Effect of high fluence Au ion irradiation on nanocrystalline tungsten film

Irradiation-induced microstructure evolution and phase transformation have been studied on the nanocrystalline tungsten film with simple cubic structure (β phase). The samples were irradiated by 4 MeV Au ions at different fluences ranging from 6 × 1014 to 1 × 1016 ions/cm2, corresponding to the peak damage levels from 6 to 100 dpa (displacements per atom). Analysis by GIXRD and TEM reveals that the structure of tungsten film undergoes a distinct transition from simple cubic phase to bcc phase when the fluence is above 3 × 1015 ions/cm2 (30 dpa) and grain growth occurs with the increasing fluence. Radiation-induced small voids are clearly observed in the interior of coarsened grains at the highest fluence, 1 × 1016 ions/cm2 (100 dpa).