Effect of Laves phase on hydrogen behavior in V-Zr-Ti-Ni hydrogen absorption alloys : Special issue on hydrogen absorbing materials

Hydrogen behavior in V-Zr-Ni-Ti alloys with different amount of Laves phase has been examined by the tritium radioluminography and the PCT measurement. Tritium radioluminography has shown that the local hydrogen concentration in the Laves phase is higher than that in the BCC phase in the range of lower hydrogen content of ppm order, that is, hydrogen preferentially dissolves into the Laves phase. PCT measurement has shown that the maximum hydrogen concentration decreases as the ratio of the Laves phase to the BCC phase increases in the range of higher hydrogen content of percent order. This means that the BCC phase mainly absorbes hydrogen. It has been concluded that the Laves phase acts as the penetration path for hydrogen in the early stage of hydrogenation, and that the BCC phase is the main hydrogen storaging phase. An extraordinary phenomenon has been observed in the time dependence of the local hydrogen concentration in V 54.5 Zr 18.25 Ti 11.25 Ni 16 alloy. The local hydrogen concentration in the BCC rich region decreases for a few days after hydrogen charging and then changes to increase, while the hydrogen concentration in the Laves phase rich region gradually decreases. This phenomenon has been thought to be related to the microstructure in the specimen.