Chair of

High Temperature Materials

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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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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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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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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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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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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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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