Abstract
The aim of the present study is to investigate the impact of coatings and their combination with diffusion treatments (duplex processes) on the hydrogen barrier effect to avoid hydrogen penetration in steel. This is necessary in order to use tempered steel as a material for hydrogen applications, including hydrogen storage systems and pipelines. For this purpose, coated samples of tempered steel grade 34CrMo4 are exposed to hydrogen and afterwards experimentally examined.
The experimental investigations focus on the comparison between conventional nitride vacuum coatings, like PA-CVD or PVD, with duplex processes. Duplex processes are a combination of base material coatings and a subsequent surface functionalization with e. g. nitrogen by a (plasma-assisted) diffusion treatment. The considered coatings in this study are based on titanium and chromium, because they have either a lower solubility (Cr) or diffusion rate (Ti) for hydrogen compared to iron [9, 17].
To evaluate the barrier effect, the samples with modified surfaces are exposed to pressurized hydrogen gas and analyzed by Carrier Gas Hot Extraction (CGHE) as well as Secondary Ion Mass Spectrometry (SIMS). The depth of penetration is measured in comparison to untreated material. In addition, standardized surface analytics, like Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-ray spectroscopy (EDX) have been applied.