Laser-based coating process of PEEK powder on stainless steel substrates by using a thulium-doped fiber laser.

PEEK is an excellent thermoplastic material for functional coatings due to its outstanding material properties (e.g. biocompatibility, temperature stability, corrosion and wear resistance). In order to reduce the heat input into the base material and to enable a high local selectivity of polymer deposition, a laser-based coating process is a promising approach. In this study, the consolidation of PEEK coatings on stainless steel substrates was investigated experimentally for the first time by using a thulium-doped fiber laser with a wavelength of 1.94 µm. As most polymers exhibit characteristic absorption bands at wavelengths above 1.5 µm, a thulium-doped fiber laser is more appropriate for consolidating thermoplastics in comparison to more common near-infrared laser beam sources with wavelengths of around 1 µm. The effect of admixing fumed silica particles on the flow behavior of the PEEK powder was analyzed by degree of coverage tests to improve the powder deposition process via doctor blade. Furthermore, the influence of an additional substrate heating on the resulting coating characteristics was investigated. Optical microscopy analyses were conducted to characterize the coating surfaces and cross-sections in terms of possible defects. As a result, the flow behavior and hence the deposition process were significantly improved by admixing 1.0 wt. % fumed silica. Optical microscopy analyses verify the basic feasibility of a laser-based coating process with a thulium-doped fiber laser for the consolidation of PEEK powder on stainless steel substrates. In this context, a substrate heating is an important prerequisite to enhance the wetting of the stainless steel substrate and to produce dense as well as adherent PEEK coatings. [ABSTRACT FROM AUTHOR]