modern V-Si-B alloys.

Orignality
Basic research on the effects of various alloying elements in vanadium solid solution, as well as in promising ternary V-Si-B high temperature alloys.

Keywords
Vanadium-based alloys, microstructure-property-relationship, intermetallics, V-Si-B-X, vanadium solid solution phase

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Multiphase vanadium alloys are the focus of current research into new high-temperature materials due to their outstanding mechanical properties. By combining the ductile vanadium solid solution phase with high-strength intermetallic or intermediate phases, a material with optimized properties is being developed.

In the LextrA (https://forschung-sachsen-anhalt.de/project/lextra-laserbasierte-additive-fertigung-20506) project, various vanadium materials were processed into compact test specimens for the first time using the additive manufacturing process DED (Direct Energy Deposition).
Using DED, oxide particles were introduced into multiphase vanadium materials at the ILT Aachen in order to optimize the mechanical properties. The research task at OVGU is to investigate the new materials with regard to the homogeneous distribution of the particles in the microstructure and to describe their mode of action. The strength-enhancing effect of the introduced particles will be quantitatively evaluated in comparison to a particle-free reference material.
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Due to their excellent mechanical properties, vanadium alloys have the potential to be used as future structural materials. However, vanadium materials oxidize strongly at elevated temperatures, which means that their range of application is currently limited to typical ambient temperatures.

In the DFG-funded cooperation project "Oxidation protection coatings for vanadium materials" (project number 39807701, duration until 02/2019), suitable oxidation protection coatings were developed. These were applied in the laboratory of Prof. J. Perepezko (University of Wisconsin-Madison, USA) using the special powder packaging process. At the IWF, these layer-substrate composites are examined in detail using various microscopic methods and their protective effect is tested.
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As part of the cooperation with the "High Temperature Materials and Powder Metallurgy" working group at the National Technical University of Ukraine "KPI" in Kiev, complex, refractory materials are being developed. These are produced using either powder metallurgical processes or a crucible-free zone melting process. The new materials are examined at OVGU with regard to their microstructural characteristics and tested at high temperatures.
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The aim of this project is to develop a coating system to build up complex functions for the effective component protection of Mo-Si-B alloys; this system consists of an oxygen-free preceramic polymer of the polysilazane type that can be processed in air and filled with ceramic and/or metallic particles. The fillers have three functions: to increase the coating thickness compared to the unfilled coating system; to reduce the shrinkage of the coating material caused by the transition from polymer to ceramic; and to form new phases by reaction between the preceramic polymer, filler and component(s) and the service atmosphere, which should compensate for a possible volume change due to abrasive/oxidative processes on the (coated) component surface (volume expansion of the fillers when oxygen is absorbed). Phase analysis, composition and state are determined using X-ray diffraction (XRD; Rietveld analyses are carried out if there are significant proportions of crystalline phases).
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Ziel dieses Projektes ist die Entwicklung eines Beschichtungssystems zum Aufbau komplexer Funktionen für den effektiven Bauteilschutz von Mo-Si-B-Legierungen; dieses System besteht aus einem sauerstofffreien präkeramischen Polymer vom Polysilazantyp, das sich an Luft verarbeiten und mit keramischen und/oder metallischen Partikeln füllen lässt. Die Füllstoffe haben drei Funktionen: die Erhöhung der Schichtdicke im Vergleich zum ungefüllten Beschichtungssystem; die Reduzierung der durch den Übergang vom Polymer zur Keramik bedingten Schwindung des Schichtwerkstoffs und die Bildung neuer Phasen durch Reaktion zwischen präkeramischem Polymer, Füllstoff und Komponente(n) und der Serviceatmosphäre, die eine mögliche Volumenänderung durch abrassive/oxidative Prozesse an der (beschichteten) Bauteiloberfläche kompensieren sollen (Volumenausdehnung der Füllstoffe bei Aufnahme von Sauerstoff). Phasenanalyse, -zusammensetzung und -zustand werden mittels Röntgendiffraktometrie erfasst (XRD; bei Vorliegen nennenswerter Anteile kristalliner Phasen werden Rietveld-Analysen durchgeführt).

