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Radiation damage evolution in pure W and W-Cr-Hf alloy caused by 5MeV Au ions in a broad range of dpa

Mackova, A.; Havranek, V.; Fernandes, S.; Matejicek, J.; Vilemova, M.; Holy, V.; Liedke, M. O.; Martan, J.; Vronka, M.; Potocek, M.; Babor, P.; Butterling, M.; Elsherif, A. G. A.; Hirschmann, E.; Wagner, A.

Pure W and W-Cr-Hf alloy which are prospective materials for nuclear fusion reactors, such as DEMO,
were irradiated at room temperature with 5 MeV Au2+ ions with fluences between 4 × 1014 and 1.3
× 1016 to generate various levels of lattice damage from about units up to tens of dpa. The distinct
character of radiation damage accumulation, microstructure and defect nature have been observed in
both pure W and W-Cr-Hf alloys, the latter exhibited interesting ability of damage reorganisation and
defect size decrease at the higher ion fluences as determined by positron annihilation spectroscopy (PAS),
X-ray diffraction analysis (XRD) identified vertical grain size modification as a function of the Au-ion
fluence. Originally more strained subsurface layer influenced by polishing procedure exhibited the defect
and strain release with the increased Au-ion irradiation fluence in both materials. Radiation damage
saturation has been observed in the deep buried layer at the lower Au-ion fluences in the W-samples
compared to W-Cr-Hf samples; contrary for the higher Au-ion fluence a slight damage decrease was
evidenced in W-Cr-Hf alloys. The distinct defect accumulation was accompanied with the different Au-ion, implanted distribution in the irradiated layer determined by Secondary Ion Mass Spectrometry (SIMS) as
well as the thermal properties have shown the consequent worsening in the depth in good agreement
with the Au-depth concentration profiles. TEM corroborated above mentioned findings, where the subsurface
layer exhibited defect release after the irradiation, the maximum of dislocation loop density has
been identified in the depth according the predicted dpa (displacement particles per atom) maximum for
the lower Au-ion fluences. Moreover, TEM shows the dislocation density band structure appeared in WCr-
Hf samples exhibiting the high density defect band according the projected range of the Au-ions
simultaneously with the additional layer with larger isolated dislocations pronounced in the higher depth
as a growing function of Au-ion ion fluence. Such phenomenon was not observed in W samples.

Keywords: positron annihilation lifetime spectroscopy; SIMS; alloys; W Tungsten

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Publ.-Id: 33025