Geometrically defined surface structuring for the form-locked bonding of thermal sprayed coatings
Final Report Abstract
The aim of this research project was to design a reliable process combination of knurling milling and deep rolling as an alternative to conventional substrate preparation using corundum blasting. With the help of systematic investigations, the creation of reproducible surface topologies in the substrate should be ensured, which have undercuts in relation to the knurling pitch and the deep rolling force used and thus enable a form-fit connection of thermally sprayed NiCr8020 layers. The great potential of this innovative substrate pre-treatment had already been demonstrated in preliminary studies. However, this also demonstrated the major challenges that had to be taken into account when working on this project. For example, the pitch of the initial knurling and the deep rolling force with the associated deep rolling strategy were identified as key factors whose complex interactions significantly affect the coating's adhesive tensile strength. The required symmetry of the generated undercuts and the necessary adjustment of the spraying parameters, also to completely fill the cavities, should be emphasized. Furthermore, the rolling of the knurling results in corresponding plateaus adjacent to the undercuts, which have a process-related, clearly smoothed surface that inhibits an adequate mechanical interlocking of the spray particles with the substrate when coating. Additional roughening of the smoothed plateaus before spraying is therefore essential. This is the only way to achieve a more homogeneous coating adhesion, which is also fundamental in terms of wear behavior in the application. The initial focus of the project was therefore on generating an increased number of undercuts in the substrate with adequate symmetry. For this purpose, the pitch of the initial knurling was reduced by a factor of three in relation to the tools used in the preliminary investigations by using specially manufactured knurling wheels, which also tripled the number of undercuts subsequently produced. By dividing the total infeed of the deep rolling tool into four adapted infeed increments and simultaneously reversing the rolling direction, it was possible to generate almost symmetrical undercuts in the substrate. Subsequent brushing of the smoothed plateaus in conjunction with spray parameters, systematically adjusted to the comparatively small cavities, enabled a layer system of a relatively homogeneous substrate bonding. In addition to a further smoothing, a final hydrostatic deep rolling of the coating made it possible to achieve adhesive tensile strengths that exceed those of conventionally blasted reference samples.
Publications
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Festwalzen gerändelter Oberflächen zur formschlüssigen Substratanbindung von HVOF-Beschichtungen. Unter Span - Das Magazin des Machining Innovations Network e. V, (2018), S. 19
Vogel, F.; Biermann, D.; Rodriguez, M.; Nicolaus, M. & Möhwald, K.
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Geometrisch bestimmte Oberflächen-strukturen zur formschlüssigen Substratanbindung thermisch gespritzter Schichten. Tagungsband 3. Niedersächsisches Symposium Materialtechnik, (2019), S. 483-494
Rodriguez, M.; Nicolaus, M.; Möhwald, K.; Vogel, F. & Biermann, D.
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Innovative Kombination von Verfahren zur Anbindung thermisch gespritzter Schichten. phi - Produktionstechnik Hannover informiert (online), 23 (2019).
Rodriguez Diaz, M.; Möhwald, K.; Vogel, F. & Biermann, D.
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Neue Verfahren der Oberflächenvorbehandlung zur Steigerung der Haftfestigkeit von thermisch gespritzten Schichten. Tagungsband 14. Aachener Oberflächentechnik Kolloquium, (2019), S. 69-79
Nicolaus, M.; Rodriguez Diaz, M.; Möhwald, K.; Maier, H. J.; Vogel, F. & Biermann, D.
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Innovative Verfahrenskombination zur Steigerung der Haftzugfestigkeit thermischer Spritzschichten. Unter Span - Das Magazin des Manufacturing Innovations Network e. V, (2020), S. 15
Vogel, F.; Biermann, D.; Rodriguez, M.; Nicolaus, M. & Möhwald, K.
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Erhöhte Haftfestigkeit thermischer Spritzschichten/Increased adhesion of thermal sprayed coatings – Innovative process combination enables substitution of conventional blasting processes. wt Werkstattstechnik online, 112(01-02), 28-33.
Vogel, Florian; Biermann, Dirk; Rodriguez, Diaz Manuel & Möhwald, Kai
