https://doi.org/10.3365/KJMM.2026.64.9.771

전상명(Sangmyeong Jeon) ; 위영욱(Young Uk Wi) ; 정재석(Jaesuk Jeong) ; 송전영(Jeon Young Song) ; 서동우(Dong-Woo Suh)

The effects of Nb content on the austenite grain growth behavior of high-nitrogen austenitic stainless steels were investigated during isothermal annealing. Three alloys containing 0.02, 0.11, and 0.30 wt.% Nb designated 2Nb, 11Nb, and 30Nb, respectively were hot-rolled and subsequently isothermally annealed at 1100 °C for 0.5 to 96 h. In the as-hot-rolled condition, few precipitates were observed in 2Nb, whereas 11Nb and 30Nb contained fine spherical MX carbonitrides and Z-phase along with coarse rod-like Z-phase. Extraction residue ICP analysis revealed that most of the added Nb (0.07 of 0.11 wt.% in 11Nb and 0.29 of 0.30 wt.% in 30Nb) had precipitated. During annealing, 2Nb exhibited typical parabolic grain growth, reaching a mean grain size of approximately 300 μm after 96 h. In contrast, grain growth in 11Nb and 30Nb was strongly suppressed, with mean grain sizes remaining at around 50 μm even after 96 h owing to grain-boundary pinning by the fine Nb precipitates. After prolonged annealing, however, a few grains grew remarkably in 11Nb (≥ 48 h) and 30Nb (≥ 96 h), producing long-tailed grain size distributions. This abnormal coarsening was attributed to a local loss of pinning force caused by precipitate coarsening. Notably, the maximum size of these coarsened grains approached the mean grain size of 2Nb under the same annealing conditions, indicating that the locally unpinned regions grew in a manner comparable to the precipitate-free 2Nb alloy.

https://doi.org/10.3365/KJMM.2026.64.9.780

이범무(Beom-Mu Lee) ; 김왕렬(Wang Ryeol Kim) ; 박인욱(In-Wook Park) ; 허성보(Sung-Bo Heo) ; 이욱진(Wook-jin Lee)

Cr-Al-N/Al2O3 composite coatings were deposited via magnetron sputtering to improve the wear resistance and high-temperature stability of conventional Cr-Al-N hard coatings. The Cr-Al-N layer was deposited using reactive DC magnetron sputtering, followed by the deposition of an Al2O3 top layer by RF magnetron sputtering at temperatures ranging from 400 to 700 °C. The effects of the Al2O3 deposition temperature on the microstructure, mechanical properties, tribological behavior, adhesion, and oxidation resistance of the coatings were systematically investigated. X-ray diffraction analysis confirmed that all coatings maintained a cubic-structured c-(Cr, Al)N phase with a preferred (200) orientation, while the crystallinity of the Al2O3 layer gradually increased with increasing deposition temperature. In particular, γ-Al2O3 diffraction peaks were observed above 500 °C, indicating enhanced crystallization of the oxide layer. Mechanical properties, including hardness, elastic modulus, H/E, and H3/E2, were strongly dependent on the Al2O3 deposition temperature, with the coating deposited at 700 °C exhibiting the highest hardness of approximately 28 GPa along with improved resistance to plastic deformation. Rockwell adhesion tests revealed severe cracking and delamination at 400 °C, whereas coatings deposited at 500-700 °C showed stable adhesion with minimal interfacial failure. Tribological tests demonstrated that the coatings deposited at higher temperatures exhibited lower friction coefficients and improved wear resistance, owing to the formation of stable Al-O-based tribolayers and enhanced interfacial bonding between the nitride and oxide layers. Furthermore, high-temperature oxidation tests performed at 900-1,100 °C revealed that the Al2O3 top layer effectively suppressed oxygen diffusion and reduced the formation of porous oxide scales compared to the monolithic Cr-Al-N coating. These results indicate that the deposition temperature of the Al2O3 layer plays a critical role in determining the structural stability, tribological performance, and oxidation resistance of Cr-Al-N/Al2O3 composite coatings, with the 700 °C condition demonstrating the optimal overall performance.

https://doi.org/10.3365/KJMM.2026.64.9.792

소병진(Byoungjin So) ; 류재수(Jae Soo Ryu)

