In-situ TEM bubble to cavity evolution due to annealing post helium and dual ion irradiation in Cu-10Ta and Cu-3Ta

Materials have been essential to every major invention in the history of mankind, e.g. satellites, nuclear reactors, or space shuttles would not exist without advancements in materials withstanding temperature and radiation environments. In this work, we investigate room-temperature implantations of helium and concurrent He and Au via in-situ transmission electron microscopy (TEM) followed by isochronal annealing up to 450 °C to understand the microstructural stability and bubble to cavity evolution in advanced nanocrystalline (NC) Cu-3 at.%Ta and Cu-10 at.%Ta alloys. The room temperature irradiation to high helium concentration and displacements per atom (dpa) levels did not lead to significant coarsening of grains in both Cu-10Ta and Cu-3Ta. Overall grain sizes remained <150 nm indicating extraordinary microstructural stability in both alloys. Post-irradiation, incubation for a few days resulted in the observation of ∼1 nm diameter bubbles homogenously distributed in both the alloys and both irradiation conditions. Further evolution of these bubbles to cavities with annealing to 450 °C indicated Brownian motion migration and coalescence to be the dominant coarsening mechanism involved. A comparison of bubble to cavities evolution in Cu-3Ta and Cu-10Ta under similar conditions showed smaller bubble size and density in Cu-3Ta indicating an overall enhanced resistance of Cu-3Ta to swelling under both helium and dual-beam irradiation at high temperatures. This is primarily attributed to the high fraction of essential coherent/incoherent precipitates that act as effective defect sinks in Cu-3Ta.