https://doi.org/10.3365/KJMM.2026.64.4.267

황정우(Jung Woo Hwang) ; 양준하(Junha Yang) ; 김재호(Jae Ho Kim) ; 정영웅(Yeongwoong Jung) ; 염종택(Jong-Taek Yeom)

Ti?6Al?4V alloys for aerospace structures require damage-tolerant design, so their impact resistance should be quantitatively interpreted by separating crack initiation and crack propagation contributions. In this study, microstructures were tailored by fixing the annealing time and air cooling while varying the annealing temperature from 820 to 1040 °C, resulting in equiaxed (EM, 820?860 °C), bimodal (BM, 920?960 °C), and lamellar (LM, 1000?1040 °C) microstructures. Microstructural characterization was performed using SEM and EBSD analyses, followed by tensile testing. Instrumented Charpy impact tests were conducted to partition the total absorbed energy (ET) into crack initiation energy (EI) and crack propagation energy (EP), enabling correlations among microstructural features, tensile properties, and toughness. Tensile test results indicated that EM maintained nearly constant ultimate tensile strength (UTS, 995?997 MPa) with a slight increase in elongation (24.9?25.8%). In contrast, BM exhibited gradual decreases in UTS (966?979 MPa) and yield strength (YS, 848?875 MPa), with elongation decreasing from 25.5 to 22.8%. LM exhibited a pronounced loss of ductility, with elongation decreasing from 12.2% to 7.8%. Impact test results indicated that ET ranked as BM > EM > LM, with values of 15.8?18.9 J, 13.0?14.8 J, and 10.1?11.6 J, respectively. In the EM condition, ET degradation was dominated by reduced EP, while EI remained nearly unchanged. In contrast, EI and EP in the BM condition were maximized at lower annealing temperatures and decreased concurrently with increasing temperature. Crack-path analysis demonstrated that enhanced EP in BM arose from frequent crack deflection at primary α (αp)?transformed β (βt) interfaces and packet/lamellar boundaries, whereas crack propagation remained relatively straight in EM and LM. These results provide quantitative annealing?microstructure guidelines for optimizing impact toughness in Ti?6Al?4V alloys by identifying key microstructural factors controlling EP.

https://doi.org/10.3365/KJMM.2026.64.4.282

백다경(Dakyeong Baek) ; 임유진(Yoojin Lim) ; 유경근(Kyoungkeun Yoo) ; 이상훈(Sang-Hun Lee) ; Manis Kumar Jha(Manis Kumar Jha)

In the zinc hydrometallurgical process, a cementation process using zinc powder, copper, and antimony is employed to remove cobalt impurities from the electrolyte. However, the precipitate from this process contains not only cobalt but also unreacted zinc, copper, and antimony, making it difficult to recover cobalt, a critical mineral. This study aimed to develop a cementation process that facilitates cobalt recovery by using activated carbon instead of copper as an activator. Experiments were conducted at 85 oC and pH 3.3-3.7 using a simulated solution containing 150 g/L zinc and 10 mg/L cobalt. Complete cobalt removal (100%) was achieved within 30 minutes when 10 g/L activated carbon and 20 mg/L antimony were added, which is equivalent to the performance obtained with 200 mg/L copper. The activated carbon could be easily recovered by sieving through a 1 mm screen and was successfully reused five times. More than 94.5% of the precipitated cobalt was found on zinc powder, while only 1.9-5.5% was deposited on activated carbon. The addition of activated carbon increased the dissolution rate of zinc in sulfuric acid solution, suggesting that activated carbon enhances cobalt cementation by promoting zinc dissolution rather than serving as an electron transfer pathway. This study demonstrates the feasibility of developing an environmentally friendly zinc hydrometallurgical process that facilitates cobalt recovery using reusable activated carbon.

https://doi.org/10.3365/KJMM.2026.64.4.288

(Jin Kim) ; (Seungyoung Park)