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The use of innovative materials contributes to the energy and resource efficiency of technical processes. Ultra-high temperature materials based on intermetallic phases and refractory metals have the potential to substantially increase the efficiency of gas turbines. This requires fundamental scientific research on microstructure-properties relationships of potential multi-phase alloys.
For the project LextrA we selected different intermetallic materials based on iron aluminides, vanadium silicides and molybdenum silicides. Conventional ingot metallurgical processes are limited in their applicability due to the high melting point of the intermetallic and refractory materials. Additive manufacturing techniques provide new options to allow the integration of complex cooling structures in turbine blades and are resource efficient alternatives of conventional processes. This combination of optimized material and improved cooling system will result in a significant increase in the operation temperature of modern gas turbines, which leads to higher process efficiency. The project consortium evaluates the applicability of two additive manufacturing processes, namely directed energy deposition (DED) and laser powder bed fusion (LPBF).

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As part of the doctoral project, a material fatigue model for lifetime prediction is to be derived in cooperation with the Institute of Mechanics (apl. Prof. Naumenko). The basic aim is to determine the mechanical properties of current nickel-based materials and new molybdenum-based materials in the potential application temperature range of the turbine. The model is to be applied to selected blade geometries.
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In cooperation with the Karlsruhe Institute of Technology (KIT), the FlexiDS project aims to investigate the process of directional solidification in various high-temperature materials using in-situ X-ray diffraction. Within this framework, an innovative in-situ sample environment for directional solidification is to be developed and set up at the HEMS (High Energy Material Science) beamline at DESY (Deutsches Elektronen Synchrotron, Hamburg) . This will offer the partners involved completely new research and characterization possibilities through direct observation of the directional solidification process. The Helmholtz-Zentrum-Geesthacht (HZG), which is in charge of this beamline, will support the design, construction and operation of the sample environment.
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Subproject: Microstructural damage of coated AlSi materials under mechanical and thermal stress

Editing: Dipl.-Ing. Philipp G. Thiem     
  
New intermetallic coating systems on AlSi substrates are being investigated. The coated materials are subjected to both static and cyclic loads in order to investigate the effects of the alloy composition, the microstructure and the coating thickness on crack formation and crack propagation in the application-relevant temperature range. Material parameters, e.g. the modulus of elasticity, and other parameters such as the adhesive strength of the coating are to be included in the modeling of the damage mechanisms in this material composite.  

Subproject: Crack initiation and crack propagation in multiphase high-temperature materials

Editing: M.Sc. Julia Becker    

Multiphase high-temperature materials are investigated with regard to crack initiation in the individual phases, crack propagation and their fracture toughness. Initial experiments on crack initiation and crack propagation were carried out on Mo-Si-B alloys produced by powder metallurgy using the indentation fracture mechanics method. The findings are to be transferred to directionally solidified multiphase molybdenum materials.

Collaboration in other sub-projects:
* Experimental Investigations and Numerical Simulations of Lamellar Cu-Ag Composites

Editing: M. Sc. Srihari Dodla
Supervision: Prof. A. Bertram, Prof. M. Krüger

* Crystal Viscoplasticity Based Simulation of Ti-Al Alloy under High-Temperature Conditions

Editing: M. Sc. Helal Chowdhury
Supervision: Prof. K. Naumenko, Prof. H. Altenbach, Prof. M. Krüger
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The invention relates to a metal cast component, which is intended in particular for parts of internal combustion engines or piston compressors, such as pistons, gearboxes, crankcases and other housings and/or cylinder heads, wherein the cast component consists at least in certain portions of an iron aluminide and/or is a composite cast component comprising at least two portions, which consist of a cast iron and/or an iron aluminide and/or a light metal. The invention also relates to a method for producing a metal cast component, in particular for parts of internal combustion engines or piston compressors, such as pistons, gearboxes, crankcases and other housings and/or cylinder heads, which consists of one or more cast materials such as cast iron and/or iron aluminide and/or light metal, in which method a first portion of the cast component is produced in a first casting operation and a further portion of the cast component is produced in a further casting operation and a coating, in particular of iron aluminide and/or a nickel alloy, is applied as a coupling agent layer to the first portion before the further casting operation.

