Subsurface morphology changes due to deuterium bombardment of tungsten

Recrystallized polycrystalline tungsten was exposed to a deuterium plasma beam with high flux (1022 D m-2 s-1) and low energy (38 eV D-1) to fluences up to 1027 D m-2. The sample temperature was varied between 320 and 800 K. The three-dimensional morphology of blister-like structures and the grain orientation were investigated by scanning electron microscopy combined with focused ion beam cross-sectioning and electron backscattering diffraction. Cracks with distorted areas (<650 K) and large cavities (100-1000 μm3) at grain boundaries (>480 K) were observed beneath the surface. The surface blister-like structures and the defects underneath are correlated along crystallographic orientation of the W grains in accordance to the low-indexed slip system {110}(111). The defects are mobile and accumulate under deuterium loading. Samples exposed near room temperature do not form such large cavities by subsequent heating up to 1300 K. Deuterium bombardment above 700 K does not lead to blister-like structures.