Abstract:

The permeability and diffusivity of hydrogen in directionally solidified polycrystalline and single crystal nickel foils were measured by gas permeation method. The results showed that both hydrogen diffusivity and permeability were higher in directionally solidified nickel specimen than those in single crystal one at the temperature ranging from 300 to 480 °C, and confirmed the existence of short-circuit diffusion along the grain boundaries (GBs) in the directionally solidified nickel. The results suggested that the rapid diffusion along GBs was more obviously characterized in terms of higher permeability rather than higher diffusivity. The contribution of grain boundary to hydrogen transportation was represented by the differences of diffusivity (and permeability) in single crystal nickel and directionally solidified nickel. By modifying the Fick’s first diffusion law and counting the grain boundary density, the hydrogen diffusivity and permeability of rapid diffusion along GBs were calculated. The results suggested both the diffusivity and permeability fit the Arrhenius relationship well at different temperature.

Key words: Hydrogen trapping, Hydrogen embrittlement, Grain boundary diffusion, Nickel