Open-cell ceramic filters have attracted considerable attention as promising candidates for capturing volatile radioactive species generated during the pyroprocessing of spent nuclear fuel. Among these species, cesium is regarded as one of the major concerns due to its high volatility and high decay heat. Aluminosilicate-based foam filters are particularly attractive for cesium capture because they form stable Cs-aluminosilicates (CsAlSiO4 and CsAlSi2O6) and possess a highly porous structure, excellent thermal stability, and superior chemical compatibility. Additionally, the compression molding process provides a simple, scalable, and cost-effective fabrication route that allows for facile control over porosity and pore structure. In this study, aluminosilicate foam filters were fabricated via a sacrificial template-assisted compression molding and sintering process. Kaolinite-based aluminosilicate powders were utilized as the ceramic matrix, while charcoal particles were employed as sacrificial space holders to generate interconnected open-cell pore structures. The resulting porous ceramics exhibited high porosities values ranging from 0.692 to 0.730 depending on the charcoal content. Increasing the charcoal content led to larger pore sizes and a concomitant reduction in compressive strength. Three-dimensional micro-computed tomography (micro-CT) analysis revealed well-interconnected pore networks and a decrease in tortuosity with increasing porosity, indicating enhanced fluid transport characteristics. These results demonstrate that the proposed compression molding and sintering approach provides a simple, scalable, and effective route for fabricating porous ceramic filter media suitable for volatile cesium capture systems in pyroprocessing applications.

https://doi.org/10.3365/KJMM.2026.64.9.799

이지현(Ji Hyeon Lee) ; 김재형(Jea Hyung Kim) ; 문병화(Byeonghwa Moon) ; 홍현선(Hyun Seon Hong)

In this study, the effects of the composition of choline chloride (ChCl)-based deep eutectic solvents (DESs) on the leaching behavior of transition metals from NCM (Ni-Co-Mn) black mass were systematically investigated. DESs with various compositions were prepared using ChCl as the hydrogen bond acceptor (HBA) along with citric acid (CA) and L-ascorbic acid (LAA) as hydrogen bond donors (HBDs), and the leaching efficiencies of Li, Ni, Co, and Mn were comprehensively compared. The ternary DES system exhibited superior leaching performance compared to its binary counterparts. Among the tested formulations, a ChCl:CA:LAA molar ratio of 2:0.5:0.5 yielded the highest total leaching efficiency of 79.5%. Optical analyses of the DESs and subsequent leachates revealed that the solution color and UV-Vis absorption behavior were strongly dependent on the coordination environment and distribution of dissolved metal species. The broad absorption observed in the range of approximately 350-450 nm was associated with changes in the coordination environment of Ni species, whereas the absorption in the 600-700 nm region was attributed to the optical contribution of Co-based coordination complexes. Despite similar Ni concentrations, variations in the UV-Vis absorption characteristics and solution color suggested that the optical properties of the leachates were governed not only by the concentration of metal ions but also by their coordination environment and speciation. Collectively, CA stabilizes dissolved metal ions through complex formation, whereas LAA facilitates metal dissolution via reductive reactions. These complementary functions indicate that the DES composition plays a critical role in controlling both the leaching efficiency and the solution characteristics.

https://doi.org/10.3365/KJMM.2026.64.9.808

(Junhyuk Shin) ; (Minseong Hwang) ; (Youngseok Kim) ; (Bongki Ryu) ; (Jaeyeop Chung)

The structure-property relationships of xCaF2-(20-x)CaO-20ZnO-50B2O3-10SiO2 glasses (x = 0, 5, 10, 15, and 20 mol%) were investigated using experimental characterization and molecular dynamics (MD) simulations. The 29Si and 11B magic-angle spinning nuclear magnetic resonance spectra, supported by MD-derived Qn distributions, revealed locally polymerized Si/B structural unit resulting from the suppression of non-bridging oxygens. Structural analyses indicated that highly electronegative fluorine preferentially bonds with modifier cations (Ca2+ and Zn2+), forming stable [Ca-F] and [Zn-F] species. Although these local bonds are stable, the single-bond nature of fluorine perturbs the three-dimensional network connectivity, thereby promoting atomic clustering and creating loosely packed, percolated diffusion channels. Consequently, MD-derived mean square displacement and inductively coupled plasma-optical emission spectrometry results demonstrated enhanced diffusivity and increased Ca2+ and Zn2+ release with higher CaF2 content, which is attributed to the expanded free volume within these modifier-rich pathways. Fourier transform infrared spectroscopy analysis confirmed that a higher fluorine substitution suppressed hydroxyl group formation, reduces OH band intensity, and increased the zeta potential. The resulting ion release contributes positively to the antibacterial performance, achieving 99.9% bacterial reduction against Escherichia coli and Staphylococcus aureus after 24 h. Cytotoxicity tests confirmed that all compositions are nontoxic, indicating excellent biocompatibility. These results provide molecular-level insights into how fluorine incorporation modulates glass structures and dissolution dynamics, thereby offering practical guidance for the design of multifunctional antibacterial and bioactive glasses.

