Weak-beam scanning transmission electron microscopy for quantitative dislocation density measurement in steels

Abstract

To evaluate dislocations induced by neutron irradiation, we developed a weak-beam scanning transmission electron microscopy (WB-STEM) system by installing a novel beam selector, an annular detector, a high-speed CCD camera and an imaging filter in the camera chamber of a spherical aberration-corrected transmission electron microscope. The capabilities of the WB-STEM with respect to wide-view imaging, real-time diffraction monitoring and multi-contrast imaging are demonstrated using typical reactor pressure vessel steel that had been used in an European nuclear reactor for 30 years as a surveillance test piece with a fluence of 1.09 × 1020 neutrons cm-2. The quantitatively measured size distribution (average loop size = 3.6 ± 2.1 nm), number density of the dislocation loops (3.6 × 1022 m-3) and dislocation density (7.8 × 1013 m m-3) were carefully compared with the values obtained via conventional weak-beam transmission electron microscopy studies. In addition, cluster analysis using atom probe tomography (APT) further demonstrated the potential of the WB-STEM for correlative electron tomography/APT experiments.

Characterizing accelerated precipitation in proton irradiated steel

“…Taking the sink strength S as the dislocation density, values between 10 13 m −2 and 10 15 m −2 are expected in RPV steels (see e.g. [23,51,54,100]). With S = 10 14 m −2 for example, D v 10 −15 m 2 s −1 at 300 • C, consistent with suppressed D v associated with higher effective vacancy migration energy 1.2 eV in ferrite compared to pure iron.…”

Towards bend-contour-free dislocation imaging via diffraction contrast STEM

“…For decades, dislocation analysis has been in the purview of conventional TEM (CTEM), supported by well-developed theories and simulations for understanding the contrast of dislocations in CTEM micrographs. However, with the recent advent of scanning transmission electron microscopes with more intense probes and faster, higher resolution detectors, there is a renewed interest in using convergent-beam scanning transmission electron microscopy (STEM) to image dislocation structures [3,4]. Development of STEM has already demonstrated advantages in many other characterization applications, including the determination of dislocation core structure [5], high-resolution mapping of lattice strain fields [6], and even in in situ environmental imaging [7].…”