The STEM characterization of dislocation loops in MA956 ODS steel after swift heavy ion irradiation

For the purpose of clarifying the basic mechanism of material failure caused by irradiation damage, the microstructures of materials under extreme radiation conditions were evaluated by transmission electron microscopy (TEM). In the present study, swift heavy ion irradiation ( 345 M e V Fe ions) was employed to introduce dislocation loops in the MA956 ODS steel, and the subsequent S/TEM characterization was conducted. While TEM has traditionally used as the primary tool for dislocation loops imaging, recent advancements in scanning transmission electron microscopy (STEM) technology have increased interest in defects imaging. The principal STEM-based approaches for dislocation/dislocation loops characterizing include diffraction-selected on-zone STEM (DsoZ-STEM), diffraction-contrast imaging STEM (DCI-STEM), and weak-beam dark-field STEM (WBDF-STEM). This study compared these STEM methods for dislocation loops imaging, demonstrating the usage of objective lens aperture in the enhancement of dislocation loops contrast. Experimental findings indicated that DCI-STEM method performed under a systematic row diffraction condition with s g > 0 surpassed the other approaches, yielding an enhanced contrast of dislocation loops with a clean background free of dynamical diffraction artifacts.