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Intermetallic phases, carbides and oxides are ideally suited as reinforcing phases for high-melting composite systems. In this project, in-situ composites are to be produced using a special crucible-free zone melting process. With the aim of achieving a fiber-like or lamellar morphology of the reinforcing phases, suitable alloy systems are identified in the first step. The starting materials in powder form are then mixed according to the nominal composition and cold pressed before being locally melted and directionally cooled. The physical and mechanical properties are then determined in the next step using suitable measurement and analysis methods. A comparison is made with known high-temperature materials.
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The requirement profile for high-temperature materials for complex technical applications consists of good mechanical properties across the entire application range and sufficient oxidation resistance. In the case of dynamically moving components, density is also an important criterion for material selection. High-melting-point materials based on vanadium (T_s = 1910°C) have the advantage that the density can be reduced by around 30% compared to reference materials such as nickel alloys and by around 20% compared to steels. This project aims to lay the foundation for the development of high-strength vanadium materials. In the first approach, vanadium-silicon solid solution materials are produced via the process of mechanical alloying and their properties are determined. The application of kinetic models, taking into account the real process variables, serves to understand and optimize the process of mechanical alloying for this material system. In the next step, silicide phases (e.g. V₃Si and V₅SiB₂) are integrated into the solid solution materials in order to optimize the high-temperature strength.
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Molybdenum-silicon-boron alloys are regarded as attractive high-temperature materials with properties that go beyond those of conventional nickel-based superalloys. Eutectic Mo-Si-B alloys are particularly interesting for processes such as directional solidification by zone melting or selective laser melting because they are suitable for producing fiber-matrix structures.
To determine the eutectic point in the three-phase region Mo-Mo₃Si-Mo₅SiB₂, the cooling paths of different alloys are investigated and compared with thermodynamic simulations. The microstructural characteristics of these materials are correlated with the mechanical properties up to 1400°C.
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The project relates to the application of an energy-efficient method for the production of novel refractory metal alloys with melting temperatures above 2000°C. These materials have the potential to substitute the currently used nickel-based superalloys with maximum application temperatures of around 1100°C. With the help of such a material substitution, a contribution can be made to increasing thermodynamic efficiency, for example in power generation units.
In our approach, alloys with intermetallic structures are produced directly from a mixture of elemental powders in just one process step, whereby the size and distribution of the microstructure components are specifically influenced by the production parameters. The Ukrainian partner is providing a zone melting furnace specially designed for such high-melting-point materials. The expertise of the German partner will be used to characterize the relationships between the microstructure and the properties of the new materials. The new materials and the unique production technology can be used in the energy supply sector, the aircraft industry and other areas where extreme conditions are required in terms of thermal and mechanical stress.
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In the context of increasing safety requirements in automotive engineering, materials that can absorb energy during a collision and distribute it optimally across the entire component should be used for crash-relevant components. The high degree of energy absorption of currently used TWIP steels is based on the formation of deformation twins in the crystal lattice. This deformation mechanism enables high energy absorption with low deformation. However, the production of TWIP steels is cost-intensive, primarily due to the use of expensive alloying elements. TWIP steels also have limited weldability and are difficult to form.
As part of the planned project, a deeper understanding of the mechanisms of impact deformation of steels with different alloying elements is to be developed in order to obtain a statement on their suitability as materials for crash-relevant components.
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Alloy having a content of cobalt C(Co) that is greater than the content C(i) of a further any desired alloy element (i), a content of rhenium C(Re) and a content of boron C(B), is claimed, where the content of rhenium C(Re) in atom% compensates 5= C(Re) less than C(Co) and the content of boron C(B) in atom% compensates 0.007= C(B) less than MIN (7; C(Co)), where MIN (7; C(Co)) defines the smaller of the two values.

