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Tape-casting Process Electrochemical Characteristic Test for Fabrication of LST-GDC for Anode Supported SOFCs
Min Ji Kim, Chunghyun Kim, Young-Beom Kim
J. Korean Soc. Precis. Eng. 2025;42(11):937-942.
Published online November 1, 2025
DOI: https://doi.org/10.7736/JKSPE.025.073

In this study, we developed a composite anode support composed of La-doped SrTiO3 (LST) and Gd-doped CeO2 (GDC) using a tape casting process for solid oxide fuel cells (SOFCs). By adjusting the pore former content in the slurry, we constructed a bilayered structure consisting of a porous anode support layer (ASL) and a dense anode functional layer (AFL) with the same material composition. The number of tape-cast sheets was controlled to tailor the overall thickness, and lamination followed by co-sintering at 1250oC resulted in a mechanically robust bilayer. We characterized the microstructural evolution concerning sintering temperature and pore former content using SEM, while XRD confirmed the phase stability of LST and GDC. The measured electrical conductivity at 750oC ensured sufficient electron transport. To enhance interfacial adhesion and suppress secondary phase formation, we introduced a GDC buffer layer and a pre-sintering treatment prior to electrolyte deposition. A full cell with a YSZ electrolyte and LSCF cathode achieved a stable open circuit voltage of approximately 0.7 V and demonstrated continuous operation at 750oC. These findings highlight the suitability of LST-GDC composite anodes as thermochemically stable supports, potentially enabling direct hydrocarbon utilization in intermediate-temperature SOFCs.

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Study on UV Energy Effects in High Aspect Ratio Patterning via the Self-propagating Photopolymer Waveguide (SPPW) Method
Jun Ho Song, Woo Young Kim, Seungwoo Shin, Seok Kim, Young Tae Cho
J. Korean Soc. Precis. Eng. 2025;42(9):757-762.
Published online September 1, 2025
DOI: https://doi.org/10.7736/JKSPE.025.041

This study quantitatively examines the impact of ultraviolet (UV) intensity and energy on the formation of high aspect ratio (HAR) microstructures using the Self-Propagating Photopolymer Waveguide (SPPW) process. This mechanism relies on the self-focusing of UV light within a refractive index gradient, allowing the light to propagate and polymerize vertically beyond the initial exposure zone. Experiments were performed at UV intensities of 7.5, 12.5, and 17.5 mW/cm2, with energy levels ranging from 0.0375 to 13.5 J/cm2. The results indicated that a lower UV intensity of 7.5 mW/cm2 produced uniform and vertically elongated structures, achieving a maximum aspect ratio of 12.26 at 0.9 J/cm2. In contrast, higher UV intensities led to lateral over-curing, base expansion, and shape distortion, primarily due to rapid polymerization and the oxygen inhibition effect. These findings emphasize the importance of precisely controlling both UV intensity and energy to produce uniform, vertically aligned HAR microstructures, offering valuable insights for optimizing the SPPW process in future microfabrication applications.

