Ceramic protective coatings on C-fiber-reinforced and unreinforced plastics through laser pyrolysis of filled silazanes

• Applicants: Dr. Günter Motz; Professor Dr.-Ing. Michael Schmidt
• Subject Area: Coating and Surface Technology ; Synthesis and Properties of Functional Materials
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405583003

In the DFG research project “Ceramic protective layers on CFRP and plastics through laser pyrolysis of filled silazanes” it was successfully demonstrated that it is possible to create ceramic layers on low-melting light metals using laser radiation based on precursor technology without damaging the substrates. Problems such as the very different coefficients of thermal expansion (CTE) between the ceramic layer that forms and the light metal substrates as well as the high thermal conductivity of the substrates, which leads to a faster dissipation of the heat generated, were solved. The layers created in this way are characterized by very good adhesion, high hardness and abrasion resistance and also effectively protect the substrates against corrosion. Afterwards experiments were conducted to transfer the developed technology to carbon fiber-reinforced plastics and pure plastic substrates (PEEK, PA), as there was no evidence of thermal stress on the light metal substrates. Despite modification of the absorption properties of the layers and reduced laser power, the very low thermal conductivity during laser pyrolysis resulted in an excess of heat underneath the layer and thus melting of the plastic substrates. However, these experiments provided important insights that the substrates need to be additionally protected from heat. After the end of the project period, the first tests were carried out with a thermal insulation layer (TBC), which were promising. However, this concept needs to be intensively researched and the adaptation of the coating systems to laser pyrolysis, especially for plastic substrates, needs to be fundamentally reworked. First of all, it is necessary to develop a mechanically and thermally stable TBC that not only minimizes the heat flow to the substrate during laser treatment of the top coat, but also compensates for the CTE differences and ensures a very good connection to both the substrate and the top coat guaranteed. Top coats are then developed that are perfectly tailored to the properties of the TBC and the corresponding laser parameters for successful ceramization. The main properties of the top coat are increasing surface hardness, improving wear and chemical resistance. This requires dense, pore- and crack-free layers that are as hard as possible, chemically stable, and adhere well. Additional modifications and functionalizations are then carried out in order to further improve the wear resistance of the coated plastics or to create electrical and magnetic properties that expand the range of applications of the coated plastic substrates. Fiber-reinforced and pure polymers suitable for lightweight construction are used as substrates.

• DFG Programme: Research Grants