水素チャージしたFe-Ni合金の内部摩擦

抄録

Internal friction was measured at about 500 Hz from 160 K to 370 K in FCC Fe-Ni alloys subjected to electrolytic hydrogen charging. A relaxation peak of internal friction caused by hydrogen was found at 260 K in an Fe-54.0%Ni alloy and at 240 K in an Fe-72.8%Ni alloy, together with two small sub-peaks around 225 K and 265 K. The main hydrogen peak was always larger in the Fe-54.0%Ni alloy than in the Fe-72.8%Ni alloy. Their heights increased with the current density of electrolytic hydrogen charging and decreased with the hydrogen outgassing during repeated measurements. The activation energy of the hydrogen peak was estimated by the peak-shift method to be E=43.2 kJ/mol in the Fe-54.0%Ni alloy and E=42.3 kJ/mol in the Fe-72.8%Ni alloy. These values of the activation energy are comparable to recent data on hydrogen diffusion in the corresponding Fe-Ni alloys. Plastic deformation did not change the height and the shape of the hydrogen peak but affected considerably the higher-temperature sub-peak. Therefore, the hydrogen peak is independent of the presence of dislocations and might be a Snoek-type relaxation of dissolved hydrogen atoms, presumably being caused by the stress-induced ordering of hydrogen atom-pairs or clusters in the FCC lattice of Fe-Ni alloys. On the other hand, the higher-temperature sub-peak is a kind of the hydrogen cold work peak and might be caused by dislocation motion with hydrogen atmosphere.