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Optimized Microstructures for High Performance Ag/MWCNT/Ecoflex- based Flexible Pressure Sensors
Hyeon Yun Jeong, Jeong Beom Ko
J. Korean Soc. Precis. Eng. 2025;42(8):657-664.
Published online August 1, 2025
DOI: https://doi.org/10.7736/JKSPE.025.065
Recently, flexible pressure sensors featuring enhanced sensitivity and durability through nano/micro additive manufacturing have been employed in various fields, including medical monitoring, E-skin technology, and soft robotics. This study focuses on the fabrication and verification of an interdigitated electrode (IDE) based flexible pressure sensor that incorporates microstructures, utilizing a direct patterning-based additive process. The IDE-patterned sample was designed with a total size of 7.95 × 10 mm2, a line width of 150 µm, a spacing of 200 µm, and a probe pad measuring 1.25 × 2 mm2. It was fabricated using AgNP ink on a primed 100 µm thick polyethylene naphthalate (PEN) substrate. The electrode layer was subsequently covered with a sensing layer made of a MWCNT/Ecoflex composite material, resulting in the final pressure sensor sample. Measurements indicated that the sensor exhibited good sensitivity and response speed, and it was confirmed that further improvements in sensitivity could be achieved by optimizing the size, spacing, and height of the microstructures. Building on the flexible pressure sensor structure developed in this study, we plan to pursue future research aimed at fabricating array sensors with integrated circuits and exploring their applicability in wearable devices for pressure sensing and control functions.
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Laser-induced Process for Fabrication of Silicon Microstructure
Sung Jin Park, Bongchul Kang
J. Korean Soc. Precis. Eng. 2025;42(7):499-503.
Published online July 1, 2025
DOI: https://doi.org/10.7736/JKSPE.025.053
Silicon is a key material in advanced technologies due to its thermal stability, appropriate bandgap, and wide applicability for advanced devices. Si microstructures offer enhanced surface area, thus improving performances for energy storage and biosensing applications. However, conventional top-down fabrication methods are complex, costly, and environmentally unfriendly as they rely on cleanroom facilities and toxic chemicals. This study proposed a simplified, eco-friendly bottom-up laser-based process to fabricate silicon microstructures. By controlling laser parameters during the interaction with silicon nanoparticles, diverse Si structures can be fabricated by Si nanoparticle coating and laser irradiation.
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Study on Repair of SKD 61 Using Directed Energy Deposition with H13 and P21 Powders
Bit-na Yun, Min-seong Ko, Hyo-jeong Kang, Do-Sik Shim
J. Korean Soc. Precis. Eng. 2024;41(11):849-856.
Published online November 1, 2024
DOI: https://doi.org/10.7736/JKSPE.024.073
In this study, we investigated characteristics and mechanical properties of SKD61 repaired using the direct energy deposition (DED) process. Mechanical properties of the repaired product can vary depending on the base material and powder used in the DED process. To prepare for DED repairing for a damaged part, we conducted experiments using two different powders (H13 and P21). Experimental results showed that both powders were deposited without defects in the surface or interface between the deposited zone and the substrate. Hardness measurements indicated that the repaired region of the Repaired-H13 sample exhibited higher hardness than the base material, while the Repaired-P21 sample showed a sharp increase in hardness in the heat-affected zone (HAZ). Additionally, tensile test results revealed that the Repaired-H13 sample had lower tensile strength and elongation than the base material, whereas the Repaired-P21 sample demonstrated higher tensile strength and yield strength with a higher elongation than the Repaired-H13 sample. In case of Repaired-H13, it was confirmed that interfacial crack occurred due to a high hardness difference between the repaired part and the substrate.

