Geometrically defined surface structuring for the form-locked bonding of thermal sprayed coatings

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The pre-treatment of substrates for thermal sprayed coatings is conventionally done by abrasive blasting processes using corundum. This step is characterized by a long process time. Moreover, an additional machine is required to realize this kind of pre-treatment. Because of this, it is necessary to evaluate alternative processes to generate a suitable surface structure for the final coating process. Thus, this research project will investigate the possibility to generate a reproducible surface topology of substrates by the combination of the processes knurl milling and deep rolling. This combination leads to undercuts at the surface that enable an improved adhesion of sprayed coatings onto the substrate. The potential of this innovative pre-treatment process could be pointed out by preliminary investigations. Due to the undercuts the adhesive tensile strength of the coating was significantly increased in comparison to knurled surfaces. By using an additional deep rolling process as post-treatment of the sprayed coating, the adhesive tensile strength can nearly reach the amount of abrasive blasted and coated substrates. Furthermore, a smooth surface and a compaction of the coating is also realized by the rolling process. Investigations pointed out, that the failure of the laminate occurs in the areas between the undercuts which are characterized by a smoothed surface. Based on this, the knurl pitch size will be reduced in the project to affect the dimension of the smoothed surfaces between the undercuts and enable an increased adhesive tensile strength of the coating. All in all, the new process chain can increase the productivity of thermal spraying and enlarge the application area of thermal sprayed coatings. It could be possible to develop innovative wear protection coatings for the usage in engines. Moreover, the smoothed and compacted coatings can be used as functional surfaces.