Experimental study on the diffusion of hydrogen along individual grain boundaries in nickel

Whether hydrogen diffusion can be accelerated by grain boundaries (GBs) still remains controversial. In this study, the impact of different types of GBs within the directionally solidified polycrystalline nickel specimens on hydrogen diffusion was directly observed at room temperature by combining Electron Back Scattered Diffraction (EBSD) and scanning Kelvin probe force microscopy (SKPFM). The results suggest that the coherent Σ3 twin GB provides a fast path for hydrogen diffusion, while the random GB cannot significantly accelerate the transport of hydrogen atoms. In addition, this study confirms that SKPFM is a reliable technique to allow the detection of the local diffusion and distribution of hydrogen in metals with high lateral resolution down to the GBs.