Influence of thickness and morphology on hydrogen permeation assessed by the Devanathan-Stachurski method: A case study for arc-evaporated TiN

Hydrogen permeation poses a significant challenge for hydrogen energy systems, emphasizing the importance of barrier coatings to reduce hydrogen ingress and prevent embrittlement in structural materials. This study examines how coating thickness, as a simple parameter, affects the growth morphology and hydrogen uptake of cathodic arc-evaporated TiN barrier coatings on ferritic steel substrates. Especially in industrially important arc processes, the incorporation of macroparticles disrupts film growth, creating cavities and facilitating hydrogen pathways. However, as film growth continues these pores close, reducing hydrogen uptake. Using a Devanathan-Stachurski cell, we assessed hydrogen diffusion and permeation reduction across various TiN coating thicknesses ranging from 1.5 μm to 5.5 μm. Electron microscopy revealed thickness-dependent morphological changes associated with defect overgrowth and open porosity. This is quantified by linear sweep voltammetry measurements, where the thickness-dependent open porosities were reduced from 7.18% for the 1.5 μm coating down to 0.06% for the 5.5 μm coating. Hydrogen permeation tests reveal that the 1.5 μm coating can halve the hydrogen uptake into the substrate compared to an uncoated reference, with further reductions down to a tenth for the 5.5 μm coating. These results underscore the impact of coating thickness and microstructural engineering on the effectiveness of barrier coatings proven for TiN as a model system.