Atomic displacement cascades near symmetrical tilt grain boundaries in HCP Zr: molecular dynamics simulation

Background. The work is devoted to the atomistic modeling of symmetric tilt grain boundaries (GBs) in HCP Zr and to the study of the radiation damage processes near such boundaries. Four symmetrical tilt GBs: $\sum$14(2 1 $\bar{3}$ 0), $\sum$14(4 $\bar{5}$ 1 0) with the axis of rotation [0 0 0 1] and $\sum$32(23 46 $\bar{23}$ 27), $\sum$32($\bar{1}$ 2 $\bar{1}$ 3) with the axis of rotation [1 0 $\bar{1}$ 0] are considered. The value of the free and grain boundary specific energy is calculated, the intergrain regions width at the temperature of 0 and 300 K is estimated. Materials and methods. The molecular dynamics simulation of atomic displacement cascades from PKA with the energy of 10 keV in the composite crystals with GB at 300 K was conducted. A tendency of the point defects produced in the cascade to accumulate near the GB plane, which is an obstacle to the spread of the cascade, has been discovered. It has been found that the number of surviving vacancies in the cascade out of the intergrain region exceeds the number of self-interstitial atoms for all types of GBs. For the most of the considered boundaries the number of SIAs remaining outside the intergrain region is considered to be fewer than in an ideal crystal without a GB. Results. The results of the point defects clustering produced in the cascade were obtained. For the GB with the axis of rotation [1 0 $\bar{1}$ 0] the proportion of the clustered vacancies is 1.5-2 times higher than the proportion of the clustered SIAs. At the same time for the boundaries with the axis of rotation [0 0 0 1] the proportion of SIAs, which create clusters, is slightly bigger than the fraction of the clustered vacancies. The clusters of both types are represented mainly by small formations (from 2 to 4 defects per cluster). At the same time vacancies often form clusters of a large size (more than 20 vacancies per cluster), while SIA clusters are small.