Atomistic investigation of irradiation-induced defect dynamics in FeNiCu medium-entropy alloy: effect of local chemical order

Medium and high-entropy alloys (M/HEAs) have garnered significant attention as potential nuclear structural materials due to their excellent stability at high temperatures and resistance to radiation. However, the common use of Co in M/HEAs, which exhibits high radioactivity under radiation has prompted the development of Co-free M/HEAs for nuclear applications. In this study, we investigate the irradiation behavior of FeNiCu, a promising Co-free medium-entropy alloy (MEA) with a focus on the effect of local chemical order (LCO) using hybrid-molecular dynamics and Monte Carlo simulations. Considerable LCOs in Cu-Cu and Fe-Ni pairs were observed in the thermodynamically stable ordered system. To conduct a comprehensive comparative study of irradiation-induced defect formation and dynamics, cumulative displacement cascades up to 500 were performed in random and ordered configurations of the MEA as well as in pure Ni for benchmark. Our study revealed LCO configuration as the most radiation resistant structure among the three. Complex potential energy landscape (PEL) in MEAs disrupts dislocation growth resulting in its dispersed distribution. The Cu-rich uniform regions in the ordered system act as defect traps enabling faster diffusion and high defect recombination resulting in formation of the dislocation networks in/near these regions. The lower stair-rod dislocation density in the ordered system revealed its high resistance to irradiation swelling signifying the effect of LCO even more, positioning FeNiCu MEA as a strong candidate for future nuclear application. Additionally, the theoretical insights into defect evolution covering formation and diffusion in both random and ordered structures enhance our understanding of LCO's impact, offering a solid foundation for the future development of radiation-resistant M/HEAs for nuclear applications.