Deformation-based alleviation of irradiation effects in proton irradiated nanocrystalline Cu-10at%Ta alloy

Advancements in fabrication of immiscible alloy has allowed the development of high temperature stable nanostructures. One such system is the nanocrystalline Cu-10at%Ta alloy system which has been shown to maintain its nanocrystalline structure up to temperatures of 0.7T_m, owing to the Ta nanoclusters which act as Zener pinning point and hinder grain boundary motion. High mechanical strength, high temperature stability and increased sink strength for point defects due to high volume of grain boundary volume and Cu-Ta interface boundary volumes, make it a candidate material for nuclear applications. To study the effects of radiation the material is proton irradiated at 500℃ up to a dose of 1 dpa and to study the mechanical response of the material, TEM in situ pico-indentation intermitted with Automated Crystal Orientation Mapping (ACOM) is used. Post irradiation, microstructure analysis using transmission electron microscope reveals limited grain growth and absence of irradiation induced defects in the Cu grains due to a combination of high sink volume in the material and the high irradiation temperature. TEM analysis also reveals Ostwald Ripening of Ta particles > 20 nm and Atom Probe Tomography (APT) cluster analysis shows ballistic dissolution of Ta particles < 2.5 nm which leads to supersaturation of Ta in the Cu matrix as Ta is immiscible in Cu. A closer look at the nanostructure during deformation of the alloy using TEM in situ pico-indentation reveals refining of the Ta particles > 20 nm in both as-received and irradiated sample due to a dislocation glide mediated mechanism. In the proton irradiated sample, the TEM in situ mechanical test also results in the formation of Ta particles at the grain boundaries due to the supersaturated Cu matrix after irradiation and due to the transport of Ta atoms along the grain boundaries showing effects of radiation can be alleviated via deformation.