Journal of Powder Materials

Effect of Ball Milling Conditions on the Microstructure and Dehydrogenation Behavior of TiH₂ Powder: Ji Young Kim, Eui Seon Lee, Ji Won Choi, Youngmin Kim, Sung-Tag Oh; J Powder Mater. 2024;31(2):132-136. Published online April 30, 2024; DOI: https://doi.org/10.4150/jpm.2024.00001; Funded: National Research Foundation of Korea

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Abstract PDF: This study investigated the effects of revolution speed and ball size in planetary milling on the microstructure and dehydrogenation behavior of TiH2 powder. The particle size analysis showed that the large particles present in the raw powder were effectively refined as the revolution speed increased, and when milled at 500 rpm, the median particle size was 1.47 m. Milling with a mixture of balls of two or three sizes was more effective in refining the raw powder than milling with balls of a single size. A mixture of 3-mm and 5-mm-diameter balls was the optimal condition for particle refinement, and the measured median particle size was 0.71 m. The dependence of particle size on revolution speed and ball size was explained by changes in input energy and the number of contact points of the balls. In the milled powder, the endothermic peak measured using differential thermal analysis was observed at a relatively low temperature. This finding was interpreted as the activation of a dehydrogenation reaction, mainly due to the increase in the specific surface area and the concentration of lattice defects.

The Effect of TiO₂ Addition on Low-temperature Sintering Behaviors in a SnO₂-CoO-CuO System: Jae-Sang Lee, Kyung-Sik Oh, Yeong-Kyeun Paek; J Powder Mater. 2024;31(2):146-151. Published online April 30, 2024; DOI: https://doi.org/10.4150/jpm.2024.00024; Funded: Andong National University

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Abstract PDF: Pure SnO2 has proven very difficult to densify. This poor densification can be useful for the fabrication of SnO2 with a porous microstructure, which is used in electronic devices such as gas sensors. Most electronic devices based on SnO2 have a porous microstructure, with a porosity of > 40%. In pure SnO2, a high sintering temperature of approximately 1300C is required to obtain > 40% porosity. In an attempt to reduce the required sintering temperature, the present study investigated the low-temperature sinterability of a current system. With the addition of TiO2, the compositions of the samples were Sn1-xTixO2-CoO(0.3wt%)-CuO(2wt%) in the range of x ≤ 0.04. Compared to the samples without added TiO2, densification was shown to be improved when the samples were sintered at 950C. The dominant mass transport mechanism appears to be grain-boundary diffusion during heat treatment at 950C.

Exploring Thermoelectric Transport Properties and Band Parameters of n-Type Bi_2-xSb_xTe₃ Compounds Using the Single Parabolic Band Model: Linh Ba Vu, Soo-ho Jung, Jinhee Bae, Jong Min Park, Kyung Tae Kim, Injoon Son, Seungki Jo; J Powder Mater. 2024;31(2):119-125. Published online April 30, 2024; DOI: https://doi.org/10.4150/jpm.2024.00045; Funded: KIMS’ Principal R&D, National Research Foundation of Korea

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Abstract PDF: The n-type Bi2-xSbxTe3 compounds have been of great interest due to its potential to achieve a high thermoelectric performance, comparable to that of p-type Bi2-xSbxTe3. However, a comprehensive understanding on the thermoelectric properties remains lacking. Here, we investigate the thermoelectric transport properties and band characteristics of n-type Bi2-xSbxTe3 (x = 0.1 – 1.1) based on experimental and theoretical considerations. We find that the higher power factor at lower Sb content results from the optimized balance between the density of state effective mass and nondegenerate mobility. Additionally, a higher carrier concentration at lower x suppresses bipolar conduction, thereby reducing thermal conductivity at elevated temperatures. Consequently, the highest zT of ~ 0.5 is observed at 450 K for x = 0.1 and, according to the single parabolic band model, it could be further improved by ~70 % through carrier concentration tuning.

Recent Developments in Quantum Dot Patterning Technology for Quantum Dot Display: Yeong Jun Jin, Kyung Jun Jung, Jaehan Jung; J Powder Mater. 2024;31(2):169-179. Published online April 30, 2024; DOI: https://doi.org/10.4150/jpm.2024.00073; Funded: National Research Foundation of Korea

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Abstract PDF: Colloidal quantum dot (QDs) have emerged as a crucial building block for LEDs due to their size-tunable emission wavelength, narrow spectral line width, and high quantum efficiency. Tremendous efforts have been dedicated to improving the performance of quantum dot light-emitting diodes (QLEDs) in the past decade, primarily focusing on optimization of device architectures and synthetic procedures for high quality QDs. However, despite these efforts, the commercialization of QLEDs has yet to be realized due to the absence of suitable large-scale patterning technologies for high-resolution devices., This review will focus on the development trends associated with transfer printing, photolithography, and inkjet printing, and aims to provide a brief overview of the fabricated QLED devices. The advancement of various quantum dot patterning methods will lead to the development of not only QLED devices but also solar cells, quantum communication, and quantum computers.

