Study on the microstructural evolution in NbMoTaW series refractory multi-principal element alloy films by low-energy and high-flux He ions irradiation

In this study, the nanocrystalline NbMoTaW and NbMoTaWV refractory multi-principal element alloy (RMPEA) films were selected for the research of low-energy (50 eV), high-flux (~1021 ions m−2 s−1) helium ions irradiation response and thermal conductivity at 1050 K. The NbMoTaW and NbMoTaWV RMPEA films maintained the single-phase body-centered cubic (BCC) structures after irradiation. The electrical and thermal conductivities did not decrease, and the phenomena like “fuzz” structures of W films or “fuzz-like” structures of NbMoTaW RMPEA bulks were not found, indicating that the nanocrystalline RMPEA films have inhibition effects on the growth of “fuzz” structures. The inhibition of “fuzz” structures in the RMPEA films could be attributed to: (i) The high-density columnar crystal grain boundaries could accommodate more helium and provide helium release channels. (ii) The sluggish diffusion kinetic effects of RMPEA films suppressed the helium diffusion and maintained the helium release channels at high temperatures. Moreover, the NbMoTaWV RMPEA films were discovered to produce smaller helium bubbles and less pronounced microcracks compared to NbMoTaW RMPEA films. It was due to the solid solution incorporation of V which further enhanced the lattice distortion and toughness as well as the profound suppression of helium diffusion.