Although the morphology of transition metal dichalcogenides (TMDs) can be engineered to implement efficient sensing devices and energy conversion/storage systems, expanding the applicability of TMDs across diverse fields using a limited range of TMD materials remains challenging. In particular, research on strategies to optimize nanostructures incorporating vertical nanosheets to achieve efficient multidisciplinary applications is necessary. Herein, we propose an efficient strategy to enhance and optimize the multifunctional performance of WS2, including the performance of photoelectrochemical (PEC) cell and gas sensing applications, through morphology control. WS2 vertical nanosheets were fabricated using a controllable metal?organic chemical vapor deposition method, and their morphology could be effectively tuned by adjusting the growth pressure. Comprehensive improvements in PEC performance and NO2 gas sensing characteristics achieved through growth pressure modulation validated the dual functionality of the morphology-controlled WS2 nanosheet structures. These results indicate that, irrespective of the application field, efficient charge separation and the increased specific surface area provided by the nanosheet architecture effectively enhance the performance of WS2. Furthermore, by controlling the nanosheet density and thickness, we identify an optimal WS2 nanosheet structure with appropriate dimensions that enables versatile multidisciplinary applications. This study suggests the importance of morphology control as a key strategy for multifunctional applications and demonstrates a promising pathway to expand the applicability of a limited range of WS2 across diverse fields through a simple and effective approach.

https://doi.org/10.3365/KJMM.2026.64.4.294

(Hyeonju Lee) ; (Bokyung Kim) ; (Taehui Kim) ; (Dongwook Kim) ; (Xue Zhang) ; (Jin-Hyuk Bae) ; (Youngjun Yun) ; (Sungkeun Baang) ; (Jaehoon Park)

High-permittivity zirconium oxide (ZrOx) gate dielectrics prepared by solution processing are promising for low-temperature annealing processes that are incompatible with flexible substrates. In this study, pulsed-ultraviolet (p-UV)-assisted thermal annealing was employed to rapidly activate ZrOx films at 200 oC within 5 min. These films were subsequently integrated into top-contact, bottom-gate pentacene thinfilm transistors (TFTs). The p-UV-annealed ZrOx films retained high optical transmittance (>80%) and exhibited optical band gaps of ~5.1 eV (hot plate, 200 oC/60 min) and ~5.2 eV (p-UV, 200 oC/5 min), thus confirming that the accelerated process preserves the electronic structure. Water contact angles decreased from 36.1o to 31.8o, corresponding to an increase in surface energy from 59.6 to 62.4 mJ/m2, consistent with Fourier transform infrared spectroscopy evidence of reduced carbonaceous and carboxylic species. Pentacene films grown on p-UV-annealed ZrOx exhibited larger grain sizes and smoother morphologies, with RMS roughness of approximately 7.7 nm compared to 8.8 nm for the hot plate-annealed sample, which led to improved inter-island connectivity. The device measured at VD = ? 4 V showed enhanced electrical performance with p-UV treatment, with the field-effect mobility increasing from 3.10 to 4.13 cm2/V·s. The on/ off current ratio improved from 5.63 × 105 to 4.06 × 106, whereas the threshold voltage remained nearly unchanged. These results demonstrate that p-UV-assisted annealing offers a fast, energy-efficient, and substrate-compatible approach to prepare high-quality ZrOx gate dielectrics for high-performance pentacene organic TFTs.

https://doi.org/10.3365/KJMM.2026.64.4.302

양익준(Ik Jun Yang) ; 장병록(Byoung Lok Jang)

As the transition toward carbon neutrality accelerates, the demand for alternative iron sources capable of supporting low-carbon steelmaking has grown substantially. Direct Reduced Iron (DRI), which offers significantly lower greenhouse gas emissions compared to conventional hot metal, has become an essential feedstock for electric arc furnace (EAF) operations. However, DRI often exhibits low melting efficiency and induces unstable bath behavior, underscoring the need for improved melting technologies. To address these challenges, this study investigates a bottom-blowing stirring technology designed to enhance thermal and flow control within the EAF when processing large quantities of DRI, supported by both experimental observations and computational fluid dynamics (CFD) simulations. A series of melting trials and flow-field analyses were performed to evaluate the effects of bottom inert-gas injection on temperature uniformity, melting kinetics, and the overall DRI dissolution behavior. The bottom-blowing parameters were optimized to strengthen bath circulation, promote efficient heat transfer, and eliminate localized cold regions that hinder DRI melting. CFD results further clarified the internal flow structures and mixing characteristics induced by the bottom-blowing configuration. The findings indicate that controlled bottom stirring significantly improves the dissolution rate of DRI by enhancing mixing intensity and stabilizing bath thermodynamics without inducing excessive oxidation or energy losses. This study demonstrates that integrating optimized bottom-blowing technology into DRI-charged EAF operations can meaningfully enhance melting performance and energy efficiency. The results offer valuable insight into melt behavior under modified flow conditions and provide practical guidance for industrial implementation of DRI-based EAF steelmaking in support of carbon-neutral production strategies.

