https://doi.org/10.3365/KJMM.2026.64.7.585

As mobile devices evolve toward miniaturization and high performance, thermal management of application processors (AP) has emerged as a critical challenge to ensure sustained peak performance. However, severe physical space constraints in modern devices limit introduction of additional cooling components. To overcome this, our study proposes replacing conventional shield-can materials with a high thermal conductivity alloy. Conventional Cu-Ni-Zn alloys, despite their favorable mechanical strength and formability, have low thermal conductivity (30W/mK), which result in very low heat dissipation and accelerated thermal throttling. To achieve both high mechanical strength and superior thermal conductivity, a Cu-Cr based alloy was implemented to fabricate the shield-can. Experimental results from a real smartphone implementation demonstrate that the Cu-Cr shield-cans effectively reduce both internal AP and surface temperatures of the smartphone compared to it fabricated with conventional Cu-Ni-Zn alloys, leading to a significant enhancement in benchmark scores. Furthermore, this study validates that the selective application of high thermal conductivity materials in shield-cans improves the front-to-back thermal uniformity. This approach effectively prevents system performance degradation and addresses user concerns by mitigating localized heat concentration. Notably, this work proposes a strategic design paradigm that enables the control of heat flux directionality based on the specific thermal requirements and structural configurations of the device. These findings highlight the significant potential of Cu-Cr based alloys as one of the most effective thermal management in next generation high performance electronic devices.

https://doi.org/10.3365/KJMM.2026.64.7.597

이준섭(Jun-Seob Lee) ; 이여경(Yeokyeong Lee) ; 공경호(Kyeong-Ho Kong) ; 김봉윤(Bong-Yoon Kim)

Time-dependent localised corrosion behaviour of UNS A94045 was investigated in an acidified chloride environment. Immersion tests were performed in a Sea Water Acetic Acid Test (SWAAT) solution (1.0 wt.% CH3COOH and 4.2 wt.% NaCl) for 0, 24, 48, 72, and 169 h. The alloy microstructure consisted of primary a-Al dendrites and interdendritic eutectic (a-Al+Si) regions. Localised corrosion initiated in the interdendritic eutectic regions during the early stage, while localised corrosion in the primary a-Al regions remained limited within the examined exposure periods. Three-dimensional surface profile analysis was conducted, and the maximum depth, the average depth, and the maximum-to-average depth ratio were obtained as depth-based indices. Both the maximum and average depths increased with immersion time, whereas the depth ratio increased markedly, indicating that the depth development became increasingly non-uniform and was dominated by specific locations at longer exposure rather than by uniform surface degradation. Scanning Kelvin probe force microscopy (SKPFM) measurements showed higher contact potential difference (CPD) values for eutectic Si than for the a-Al phases, indicating a microstructural potential difference within the eutectic region. On the basis of the immersion and the CPD difference, localised corrosion was considered to initiate in eutectic a-Al adjacent to eutectic Si. These results provide experimental evidence for time-dependent damage evolution and clarify microstructural susceptibility of Al-Si alloys under acidified chloride conditions.

https://doi.org/10.3365/KJMM.2026.64.7.605

김현(Hyun Kim) ; 최효남(Hyo-Nam Choi) ; 이승준(Seung-Joon Lee)

In current study, the microstructural evolution and mechanical properties were investigated for friction stir welded (FSW) metallic materials such as aluminum alloys (e.g., AA7075, AA7068) and medium Mn steel through the Zener-Hollomon parameter (Z). For three materials, an increase in the welding speed led to a decrease in the peak temperature within the stir zone (SZ) during FSW, which consequently resulted in higher Z values. The average grain size (D) in the SZ exhibited a clear power-law relationship with the Z parameter, showing pronounced grain refinement at higher Z values. For example, the derived equations on a logarithmic scale were log D = 2.73 - 0.20 log Z for AA7075, log D = 7.57 - 0.34 log Z for AA7068, and log D = 2.79 - 0.18 log Z for the medium Mn steel. The reasons why the difference in the relationship between Z and D values are strongly dependent on stacking-fault energy and dynamic recrystallization mechanism of metallic materials during FSW. However, the hardness trends differed significantly among the materials. For the aluminum alloys, the relationship between hardness and Z parameter was hardly observed in SZ, because of the suppression of precipitation hardening during FSW despite the presence of grain refinement and accumulated dislocations. Regarding the prediction of hardness for the medium Mn steel, the hardness in SZ was reduced with increasing Z parameter, due to the strain-induced martensitic transformation after FSW. Overall, these findings suggest that the D in SZ can be consistently predicted using the Z parameter, while their mechanical properties should be interpreted based on the intrinsic microstructural changes.

https://doi.org/10.3365/KJMM.2026.64.7.618

류성(Seong Ryu) ; 김도영(DoYoung Kim) ; 김준영(Junyeong Kim) ; 박지원(Jiwon Park) ; 김양도(Yangdo Kim) ; 이승기(Seoung-Ki Lee)

