Influence of mechanical roughening on hydrogen uptake, diffusion and trapping in iron-chromium alloy

This study investigates the influence of mechanical surface roughening on hydrogen uptake, diffusion and trapping in a single crystal Fe-Cr-Mo (001). Samples underwent varied mechanical roughening (grinding) to produce different surface finishes. Hydrogen diffusion and trapping behaviors were evaluated using electrochemical permeation tests, complemented by surface roughness and subsurface deformation analyses. Results revealed that increased surface roughness significantly reduces both steady-state hydrogen flux, hence subsurface lattice hydrogen concentration, and apparent hydrogen diffusion coefficients. Findings demonstrate that surface roughness impedes hydrogen entry at rougher surfaces. This was attributed to higher peak dominance that allows a higher probability of hydrogen recombination reactions at the surface. Numerical simulations of the permeation experiments on roughened specimens confirmed that subsurface defects primarily delay hydrogen breakthrough i.e . decrease the apparent diffusion coefficient. This study highlights the influence of surface morphology on hydrogen permeation behavior and confirms that surface characteristics should be considered in the case of industrial metallic surfaces exposed to electrochemically produced hydrogen.