Research ArticlePHYSICS

Origin of micrometer-scale dislocation motion during hydrogen desorption

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Science Advances  05 Jun 2020:
Vol. 6, no. 23, eaaz1187
DOI: 10.1126/sciadv.aaz1187
  • Fig. 1 The experimental procedure that revealed dislocation motion during hydrogen desorption.

    (A to E) Stages in the experiment.

  • Fig. 2 Dislocation motion during H desorption in Fe-Mn–based alloy captured by ECCI.

    (A) A planar dislocation pileup at a grain boundary (GB) at different stages of H desorption. (B) Dislocation configurations at t = 2 and 2.5 hours are shown schematically. Note the ~1.5-μm distance that dislocations b and c glide. (C) Relative positions of dislocations with respect to the GB are plotted against exposure time. (D to F) Three other examples of H desorption-induced dislocation motion are presented. The blue color indicates dislocations that are most strongly affected. Movies are available online.

  • Fig. 3 Atomistic simulation of dislocation motion during H-charging in Ni polycrystalline sample.

    Hybrid MD/GCMC simulations reveal that H mainly segregates at GBs and free surfaces, as shown in (A) 3D and (B) 2D views. Here, gray zones represent GBs, red spheres are H atoms, light blue atoms are hexagonal close-packed (hcp) atoms, and dark blue lines are the dislocation network. Snapshots of the dislocation structures in H-charged samples shown in (C) reveal clear dislocation rearrangements (see the black arrows). The red arrows point out a new dislocation generated during H-charging of the sample (see movie S7). H-free sample in (D) shows little dislocation activity.

  • Fig. 4 Atomic-level von Mises stress distribution due to hydrogen diffusion in polycrystalline Ni sample.

    (A) Atomic-level von Mises stress distribution from atomistic simulation. The stress has a higher magnitude on GBs. (B) The cumulative density function (CDF) of von Mises stress distribution of atoms in grain interiors (bulk) and GBs before and after H-charging into the sample. The two insets are the zoomed windows showing 200 MPa change in von Mises stress of atoms in bulk and GBs, due to H-charging into the sample. (C) The temporal average of the von Mises stress for different averaging time periods ranging from 500 ps to 6 ns. The temporal average converges by increasing the averaging time period.

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