Direct observation of individual hydrogen atoms at trapping sites in a ferritic steel

Abstract

The three-dimensional distribution of individual hydrogen atoms within a complex steel microstructure is characterized using isotopic doping and cryogenic-transfer atom probe tomography. AbstractThe design of atomic-scale microstructural traps to limit the diffusion of hydrogen is one key strategy in the development of hydrogen-

Atom Probe Tomography: Development and Application to the Geosciences

“…However, the APT analysis of many stable isotopes remains problematic. For example, the atom probe can potentially discriminate between singly charged hydrogen and deuterium peaks, which opens up the possibility of deuterium‐doped experiments to look at hydrogen distribution (e.g., Chen et al ). However, the potential for D + and H 2 + interferences, plus the current inability to completely remove H ions from the analysis chamber, makes the significance of any H data from geological materials difficult to unravel.…”

High resolution NanoSIMS imaging of deuterium distributions in 316 stainless steel specimens after fatigue testing in high pressure deuterium environment

“…For this set of experiments the detectors were positioned to measure 32 observed using tritium autoradiography in cathodically charged samples, [36][37][38] our data provide direct evidence that these inclusions trap hydrogen in gaseous environments as well. Further longer term exposure studies would be required on higher S content alloys to observe if the idea proposed by Hanninen 9,10 postulating that MnS inclusions act as hydrogen trap sites in low alloy steels and their subsequent dissolution in aqueous environments (as was recently directly observed through in situ TEM/EDS examination) 39 changes crack tip electrochemistry and enhances hydrogen absorption also holds in gaseous environments.…”

“…These include older studies with TEM replica-based tritium microautoradiography technique capable of spatial resolutions of 300 nm pioneered by Tiner and Co-workers [23][24][25] and refined by Lacombe et al at Universite Paris Sud [26][27][28] and secondary ion mass spectrometry (SIMS) ion microscopy 29,30 studies with lateral resolutions limited to 1 μm. Emerging more recently is work using atom probe tomography (APT), which has atomic resolution but samples a much smaller volume (~100,000 nm 3 compared to greater than 1 × 10 9 nm 3 for NanoSIMS), 31,32 as well as scanning probe methods 33,34 that show promise for quantification but whose spatial resolution is of the order of hundreds of microns. NanoSIMS imaging bridges the gap between these two methods, providing a better spatial resolution than tritium autoradiography (and also dispensing with the need to work with radioactive materials) while simultaneously sampling larger volumes than APT, while also offering the potential for absolute quantification of hydrogen concentration using well characterized matrix-matched standards.…”

The challenges of hydrogen and metals

“…These are usually transition metal carbides, many of which already play a vital role in strengthening: for example, interphase precipitates in microalloy steel. The principal outstanding questions here are: (i) how the hydrogen reaches the deepest traps if the activation barrier is, as typically found in quantum mechanical calculations, greater than 1-2 eV, (ii) whether hydrogen resides at the matrix particle interface, or deep within the particle [7], and perhaps most importantly (iii) how microstructural traps can provide protection against continuous ingress (for example during rolling contact fatigue or cathodic 'protection') as they will eventually all become filled.…”