Beyond ballistic mixing: New mechanisms for irradiation resilience of immiscible interfaces

A new mechanism for operando self-rejuvenation of irradiation damage, in which amorphization competes with cavity nucleation, is identified in immiscible Cu-10Ta (at.%) heterophase nanocomposite. These phenomena are observed using transmission electron microscopy (TEM) in situ irradiations with systematic variations in irradiating specie (Ne + , Kr 2+ , or Xe 2+ ions), temperature (100-400°C), and dose (up to 10 displacements per atom, dpa). Irradiation consistently induces amorphization of Cu-Ta interphase boundaries; the dose at which amorphization occurs increases with irradiation temperature and ion mass. At higher temperatures, cavity nucleation occurs prior to amorphization, but the cavity number density subsequently decreases upon the onset of amorphization, representing self-rejuvenation. These ion mass and temperature behaviors run counter to the conventional ballistic mixing mechanism of irradiation-induced amorphization. Instead, the amorphization mechanism entails the creation of lattice strains from irradiation-induced vacancies and implanted ions that remaining as point defects in the lattice. This raises the free energies of the immiscible phases, making the amorphous phase thermodynamically favorable. Results are used to identify regimes of irradiation damage energy ( E D ) and temperature which predict self-rejuvenation of cavities through amorphization. This new mechanism challenges longstanding beliefs that irradiation-induced amorphization requires ballistic mixing and low temperatures. Moreover, harnessing this mechanism will enable researchers to design immiscible metallic composites with operando resilience to irradiation.