New methodology for the determination of hydrogen permeation parameters in layered materials

Abstract

A new methodology for interpreting hydrogen permeation test data has been proposed with the objective of determining hydrogen permeability, solubility and diffusivity in materials containing surface-coating layers. The mathematical development of equations has been undertaken for steady-state hydrogen permeation conditions allowing the determination of all parameters of interest for the composite material and the coating layer itself. For a single-layered material, a set of three statistically significant permeation tests is enough to determine all variables 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 several orders of magnitude lower than that in the substrate. The hydrogen solubility in the layer is, by contrast, increased. The magnitudes of these effects depend on the nitrogen concentration in the surface layer.