NEW METHODOLOGY FOR THE DETERMINATION OF HYDROGEN PERMEATION PARAMETERS IN LAYERED MATERIALS

A new methodology for interpreting hydrogen permeation test data has b een proposed with the objective of determining hydrogen permeability, solubility and diffusivity in materials containing surface-coating lay ers. The mathematical development of equations has been undertaken for steady-state hydrogen permeation conditions allowing the determinatio n of all parameters of interest for the composite material and the coa ting layer itself. For a single-layered material, a set of three stati stically significant permeation tests is enough to determine all varia bles for the substrate, the composite material and the coating layer. This methodology has been applied to published results on the hydrogen permeation in nitrogen ion-implanted extra-low carbon steel, showing that the hydrogen diffusion coefficient in such a coating layer is sev eral orders of magnitude lower than that in the substrate. The hydroge n solubility in the layer is, by contrast, increased. The magnitudes o f these effects depend on the nitrogen concentration in the surface la yer.