Abstract
Large vacancy clusters (VCs), such as stacking-fault tetrahedra (SFT), are detrimental vacancy-type defects in ion-irradiated structural materials with face-centered cubic structures, such as Ni-based super alloys. The suppression of VC growth is, therefore, highly desirable for irradiation-tolerant material design. In the present study, we demonstrate that the VC growth can be suppressed in concentrated solid-solutions (CSAs) by modulating the diffusion of VCs. Two alloying elements, Fe and Cr, in Ni are investigated to illustrate their capabilities to suppress VC growth. It is shown that the diffusion coefficient of small VCs in CSAs such as Ni0.5Fe0.5, Ni0.8Cr0.2 and Ni0.4Fe0.4Cr0.2, is higher than in pure Ni, whereas it becomes lower than in pure Ni for larger VCs containing more than 10 vacancies. This observation suggests that VC can easily migrate and grow to larger sizes in pure Ni due to the relatively high mobility of large VC, while in CSAs, the growth of VC is limited to a small size due to the limited mobility of large VCs. The differences in cluster sizes and mobilities in Ni and CSAs are consistent with ion irradiation experiment.