https://doi.org/10.3365/KJMM.2026.64.9.826

김소진(So Jin Kim) ; 한우림(Woo Rim Han) ; 홍주현(Ju Hyun Hong)

This study characterized bronze mirrors dating from the Early Iron Age to the Goryeo Dynasty through chemical composition analysis and microstructural observation. The 30 analyzed mirrors consisted of copper-tin-lead (Cu-Sn-Pb) ternary alloys, exhibiting distinct compositional and microstructural variations depending on the period. Mirrors from the Early Iron Age contained an average of over 20.8 wt.% tin (Sn) and 5-7 wt.% lead (Pb), with microstructures composed of δ and α+δ phases. From the Three Kingdoms and Unified Silla periods onward, the tin (Sn) content of the alloy materials decreased, whereas the lead (Pb) content increased, resulting in a microstructure consisting of an α-phase matrix and an α+δ eutectoid structure. To examine temporal changes in materials and manufacturing techniques, the alloy compositions and microstructures of a total of 76 bronze mirrors were evaluated, incorporating data from previously excavated artifacts. The analysis confirmed that bronze mirrors produced during the Early Iron Age-when mirror production originated can be chronologically distinguished from those of subsequent periods based on these compositional and structural differences. However, given the limited sample size, further research incorporating a broader range of bronze artifacts with well-documented provenance and chronology is required to fully elucidate the historical evolution of alloy compositions and microstructures.

https://doi.org/10.3365/KJMM.2026.64.9.836

(Trung Thanh Pham) ; (Woo-Hyeok Kim) ; (Jeoung Han Kim)

Powder-based manufacturing, including powder metallurgy (PM) and additive manufacturing (AM), links powder production, handling, shaping or consolidation, post-processing, and final property development through a history-dependent process chain. The same nominal processing parameters can yield entirely different outcomes when changes occur in powder morphology, chemistry, reuse state, machine condition, sensing setup, geometry, or the post-processing route. This inherent complexity makes conventional trial-and-error optimization prohibitively costly and severely limits the transferability of empirical process rules. To address these challenges, machine learning (ML) is increasingly deployed to extract underlying patterns from powder descriptors, powder-bed images, sensor streams, process logs, simulation outputs, and mechanical property data. In this review, we examine ML applications across the entire powder lifecycle rather than treating them as isolated algorithmic tasks. The reviewed studies cover feedstock characterization and optimization, in-situ monitoring, defect and process-state detection, property prediction, powder reuse assessment, post-processing-aware modeling, and process optimization. Across these domains, ML proves most effective when predictions are directly traceable to the powder state, process history, intermediate signatures, and validation labels. The literature also highlights recurring barriers, including small and uneven datasets, costly high-fidelity labels, incomplete traceability, weak generalization across different powder lots or machines, and critical trade-offs among accuracy, interpretability, transferability, and qualification relevance. Data-efficient strategies such as transfer learning, multi-fidelity modeling, and physics-informed or hybrid learning can mitigate some of these limitations; however, their efficacy depends heavily on specific assumptions, namely source-target similarity, a meaningful fidelity hierarchy, or valid physical priors. Ultimately, future progress will depend less on algorithm complexity alone than on the curation of traceable lifecycle datasets, uncertainty-aware validation protocols, and models with explicit applicability limits. Under these conditions, ML can serve as a practical decision-support tool for powder-based manufacturing while ensuring that experimental validation and process qualification remain central.