High temperature electrochemical charging of hydrogen and its application in hydrogen embrittlement research

A high temperature electrochemical charging technique was developed for effective introduction of hydrogen or tritium into the metallic materials to a high level in a short period of time. The samples of the steels and alloys, as the cathode, were charged in an electrochemical cell consists of Pt anode and molten salt electrolyte. After 3, 6 and 12 h charging, the 304 stainless steel absorbed 25, 45 and 60 ppm of hydrogen, respectively. Correspondingly, the mechanical strength lost 10, 16 and 23%. The plasticity was also reduced to 20, 23 and 38%. The fractography showed the hydrogen embrittlement effect on the fractures. The electrochemical hydrogen charging technique was successfully used for introducing tritium, an isotope of hydrogen, into the super alloys for visualization of hydrogen trapped in the microstructure of the materials. It is found that the hydrogen is trapped at the grain boundaries, in inclusions and carbides. The deformed and twisted grain boundaries trap most hydrogen under stress.