Hydrogen permeation barrier properties and surface characterization of RF-sputtered tungsten coatings on API X60 steel

Tungsten coatings could be promising candidates for hydrogen permeation barriers both in hydrogen industry and in high temperature fusion reactor applications. In this work tungsten coatings of 3 μm and 1.5 μm thickness were deposited by RF magnetron sputtering. The surface of the W-coatings was characterized before the electrochemical permeation test using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) to ensure reproducible results. The tungsten coatings on API X60 steel substrates were tested as hydrogen permeation barriers. The build-up hydrogen permeation curves allowed us to determine the effective diffusion coefficient D eff and the effective permeability P eff of the substrate/coating system, both about an order of magnitude lower compared to the X60 steel substrate. The diffusion coefficient of hydrogen through the W coating in the coated steel substrate was determined with formulas taking into account the two-layer system coating/substrate; the diffusion coefficient of the tungsten coating D coat was estimated in the range of 7.5×10 -17 m 2 s -1 to 5×10 -16 m 2 s -1 , showing excellent hydrogen permeation barrier properties.