This study investigates the effects of temporal and spatial process parameters on microchip transfer using laser-induced forward transfer (LIFT), with the aim of establishing a reliable and scalable transfer strategy for microelectronic applications. The transfer behavior was systematically analyzed as a function of laser frequency, chip size, and the ratio between the laser spot size and chip size, which govern the temporal energy delivery and spatial energy distribution during the transfer process. From a temporal perspective, the laser frequency determines the number of effective pulse interactions and the degree of pulse overlap, both of which influence the energy accumulation within the dynamic release layer. The results show that excessively low frequencies lead to insufficient energy delivery, while excessively high frequencies induce excessive temporal overlap and thermal accumulation, resulting in unstable transfer. An intermediate frequency condition was found to provide the most stable transfer behavior under the present experimental conditions. From a spatial perspective, the spot-to-chip size ratio plays a critical role in controlling the uniformity of energy distribution across the microchip. A mismatch between the laser spot size and chip size leads to localized energy concentration, which can cause thermal damage or incomplete transfer. In contrast, an optimized ratio enables uniform energy delivery, resulting in stable transfer with minimal defects. Under the optimized conditions identified in this study, a large-area microchip array consisting of 300 devices was successfully transferred with high spatial uniformity. The transfer yield exceeded 99%, and reproducibility tests conducted over five repeated trials confirmed consistent transfer performance with minimal variation. These results demonstrate that the coupled control of temporal and spatial energy conditions is essential for achieving reliable and scalable microchip transfer.

https://doi.org/10.3365/KJMM.2026.64.7.628

신민지(Min Ji Shin) ; 정문근(Simon MoonGeun Jung) ; 정원석(Won Suk Jung)

MoS2 has emerged as a promising non-precious electrocatalyst for the hydrogen evolution reaction (HER) because of its tunable electronic structure, layered architecture, and abundant catalytically active edge sites. In this study, we systematically investigate how the precursor-solution pH during hydrothermal synthesis governs the morphology, phase composition, and alkaline HER performance of MoS2 in 1 M KOH. MoS2 catalysts were synthesized at pH 1.5, 3.5, 5.2, and 7.5 under otherwise identical reaction conditions in order to isolate the influence of pH. The results showed that a uniform nanoflower architectures assembled from well-aligned nanosheets were formed at lower pH, but at high pH, the nanosheets strongly aggregated into a densely stacked spherical structure, causing a sharp decrease in porosity and accessible surface area. XRD confirmed a dominant 2H framework for all samples, while XPS revealed that the metallic 1T-Mo4+ fraction was maximized at pH 1.5 and decreased with increasing pH. Electrochemical measurements demonstrated that the MoS2 catalyst prepared at pH 1.5 exhibited the lowest overpotential at a current density of 10 mA cm-2, the smallest Tafel slope, and the highest double-layer capacitance. The catalytic activity was largely retained after 1,000 potential cycles. These findings demonstrate that simple pH control during hydrothermal synthesis is an effective strategy for simultaneously tailoring the nanostructure and near-surface phase composition of MoS2, thereby improving its electrocatalytic performance for alkaline HER.

https://doi.org/10.3365/KJMM.2026.64.7.637

윤태환(Tae-Hwan Yun) ; 우태규(Tae-Gyu Woo) ; 박일송(Il-Song Park)

The purpose of this study is to produce electrolytic copper foil with a uniform 10 μm thickness and appropriate mechanical properties. The experiment was carried out by adding gum arabic (0-10 ppm) alone. In addition, we conducted the experiment by adding gum arabic in combination with the basic additives to 20 ppm Cl, 10 ppm MPSA, and 30 ppm PVP. When gum arabic was added alone, higher surface roughness and electrical resistivity were observed. When the concentration of gum arabic exceeded 7 ppm, large grains with sizes greater than 10 μm were formed on the surface. Therefore, to achieve the desired surface roughness, it is reasonable to add 2-5 ppm of gum arabic to the electrolytes containing Cl, MPSA, and PVP. The samples that exhibited high elongation showed pronounced crystal growth along the (200) and (111) planes, as revealed by XRD analysis with relative texture coefficient (RTC) evaluation. The combined RTC values for the (200) and (111) orientations were 70.1%, 72.3%, 69.6%, 69.1%, and 68.6% at gum arabic concentrations of 0, 2, 5, 7, and 10 ppm, respectively. The highest value was observed at 2 ppm gum arabic addition. As a result, a tensile strength above 315 MPa was achieved, and the elongation also exceeded 9.1%. Furthermore, the combined addition of 2-5 ppm gum arabic was effective in producing a uniform deposited layer with an electrical resistivity of 1.86 μΩ cm or lower.

https://doi.org/10.3365/KJMM.2026.64.7.644

천하은(Ha-Eun Cheon) ; 홍성규(Sung-Kyu Hong) ; 김성환(Sung-Hwan Kim) ; 홍성박(Seong-Pak Hong) ; 이욱진(Wook-jin Lee)

