Investigation of primary radiation damage near free surfaces in iron nanofoam with a model cylindrical nanovoids structure

Highlights: • Displacement cascades with 3, 6 and 9 keV PKA in Fe nanofoam were investigated. • 1–4 cylindrical nanovoids were employed as model structure. • Mostly, presence of nanovoids increases the number of residual vacancies in bulk. • Vacancy plane was formed in ligament in maximum interaction of cascade and surfaces. • Most of residual vacancies in the ligament, participate on vacancy clusters. -- Abstract: In this research, in order to investigate primary radiation damage in iron nanofoam, simulation of displacement cascade near cylindrical nanovoids is performed using molecular dynamics. A primary knocked-on atom with 3, 6 and 9 keV energies and velocity parallel to the cylinder axis at 300 K is considered. 1–4 nanovoids are used as the model structure for free surfaces. It is identified that interaction between the displacement cascades and free surfaces is very sensitive to PKA energy and the distance of free surfaces. Near-surface cascade mechanism is observed when the displacement cascade interacts with a single cylindrical free surface, where clusters of bulk vacancies and a rim of adatoms are formed. In this case, based on the location of these defects rather free surface, two sub-mechanisms are identified. It is recognized that the degree of the penetration of the cascade into the cylindrical surfaces, plays an important role in forming vacancies and vacancy clusters in the ligament after the cooling of the cascade. Results show that when the PKA energy is 9 keV, enhancement of number of nanovoids increases the number of vacancies in the bulk. In this case, formation of vacancy planes is observed between the cylindrical nanovoids. The absorption of bulk vacancy clusters by the free surfaces is observed when displacement cascade is generated by a 6 keV PKA in close vicinity of four cylindrical surfaces.