STEM Characterization of Dislocation Loops in Irradiated FCC Alloys

In this study, we demonstrate the methodology systematically developed for dislocation loop (perfect and faulted loops) imaging and analysis in irradiated face-centered-cubic (FCC) alloys using scanning transmission electron microscopy (STEM). On-zone [001] STEM imaging was identified as the preferred choice for its accuracy and effectiveness based on the comparison with other dislocation loop imaging techniques including: (i) on-zone STEM imaging using other major low-index zone axes, (ii) kinematic two-beam conditions bright field imaging near the [001] zone axis in conventional TEM (CTEM) mode, and (iii) Rel-Rod CTEM dark-field (DF) imaging near the [011] zone axis. The effect of STEM collection angle on the contrast formation of dislocation loops was also investigated. The developed method was confirmed by imaging all populations of perfect and faulted loops of types a/2 < 110 >{010} and a/3 < 111 >{111} found in an ion irradiated Ni(40)Fe(40)Cr(20 )alloy. The proposed STEM-based technique can easily identify said loops with a size greater than 10 nm without any assumptions such as those commonly made using the conventional Rel-Rod CTEM-DF technique. The recommended methodology in this study is developed as a quick and convenient tool that can be generally applied to irradiated FCC-based materials due to their common crystallography. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

In this study, a systematic methodology for imaging and analyzing dislocation loops in irradiated FCC alloys using STEM was demonstrated. The preferred choice of on-zone [001] STEM imaging was identified based on its accuracy and effectiveness compared to other techniques, and the effect of STEM collection angle on contrast formation of dislocation loops was investigated. The developed STEM-based technique can easily identify different types of dislocation loops in irradiated FCC-based materials and serves as a quick and convenient tool for such analyses.