Fraunhofer Institute for Mechanics of Materials IWM
Customized diamond-like coatings reduce friction losses
© Fraunhofer IWM
Tribological and functional coating systems
Application-specific coating solutions, process development and quality control from a single source.
We implement customer-specific coatings to increase the functionality, performance and service life of components and parts. We develop resource-saving, plasma-based processes through to pilot production. We adapt coating material, process technology and chamber configuration to create real competitive advantages for our customers.
We cover a wide range of applications and materials: from carbon-based coatings such as DLC (Diamond Like Carbon) to diamond reducing friction and wear in carbide tools as well as in bearings, seals and gears. Nitride and oxidic coating systems are used as protective coatings against hydrogen diffusion, as well as for forming processes, thin-film sensors and as corrosion protection. The control of growth conditions enables the structuring of the layers during deposition and thus endows the layers with additional functionalities, allowing for the control of wetting, adhesion and reflection. In addition, we also investigate the plasma processes themselves as a tool, e.g. for chemical surface layer modification, for surface structuring or for CO2 conversion and H2 generation. We continuously develop the quality and microstructure of the layers and processes and adapt them to the requirements of our customers. To this end, we also use physical simulations to realize component-adapted plasma conditions during deposition. We utilize our in-depth expertise in coater engineering and source technology to support our customers in technology selection and process transfer. A comprehensive range of plasma diagnostics and coating characterization methods are available for process and quality control.
Development of carbon-based coatings for friction and wear reduction
Based on a precise analysis of the customer's tribological system (bearing, seal, etc.), we develop a coating system adapted to the component in terms of hardness, friction and elasticity. The coating parameters can be varied in a very wide section and specifically adjusted:
- E-modulus: 80 - 500 GPa
- Hardness: 2 - 50 GPa
- Tensile strength: 1 - 3 GPa
- Adjustable contact angle
- Relatively high residual compressive stresses: 0.5 - 3 GPa
- Typical coating thicknesses: 0.5 - 20 µm
- Coating rates: 0.01 - 1 µm/min
- Coating temperatures: 50 - 250 °C
- High corrosion resistance
- Biocompatible
- Optically transparent (when very thin)
By using a plasma to split the layer-forming gas molecules (e.g. methane, toluene, acetylene, ...) instead of high temperatures as in a classic CVD process, almost all materials can be coated, i.e. metals and ceramics, but also many plastics and even elastomers.
Topography parameters
Thanks to our coating technology, a targeted surface topography can be adjusted during deposition without pre-structuring of the substrate. This leads to significant progress in friction and wear reduction and thus to a reduction in the use of lubricants and release agents. The reliability and service life of drive and system components are significantly increased.
Multilayer coating structure
The properties of DLC coatings can be adjusted via doping and deposition parameters. With different layers in a multilayer structure, the positive properties of the individual layers can be combined with each other. For example, the wear resistance and temperature resistance can be increased by adding highly wear-resistant (amorphous or hexagonal) boron nitride layers.
Further information:
Publication:
Laser structuring and DLC coating of elastomers for high performance applications, Materials, 15/9 (2022) Art. 3271, 13 Seiten; 45/2022 Link
Development of barrier coatings and measurement of hydrogen permeation
The customer-specific development of protective coatings against tribological and corrosive stresses in combination with a barrier effect against the diffusion of hydrogen requires a holistic view of the entire system. Fraunhofer IWM develops a wide range of protective and barrier coatings, mainly based on oxides and nitrides. The coating performance and barrier effect is modeled down to the atomic level and measured and evaluated using methods and test rigs, some of which were developed in-house. The application of barrier layers using plasma-based processes offers many advantages for the customer:
- Wide range of different materials can be coated: metals, polymers, ceramics
- Wide range of coating materials: metals, oxides, nitrides, carbon-based coatings
- Recyclability of coated components
- Combined protective effect
- Scalable processes with a low CO2 footprint
In addition to coating development, the Fraunhofer IWM also offers customers test options for evaluating their coatings with regard to the diffusion of hydrogen. The permeation tests can be combined with other tribological tests.
