Radiation tolerance and microstructural changes of nanocrystalline Cu-Ta alloy to high dose self-ion irradiation

Abstract Nanocrystalline materials are known to possess excellent radiation resistance due to high fraction of grain boundaries that act as defect sinks, provided they are microstructurally stable at such extreme conditions. In this work, radiation response of a stable nanocrystalline Cu-Ta alloy is studied by irradiating with 4 MeV copper ions to doses (close to the surface) of 1 displacements per atom (dpa) at room temperature (RT); 10 dpa at RT, 573 and 723 K; 100 and 200 dpa at RT and 573 K. Nanoindentation results carried out for samples irradiated till 100 dpa at RT and 573 K show exceptionally low radiation hardening behavior compared to various candidate materials from literature. Results from microstructural characterization, using atom probe analysis and transmission electron microscopy, show a stable nanocrystalline microstructure with minimal grain growth and a meagre swelling in samples irradiated to 100 dpa (~0.2%) and 200 dpa at RT, while no voids in those at 573 K. This radiation tolerance is partly attributed to the stability of Ta nanoclusters due to phase separating nature of the alloy. Additionally, the larger tantalum particles are observed to undergo ballistic dissolution at doses greater than 100 dpa and are eventually precipitated as nanoclusters, replenishing the sink strength, which enhanced material's radiation tolerance when exposed to high irradiation doses and elevated temperatures.