Temperature-dependent grain boundary permeation of hydrogen in tungsten has been investigated using a recently developed hydrogenography technique that utilizes patterned films on the back of the permeation samples. A tungsten oxide layer was first developed as a hydrogen indicator that could withstand greater temperatures than previously used yttrium, and a method for reliably quantifying the results was established. The findings indicated that the hydrogen permeation flux across the grain boundaries is dominating up to 660K, where the first signs of a transition to bulk permeation were seen.
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