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The materials sub-project will contribute to the characterization of the microstructure and properties of structured and coated cylinder running surfaces with regard to the reduction of friction losses.
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With a view to increasing the efficiency of combustion engines, e.g. by reducing the overall friction of the system by reducing the dynamically moving masses, materials with a high specific strength and rigidity should be used. Compared to other light metal alloys such as Al-Si or Ti-Al materials, iron aluminides are characterized by their increased high-temperature strength, creep resistance and fatigue strength. Fe3Al materials are predestined for use in combustion engines due to their excellent corrosion and wear properties. With this outstanding property profile, Fe3Al alloys can be used, for example, to reinforce light metal castings made of aluminum or to coat aluminum components with the aim of increasing their high-temperature and wear resistance.This text was translated with DeepL

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Comparative studies on the strength and deformation properties are carried out on welded steels. The microstructures and fracture surfaces are also characterized.
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Das Hauptaugenmerk der Werkstoffentwicklung im Bereich des Kurbeltriebs (einschließlich des Kolbens) im Hinblick auf eine Erhöhung des Wirkungsgrades durch z.B. Verringerung der Gesamtreibung des Systems ist darauf gerichtet, Materialien mit einer möglichst hohen spezifischen Festigkeit und Steifigkeit einzusetzen, da damit die dynamischen Massen im System reduziert werden können und konstruktiver Leichtbau optimal unterstützt wird. Neben den genannten Eigenschaften sind eine hinreichend gute Duktilität sowie Zähigkeit für den Widerstand gegen Rissfortschritt und eine hohe Dauerschwingfestigkeit entscheidende Kriterien für die Werkstoffauswahl.

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Das Verhalten verschiedener FeAl(-X)-Legierungen wurde mittels mechanischer Versuche unter statischer und zyklischer Beanspruchung bei Raumtemperatur sowie bei höheren Temperaturen charakterisiert. Es erfolgte eine Analyse der Gefüge-Eigenschafts-Beziehungen.

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Metallische Werkstoffe, die Oberflächentemperaturen größer 1200°C bei gleichzeitiger hoher mechanischer Belastung in Luftatmosphäre dauerhaft widerstehen können, sind nicht nur aus volkswirtschaftlichen und Umwelt-Gesichtpunkten (Schonung fossiler Ressourcen, Verringerung der Schadstoffbelastung) von großem Interesse. Für die Werkstoffwissenschaft und angrenzende Disziplinen ergibt sich daraus einerseits die reizvolle Aufgabe, mit metallurgischen bzw. metallphysikalischen Prinzipien nach Legierungen zu suchen, die das oben angesprochene Anforderungsprofil erfüllen können. Andererseits müssen diese neu zu entwickelnden Legierungssysteme eingehend charakterisiert werden, um ihre Eignung hinsichtlich der gestellten Aufgabe unter Beweis zu stellen und im Rückschluss mit den Legierungsentwicklern optimierte Lösungen zu finden. Hier setzt die Forschergruppe an, mit dem Fokus auf die nachfolgenden zwei Legierungssysteme: Mo-Si-B, das bereits seit mehreren Jahren international beforscht wird und wofür die gebildete Forschergruppe bereits sehr gute Vorkenntnisse besitzt, Co-Re, für das in der Literatur bislang nur geringe Kenntnisse vorhanden sind, das jedoch von der Forschergruppe als sehr Erfolg versprechend eingestuft wird. Beide Systeme besitzen Schmelzpunkte, die mindestens 250°C über denen der heute eingesetzten Ni-Basis-Superlegierungen liegen. Die zentrale Aufgabe der Legierungsentwicklung und das Ziel dieser Forschergruppe bestehen nun einerseits darin, weitere Legierungselemente zu finden, die eine Verbesserung der für einen (Last tragenden) Hochtemperatureinsatz essentiellen, nachfolgend aufgelisteten Eigenschaften erlauben: Oxidationsbeständigkeit, Kriechwiderstand, Zähigkeit und Duktilität bei tiefen Temperaturen (Raumtemperatur), Ermüdungswiderstand. Die drei erstgenannten Eigenschaften wurden im ersten Förderzeitraum intensiv untersucht. Als ein „Highlight“ ist in der zweiten Projektphase die Duktilisierung der Mo‑Si-Mischkristallphase, welche die Matrix im System Mo-Si-B bildet, durch (Mikro-) Legieren gelungen. Eine Zugabe von Zr bewirkt durch die Stärkung der Korngrenzen sowohl eine Festigkeitssteigerung als auch eine Erhöhung der Duktilität, wie es in der unten stehenden Abbildung anhand einer Beispiellegierung gezeigt wird. Außerdem soll das (komplexere) Ermüdungsverhalten nach Identifikation von viel versprechenden Legierungszusammensetzungen untersucht werden.

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