SKPFM study of hydrogen in a two phase material. Experiments and modelling

Abstract Scanning Kelvin Probe Force Microscopy (SKPFM) was used to study hydrogen diffusion in a duplex stainless steel. The experiments were conducted on specimens covered with a nanometric palladium layer and pre-charged with hydrogen. A finite element model (FEM) of hydrogen diffusion in a three phase system (ferrite, austenite and palladium) was developed to simulate the experiment. This model allows us to take into account the different diffusivity and solubility of hydrogen in the three phases. It is shown that the contrast observed in SKPFM correlates very swell with the distribution of hydrogen in the palladium layer determined from FEM modelling. This contrast is governed mainly by the hydrogen release into the palladium layer. On the other hand there is no direct relation between the observed contrast and the hydrogen distribution in the stainless steel microstructure. Our results show that SKPFM should be considered as a way to monitor locally the release of hydrogen into the palladium layer, rather than a way to map the hydrogen concentration in the material.