arXiv subjects

Sung-Gyu Kang

Publications and source records attributed to Sung-Gyu Kang.

5 recordsLinked to original sources

arXiv2026

Revealing the Atomic-Scale Structure of the Copper Sulfuric Acid Interface

Corrosion originates from atomistic reactions occurring at dynamic solid liquid interfaces however, direct experimental observation of these reactions has remained elusive due to the inability to preserve transient interfacial states during characterization. To refine corrosion models, advanced techniques capable of analyzing corrosion interfaces at the atomic scale are essential. Recent advancements in cryogenic atom probe tomography (cryoAPT) enabled 3D nanoscale analysis of frozen liquid metal interfaces. However, challenges remain in sample preparation for cryoAPT on metals undergoing corrosion. This study introduces a microcorrosion cell fabricated using localized electrodeposition in liquid (LEL), enabling atomic scale capture of liquid metal reactions by integrating picoliterscale electrolytes encapsulated within sealed metallic microvessels, subsequently analyzed using cryoAPT.This approach enables 3D, nanoscale mapping of corrosion reactions with simultaneous spatial, chemical, and temporal resolution. As a model system, copper exposed to aerated dilute sulphuric acid reveals temperature and time dependent interfacial evolution, including nanoscale clustering of copper sulphate species, enhanced ion pairing at elevated temperature, and the emergence of transient carbon based interfacial complexes inaccessible to conventional characterization methods.Beyond copper corrosion, the presented microcorrosion cell architecture establishes a strategy for interrogating confined electrochemical and degradation processes across a wide range of material liquid systems, using a combination of microfabrication and cryoAPT.

cond-mat.mtrl-sci↗

arXiv2024

Fabrication and extreme micromechanics of additive metal microarchitectures

The mechanical performance of metallic metamaterials with 3-dimensional solid frames is typically a combination of the geometrical effect ("architecture") and the characteristic size effects of the base material ("microstructure"). In this study, for the first time, the temperature- and rate-dependent mechanical response of copper microlattices has been investigated. The microlattices were fabricated via a localized electrodeposition in liquid (LEL) process which enables high-precision additive manufacturing of metal at the micro-scale. The metal microlattices possess a unique microstructure with micron sized grains that are rich with randomly oriented growth twins and near-ideal nodal connectivity. Importantly, copper microlattices exhibited unique temperature (-150 and 25 degree C) and strain rate (0.001~100 s-1) dependent deformation behavior during in situ micromechanical testing. Systematic compression tests of fully dense copper micropillars, equivalent in diameter and length to the struts of the microlattice at comparable extreme loading conditions, allow us to investigate the intrinsic deformation mechanism of copper. Combined with the post-mortem microstructural analysis, substantial shifts in deformation mechanisms depending on the temperature and strain rate were revealed. On the one hand, at room temperature (25 degree C), dislocation slip based plastic deformation occurs and leads to a localized deformation of the micropillars. On the other hand, at cryogenic temperature (-150 degree C), mechanical twinning occurs and leads to relatively homogeneous deformation of the micropillars. Based on the intrinsic deformation mechanisms of copper, the temperature and strain rate dependent deformation behavior of microlattices could be explained.

cond-mat.mtrl-sci↗

arXiv2023

Improving reconstructions in nanotomography for homogeneous materials via mathematical optimization

Compressed sensing is an image reconstruction technique to achieve high-quality results from limited amount of data. In order to achieve this, it utilizes prior knowledge about the samples that shall be reconstructed. Focusing on image reconstruction in nanotomography, this work proposes enhancements by including additional problem-specific knowledge. In more detail, we propose further classes of algebraic inequalities that are added to the compressed sensing model. The first consists in a valid upper bound on the pixel brightness. It only exploits general information about the projections and is thus applicable to a broad range of reconstruction problems. The second class is applicable whenever the sample material is of roughly homogeneous composition. The model favors a constant density and penalizes deviations from it. The resulting mathematical optimization models are algorithmically tractable and can be solved to global optimality by state-of-the-art available implementations of interior point methods. In order to evaluate the novel models, obtained results are compared to existing image reconstruction methods, tested on simulated and experimental data sets. The experimental data comprise one 360° electron tomography tilt series of a macroporous zeolite particle and one absorption contrast nano X-ray computed tomography (nano-CT) data set of a copper microlattice structure. The enriched models are optimized quickly and show improved reconstruction quality, outperforming the existing models. Promisingly, our approach yields superior reconstruction results, particularly when information about the samples is available for a small number of tilt angles only

cond-mat.mtrl-sci↗

arXiv2022

E-beam-enhanced solid-state mechanical amorphization of alpha-quartz: Reducing deformation barrier via localized excess electrons as mobile anions

Under hydrostatic pressure, alpha-quartz undergoes solid-state mechanical amorphization wherein the interpenetration of SiO4 tetrahedra occurs and the material loses crystallinity. This phase transformation requires a high hydrostatic pressure of 14 GPa because the repulsive forces resulting from the ionic nature of the Si-O bonds prevent the severe distortion of the atomic configuration. Herein, we experimentally and computationally demonstrate that e-beam irradiation changes the nature of the interatomic bonds in alpha-quartz and enhances the solid-state mechanical amorphization at nanoscale. Specifically, during in situ uniaxial compression, a larger permanent deformation occurs in alpha-quartz micropillars compressed during e-beam irradiation than in those without e-beam irradiation. Microstructural analysis reveals that the large permanent deformation under e-beam irradiation originates from the enhanced mechanical amorphization of alpha-quartz and the subsequent viscoplastic deformation of the amorphized region. Further, atomic-scale simulations suggest that the delocalized excess electrons introduced by e-beam irradiation move to highly distorted atomic configurations and alleviate the repulsive force, thus reducing the barrier to the solid-state mechanical amorphization. These findings deepen our understanding of electron-matter interactions and can be extended to new glass forming and processing technologies at nano- and microscale.

cond-mat.mtrl-sci↗

arXiv2022

Green laser powder bed fusion based fabrication and rate-dependent mechanical properties of copper lattices

Lattice structures composed of periodic solid frames and pores can be utilized in energy absorption applications due to their high specific strength and large deformation. However, these structures typically suffer from post-yield softenings originating from the limited plasticity of available material choices. This study aims to resolve such an issue by fabricating lattice structures made of ductile pure copper (Cu). For the first time, Cu lattice structures are fabricated through laser-powder bed fusion (L-PBF) with green laser (λ = 515 nm). Structural and microstructural analysis confirm that the lattice structures consist of well-defined unit cells and show dense microstructure. The deformation behavior is investigated under a wide range of strain rates from ~0.001 /s to ~1000 /s. The stress-strain curves exhibit a smooth and continuous deformation without any post-yield softening, which can be attributed to the intrinsic mechanical properties of Cu. Correlated with post-mortem microscopy examination, the rate-dependent deformation behavior of pure Cu lattice structures is investigated and rationalized. The current work suggests that the complex Cu architectures can be fabricated by L-PBF with green laser and the lattice structures made of ductile metal are suitable for dynamic loading applications.

physics.app-ph↗