抄録
The embritllement during the electrolytic hydrogen charging at 25-80°C and its recovery during hydrogen outgassing at 65-110°C after the charging were examined on Alloy 800 in some details with regard to tensile properties, fracture surface, and X-ray diffraction. A thin layer of hydride formed on the surface during the charging. It was unstable and disappeared after outgassing, leaving local lattice strain in the underlying metal. Many cracks on the specimen surface were observed along (111) or (110) traces on grains and grain boundaries. Brittle fracture always occurred at grain boundaries in tensile test. Tensile strength and strain at fracture decreased with the increases in charging time and temperature. There was a relation of h∝t1/2 between the depth of brittle layer (h) and charging time (t). The activation energy for the diffusion of hydrogen atoms obtained from the temperature dependence of h vs. t1/2 was estimated to be 11.0kcal/mol. On the other hand, activation energy for recovery process was calculated from Arrhenius plot of the reciprocal of the time to 50% recovery of the strain at fracture to be 12.2kcal/mol. A linear relation was held between the mean depth of brittle layer and tensile strength, and also between the depth and strain at fracture, regardless of charging and outgassing. These results show that the both processes of embrittlement and its recovery are rate-determined by the diffusion of hydrogen atoms in the metal.
