Fields of Research
- the research and development of adapted carbon precursors in terms of porosity and processability
- the LPI process (Liquid Polymer Infiltration) for the development of high-temperature resistant C/C-SiC or C/C-SiCN composites
- the LSI process or fast LSI process (Liquid Silicon Infiltration) for the development of high-temperature resistant C/C-SiC composites
- mass production of C/C-SiC composites by injection molding as a shaping step
- fiber/matrix interface adaptation by means of CVD coating for SiCf/SiC composites
- the further processing of CMCs to hybrid components
- the joining of CMCs the characterization of CMCs (e.g. microstructure, phase analysis by Raman microscopy, damping, mechanical testing in SEM).
Metal matrix composites (MMCs) are metals and alloys that are reinforced with ceramic reinforcing components. The production of MMCs can be carried out by powder or melt metallurgy. Within the Group of Composites and Material Compounds, the focus is on powder metallurgy production through mechanical alloying and field activated sintering (FAST). A recent example is the particle-reinforced aluminum matrix composites developed in the Collaborative Research Centre 692.
Ceramic Matrix Composites have excellent chemical, thermal and mechanical properties. One of the trends in CMCs is realising of mass production moulding techniques and marketable products. The Group of Composites and Material Compounds deals specifically with:
By chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques, thin layers of different materials can be produced. Single or multifilament fibre coating is one main focus of research works at the Group of Composites and Material Compounds. Through such fiber coatings, it is possible to make specific adjustment in the fiber/matrix interface of composites (interface engineering) or applying an additional functionalization on the fibers (sensor or actuator).
To qualitatively secure the functionality of novel composites and composites, the development of intrinsic condition monitoring systems is indispensable. For example, Structural Health Monitoring (SHM) measures allowable mechanical stresses within fibre-reinforced plastics. The research of the Group of Composites and Material Compounds focuses in particular on the deposition and investigation of foil-based thin film sensors and functionalized carbon single fibers. These offer the possibility to design artifact-free sensor systems for fiber-reinforced plastics. The sensory-active layer systems based on NiC and NiTi are deposited by DC magnetron sputtering. The aim is to achieve a higher sensitivity in comparison to commercially available strain sensors and a spatially resolved measurement.
Hybrid laminates also called fibre metal laminates (FML) consisting of layers of light metals and fiber-reinforced plastics. These compounds can cover a broad property profile by varying the materials as well as the number, thickness and orientation of the fiber-reinforced plastic. The thermoplastic matrix enables efficient and cost-effective production as well as good formability and recyclability. By integrating additional thin-film sensors (moisture, elongation), hybrid laminates can be perfectly functionalized. The Group of Composites and Material Compounds deals with combinations of light metal alloys based on Al, Mg and Ti and fiber reinforced thermoplastics such as polyamide 6.
Metal/plastic compounds have a great potential for industrial applications. Such mixed constructions combine the low density and versatile processability of the plastic as well as the high rigidity and strength of the metal. The realization of such construction methods requires material- as well as operationally suitable joining processes. One focus of research at the Group of Composite and Material Compounds is the design of an innovative transition region (e.g. wires or foam structures) of metal inserts which are suitable for injection molding.
- The production of reliable soldered joints for power electronics in regenerative energy systems.
- The investigation of the wetting and flow behavior of brazing alloys.
- The influence of the brazing atmosphere on the fatigue life of brazed joints.
- Ultrasonic assisted resistance brazing processes.
- The active brazing of metal-ceramic compounds.
- Fe-base brazing fillers with improved corrosion resistance for use in drinking water-contacted components.
- Co-base brazing fillers for high-temperature brazing of high-strength, thermally heavily loaded components.
- Low-melting Al base brazing fillers for the production of aluminum-steel mixed compounds.
- Heat treatment strategies to improve the corrosion resistance of brazed plate heat exchangers.
- Arc brazing processes for the production of aluminum-steel mixed compounds.
- Furnace brazing processes (inert gas and vacuum).
- Ultrasonic assisted resistance brazing processes.
- Induction brazing processes.
Brazing and soldering make it possible to produce a large number of connections within complex assemblies in one process step. Our research topics range from soldered joints in electrical engineering to high-strength and temperature-resistant brazed joints of stainless steels. In particular, the Group of Composites and Material Compounds deals with:
The continuous development of brazing processes also requires continuous development and modification of brazing fillers. Here are pursued a variety of goals. The Group of Composites and Material Compounds deals with the development and modification of:
Quelle: Effenberg, G.; Ilyenko, S.: Light Metal Systems. Part 1: Ag-Al-Cu (Silver – Aluminium – Copper). Landolt-Börnstein, Volume 11A1 (2004), pp. 1-7.
To produce reliable brazed joints, accurate process control is essential. The further development and monitoring of brazing processes contributes significantly to improving the properties of brazed joints. The Group of Composites and Material Compounds deals with the development and optimization of:
- metallic and non-metallic similar or dissimilar material compounds realized by friction stir welding with and without ultrasound enhancement (USE-FSW)
- local near-surface gradation of metallic and non-metallic materials by friction stir processing (FSP)
- generative realized metallic and non-metallic structures by friction stir build-up welding
Nanoparticles exhibit a reduced melting and sintering temperature compared to the corresponding bulk material. After melting or sintering of the nanoparticles, the material behaves like the bulk material. Therefore, high-strength and temperature-resistant joints can be produced at low temperatures, which is of big interest for various joining tasks. The Group of Composites and Material Compounds focuses in particular on the joining of metallic and polymeric substrates using Ag and Ni nanoparticles.
Friction Stir Welding (FSW) is an innovative pressure welding process for the realization of similar and dissimilar material compounds. In this process a rotating tool with a deducted probe at its head is applied on two joining partners with a defined welding force and then moved along the joint geometry. This solid-state joining process, regulated by the introduced frictional heat, results in a firmly bonded material compound.
The Group of composites and material compounds works in the department of low-heat joining processes on the realization and optimization of:
Ultrasonic metal welding is a pressure welding technique. Through superimposing a static welding force and an ultrasonic oscillation it is possible to join similar as well as dissimilar metallic or non-metallic materials. Joining of the materials takes place below their respective melting temperatures thus occurring in solid state. Therefore, undesired influences on the welding zone, e.g. the formation of brittle intermetallic phases can be avoided. Ultrasonic metal welding allows for joining various geometries, for instance sheets, foils or stranded wires.
Ultrasonic linear welding
Ultrasonic torsional welding
- Wear-resistant Fe-based alloys with high carbide contents
- High impact and abrasion resistant Fe-based alloys for wear protection layers
- Carbide-reinforced Fe base alloys with good corrosion resistance
For the wear protection of systems and components, surface coatings by thermal spraying or cladding are used. The development of new alloys opens up new fields of application. For this purpose, a laboratory arc furnace and a melt atomization plant for powder production are available. The Group of Composites and Material Compounds deals with the development and optimization:
- High resolution microstructure analysis
- failure and damage analysis
- Various analysis methods
For more information about our characterization methods, see Services.