Hydrogen embrittlement of high-strength steel is an obstacle for using these steels in sustainable energy production. Hydrogen embrittlement involves hydrogen-defect interactions at multiple-length scales. However, the challenge of measuring the precise location of hydrogen atoms limits our understanding. Thermal desorption spectroscopy can identify hydrogen retention or trapping, but data cannot be easily linked to the relative contributions of different microstructural features. We used cryo-transfer atom probe tomography to observe hydrogen at specific microstructural features in steels. Direct observation of hydrogen at carbon-rich dislocations and grain boundaries provides validation for embrittlement models. Hydrogen observed at an incoherent interface between niobium carbides and the surrounding steel provides direct evidence that these incoherent boundaries can act as trapping sites. This information is vital for designing embrittlement-resistant steels.

There has been a recent surge in the use of cryo and/or vacuum specimen preparation and transfer systems to broaden the scope of research enabled by the microscopy technique of atom probe tomography. This is driven by the fact that, as for many microscopes, the application of atom probes to air- and temperature-sensitive materials or wet biological specimens has previously been limited by transfer through air at room temperature. Here we provide an overview of areas of research that benefit from these new transfer and analysis protocols, as well as a review of current advances in transfer devices, environmental cells, and glove boxes for controlled specimen manipulation. This includes the study of catalysis and corrosion, biological samples, liquid-solid interfaces, natural aging, and the distribution of hydrogen in materials.

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The early stage oxidation of germanium-doped magnesium alloys was investigated via atom probe tomography. A catalytic reaction cell attached to a local electrode atom probe was used for controlled exposure of electropolished specimens to oxygen gas. Hydrogen was detected in certain samples, thought to be introduced during electropolishing. A preferential interaction/reaction between oxygen and hydrogen was found in samples containing hydrogen-rich regions prior to oxidation. These results suggest that hydrogen plays an important role as a catalyst to oxidation, where the increase in the H evolution rate experienced when oxidising Mg alloys, may be directly related to the presence of H within the material prior to oxidation. Results revealed the ability of this unique experimental setup to provide new information about surface/sub-surface hydrogen and its effects on magnesium oxidation. Main Text The natural abundance of magnesium (Mg) and desirable strength to weight ratios make lightweight Mg alloys appealing candidates for application within the transport industry. However, their wider application as structural components is hindered by poor corrosion resistance [1, 2] and a susceptibility to hydrogen embrittlement [3-5]. Hydrogen (H) is absorbed into engineering alloys on contact with gaseous molecular hydrogen (H2), or by a parasitic partial reaction that accompanies the hydrogen evolution reaction (HER) during metal corrosion [6]. Atomic H typically either permeates or diffuses through metal lattice interstices and may become trapped at defects such as vacancies, grain boundaries, or dislocations [6, 7]. It may also form hydrides with suitable metals [8]. The diffusible H concentration (CH, Diff) represents the resident, mobile H atoms within alloys that can readily diffuse towards regions of tri-axial stress resulting in H-assisted cracking or H embrittlement