Effect of He-ions irradiation on the microstructure and mechanical properties of TiTaNbZr refractory medium-entropy alloy film

In this work, TiTaNbZr refractory medium-entropy alloy (RMEA) films were irradiated by 60 keV helium (He) ions at the fluence of 5 x 1016 cm-2 -2 x 1017 cm-2. After irradiation, a structural transformation of amorphous-BCC single phase, namely self-healing behavior, in TiTaNbZr RMEA films was revealed on account of the enhanced diffusion and redistribution of atoms, which could also lead to a decrease of defects. In this process, increased grain boundaries, acting as effective defect sinks, have inhibited the He bubbles within crystals. The short-range migration of atoms did not destroy the uniformity of elements dramatically. In addition, the cor -relation between the structural transformation and mechanical properties evolution in the RMEA films was also further clarified. No degradation of mechanical properties even for irradiation fluence as high as 2 x 1017 cm-2 due to the increased grain boundaries and self-healing mechanism. These results all indicate that the TiTaNbZr RMEA have outstanding irradiation resistance and potential applications in reactor structural materials. Mean-while, the microstructural transformation and performance evolution of the TiTaNbZr RMEA explored in this study could provide more understanding of irradiation effect and a new perspective for the development of the alloys with self-healing ability in refractory high/medium entropy alloys (RHEAs/MEAs).