A multi-technique study of "barrier layer" nano-porosity in Zr oxides during corrosion and hydrogen pickup using (S)TEM, TKD, APT and NanoSIMS. (September 2019)

• Record Type: Journal Article
• Authors: Hu, Jing; Aarholt, Thomas; Setiadinata, Brian; Li, Kexue; Garner, Alistair; Lozano-Perez, Sergio; Moody, Michael; Frankel, Philipp; Preuss, Michael; Grovenor, Chris
• Is Part Of: Corrosion science. Volume 158(2019)
• Publication Date: 2019-09
• Subjects: Zr alloys -- Corrosion -- Hydrogen pickup -- Nano-porosity -- Fresnel imaging -- Transmission Kikuchi diffraction -- Atom probe tomography -- NanoSIMS; Corrosion and anti-corrosives -- Periodicals; 620.11223
• DOI: 10.1016/j.corsci.2019.108109
• Languages: English
• ISSNs: 0010-938X

Abstract

Graphical abstract: Highlights: Fresnel imaging in the TEM has been used to identify different types of porosity in the protective oxide near the "barrier layer", around 0˜200 nm from the metal-oxide interface. More disorganised oxide grains and nano-porosity network is found by TEM and TKD in rapidly oxidising samples. NanoSIMS analysis suggests that the transition event enables the propagation or trapping of deuterium while the pre-transition sample is a good barrier to deuterium penetration. APT data provides strong direct evidence for D segregation in the "barrier layer" at oxide grain boundaries and nano porosity. The nanopores, if interconnected, can be the dominant pathway for hydrogen transport to the metal matrix. Abstract: We have used (S)TEM, TKD, NanoSIMS and APT to study nano-porosity in the oxide grown on deuterated Zr-1.0Nb and Zr-2.5Nb alloys. A detailed analysis of "barrier layer" nano-porosity by TEM and TKD has revealed that the oxide grain structure is much more disorganised and the nano-porosity network better developed in the rapidly oxidising post-transition alloy. Direct observations of the trapped deuterium (D) distributions from NanoSIMS analysis also shows much more penetration of the oxide layer post-transition. APT analysis shows that there is Fe and D segregation to some of the oxide grain boundaries with occasional evidence of porosity containing trapped D and H. We conclude that interconnected porosity would offer a dominant pathway for the transport of hydrogenic species to the metal substrate during the aqueous corrosion of zirconium alloys in service.