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  • Microstructure and mechanical properties of P21 tool steel fabricated via laser powder bed fusion
    A. Rajesh Kannan, V. Rajkumar, S. Maheshwaran, N. Siva Shanmugam, Wonjoo Lee, Jonghun Yoon
    Materials Letters.2025; 398: 138930.     CrossRef
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Influence of Cooling Rate and Sn Addition on Microstructure Formation of As-cast GCD700 Spheroidal Graphite Cast Irons
Seong-Ho Ha, Jaegu Choi, Dong-Hyuk Kim, Sang-Yun Shin
J. Korean Soc. Precis. Eng. 2024;41(3):175-182.
Published online March 1, 2024
DOI: https://doi.org/10.7736/JKSPE.023.118
This study investigated the influence of cooling rate and Sn addition on the microstructure formation of as-cast GCD700 spheroidal graphite cast irons. Changes in cooling rate manifested as step cast thickness differences. Optical microstructures of as-cast GCD700 alloys revealed α-ferrite and pearlite and dispersed graphite nodules. In all examined thicknesses without Sn, the α-ferrite, rather than the pearlite, surrounding graphite nodules appeared to dominate microstructures, and the graphite looked well rounded, whereas microstructure containing 0.09% Sn had a significantly expanded pearlite area. Image analysis showed numbers of graphite nodules increased only on decreasing cast thickness. However, the phase fractions of ferrite and pearlite were not dependent on thickness. For samples containing Sn, pearlite fractions significantly increased with Sn content. Thermodynamic calculations and scanning electron microscopy-based microstructural analysis confirmed that the Sn contents examined had no significant effect on phase formation, Sn segregation, or the relationships between ferrite and Fe3C orientations in pearlite.
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Study on Effect of Ultrasonic Nanocrystal Surface Modification in Bolt Manufactured by Screw Rolling
Hyeong-Jin Ha, Han-Byeol Park, Tae Hyung Jung, Do-Sik Shim
J. Korean Soc. Precis. Eng. 2023;40(8):625-632.
Published online August 1, 2023
DOI: https://doi.org/10.7736/JKSPE.023.023
This study aimed to determine effects of ultrasonic nanocrystal surface modification (UNSM) as a surface pre-process on performance and surface characteristics of bolts manufactured through a screw rolling process. Surface roughness, hardness, and microstructural changes after UNSM treatment were examined. Results showed no significant defects such as cracks in all fabricated samples after screw rolling of bolt pre-processed by UNSM treatment. In addition, material flow was continuously maintained without disconnection. After UNSM treatment, surface roughness was improved for both body and screw parts. The surface roughness of the UNSM treated screw part was improved the most at 43%. Hardness test showed the greatest increase in hardness on the surface hit by the UNSM ball tip, with hardness improved to about 500 μm deep from the surface. The hardness at the screw part was the highest at 471 HV, which was attributed to the fact that grains near the surface were deformed and refined by UNSM treatment followed by screw rolling. Near the surface of the screw, refined grains and high dislocation density were clearly observed by EBSD mapping. These results confirm that UNSM treatment before screw rolling is effective in improving mechanical properties of screw rolled bolts.
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Study on Wear Behavior of 630 Stainless Steel Fabricated by Sequential Metal Additive Manufacturing (Powder Bed Fusion and Directed Energy Deposition)
Tae-Geon Kim, Gwang-Yong Shin, Ki-Yong Lee, Do-Sik Shim
J. Korean Soc. Precis. Eng. 2023;40(6):483-492.
Published online June 1, 2023
DOI: https://doi.org/10.7736/JKSPE.022.131
Hybrid additive manufacturing (AM) refers to a combination of two metal AM techniques: material deposition by powder bed fusion (PBF) and additional building by directed energy deposition (DED). This study focused on different characteristics in accordance with relative deposition directions of PBF and DED during hybrid AM production. Characteristics of the sample fabricated by hybrid AM (i.e., hybrid sample) were compared with those of the sample fabricated by PBF or DED. Ferrite was dominant in the microstructure of PBF deposits with very fine retained austenite observed locally. In contrast, lath martensite and retained austenite were formed uniformly in the microstructure of DED deposits. Different microstructures in the two processes were attributed to differences of cooling rate. In DED deposits, microhardness was significantly decreased owing to a high retained austenite fraction. However, in the hybrid sample, microhardness was rapidly increased in the HAZ owing to aging heat treatment for long-term deposition. Principal wear mechanisms of PBF and DED samples were oxidative wear and plastic deformation, respectively.
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Analysis of Springback Characteristics of Magnesium Alloy Sheet (AZ31B) Considering Time-Dependence in Warm Bending
JaeHyeong Yu, Chang-Whan Lee
J. Korean Soc. Precis. Eng. 2020;37(3):201-207.
Published online March 1, 2020
DOI: https://doi.org/10.7736/JKSPE.019.106
The purpose of this study was to investigate the springback behavior of magnesium alloy (AZ31B) at high temperature with respect to the holding time in the die-set. The changes of microstructure in the springback during V-Bending were analyzed. The springback of the magnesium alloy sheet showed a tendency to decrease as the forming temperature and the retention time in the die increase. In the microstructure analysis, there was minimal change in the microstructure at room temperature, while at high temperature the microstructure changed markedly. The increasing material holding time in die has been shown to reduce springback from internal energy reduction because of recrystallization and grain growth at high temperature.

