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-

Abstract:Ultrathin passive films effectively prevent the chemical attack of stainless steel grades in corrosive environments; their stability critically depends on the interplay between structure and chemistry of the constituents Fe-Cr-Mo. In particular, nanoscale inhomogeneities along the surface can have a tremendous impact on material failure, but are yet barely understood. Addressing a stainless-type glass-forming Fe 50 Cr 15 Mo 14 C 15 B 6 alloy and utilizing a combination of complementary high-resolution analytical techniques, we relate near-atomistic insight into different gradual nanostructures with time-and element-resolved dissolution behavior. The progressive elemental segregation on the nanoscale is followed in its influence on the concomitant degree of passivity. A detrimental transition from Cr-controlled passivity to Mo-controlled breakdown is dissected atom-by-atom demonstrating the importance of nanoscale knowledge for understanding corrosion.

We demonstrate experimentally that a part-per-million addition of Sn solutes in Al-Mg-Si alloys can inhibit natural aging and enhance artificial aging. The mechanism controlling the aging is argued to be vacancy diffusion, with solutes trapping vacancies at low temperature and releasing them at elevated temperature, which is supported by a thermodynamic model and first-principles computations of Sn-vacancy binding. This "diffusion on demand" solves the long-standing problem of detrimental natural aging in Al-Mg-Si alloys, which is of great scientific and industrial importance. Moreover, the mechanism of controlled buffering and release of excess vacancies is generally applicable to modulate diffusion in other metallic systems.

SummaryStandard atom probe tomography spatial reconstruction techniques have been reasonably successful in reproducing single crystal datasets. However, artefacts persist in the reconstructions that can be attributed to the incorrect assumption of a spherical evaporation surface. Using simulated and experimental field evaporation, we examine the expected shape of the evaporating surface and propose the use of a variable point projection position to mitigate to some degree these reconstruction artefacts. We show initial results from an implementation of a variable projection position, illustrating the effect on simulated and experimental data, while still maintaining a spherical projection surface. Specimen shapes during evaporation of model structures with interfaces between regions of low-and high-evaporation-field material are presented. Use of two-and three-dimensional projection-point maps in the reconstruction of more complicated datasets is discussed.

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