Data-driven Approach to Explore the Contribution of Process Parameters for Laser Powder Bed Fusion of a Ti-6Al-4V Alloy: Jeong Min Park, Jaimyun Jung, Seungyeon Lee, Haeum Park, Yeon Woo Kim, Ji-Hun Yu; J Powder Mater. 2024;31(2):137-145. Published online April 30, 2024; DOI: https://doi.org/10.4150/jpm.2024.00038; Funded: Korean Institute of Materials Science, Korea Institute of Machinery and Materials, Ministry of Trade, Industry, and Energy

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Abstract PDF: In order to predict the process window of laser powder bed fusion (LPBF) for printing metallic components, the calculation of volumetric energy density (VED) has been widely calculated for controlling process parameters. However, because it is assumed that the process parameters contribute equally to heat input, the VED still has limitation for predicting the process window of LPBF-processed materials. In this study, an explainable machine learning (xML) approach was adopted to predict and understand the contribution of each process parameter to defect evolution in Ti alloys in the LPBF process. Various ML models were trained, and the Shapley additive explanation method was adopted to quantify the importance of each process parameter. This study can offer effective guidelines for fine-tuning process parameters to fabricate high-quality products using LPBF.

Effect of Hot Isostatic Pressing on the Stellite 6 Alloy prepared by Directed Energy Deposition: Joowon Suh, Jae Hyeon Koh, Young-Bum Chun, Young Do Kim, Jinsung Jang, Suk Hoon Kang, Heung Nam Han; J Powder Mater. 2024;31(2):152-162. Published online April 30, 2024; DOI: https://doi.org/10.4150/jpm.2024.00066; Funded: Korea Atomic Energy Research Institute

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Abstract PDF: The directed energy deposited (DED) alloys show higher hardness values than the welded alloys due to the finer microstructure following the high cooling rate. However, defects such as microcracks, pores, and the residual stress are remained within the DED alloy. These defects deteriorate the wear behavior so post-processing such as heat treatment and hot isostatic pressing (HIP) are applied to DED alloys to reduce the defects. HIP was chosen in this study because the high pressure and temperature uniformly reduced the defects. The HIP is processed at 1150oC under 100 MPa for 4 hours. After HIP, microcracks are disappeared and porosity is reduced by 86.9%. Carbides are spherodized due to the interdiffusion of Cr and C between the dendrite and interdendrite region. After HIP, the nanohardness (GPa) of carbides increased from 11.1 to 12, and the Co matrix decreased from 8.8 to 7.9. Vickers hardness (HV) decreased by 18.9 % after HIP. The dislocation density (10-2/m2) decreased from 7.34 to 0.34 and the residual stress (MPa) changed from tensile 79 to a compressive -246 by HIP. This study indicates that HIP is effective in reducing defects, and the HIP DED Stellite 6 exhibits a higher HV than welded Stellite 6.

Microstructural Evolution and Mechanical Properties of Ti-6Al-4V Alloy through Selective Laser Melting: Comprehensive Study on the Effect of Hot Isostatic Pressing (HIP): Gargi Roy, Raj Narayan Hajra, Woo Hyeok Kim, Jongwon Lee, Sangwoo Kim, Jeoung Han Kim; J Powder Mater. 2024;31(1):1-7. Published online February 28, 2024; DOI: https://doi.org/10.4150/KPMI.2024.31.1.1; Funded: Korea Institute of Materials Science, Ministry of Trade, Industry and Energy

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Abstract PDF: This study explores the profound impact of varying oxygen content on microstructural and mechanical properties in specimens HO and LO. The higher oxygen concentration in specimen HO is found to significantly influence alpha lath sizes, resulting in a size of 0.5-1 μm, contrasting with the 1-1.5 μm size observed in specimen LO. Pore fraction, governed by oxygen concentration, is high in specimen HO, registering a value of 0.11%, whereas specimen LO exhibits a lower pore fraction (0.02%). Varied pore types in each specimen further underscore the role of oxygen concentration in shaping microstructural morphology. Despite these microstructural variations, the average hardness remains consistent at ~370 HV. This study emphasizes the pivotal role of oxygen content in influencing microstructural features, contributing to a comprehensive understanding of the intricate interplay between elemental composition and material properties.

