Annihilation of freely migrating defects by cascade remnants in Cu-1% Au alloys

The effects of cascade remnants on freely migrating defects (FMD) were studied by measuring radiation-induced segregation in Cu-1%Au at 400°C during simultaneous irradiation with 1.5 MeV He and (400-800) keV heavy ions (Ne, Ar or Cu). Radiation induced segregation during single-ion irradiation with He, Ne, Ar and Cu, and the effects of pre-irradiation with the same ions, were also investigated. The large segregation observed during 1.5 MeV He-only irradiation was dramatically suppressed under simultaneous Cu irradiation. This suppression disappeared immediately after the Cu irradiation ceased, indicating that it was caused by a transient population of cascade remnants, i.e., vacancy and/or interstitial clusters. For simultaneous inert-gas (He and Ne or Ar) irradiation, a similar suppression of the radiation induced segregation was observed. However, in contrast to the Cu-irradiation results, the suppression persisted after the Ne or Ar beam was turned off. The present results demonstrate that the energetic displacement cascades created by heavy ions introduce additional point-defect annihilation sites, which reduce the steady-state concentration of FMD. This finding implies that recombination dominates defect annihilation under the present irradiation conditions, which is indeed what is observed experimentally. As the cascade remnants produced by the Cu ions are thermally unstable at 400°C, the suppression of radiation induced segregation occurs only during simultaneous irradiation. During Ne and Ar irradiation, the inert gas atoms which accumulate in the specimen apparently stabilize the cascade remnants, allowing the suppression to persist during subsequent He-only irradiation.