Zoltán Hegedűs

The precise characterization of near-surface residual stress is critical for in-service fatigue performance in high-strength components, yet conventional techniques often lack the depth-resolution to capture steep micrometer-scale gradients and their crystallographic (hkl-dependent) variations. In this study, depth-resolved residual strain and stress tensors in machined and shot peened Inconel 718 were quantified using high-energy synchrotron X-ray diffraction (HEXRD) combined with full Debye–Scherrer ring analysis. The as-machined surface exhibits high tensile in-plane stress, accompanied by pronounced hkl-dependent strain partitioning, particularly along the cutting direction. Shot peening transforms this state into a compressive in-plane condition and redistributes the anisotropic residual strain and stress field. While the hkl-dependent variation is reduced along the cutting direction, it remains present in other orientations, indicating a partial suppression of crystallographic anisotropy. Although the hkl-averaged out-of-plane stress remains close to zero at the free-surface, as expected for the macroscopic stress component, significant hkl -dependent stress variations persist, suggesting a fine domain size and intergranular stress heterogeneity. Strain pole figure representation further shows that machining produces a strongly direction-dependent strain distribution, whereas shot peening leads to a more uniform and nearly axisymmetric strain field with weak directional variations. The full-ring HEXRD approach enables quantitative characterization of multiaxial residual stress tensors and their crystallographic dependence and enables excellent grain statistics at high depth resolution. The results provide a detailed description of the depth-dependent redistribution of residual strain and stress following sequential surface treatments which forms the basis of the understanding of fatigue performance of safety-critical alloys.

We explore the effect of Rh steps on the NO dissociation process at 0.05 mbar NO, which is a crucial step of the NO reduction reaction. By using a curved Rh(111) crystal and ambient-pressure X-ray photoemission spectroscopy, data demonstrate a lower temperature onset for NO dissociation at stepped surfaces compared to Rh(111), and suggest that dissociation occurs predominantly at the lower side of the step. We also observe that surface oxidation arises at a lower temperature for Rh(111) and its B-type vicinals, with respect to A-type stepped surfaces. Surface X-ray diffraction was employed to characterize the Rh surface oxides. At the atomic scale, these were found structurally similar in flat Rh(111), A-type Rh(223) and B-type Rh(553), but they exhibited different growth behavior depending on the substrate orientation. These results showcase the structural sensitivity of NO dissociation, which is likely to affect the reactivity of these Rh surfaces under operando NO reduction conditions.

We explore the effect of Rh steps on the NO dissociation process at 0.05 mbar NO, which is a crucial step of the NO reduction reaction. By using a curved Rh(111) crystal and ambient-pressure X-ray photoemission spectroscopy, data demonstrate a lower temperature onset for NO dissociation at stepped surfaces compared to Rh(111), and suggest that dissociation occurs predominantly at the lower side of the step. We also observe that surface oxidation arises at a lower temperature for Rh(111) and its B-type vicinals, with respect to A-type stepped surfaces. Surface X-ray diffraction was employed to characterize the Rh surface oxides. At the atomic scale, these were found structurally similar in flat Rh(111), A-type Rh(223) and B-type Rh(553), but they exhibited different growth behavior depending on the substrate orientation. These results showcase the structural sensitivity of NO dissociation, which is likely to affect the reactivity of these Rh surfaces under operando NO reduction conditions.

Silica (SiO₂) anodes are promising candidates for enhancing the energy density of next‐generation Li‐ion batteries, offering a compelling combination of high storage capacity, stable cycling performance, low cost, and sustainability. This performance stems from SiO₂ unique lithiation mechanism, which involves its conversion to electroactive silicon (Si) and electrochemically inactive species. However, widespread adoption of SiO₂ anodes is hindered by their slow initial lithiation. To address this, research has focused on developing electrochemical “activation protocols” that involve prolonged low‐potential holding steps to promote SiO₂ conversion. Despite these efforts, the complex and multi‐pathway nature of SiO₂ lithiation process remains poorly understood, impeding the rational design of effective activation strategies. By introducing a multi‐probe characterization approach, this study reveals that, contrary to the previously proposed reaction mechanism of SiO₂ anodes, the lithiation process initiates at low potentials with the direct formation of Li₄SiO₄ and Li_xSi. Electrochemical activation potential was found to significantly influence the degree of conversion, with 10 mV identified as the optimal cut‐off potential for maximizing SiO₂ utilization. These findings provide key enablers to unlock the full potential of SiO₂ anodes for battery technology.