Further information:
Press release: Almost no evidence of brittleness
Publications:
Gröner, L.; Mengis, L.; Galetz, M.; Kirste, L.; Daum, P.; Wirth, M.; Meyer, F.; Fromm, A.; Blug, B.; Burmeister, F., Investigations of the deuterium permeability of as-deposited and oxidized Ti2AlN coatings, Materials, 13/9 (2020) Art. 2085, 9 Seiten; 51/2020 Link
Gröner, L.; Kirste, L.; Oeser, S.; Fromm, A.; Wirth, M.; Meyer, F.; Burmeister, F.; Eberl, C., Microstructural investigations of polycrystalline Ti2AlN prepared by physical vapor deposition of Ti-AlN multilayers, Surface and Coatings Technology, 343/ (2018) 166-171; 43/2018 Link
Development of corrosion protection coatings
Based on research and atomistic simulations, nanolaminar ternary nitrides were identified as potential materials with good corrosion protection properties. In these “MAX-phase” materials, atomic metal layers alternate with nitride layers. They unite metallic and ceramic properties and combine good chemical resistance with high mechanical damage tolerance. One representative is Ti2AlN, for whose deposition a reactive sputtering process was developed, with which very phase-pure MAX phases with crystallographic preferred orientation can be produced. The growth of an oxide layer at temperatures up to almost 1000°C was investigated in detail on the layers and a favorable, very low growth rate was observed. Potential applications are coatings of bipolar plates for high-temperature fuel cells (SOFC) and the prevention of chromium diffusion.
In energy technology, e.g. solar power plants, materials come into contact with hot molten salts. Here, as with the hot forming of glass, metallic corrosion protection coatings based on precious metals have been developed and validated.
Publications:
Gröner, L.; Kirste, L.; Oeser, S.; Fromm, A.; Wirth, M.; Meyer, F.; Burmeister, F.; Eberl, C., Microstructural investigations of polycrystalline Ti2AlN prepared by physical vapor deposition of Ti-AlN multilayers, Surface and Coatings Technology, 343/ (2018) 166-171; 43/2018 Link
Gurr, M.; Bau, S.; Burmeister, F.; Wirth, M.; Piedra-Gonzales, E.; Krebser, K.; Preußner, J.; Pfeiffer, W., Investigation of the corrosion behavior of NiVAl multilayer coatings in hot salt melts, Surface and Coatings Technology, 279/ (2015) 101-111; 1292/2015 Link
Hagen, J.; Burmeister, F.; Fromm, A.; Manns, P.; Kleer, G., Iridium coatings with titanium sub‐layer deposited by RF magnetron sputtering: Mechanical properties and contact behavior with RoHS‐compliant glass melt, Plasma Processes and Polymers, 6/Supplement 1 (2009) 678-683 Link
Development of coatings for plastic molding, optics and microsystems
Applications in optics, medical or tool technology require differently designed surface textures on the micro and nano scale. These can be generated by self-organization effects during the growth of PVD coatings.
Our Tegonit® coating systems enable high-quality manufacturing processes for optical components with new functionalities such as controllable light distribution, true color and anti-reflective properties.
In injection molding and related processes, they offer a wide range of possibilities for direct in-process functionalization of surfaces, such as anti-reflective surfaces of plastic components directly in the molding process by replicating nanostructured layers (Tegonit® PTAn)
They allow process monitoring by, for example, recording the temperature in the previously inaccessible interface between the mold wall and the melt with temperature-sensitive layers (Tegonit® PNCN)
They enable local additional temperature control directly on the mold surface for laminating weld lines, increasing the gloss level and extending flow paths through thermal insulation or heating layers (Tegonit® PTA)
They improve demoldability through contour-following anti-adhesive layers (Tegonit® CS)
Development of thin-film sensors
Thin-film sensors can always provide valuable contributions for the customer in situations in which measurement values and control variables that are not accessible using conventional methods need to be recorded. For example, in a sealing gap of a heat-sealing machine, on the surface of an injection mold or forming tool and on a head for ball joints. Fraunhofer IWM develops customer-specific solutions and thus enables, for example, in-situ process control as well as the validation of simulations with experimental data.