https://doi.org/10.3365/KJMM.2026.64.4.312

(Bo Raadam) ; (Jaeheon Lee)

Gallium-based liquid metal alloys are often used to model high temperature metallic flows because of the ease of materials handling and their similar properties. A Ga68.5In21.5Sn10 (wt. pct) alloy was made from the constituent metals and various properties were measured and compared against those available in the literature, which itself contained a variety of values. Density was found to be 6.488 ± 0.265 g/cm3, kinematic viscosity 0.474 ± 0.018 cSt, and electrical conductivity 3.46*106 ± 0.09*106 S/m, all at room temperature (approximately 21 oC). Electrical conductivity was measured using a 4-point probe that was constructed in-house using tungsten electrodes and calibrated with Wood’s metal. Despite the non-commercial origin of the instrument, the measured value agreed well with values reported in literature. A size-0 Ubbelohde viscometer used to measure viscosity was calibrated with the N.4 viscosity standard, although metal alloy viscosity values were found to be above what is typically seen in the literature. It is believed partial obstruction of the capillary by untreated oxides was responsible for this deviation. The issue of oxidation often noted with the alloy was observed at the macroscopic scale though it did not appear in the SEM-EDS results from inside the fluid volume. Oxidation was alleviated by treatment with sulfuric acid at pH 0 which restored flowability in a simple and easy to scale manner.

https://doi.org/10.3365/KJMM.2026.64.4.325

(Ji Hee Pi) ; (Yong Whan Kim) ; (Yan Gu) ; (Nosang Vincent Myung) ; (Kyu Hyoung Lee) ; (Jeong Yun Hwang)

Thermoelectric (TE) films offer a promising way to integrate energy harvesting and thermal management, however, their widespread adoption is often limited by fabrication routes that are complex, costly, and difficult to scale. Many existing approaches rely on vacuum-based equipment or high-temperature processing, which increases manufacturing burdens and constrains practical deployment. Electroless plating provides a convenient and low-cost method to introduce metals and tailor electrical transport properties, yet it has not been widely utilized as a performance-optimization strategy for TE films. Here, we demonstrate a simple two step plating strategy, electrodeposition followed by electroless Ag plating, combined with lowtemperature annealing to fabricate polycrystalline p-type Sb2Te3-based TE films and to achieve high TE performance (conversion efficiency and reliability). Sb2Te3 films were first prepared by electrodeposition, achieved by reducing the tartaric acid content in the electrolyte. The as-deposited Sb2Te3 film exhibited a high electrical conductivity of ~3502 S cm-1, however, substantial variation in the batch-to-batch electronic transport properties was observed, limiting their practical applications. To address this issue, Ag was introduced by electroless plating, followed by annealing at 393 K, which produced a multiphase Ag/Ag2Te/Sb2Te3 architecture. This multiphase structure improves the reliability of TE properties: batch-to-batch variations in both electrical conductivity and the Seebeck coefficient were significantly reduced compared with those of the electrodeposited Sb2Te3 film. Consequently, a high and stable room-temperature power factor of 648 μW m-1 K-2 was achieved. These results indicate that plating-based fabrication can simultaneously simplify processing and improve TE performance, enabling scalable production and performance tuning of TE films.

https://doi.org/10.3365/KJMM.2026.64.4.331

황병철(Byoungchul Hwang)

