Transmission electron microscopy characterization of dislocation loops in irradiated zirconium

Abstract

Characterization of irradiation defects is of great importance to mitigate irradiation damage, reduce irradiation growth and tune mechanical properties in Zr alloys. Here, we describe a practical method to characterize the dislocation loops in irradiated Zr using conventional transmission electron microscopy (TEM). Vacancy or interstitial nature of dislocation loops is determined using the inside and outside contrast method. The habit plane of dislocation loops is determined by tilting the sample to multiple zone axes and judged based on the projected loop shape. The size of $\left\langle a \right\rangle$ loops is measured by tilting the sample to an edge-on position and the loop number is counted under a weak-beam dark-field TEM condition. $\left\langle c \right\rangle$ loops have a line contrast under viewing direction of a-axis and a circular shape under viewing direction of c-axis. In addition, a large number of triangle-shaped vacancy platelets (TVPs) were formed on the basal plane. With increasing the irradiation damage from 0.5 to 1.5 dpa, the number density of $\left\langle a \right\rangle$ loops keeps constant, while the number density of TVPs increased significantly, owing to the anisotropic diffusion and accumulation of point defects within basal plane. The methods introduced here are easy to follow and extend into other related investigations.