Corrosion resistant layers produced by conventional and high-speed laser cladding with recycled powder
Josu Leunda, Ander Trinidad, Gemma Mendoza, Xabier Garmendia, Tomasz Dudziak, Filip Kateusz

Stainless steel powders, produced from machining scrap, were used as coating material for corrosion resistant layers deposited on cylindrical parts by both conventional and high-speed laser cladding. Powders of two different particle sizes were analyzed and compared with commercial AISI 316L powders by optical and scanning electron microscopy. The final coatings were also studied in terms of chemical composition, microstructure and hardness, and their corrosion behavior was evaluated by a salt spray test chamber. The results show that laser cladding with recycled material can be a potential methodology, aligned with the principles of circular economy, for producing corrosion resistant layers to work under critical conditions, such as coastal marine environments.

Keywords: Laser cladding; Corrosion; Recycled powder; Stainless steel

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Surface smoothening of thermal sprayed Hastelloy® C-276 coatings by laser polishing
N. Seiler, M. Hofele, M. Dauner, H. Riegel

Thermal sprayed coatings of the nickel-base alloy Hastelloy provide highly effective corrosion protection and thermal resistance. However, the sprayed surfaces exhibit a rough surface topography (Ra = 5.6 μm) with exposed porosity. In addition, thicker layers of material than necessary must be applied to compensate the material removal during mechanically surface finishing. This research work investigates the possibility of volume-preserving laser polishing to smoothening the rough surface structure of thermal sprayed Hastelloy C-276 coatings while closing the exposed porosity. In the future, laser remelting is expected to eliminate the material waste produced by conventional mechanical post-processing. Correlations between the laser parameters and the resulting coating layer properties such as roughness, residual surface structures are worked out enabling a relative roughness improvement of up to 81%. However, delamination and the formation of cracks occurs even at less energy density and created remelting depths, limiting the process ability.

Keywords: Laser remelting; post-processing; surface treatment; thermal spraying; flame spraying; high velocity flame spraying (HVOF); Hastelloy

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Monitoring of a single-mode cw-laser process for texturing of aluminum cylinder bore surfaces of combustion engines for coating preparation
Nick Schwarz, Laura Budde, Marius Lammers, Marijan Tegtmeier, Jörg Hermsdorf, Stefan Kaierle

Aluminum cylinder crankcases are more lightweight and thermally conductive than their conventional predecessors made of cast iron, but the cylinder bore surfaces must be coated with a wear-resistant material to achieve better or similar tribological performance. Thermally sprayed coatings can only achieve required adhesive strength when applying a roughening process. This enhances the mechanical form fit between the coating and the cylinder bore. The described laser system technology for texturing cylindrical inner surfaces enables helical trench-like structures to be inserted into the cylinder bore surfaces to improve the adhesion mechanism of the coating to the substrate. The laser-based process has additional manufacturing benefits compared to conventional roughening regarding tool wear and soiling of the produced parts. The presented work describes the development of the technology from fundamental process development via application in serial production to inline process monitoring.

Keywords: surface structuring; coating preparation; laser texturing; engine manufacturing; process monitoring