Anisotropic evolution of Frank loops in ion-irradiated silicon carbide

Frank loop evolution in highly damaged polycrystalline cubic silicon carbide irradiated with 5.1 MeV Si²⁺ ions at 1673 K was studied by transmission electron microscopy (TEM). Individual TEM images of Frank loops formed on each {1 1 1} plane revealed that their population strongly depended upon their orientation with respect to the incident beam direction. However, no significant difference in loop growth rates was observed between each habit plane. The anisotropic loop evolution has not been reported for neutron-irradiated SiC. Our examination shows that a grain, containing {1 1 1} planes nearly parallel to the irradiated surface, was largely strained toward the free surface by the preferential formation of Frank loops on the plane. Compressive stress following the anisotropic swelling in ion-irradiated specimen may affect the loop evolution. The possible mechanism of the anisotropic loop evolution observed here is accounted for by the stress induced preferential nucleation of Frank loops.