Penetration of corrosive species into copper exposed to simulated O2-free groundwater by time-of-flight secondary ion mass spectrometry (ToF-SIMS)

ToF-SIMS analysis of copper samples after exposures to simulated groundwater with and without sulfide addition was performed to investigate the penetration of corrosive species containing H, S, O, and Cl, into copper. Depth profiles show extent of penetration and 2D/3D images reveal local elemental distribution of the corrosive species at different depths inside copper. Pre-oxidation did not reduce the penetration while sulfide additional in groundwater and exposure at 60 \ub0C significantly promoted the penetration. The extent of penetration of the corrosive species into copper demonstrates the need for risk assessment of complex corrosion forms such as sulfide-induced embrittlement and cracking

Microstructural characterisation of subsurface deformation and the degradation of Stellite 6 induced by self-mated sliding contact in a simulated PWR environment

© 2021 Elsevier Ltd Stellite 6 (Co-29.5%Cr-5%W-1.2%C in wt%) is traditionally used as a hardfacing material in the primary circuit of pressurised water reactors (PWRs) due to its good corrosion and wear resistance in water at up to 300 °C. In this study, pin-on-disc type sliding contact tribocorrosion testing was conducted on HIPed Stellite 6 at 20 °C and 250 °C using a bespoke tribometer to simulate a primary circuit environment. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize, for the first time, the material affected by tribocorrosion. Whilst the material loss increases by 16–39 times when the test temperature is increased from 20 °C to 250 °C, the mechanisms of degradation and deformation remain largely unchanged. Furthest from the sliding contact, strain is principally accommodated by the deformation-induced transformation of the γ Co-based matrix to ε-martensite. Closer to the sliding contact, the ε-martensite phase accommodates further strain via twinning and dislocation slip. At the sliding contact the intense deformation generates a nanocrystalline structure. The tribologically affected material is resistant to plastic strain localisation; this confines wear to the nanoscale where the synergistic effects of chemical degradation and mechanical deformation permit the removal of nanoscale particulates (corrosion enhanced nanowear (tribocorrosion)). The increased wear rate at 250 °C is attributed to a temperature dependent increase in corrosion enhanced nanowear. The degradation mechanisms revealed are important for the design of future hardfacings

Applied DNA HCR-FISH for Biofilm Distribution Imaging on Stainless Steel in Brackish Seawater

Microbially-induced corrosion or biocorrosion driven by microorganisms in brackish seawater has been associated with the destruction of the passivation layer on stainless steel. This has been especially linked to the metabolisms of sulphate-reducing bacteria (SRB). In recent years, various methods have been employed to investigate the phenomena, including open circuit potential (OCP) and anodic cyclic polarization methods, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) analyses, as well molecular biological methods such as enumeration by quantitative polymerase chain reaction (qPCR) and characterization of biofilm microbial communities by amplicon sequencing.Hybridization chain reaction fluorescence in situ hybridization (HCR-FISH) is a bio-imaging technique that provides unique microbial distribution maps of multispecies biofilms on the steel surface, supporting current methods employed for a biocorrosion study. The technique uses DNA nucleotide probes labelled with fluorescence dyes, binding to the 16S ribosomal RNA (16S rRNA) to visualize simultaneously targeted multispecies microbes at the single-cell level. HCR-FISH protocol introduced by Yamaguchi et al. (2015a and 2015b) has been further adapted for bio-imaging marine sediment and seawater in recent years due to its simplicity, and high efficiency. We modified the standard HCR-FISH protocol to be applicable directly on stainless steel surfaces to study the biocorrosion of austenitic stainless steel EN 1.4404 that had been exposed to natural brackish seawater circulated in a lab-scale loop. HCR-FISH enabled simultaneous visualization of two microbial groups forming biofilm (bacteria and archaea or, bacteria and SRB). In addition, HCR-FISH was counterstained with 4,6-diamidino-2-phenylindole (DAPI), a cell-permeable fluorescent stain binding all double-stranded DNA.The modified HCR-FISH protocol produced promising results for the studied environmental mix species biofilms on stainless steel but requires further method development. The targeted cell detection was clear, specified, and intensive, resulting in high-contrast epifluorescence microscopy images which were applicable and supportive for biocorrosion investigation