Comparison of surface morphologies and helium retention of nanocrystalline W and W-Cr films prepared by magnetron sputtering

•Pure W films and W-Cr alloy films were deposited by magnetron sputtering.•The incorporation of chromium into tungsten leads to grain refinement.•Helium blister formation and retention of W-Cr alloy film has been suppressed compared to pure W film under helium irradiation. This study focuses on the influence of helium ion irradiation on the microstructure and retention of tungsten (W) and tungsten-chromium (W-Cr) alloy films. Under helium irradiation with fluence of 1.04 × 1022 He2+ / m2, blisters are found on the surfaces of both W film and W-Cr alloy film. The size and density of blisters on the surface of W-Cr alloy film are smaller than those of W film. As a result of grain refinement by the addition of 5% chromium, the density of grain boundaries in W-Cr alloy film is higher than that of W film. These grain boundaries trap helium atoms and reduce the effective mobility of helium atoms. Thereby, helium blister formation and helium released amount of W-Cr alloy film have been reduced compared to W film under helium irradiation.