Hydrogen embrittlement (HE) resistance of cold-drawn austenitic stainless steels was investigated by comparing STS316L and high-nitrogen stainless steel under identical cold drawing and high-pressure gaseous hydrogen charging conditions (10 MPa, 150°C, 600 h). Microstructural characterization, slow strain rate tensile (SSRT) tests, thermal desorption spectroscopy (TDS), and fractographic analysis were conducted to examine the effects of compositional differences on strain-induced martensite formation, hydrogen trapping behavior, and deformation characteristics. X-ray diffraction analysis revealed that both steels showed no detectable martensite after cold drawing. After SSRT, the a'-martensite fraction was 39 vol% in STS316L and 28 vol% in high-nitrogen stainless steel, indicating that the compositional differences of high-nitrogen stainless steel, including higher austenite stability, suppressed strain-induced martensitic transformation. The relative reduction of area (RRA) was 91% for STS316L and 100% for high-nitrogen stainless steel, demonstrating superior HE resistance of the high-nitrogen steel. TDS analysis showed that high-nitrogen stainless steel exhibited a higher total diffusible hydrogen content (6.65 wtppm) compared to STS316L (4.72 wtppm), yet maintained greater HE resistance. Peak deconvolution revealed that STS316L exhibited greater concentration of desorption in the high-temperature region, suggesting differences in the binding energy distribution of hydrogen trap sites between the two steels, consistent with the higher a'-martensite fraction observed after SSRT. These findings suggest that the superior HE resistance of high-nitrogen stainless steel is associated with suppression of martensitic transformation and reduction of high-energy trap site density through its overall compositional design, supporting its potential as a structural material for hydrogen infrastructure applications.

https://doi.org/10.3365/KJMM.2026.64.7.655

김대원(Dae-Weon Kim) ; 김희선(Hee-Seon Kim) ; 김성원(Seong-Won Kim) ; 김재찬(Jae-Chan Kim)

This study comparatively investigated the differences in lithium leaching behavior between reagent-grade NCM and recycled NCM(R-NCM) powders using eco-friendly oxalic acid from crystallographic and kinetic perspectives. Both powders were characterized by ICP-OES, PSA, SEM, XRD, and GSAS-II Rietveld refinement, and leaching experiments were conducted in 0.5 M oxalic acid at 40, 60, and 80°C. Recycled R-NCM showed very high initial Li leaching efficiencies of 86-89% within 10 min at all temperatures, followed by a gradual decrease or stagnation with time. In contrast, reagent-grade NCM exhibited a clear time and temperature dependent leaching behavior, reaching nearly complete Li extraction of approximately 99.9% at 80°C after 80 min. XRD and Rietveld analysis revealed that reagent-grade NCM retained a highly ordered layered structure with a high I003/I104 ratio and a smaller cation mixing, whereas recycled R-NCM showed a reduced I003/I104 ratio, c-axis contraction, and changed Li slab height, indicating increased cation disorder and structural degradation. Kinetic analysis showed that Li leaching from reagent-grade NCM was most consistently described by the product-layer diffusion equation of the shrinking-core model, indicating product-layer-diffusion-dominant mixed control behavior. Based on origin-fixed uncentered R2, the fitting values were 0.9809, 0.9142, and 0.8627 at 40, 60, and 80°C, respectively, and the apparent activation energy derived from the Arrhenius plot was 39.6 kJ/mol. These results indicate that the lower final lithium recovery of recycled powder is closely related to layered-structure degradation, Li slab change, increased cation mixing, and hindered Li diffusion pathways.

https://doi.org/10.3365/KJMM.2026.64.7.670

성민수(Minsu Sung) ; 오지은(Jieun Oh) ; 김성진(Sung-Jin Kim) ; 이수석(Sooseok Lee) ; 박세민(SeMin Park)

Optimizing the magnetic properties of 0.1 mm ultra-thin non-oriented electrical steel is essential for improving electric vehicle (EV) traction motor efficiency. However, traditional experimental trial-and-error methods incur massive time and costs and suffer from limited data availability. To overcome these limitations, this study aims to confirm the effectiveness of data augmentation without additional experiments, enhancing modeling accuracy for magnetic property optimization using limited data. An integrated artificial intelligence (AI) pipeline combining Denoising Diffusion Probabilistic Model (DDPM)-based data augmentation with the FLAML framework was investigated for predicting the steel's magnetic flux density (B) and hysteresis loss (Wh). A systematic three-step validation strategy was conducted, which included initial performance evaluation, augmentation scale optimization, and final interpolation performance evaluation on specific evaluation conditions within the explored domain. Consequently, the boosting-based LightGBM was chosen as the final model for magnetic flux density prediction using large-scale augmented data and a 300-second computation time. For hysteresis loss prediction, the ascending and descending branches of the loop were trained separately, selecting Extra Trees and CatBoost as optimal algorithms to minimize prediction errors. Based on the selected models, a grid search within the process parameter space identified 1,050°C for 16 minutes as the optimal process among candidates satisfying the target magnetic flux density (B25 >= 1.5T). This condition achieved a magnetic flux density of 1.6143 T while minimizing energy loss to 409.18 J/m3. These predictions showed an error of less than 2% against actual experimental measurements. In this study, the data-driven optimization framework significantly reduces the number of experiments required to develop high-performance electrical steel compared to conventional trial-and-error approaches, demonstrating its potential for broad application in alloy design and microstructure control.