Hydrogen blister formation in single crystal and polycrystalline tungsten irradiated by MeV protons

Single and polycrystalline tungsten samples were irradiated with 2.2 MeV protons at Soreq Applied Research Accelerator Facility (SARAF). Hydrogen blisters were obtained for both single crystal and polycrystalline samples, elucidating the role of grain boundaries in blister formation. The effect of temperature and flux on the critical formation dose for blisters and on their dimensions was studied. It was found that for single crystals, the critical formation dose is one order of magnitude higher than for polycrystalline tungsten at high temperature irradiation conditions. Upon reducing the irradiation temperature to ambient, the critical dose for formation of blisters in single crystals was reduced by a factor of three while in polycrystalline tungsten there was no significant change with temperature, thus indicating the role of grain boundaries in blister formation. Larger blisters were obtained in single crystals than in polycrystalline tungsten at ambient temperature conditions, identifying the grain boundaries as a preferential additional hydrogen trap. The height to area ratio of the blisters is found to be strongly temperature dependent and only weakly dependent on irradiation flux for both single and polycrystalline samples.