Surface Engineering

The aim of the Surface Engineering Group is to design surfaces in such a way that they have optimum properties for the respective application area. For this purpose, different methods of surface treatment from the nano- to macro-scale are used in order to be able to influence the surface properties in different fields of application.

Methoden

Direct Laser Interference Patterning (DLIP)

One of the group's research priorities is the precise processing of surfaces with the help of laser interference structuring (DLIP=direct laser interference patterning), which has been thoroughly investigated and is now well established at the institute. In 2016, the group received the Berthold-Leibinger Innovation Award for the innovative application of DLIP in laser research to improve the friction and electrical properties of industrially produced electrical connectors. In DLIP, high-energy, pulsed laser beams are superimposed with each other in order to generate defined intensity distributions and thus surface topographies with a precise, lateral dimension from the sub-µm to the µm range (structural wavelength P). The exact distribution of the laser intensity can be defined by the number of combined beams and their respective angles. Figure 1a schematically illustrates the principle of laser interference for a two-beam interference setup. Figure 1 also shows the distribution of laser intensity when combining two (b) or three (c) beams.
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Figure 1: Schematic of the laser interference structuring and calculated intensity distributions for b) two-beam interference and c) three-beam interference.

further information:

  • Lasagni, A., D’Alessandria, M., Giovanelli, R. & Mücklich, F. Advanced design of periodical architectures in bulk metals by means of Laser Interference Metallurgy. Appl. Surf. Sci. 254, 930–936 (2007).
  • Mücklich, F., Lasagni, A. & Daniel, C. Laser Interference Metallurgy – using interference as a tool for micro / nano structuring. Int. J. Mat. Res. 97, 1337–1344 (2006).
  • Lasagni, A. F., Acevedo, D. F., Barbero, C. A. & Mücklich, F. One-step production of organized surface architectures on polymeric materials by direct laser interference patterning. Adv. Eng. Mater. 9, 99–104 (2007).
 
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Mechanical surface treatment

Mechanical surface treatments provide effective methods for increasing the service life of components. Due to the introduction of macroscopic residual compressive stresses and microscopic defects, near-surface crack initiation and growth is delayed. The research focus of the group is on the investigation of microstructural processes in laser peening and shot peening. Particularly interesting are the deformation of the microstructure on a microscopic scale and the residual stresses1,2.

further information:

  • S. Slawik, P. Leibenguth, H. Welsch, H. Jung, K. Weiss, B. Busskamp, and F. Mücklich, Österreichische Giesserei Rundschau, vol. 60, no. 11, pp. 348–355, 2013.
  • S. Slawik, P. Leibenguth, D. Rathmann, C. Gachot, and F. Mücklich, in International Conference on Shot Peening (ICSP 12), 2014, pp. 232–235.
 
 

Direct Laser Writing

In Direct Laser Writing, an ultrashort pulsed laser beam with a pulse duration in the femtosecond range (10-15 s) is rastered over a substrate. Due to the extremely short pulse duration, almost no melting of the surface occurs with ablation of the material being the dominant laser-material interaction. Thus very high aspect ratios (ratio of the depth of the structures to their width) can be achieved. With this process, it is possible to structure a wide range of different materials, from metals and polymers to glass.
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By moving the sample with the velocity v, the individual laser spots are overlapped and a line pattern is created. The overlapping area can be adjusted by varying the travel speed.

further information:

  • P.G. Grützmacher, A. Rosenkranz, C. Gachot, How to guide lubricants – Tailored laser surface patterns on stainless steel, Appl. Surf. Sci. 370 (2016) 59–66.
 
 

Laser Cladding

Laser cladding or laser deposition welding is a process technology of additive manufacturing. The research group employs the process to melt metallic powder mixtures with a focused laser at the same time as a substrate surface. After solidification of the molten metals, there is a firm bond between the coating and the substrate. Special phases (e. g. intermetallic phases such as RuAl) can be produced locally by selecting the supplied powders. By precisely moving the nozzle head above the substrate, different structures and layers with variable geometry can be created.
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Schematic of laser cladding (Benjamin Bax,' ‘Rutheniumaluminid - Herstellung Durch Laserauftragschweißen Und Der Einfluss von Eisen Auf Die Phasenbildung’, 2015).

further information:

