Visualization of local hydrogen diffusion in stainless steel using time resolved electron stimulated desorption

We have improved an electron stimulated desorption (ESD) apparatus to obtain the time evolution of hydrogen permeation for cold-worked stainless steel. Hydrogen permeation through grain structures was visualized by using the operando hydrogen microscope combining ESD and hydrogen supply system. The diffusion coefficients in grains were calculated from time evolution curves of hydrogen permeation. Principal component analysis (PCA) of hydrogen maps was used to classify crystal grains by the degrees of hydrogen diffusion and permeation flux. Grain structures such as the ratio of austenite/martensite, crystallographic orientations and coherent/random grain boundaries were determined by electron backscatter diffraction (EBSD) analysis. The areas with high-speed and high flux permeation of hydrogen were characterized as smaller austenitic grains with grain boundaries. The usefulness of a combined ESD-PCA-EBSD analysis on hydrogen permeation in materials was demonstrated in the present study.