Using local GND density to study SCC initiation

Naganand Saravanan; Phani S Karamched; Junliang Liu; Claire Rainasse; Fabio Scenini; Sergio Lozano-Perez

doi:10.1016/j.ultramic.2020.113054

Using local GND density to study SCC initiation

Ultramicroscopy. 2020 Oct:217:113054. doi: 10.1016/j.ultramic.2020.113054. Epub 2020 Jul 3.

Authors

Naganand Saravanan¹, Phani S Karamched², Junliang Liu², Claire Rainasse³, Fabio Scenini⁴, Sergio Lozano-Perez²

Affiliations

¹ Department of Materials, University of Oxford, Parks Road, OX1 3PH Oxford, UK. Electronic address: naganand.saravanan@seh.ox.ac.uk.
² Department of Materials, University of Oxford, Parks Road, OX1 3PH Oxford, UK.
³ EDF R&D, Avenue des Renardieres, Moret sur Loing Cedex 77818, France.
⁴ The University of Manchester, Department of Materials, Materials Performance Centre, Manchester M13 9PL, UK.

PMID: 32663722
DOI: 10.1016/j.ultramic.2020.113054

Abstract

Strain and geometric necessary dislocations (GNDs) have been mapped with nm-resolution around grain boundaries affected by stress corrosion cracking (SCC) or intergranular oxidation with the aim of clarifying which local conditions that trigger SCC initiation of Alloy 600 in primary water reactor (PWR) water environment. Regions studied included the cracked and uncracked portion of the same SCC-affected grain boundaries and a comparable grain boundary in the as-received condition. High-resolution "on-axis" Transmission Kikuchi Diffraction (TKD) was used to generate strain and GND density based on the cross-correlation image processing method to probe shifts of specific zone axis in the TKD patterns from all regions. All cracked boundaries analyzed had local GND densities higher than 1 × 10¹⁶ m^-2. Similar grain boundaries, from as-received samples had GNDs of 5 × 10¹⁴ m^-2, while an intermediate level was found in the oxidized but uncracked portion of the same GB. Results, together with a discussion on the advantages and limitations of the approach, will be presented.

Keywords: Alloy 600; Geometric necessary dislocations; Stress corrosion cracking; Transmission Kikuchi diffraction.