Damage threshold of CuCrFeTiV high entropy alloys for nuclear fusion reactors

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A CuCrFeTiV high entropy alloy was prepared and irradiated with swift heavy ions in order to check its adequacy for use as a thermal barrier in future nuclear fusion reactors. The alloy was prepared from the elemental powders by ball milling, followed by consolidation by spark plasma sintering at 1178 K and 65 MPa. The samples were then irradiated at room temperature with 300 keV Ar+ ions with fluences in the 3 × 1015 to 3 × 1018 Ar+/cm2 range to mimic neutron-induced damage accumulation during a duty cycle of a fusion reactor. Structural changes were investigated by X-ray diffraction, and scanning electron microscopy and scanning transmission electron microscopy, both coupled with X-ray energy dispersive spectroscopy. Surface irradiation damage was detected for high fluences (3 × 1018 Ar+/cm2) with formation of blisters of up to 1 μm in diameter. Cross-sectional scanning transmission electron microscopy showed the presence of intergranular cavities only in the sample irradiated with 3 × 1018 Ar+/cm2, while all irradiation experiments produced intragranular nanometric-sized bubbles with increased density for higher Ar+ fluence. The Williamson-Hall method revealed a decrease in the average crystallite size and an increase in residual strain with increasing fluence, consistent with the formation of Ar+ bubbles at the irradiated surface.