In situ studies on radiation response of supersaturated NbCu alloy

Immiscible metallic systems provide opportunities for controlling radiation-induced defect accumulation through defect-interface and defect-solute interactions; however, radiation-induced defect evolution in metastable supersaturated solid solutions remains comparatively less well understood. In this work, we have investigated the radiation response of a sputtered supersaturated Nb-15 at.% Cu alloy containing pre-existing grain boundary (GB) voids and Cu-rich precipitates using in situ 1 MeV Kr ion irradiation at room temperature up to ~2.30 dpa. In situ TEM observations reveal progressive shrinkage and elimination of pre-existing GB voids with increasing radiation dose, together with migration and absorption of irradiation-induced defect clusters at GBs. Post-irradiation HRSTEM and EDS analyses reveal the formation of nanovoids within the Nb-rich matrix accompanied by Cu segregation. Irradiation also induces compositional and structural evolution of the Cu-rich GB precipitates, which become more diffuse and discontinuous with reduced Cu concentration and predominantly BCC structures. These observations reveal the coupled nature of defect migration, void evolution, solute redistribution, and local phase evolution during irradiation of a nonequilibrium immiscible alloy. The findings improve the understanding of radiation-damage evolution in metastable immiscible systems and highlight the roles of GB defect sinks and solute-defect interactions in controlling radiation-induced microstructural evolution.