Effect of helium ion irradiation on micro-structures, defects and superficial swelling in WTaTiVCr refractory high entropy alloy with columnar crystalline structures

Exploring novel plasma-facing materials (PFMs) with exceptional irradiation resistance is a pivotal and challenging endeavor for applications in the harsh environment of energetic ion irradiation in future fusion reactors. In this work, tungsten-containing WTaTiVCr refractory high-entropy alloy (RHEA) featuring nano-columnar crystalline structures were subjected to irradiation with 60 keV helium ion (He+) beams at the fluence ranging from 1×1016 cm-2 to 2×1017 to elucidate fundamental mechanisms governing He behavior and superficial swelling height. After irradiation, the WTaTiVCr RHEAs demonstrated remarkable micro-structural stability, exhibiting only minimal grain growth while maintaining their characteristic of columnar architecture. At the highest fluence (2×1017 cm-2), detailed characterization revealed the preferential formation of distinctive ribbon-like He bubbles along grain boundaries, confirming these interfacial regions as favorable nucleation sites. While the overall phase structure remained stable throughout the irradiation process, advanced micro-structural analysis detected localized elemental segregation phenomena. This segregation behavior appears directly correlated with the development of highly-pressurized bubbles and associated micro-crack formation within the columnar grain boundaries. Meanwhile, the study provides comprehensive insights into the complex interactions between internal bubble formation and surface blister development, revealing these mechanisms collectively contribute to the observed irradiation induced swelling behavior.