Gaurav Arora1 Arron Harms1 Kanishk Rawat1 Dilpuneet Aidhy1

1, University of Wyoming, Laramie, Wyoming, United States

Concentrated random solid-solution alloys (CSAs) have drawn wide interest as structural materials for next-generation nuclear reactors due to their exemplary mechanical and radiation tolerance properties over conventional dilute alloys. However, recent irradiation experiments show that some of these alloys can undergo disorder-to-order transition, i.e., the atoms that are initially randomly distributed on a crystal lattice undergo ordering (e.g. L10 or L12) due to irradiation. In nuclear reactors, such transitions can potentially impact the long-term microstructure evolution including grain growth and segregation properties, thereby damaging the chemical and mechanical integrity of materials. In this work, we elucidate the effect of atomic structure (i.e., ordered vs disordered) on the irradiation-induced microstructure evolution of CSAs. While working on Ni and NiFe alloys, from atomistic simulations of over 150 grain boundaries (GBs), we show that there is a direct correlation between Cr segregation and GB energy, i.e., segregation increases with increase in the GB energy. In addition, we show that Cr segregation is higher for disordered NiFe compared to ordered NiFe, albeit both have identical alloy composition. Using molecular dynamics simulation on grain growth, we find that higher grain growth is observed in disordered NiFe compared to ordered NiFe, supporting the previous postulation that disordered structures have higher GB energy compared to their ordered counterparts. Finally, the effect of impurity pinning of GB mobility between ordered and disordered alloys is shown.