Development of polycrystalline and monocrystalline diamond coatings
For special applications, e.g. for coatings and to increase the service life of carbide tools, Fraunhofer IWM is developing polycrystalline diamond coatings that are deposited in a custom-built microwave system. For applications in power electronics and quantum technologies, however, monocrystalline diamond coatings are required, preferably in wafer form. Fraunhofer IWM is involved in several development projects whose aim is to produce monocrystalline diamond layers and is researching heteroepitaxy processes for the production of monocrystalline iridium substrates.
Publications:
Yoshikawa, T.; Herrling, D.; Meyer, F.; Burmeister, F.; Nebel. C.E.; Ambacher, O.; Lebedev, V., Influence of substrate holder configurations on bias enhanced nucleation area for diamond heteroepitaxy: Toward wafer-scale single-crystalline diamond synthesis, Journal of Vacuum Science & Technology B, 37/2 (2019) 021207 1-8; 26/2019 Link
Lebedev, V.; Yoshikawa, T.; Giese, C.; Kirste, L.; Zukauskaite, A.; Graff, A.; Meyer, F.; Burmeister, F.; Ambacher, O., Formation of icosahedron twins during initial stages of heteroepitaxial diamond nucleation and growth, Journal of Applied Physics, 125/7 (2019) 075305 1-10; 25/2019 Link
Coating evaluation and surface analysis
Common tests for coating adhesion such as ball indentation, cross-cutting or scotch tape tests all have their raison d'être, but also their weaknesses, especially with thin coatings. Due to its extremely accurate force and depth resolution, the Nano Scratch Tester, available at the Micro-Tribology Center, is ideal for accompanying coating development and a comparative evaluation of the effect of different pre-treatment methods on coating adhesion and subsequent coating performance. For this purpose, a diamond tip with a typical radius of 5 µm is incised linearly over the coating surface to be tested and the load is also increased linearly up to a maximum force of up to 1000 mN. A high-sensitivity mode of approx. 1 mN - 10 mN is now also available for very thin coatings. The penetration depth, the remaining penetration depth, the transverse force (~friction value) and light microscopic analyses synchronized with the scratch image can be used with nm resolution to define layer-specific, critical forces.
The functionality and service life of coatings in use is determined not only by coating adhesion but also by other factors such as hardness, microstructure, topography, stoichiometry, etc. With our many years of experience and diverse analytical methods, we are able to identify and evaluate critical success factors both in the investigation of damage cases as well as in the targeted development of coatings for customers. We provide the customer with valuable information on system optimization. We combine component and application-specific characterization with the comprehensive evaluation of coating performance paired with simulations down to the atomic level.
A wide range of state-of-the-art analysis methods are available, and we will be happy to advise and support you in selecting the most suitable method for you. Confidential order processing is a matter of course.
Available methods:
Chemical analysis: Infrared spectroscopy, energy and wavelength dispersive X-ray spectroscopy, optical glow discharge spectroscopy, X-ray diffraction and photospectroscopy, Raman microscopy, contact angle measurement
Microscopy and surface analysis: Atomic force microscopy, optical microscopy, white light interferometry, laser scanning microscopy, profilometry, scanning electron microscopy, focused ion beam, glass fiber spectrometry, transmission and reflection measurement (direct, diffuse), color measurement
Tribological / mechanical analysis: micro- and nanoindentation to determine the hardness and modulus of elasticity of thin layers, layer thickness measurement (white light interferometric, profilometric, cross-section, calotte), layer adhesion (scratch test, ball or rock wave indentation, cross-cut, pin-on-disk test, residual stress measurement (temperature-dependent up to 500 °C)
Further information:
Development of system technology and deposition processes
We are developing new process combinations such as RF and HiPIMS sputtering and researching their potential for optimizing the properties of coatings. New peripheral components are validated in collaboration with component manufacturers. Extremely fast deposition processes for DLC coatings with a deposition rate of up to 10 µm/h are realized using a special electrode configuration. The adaptation of coating processes extends to the construction of customer-specific coating systems.
