The formation of solute clusters in irradiated low-alloy steels, such as reactor pressure vessel steels, is a critical cause of radiation hardening and embrittlement. However, the chemical coupling among solute elements and excess vacancies remains to be fully understood. This study utilizes density functional theory, cluster expansion, and lattice-based Monte Carlo simulations to investigate the stability and morphology of nano-size coherent solute clusters with excess vacancies. The results show that excess vacancies play a key role in stabilizing and promoting the growth of Mn-Ni-Si-vacancy clusters. The critical number of vacancies required for stable nucleation and growth of Mn-Ni-Si clusters is seven. These Mn-Ni-Si clusters act as defect sinks, effectively trapping and absorbing mobile vacancies generated under irradiation. Moreover, phosphorus (P) preferentially dissolves in Mn-Ni-Si clusters due to chemical coupling with vacancies. This study provides new insights into solute-vacancy interactions, enhancing our understanding of the mechanisms behind solute-defect cluster formation and embrittlement in low-alloy steels.
