Interaction between collision cascades and nanocrack in hcp zirconium by molecular dynamics simulations

The evolution of the collision cascades at different times upon 10 keV PKA energy. The distance between the crack surface and the PKA is 32 Å, and the PKA direction is perpendicular to the crack surface. (a-c) the 3-D snapshots with hcp atoms erased for better visualization of the irradiation defects, and (d-f) the corresponding cross-section snapshots. • Thermal spike of collision cascades overlaps with nanocrack induce its healing. • Degree of crack healing decreases with longer distance between crack and PKA. • Transformation of nanocrack in basal plane into prismatic vacancy loop is captured. • Pre-existing nanocrack may induce subcascade in Zr even at lower PKA energy. In this work, molecular dynamics simulations are performed to investigate the interaction between the collision cascades and nanocrack in hcp zirconium. When the thermal spike overlaps with the nanocrack, the collision cascades will induce the healing of the nanocrack. Higher PKA energy leads to higher degree of crack healing at the same separation distance between PKA and nanocrack. The PKA velocity direction changes the fraction of atoms entering the crack by influencing the shape and distribution of the thermal spike. Furthermore, both Zr #3 and #2 potentials show that the degree of crack healing drops as the distance between the nanocrack and PKA decreases. In particular, collision cascades induce the transformation of nanocrack in the basal plane into prismatic vacancy loop is captured due to the interaction between thermal spike with nanocrack. Lastly, the pre-existing nanocrack may induce cascade splitting of hcp Zr. This work provides a mechanistic understanding of the interaction between the nanocrack and irradiation damages in Zr and other hcp metals.