A clean and defect-free substrate/coating interface is required to guarantee good adhesion of coatings under service conditions. For this purpose, an etching pre-treatment using High-Power Impulse Magnetron Sputtering (HiPIMS) was performed to modify the surface of 304L stainless steel. The effect of three etching procedures on the substrate properties, such as corrosion resistance and adhesion, was investigated with unprecedented spatial resolution and spectroscopic details. Glancing angle X-ray diffraction showed modification in phase content but no neoformation after steel etching. X-ray photoelectron spectroscopy confirmed the presence of etchant species (6–7 at.%) on the extreme surface of the substrate. Transmission Electron Microscopy and Atomic Probe Tomography showed that the interface was less than a few nanometers wide. Polarization curves in a nitric acid solution at boiling temperature showed, for the first time, that the Ti+ and Zr+ etchings decreased the corrosion current density compared to the untreated original surface. Scratch-test measurements indicated better substrate/coating adhesion using HiPIMS metal ion etching. Electrochemical characterization revealed that Zr etching and thin coating improve the anti-corrosion properties of stainless steel in strong nitric acid conditions.

The effect of process parameters on the microstructure and corrosion behavior of additively manufactured 316L stainless steel was reported. Immersion tests were performed in nitric acid solution at boiling temperature and the corrosion behaviour was correlated to microstructure of 316L stainless steel specimens produced by laser powder bed fusion (L-PBF) as a function of the process parameters such as scanning strategy, laser power and hatching distance. These parameters were found to influence the porosity, the grain size and the cellular microstructure. The corrosion tests revealed a higher impact of hatching distance on corrosion behaviour. Post-mortem microstructural examination revealed that the corrosion preferentially occurred at cellular structures and at grain boundaries and melt pools when the scanning strategy and hatching distance were respectively modified. The solute segregation at boundaries cells, the grain size distribution and the porosity could explain this corrosion behaviour. The results were compared with those of solution annealed counterpart, which would provide a factual basis for future applications of L-PBF 316L stainless steel.

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