MECHANISMS OF IRRADIATION-INDUCED HARDENING IN Fe–Ni–Cr ALLOYS: A MOLECULAR DYNAMICS STUDY Aneta Ustrzycka*¹ and F. Javier Dominguez-Gutierrez² ¹Institute of Fundamental Technological Research, Polish Academy of Sciences Pawinskiego 5B, Warsaw, 02-106, Poland ²NOMATEN Centre of Excellence, National Centre for Nuclear Research ul. A. Soltana 7, Otwock, 05-400, Poland This study employs large-scale Molecular Dynamics (MD) simulations to investigate the effects of irradiation-induced defects on the mechanical behavior of Fe–Ni–Cr alloys, focusing particularly on shear deformation and irradiation hardening. Radiation defects affect the material’s strength and ductility. Understanding these atomic-scale mechanisms is essential for predicting the long-term performance and reliability of structural materials used in nuclear reactors. MD simulations reveal that dislocation loops act as effective obstacles to dislocation motion, increasing flow stress and contributing to irradiation hardening [1]. As the material undergoes shear deformation, these loops expand, rearrange, and interact with moving dislocations, altering the evolution of defects and plastic flow behavior. Moreover, radiation-induced voids collapse under mechanical stress, leading to the formation of new dislocation loops that further contribute to strain hardening [1]. These processes become more pronounced as the displacement-per-atom (dpa) increases. This leads to an overall increase in material strength but a corresponding reduction in plasticity, making the material more prone to brittle fracture. The simulations also demonstrate that irradiation hardening is governed by complex interactions between mobile dislocations and radiation-induced defects. These interactions cause both hardening and softening effects that are dependent on the type, structure, and density of the defects present. The overall effect on the material’s mechanical properties is the result of a delicate balance between defect accumulation and dislocation behavior, with the increased density of defects leading to higher strength but reduced deformability. These insights offer valuable atomic-scale understanding of irradiation hardening and its impact on material performance in radiation environments. REFERENCE [1] Ustrzycka A., Dominguez-Gutierrez F., Chromiński W., Atomistic analysis of the mechanisms underlying irradiation-hardening in Fe–Ni–Cr alloys, International Journal of Plasticity, Vol. 182, 104118, 2024.