Visualization of Hydrogen and Hydrogen-induced Defects in Tensile-deformed Pure Iron Using Hydrogen Microprint and Tritium Autoradiography

To understand the process and mechanism for hydrogen embrittlement in steels, visualization of the location of hydrogen is essential. In the present study, two visualization techniques, hydrogen microprint technique (HMT) and tritium autoradiography (TAR), were applied to a pure iron sheet 20% tensile-deformed with cathodic hydrogen charging. When the specimen was covered with photographic emulsion shortly (40 min) after the deformation, HMT showed that the charged hydrogen atoms diffused out at majorly grain boundaries and minorly in the grain interiors. The TAR, conducted on the same sample but completely de-hydrogenated and then charged with tritium, revealed that hydrogen enhances the formation of vacancies or vacancy clusters with plastic deformation, which are located along grain boundaries and deformation bands and act as relatively stable trapping sites for tritium.