(332e) Elucidating the Mechanisms of Hydrogen Blister Formation in Plasma-Facing Tungsten

Hydrogen plasmas are known to form blisters in tungsten. While this a well-known phenomenon, the mechanism of blister formation is not well understood. Evolution of these blisters does not appear to be caused by hydrogen self-trapping or trapping at vacancies, and prior studies have suggested that grain boundaries may play an important role in blister formation. To this end, we used molecular dynamics to study how hydrogen adsorbs onto grain boundaries in tungsten and how adsorbed hydrogen affects polycrystalline tungsten's mechanical properties. We find that hydrogen will collect at grain boundaries and that grain boundaries initially inhibit the transport of hydrogen through the grain boundary plane. For grain boundaries parallel to the plasma-facing surface, however, hydrogen will be "pushed" through the grain boundary once the entire grain boundary plane is covered with hydrogen. The mechanical properties, in particular the yield stress, will also be altered when the grain boundary is loaded with hydrogen. This may cause delamination of the grain boundaries to occur more readily, leading to blister formation.