The widening use of hydrogen energy infrastructure has increased concern about the hydrogen embrittlement (HE) resistance of metallic materials, a critical property throughout the entire lifecycle of design, manufacturing, and certification. HE arises from the coupled interaction of hydrogen ingress, diffusion, trapping, and stress/strain fields. This makes direct comparison of results difficult due to variations in testing methods, including hydrogen charging modes (electrochemical/high-pressure gas), hydrogen retention during testing (in situ/ex situ), loading configurations (monotonic/sustained/cyclic), specimen geometries (smooth/notched/precracked), and data reduction procedures. In particular, slow strain-rate tests (SSRT), notched tensile tests, sustained load delayed fracture tests, and incremental step loading (ISL) tests can efficiently assess crack initiation and time-delayed fracture susceptibility, while fracture toughness (K or J) and fatigue crack growth rate (da/dN?ΔK) tests provide data about crack propagation-based design properties that are directly applicable to defect-tolerant design and life assessment. This review systematically classifies HE evaluation test methods for steels from the perspective of hydrogen introduction?loading mode?crack process (initiation/propagation), and compares the physical meaning and applicability of quantitative metrics provided by each test. Furthermore, the ISO/ASTM standardization framework is organized from the viewpoint of ‘procedural standards (reproducibility)’ versus ‘design property standards (transferability)’. Then the influence of key governing factors including stress state (constraint/triaxiality), hydrogen concentration (absolute amount/distribution/trapping), strain rate and frequency, temperature and pressure, microstructure, and alloying elements is comprehensively discussed. Finally, test selection strategies tailored to the objectives of material screening, design data acquisition, and process quality control are proposed, along with minimum reporting requirements, providing guidance to enhance the reliability and engineering utility of HE data.

https://doi.org/10.3365/KJMM.2026.64.4.350

이수(Su Lee) ; 김현식(Hyun-Sik Kim) ; 정도현(Do Hyun Jung) ; 정재필(Jae Pil Jung)

Copper and silicon dioxide (Cu-SiO2) hybrid bonding is a pivotal technology for realizing ultra-fine pitch and high-density input/output (I/O) in 3D semiconductor packaging, specifically for artificial intelligence (AI) and high-performance computing (HPC) applications. However, the chemical mechanical polishing (CMP) process, critical for planarization, inherently suffers from dishing. This defect is driven by the significant disparity in material removal rates between ductile Cu pads and the surrounding rigid dielectric, leading to excessive Cu recession. Dishing is a critical failure mode that jeopardizes device reliability. It not only creates interfacial voids that impede atomic diffusion bonding but also exacerbates thermal stress concentration due to the coefficient of thermal expansion (CTE) mismatch during post-annealing. These topographical imperfections can lead to severe cracking and delamination. To mitigate these challenges, this paper provides a systematic review of dishing mechanisms and control strategies across three dimensions: process, material, and design. In process optimization, we highlight advanced slurry formulations, such as Fenton reactionbased chemistries, and multi-step CMP techniques capable of correcting surface topography. Regarding materials, the transition from SiO2 to silicon carbonitride (SiCN) is analyzed for its superior mechanical hardness and erosion resistance. Furthermore, design-based solutions, specifically the insertion of dummy patterns to ensure uniform pattern density and minimize the loading effect, are discussed. This comprehensive review provides actionable guidelines for achieving nanometer-level surface control, ensuring the yield and reliability of next-generation heterogeneous integration.

https://doi.org/10.3365/KJMM.2026.64.4.364

정효연(Hyo Yun Jung) ; 심누리(Nuri Sim)

Metal additive manufacturing (AM) enables the production of complex metallic components, but the use of concentrated energy sources and rapid solidification often results in process-induced defects. These defects, together with microstructural heterogeneity and anisotropy, can significantly influence the mechanical performance and reliability of AM parts. The two most widely adopted metal AM processes, Powder Bed Fusion (PBF) and Directed Energy Deposition (DED), produce distinctive defect characteristics due to differences in process conditions and material deposition mechanisms. This review summarizes the formation mechanisms of major defects in metal AM processes and discusses their relationship with microstructural evolution. Evaluation methods defined in relevant ISO and ASTM standards are systematically examined, based on the links between defects, microstructure, and mechanical properties. Standardized test methods for tensile, compression, fatigue, and hardness properties are comparatively analyzed in terms of specimen configuration, testing conditions, and applicable scope, highlighting differences that may influence data interpretation. In addition, interpretation uncertainties and potential risks arising from variations in standard selection, specimen orientation, and location-dependent behavior are addressed within a structured analytical perspective. Based on the above discussion, a standard-based reliability assessment framework is presented, linking defect characteristics, microstructural analysis, standard-based test method selection, interpretation risk evaluation, and final decision-making. This framework clarifies that performance evaluation in metal AM should not rely solely on isolated test results, but should be conducted within an integrated evaluation structure governed by applicable standards. By organizing defect characteristics, microstructure, and mechanical properties under ISO/ASTM standard systems, this study provides a structured basis for reliability-oriented material evaluation in metal AM. The framework may contribute to improving the interpretability, reproducibility, and comparability of experimental data, and offers a reference for establishing consistent evaluation strategies and future standardization directions.