Effects of Fe concentration on helium bubble formation in NiFe_x single-phase concentrated solid solution alloys

The formation of helium bubbles and the consequential property degradation are critical challenges for materials used in advanced nuclear energy systems. The mechanism of helium bubble formation in a series of NiFe_x (x = 0, 20, 35, or 50 at.%) single-phase concentrated solid solution alloys (SP-CSAs) are studied in this work. Transmission electron microscopy analysis shows that with increasing Fe concentration, the average bubble size decreases while the bubble number density increases, indicating the growth of large helium bubbles in NiFe_x SP-CSAs is suppressed by increasing the alloy chemical complexity through increased Fe concentration. Mechanisms for the slower bubble growth rate in NiFe_x binary SP-CSAs compared Ni are identified. These mechanisms include promotion of Frenkel pair recombination, denser and more homogeneously distributed nucleation sites, and increased helium atom densities inside the bubbles. The results demonstrate that optimizing the chemical complexity in SP-CSAs can be an effective approach to design materials with superior resistance to helium bubble nucleation and growth.