  • Benjamin Bax and others, ‘Synthesis of B2-RuAl Coatings on Mild Steel by Laser Cladding’, Surface and Coatings Technology, 206.19–20 (2012), 3931–37
  • Michael Hans and others, ‘Laser Cladding of Stainless Steel with a Copper-Silver Alloy to Generate Surfaces of High Antimicrobial Activity’, Applied Surface Science, 320 (2014), 195–99
 
 

Applications

 
 

Tribology

One of the group's main research areas is tribology, which is defined as the theory of friction, wear and lubrication of bodies in relative motion. In this context, various methods such as DLIP 1-3, Direct Laser Writing or coating methods (EPD)4 are used to specifically influence or control friction and wear of surfaces. Particular emphasis is placed on transferability to technical surfaces. Both lubricated and non-lubricated systems under varying loads, friction velocities, humidity or temperature ranges are considered. Research is also being carried out on self-lubricating systems, for using carbon nanoparticle reinforced composite materials.
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Abbildung 2: Schematische Darstellung des anisotropen tribologischen Kontaktes von durch DLIP strukturierte Kugel und Grundkörper.[en:]Figure 2: Schematic of the anisotropic tribological contact of a DLIP-structured sphere and counter body.[

further information:

  • Gachot, C. et al. Dry Friction Between Laser-Patterned Surfaces: Role of Alignment, Structural Wavelength and Surface Chemistry. Tribol. Lett. 9, 193–202 (2013).
  • Rosenkranz, A., Heib, T., Gachot, C. & Mücklich, F. Oil film lifetime and wear particle analysis of laser-patterned stainless steel surfaces. Wear 334-335, 1–12 (2015).
  • Rosenkranz, A., Reinert, L., Gachot, C. & Mücklich, F. Alignment and wear debris effects between laser-patterned steel surfaces under dry sliding conditions. Wear 318, 49–61 (2014).
  • Reinert, L. et al. Long-lasting solid lubrication by CNT-coated patterned surfaces. Sci. Rep. 7, DOI: 10.1038/srep42873 (2017).
  • Suárez, S., Rosenkranz, A., Gachot, C. & Mücklich, F. Enhanced tribological properties of MWCNT/Ni bulk composites – Influence of processing on friction and wear behaviour. Carbon N. Y. 66, 164–171 (2014).
 
 

Wetting

The wettability of surfaces can be influenced by modifying the topography or chemistry. We achieve this modification by means of DLIP or direct laser writing1, which enables us to control friction properties or the spread of liquids, such as lubricants, on surfaces by adapting the wettability.
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SThe spreading of an oil droplet can be given a preferred direction when the droplet propagates on the surface with a specific surface topography (e. g. line pattern). In this way, lubricants can be guided on the surface

further information:

  • M. Hans, F . Müller, S. Grandthyll, S. Hüfner, F. Mücklich, Anisotropic wetting of copper alloys induced by one-step laser micro- patterning, Appl. Surf. Sci. 263 (2012) 416–422.
  • P.G. Grützmacher, A. Rosenkranz, C. Gachot, How to guide lubricants – Tailored laser surface patterns on stainless steel, Appl. Surf. Sci. 370 (2016) 59–66.
 
 

Antimicrobial surfaces

In the area of "antimicrobial metallic surfaces" contact materials with active antibacterial properties are investigated and developed. In this way, transmission of infections and biofouling, which can lead to damage to technical systems in the form of biological deposits and corrosion, are to be reduced. In this context, the groups research is focused on biochemical mechanisms with respect to kill germs on metallic surfaces. Based on this research activity, the antimicrobial performance of the materials should be increased and optimized for specific application fields. Especially in the space sector, antimicrobial surfaces can contribute to the safety of astronauts. For this reason, the effects of such surfaces are currently being investigated together with ESA and NASA. The interaction between germ and material is defined, among other things, by its surface, which is specifically modified by laser techniques such as DLIP and Direct Laser Writing.
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Staphylococcus aureus on a DLIP-structured Copper surface (Source: FuWe)

further information:

  • M. Hans, S. Mathews, F. Mücklich and M. Solioz, Physicochemical properties of copper important for its antibacterial activity and development of a unified model. Biointerphases, vol. 11, no. 1, 2016
  • Rosenkranz, M. Hans, C. Gachot, A. Thome, S. Bonk, and F. Mücklich, Direct laser interference patterning: Tailoring of contact area for frictional and antibacterial properties. Lubricants, vol. 4, no. 2, pp. 2–15, 2016.