Semi-quantitative characterisation of coherency-dependent hydrogen diffusion at Σ3 grain boundaries in pure Ni

Hydrogen diffusion behaviour at the coherent and incoherent Σ3 grain boundaries (GBs) of pure polycrystalline Ni was observed <i>in situ</i> using a polyaniline-based hydrogen video imaging system. The hydrogen flux at the coherent Σ3 GBs, also referred to as twin boundaries, was found to be the same as that in the grain interior. In contrast, enhanced hydrogen diffusion was observed at the incoherent portions of the Σ3 GBs. Hydrogen diffusion was notably enhanced at the micro/nanoscale incoherent portion, and the deviation angle of Σ3 GBs was identified as a critical factor influencing the hydrogen flux therein. Hydrogen diffusion was enhanced at the incoherent portions of the Σ3 GBs, and the deviation angle of the Σ3 GBs was identified as a key factor determining the hydrogen flux.