With specially developed and patented coating systems, fast-growing DLC coatings can be applied to components in efficient processes with high plasma density. The systems can be adapted to the size and geometry of the components, allowing complex component shapes to be coated over the entire surface with extremely high homogeneity in terms of coating thickness and properties. Thanks to the 2-chamber principle (inert gas chamber and reactive gas chamber), the systems are also easy to clean. As part of several industrial projects, a complete system including the process has been transferred to a customer and is being used in production there.
In total, the following systems and technologies are available at Fraunhofer IWM for customer-specific developments:
- Reactive and non-reactive processes
- DC, MF and HF magnetron sputtering under clean room conditions
- HiPIMS excitation under clean room conditions
- HF substrate biasing
- Ion (IBS) and electron beam evaporation
- Substrate heating up to 1000 °C
- Plasma polymerization
- Cosputter coatings
- Large-area PECVD coatings, inductively and capacitively coupled
- Microwave PECVD
- CCP-HF plasma etching process
Of the above-mentioned processes, HiPIMS sputtering is an advancement of pulsed DC sputtering (MF) with the aim of generating plasmas with a very high density and an extremely high degree of ionization of the sputtered metal atoms using high power pulses. A joint development with MELEC GmbH has made it possible for the first time to realize a hybrid process with simultaneous RF and HiPIMS excitation.
Plasma-based surface functionalization
Functionalization of glasses and hard metals
Nitriding, hydrogen generation
The milling of glass fiber-filled plastics often requires the use of extremely expensive carbide tools, which must be diamond-coated to increase their service life. For contract coaters and manufacturers of carbide tools, we offer a plasma-based process to chemically passivate the cobalt-containing binder phase in the carbide. Without this conversion, the applied diamond layer would graphitize and wear quickly due to poor layer adhesion. Our patented and licensable process does not require the use of environmentally harmful chemicals.
For very large tools, especially forming tools, coating solutions to increase hardness are usually uneconomical and are often replaced by nitriding solutions. However, this requires complex and expensive process technology that is almost impossible to operate economically. Here, Fraunhofer IWM is working on solutions for 'onsite' nitriding, which will enable users to nitride their tools themselves on site and save on costly tool shipping.
Reactive plasma etching processes on float glass are currently being investigated for the anti-reflective functionalization and finishing of cover lenses with anti-fogging properties. Self-organized processes lead to the formation of nanostructures which, similar to the biological role model of the glass wing butterfly, makes the surface anti-reflective.
A current research project at Fraunhofer IWM is concerned with the production of hydrogen from methane. For this purpose, the so-called hollow cathode effect is being utilized, which leads to an amplification of the plasma between two electrode plates and should thus significantly increase the efficiency of the plasma-based splitting of hydrocarbons.
Further information:
Press release: New innovative process improves the adhesion of diamond to cemented carbide
Why should my company collaborate with Fraunhofer IWM on tribological and functional coating systems?
Understanding the coating behavior in use is the basis for tailor-made coatings
Our approach, which is based on material mechanics, aims to understand tribological systems holistically, identify weak points and performance limits in materials and components, clarify their causes and offer solutions for coatings, application assurance and performance enhancement of components and parts.
Simulation-based coating and material development
We use multi-scale simulations to predict the behavior of coatings and surfaces in use. We simulate chemical processes on surfaces and the interaction of coatings in contact with different media. Thanks to our comprehensive and in-depth understanding of the processes close to the surface, we can control coating properties in a targeted manner and respond to chemical and mechanical stresses.
For hydrogen applications, we leave nothing to chance and develop reliable solutions from a single source
We measure the permeation properties of materials and the barrier effect of coatings using our own permeation test rigs. We also evaluate the friction and wear properties under application-related conditions in our tribology laboratory. The flexibility of our coating processes and system technology enables us to incorporate test results directly into the coating design and to develop hydrogen barrier coatings based on specific customer requirements.
We transfer coating processes into industrial practice
The development of customer-specific coating solutions and the corresponding process technology go hand in hand . We are familiar with the challenges of transferring and scaling up coating processes from laboratory scale to industrial scale and have the necessary system know-how. Development times are shortened by accompanying physical plasma simulations.