Effect of plastic deformation on deuterium retention in tungsten

The effect of severe plastic deformation on the deuterium retention in tungsten exposed to high-flux low-energy plasma (flux ~1024 D/m2/s, energy ~50 eV, and fluence up to 3×1026 D/m2) at the plasma generator Pilot-PSI was studied by thermal desorption spectroscopy and scanning electron microscopy. The desorption spectra in both reference and plastically-deformed samples were deconvoluted into three contributions attributed to the detrapping from dislocations, deuterium-vacancy clusters and pores, respectively. The plastically-induced deformation, resulting in high dislocation density, does not change the positions of the three peaks but alters their amplitudes as compared to the reference material. The appearance of blisters detected by scanning electron microscopy and the desorption peak attributed to the release from pores (i.e. deuterium bubbles) were suppressed in the plastically-deformed samples but only up to a certain fluence. Beyond 5×1025 D/m2, the release from the bubbles in the deformed samples is essentially higher than in the reference material. Based on the presented results, we suggest that a dense dislocation network increases the incubation dose needed for the appearance of blisters - associated with deuterium bubbles - by offering numerous nucleation sites for deuterium clusters eventually transforming into deuterium-vacancy clusters by punching out jogs on dislocation lines.