Citations

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  • Analysis of acoustic emission signals during bending deformation of magnesium alloy sheet
    Jae-Hyeong Yu, In-Gyu Choi, Jung-Sik Yoon, John S. Kang, Wan-Jin Chung, Chang-Whan Lee
    Nondestructive Testing and Evaluation.2025; : 1.     CrossRef
  • Analysis on the Warm Bending Process of Magnesium Alloy Sheet Using Additively Manufactured Polymer Die-Set
    Hyung-Won Youn, Jun-Hyun Kyeong, Keun Park, Chang-Whan Lee
    Journal of the Korean Society for Precision Engineering.2021; 38(10): 775.     CrossRef
  • Study on the Time-Dependent Mechanical Behavior and Springback of Magnesium Alloy Sheet (AZ31B) in Warm Conditions
    Jae-Hyeong YU, Chang-Whan Lee
    Materials.2021; 14(14): 3856.     CrossRef
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Low Cycle Fatigue Characteristics of a Ni-Based Single Crystal Superalloy CMSX-4 at Elevated Temperature
Jae Gu Choi, Chang-Sung Seok, Sung Uk Wee, Eui-Suck Chung, Byoung-Gwan Yun, Suk-Hwan Kwon
J. Korean Soc. Precis. Eng. 2019;36(3):271-279.
Published online March 1, 2019
DOI: https://doi.org/10.7736/KSPE.2019.36.3.271
Isothermal low cycle fatigue (LCF) behavior of a crystal nickel-based superalloy CMSX-4, a material for high-pressure turbine first stage rotor blade, was investigated at elevated temperatures. Strain-controlled LCF tests were performed under various test conditions, such as mechanical strain amplitude. Stress response and cyclic deformation were investigated, and equations of LCF life prediction were derived through the Coffin-Manson method. In addition, fatigue-induced fracture mechanism and microstructural evolution were investigated, using scanning electron microscopy (SEM). Results revealed that cyclic behavior of the CMSX-4 superalloy, was characterized by cyclic softening with increasing number of cycles at 800oC and 900oC. LCF of the CMSX-4 superalloy at 800oC and 900oC could be affected mainly by elastic damage in fatigue processing. Fatigue cracks were initiated in the surface oxide layer of the specimen. The plane of fracture surface was tilted toward <001> direction. The fatigue fracture mechanism was quasi-cleavage fracture at 800oC and 900oC. In all broken specimens, the γˊ phase morphology maintained cuboidal shape.

Citations

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  • Mechanical Loading Effect on Stress States and Failure Behavior in Thermal Barrier Coatings
    Da Qiao, Wengao Yan, Wu Zeng, Jixin Man, Beirao Xue, Xiangde Bian
    Crystals.2023; 14(1): 2.     CrossRef
  • A method for predicting the delamination life of thermal barrier coatings under thermal gradient mechanical fatigue condition considering degradation characteristics
    Damhyun Kim, Kibum Park, Keekeun Kim, Chang-Sung Seok, Jongmin Lee, Kyomin Kim
    International Journal of Fatigue.2021; 151: 106402.     CrossRef
  • Low-cycle fatigue behavior of K416B Ni-based superalloy at 650 °C
    Jun Xie, De-long Shu, Gui-chen Hou, Jin-jiang Yu, Yi-zhou Zhou, Xiao-feng Sun
    Journal of Central South University.2021; 28(9): 2628.     CrossRef
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Fabrication of Superhydrophobic Surface on Various Metals Using Abrasive Blasting and Self-Assembled Monolayer Coating
Byungrak Park, Woonbong Hwang
J. Korean Soc. Precis. Eng. 2018;35(2):197-201.
Published online February 1, 2018
DOI: https://doi.org/10.7736/KSPE.2018.35.2.197
A study about superhydrophobic surface started from the analysis of lotus leaf, and superhydrophobic surface fabrication methods have been researched. These methods cannot be used on various metals because the fabrication methods have complex and material-selective processes. In this work, we report a simple fabrication method using abrasive blasting and a self-assembled monolayer coating to produce a superhydrophobic surface. Abrasive blasting was used to create microstructures on metal surfaces. Random peak and valley microstructures were created after abrasive blasting, and a surface profile was measured to analyze the relationship between blasting pressure and a roughness parameter. A hydrophobic material coating was performed by a self-assembled monolayer method. Six kinds of metal surfaces displayed superhydrophobic properties. This utilitarian method could be applied to diverse applications.
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