Cryogenic Tensile Behavior of Ferrous Medium-entropy Alloy Additively Manufactured by Laser Powder Bed Fusion: Seungyeon Lee, Kyung Tae Kim, Ji-Hun Yu, Hyoung Seop Kim, Jae Wung Bae, Jeong Min Park; J Powder Mater. 2024;31(1):8-15. Published online February 28, 2024; DOI: https://doi.org/10.4150/KPMI.2024.31.1.8; Funded: National Research Foundation of Korea, Ministry of Science and ICT, Korea Institute of Materials Science, Korea Institute of Machinery and Materials

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Abstract PDF: The emergence of ferrous-medium entropy alloys (FeMEAs) with excellent tensile properties represents a potential direction for designing alloys based on metastable engineering. In this study, an FeMEA is successfully fabricated using laser powder bed fusion (LPBF), a metal additive manufacturing technology. Tensile tests are conducted on the LPBF-processed FeMEA at room temperature and cryogenic temperatures (77 K). At 77 K, the LPBF-processed FeMEA exhibits high yield strength and excellent ultimate tensile strength through active deformation-induced martensitic transformation. Furthermore, due to the low stability of the face-centered cubic (FCC) phase of the LPBF-processed FeMEA based on nano-scale solute heterogeneity, stress-induced martensitic transformation occurs, accompanied by the appearance of a yield point phenomenon during cryogenic tensile deformation. This study elucidates the origin of the yield point phenomenon and deformation behavior of the FeMEA at 77 K.

Development of Composite-film-based Flexible Energy Harvester using Lead-free BCTZ Piezoelectric Nanomaterials: Gwang Hyeon Kim, Hyeon Jun Park, Bitna Bae, Haksu Jang, Cheol Min Kim, Donghun Lee, Kwi-Il Park; J Powder Mater. 2024;31(1):16-22. Published online February 28, 2024; DOI: https://doi.org/10.4150/KPMI.2024.31.1.16; Funded: Ministry of Science and ICT, National Research Foundation of Korea

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Abstract PDF: Composite-based piezoelectric devices are extensively studied to develop sustainable power supply and selfpowered devices owing to their excellent mechanical durability and output performance. In this study, we design a leadfree piezoelectric nanocomposite utilizing (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (BCTZ) nanomaterials for realizing highly flexible energy harvesters. To improve the output performance of the devices, we incorporate porous BCTZ nanowires (NWs) into the nanoparticle (NP)-based piezoelectric nanocomposite. BCTZ NPs and NWs are synthesized through the solidstate reaction and sol-gel-based electrospinning, respectively; subsequently, they are dispersed inside a polyimide matrix. The output performance of the energy harvesters is measured using an optimized measurement system during repetitive mechanical deformation by varying the composition of the NPs and NWs. A nanocomposite-based energy harvester with 4:1 weight ratio generates the maximum open-circuit voltage and short-circuit current of 0.83 V and 0.28 A, respectively. In this study, self-powered devices are constructed with enhanced output performance by using piezoelectric energy harvesting for application in flexible and wearable devices.

Effect of Abnormal Grain Growth on Ionic Conductivity in LATP: Hyungik Choi, Yoonsoo Han; J Powder Mater. 2024;31(1):23-29. Published online February 28, 2024; DOI: https://doi.org/10.4150/KPMI.2024.31.1.23; Funded: Ministry of Trade, Industry and Energy, Korea Planning and Evaluation Institute of Industrial Technology

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Development of High-strength, High-temperature Nb-Si-Ti Alloys through Mechanical Alloying: Jung-Joon Kim, Sang-Min Yoon, Deok-Hyun Han, Jongmin Byun, Young-Kyun Kim; J Powder Mater. 2024;31(1):30-36. Published online February 28, 2024; DOI: https://doi.org/10.4150/KPMI.2024.31.1.30; Funded: National Research Foundation of Korea

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Effect of Tool Shape and Insertion Depth on Joining Properties in Friction Stir Spot Welding of Aluminum Alloy/high-strength Steel Sheets: Su-Ho An, Young-Keun Jeong; J Powder Mater. 2024;31(1):37-42. Published online February 28, 2024; DOI: https://doi.org/10.4150/KPMI.2024.31.1.37; Funded: Pusan National University

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Fabrication of Ti-Mo Core-shell Powder and Sintering Properties for Application as a Sputtering Target: Won Hee Lee, Chun Woong Park, Heeyeon Kim, Yuncheol Ha, Jongmin Byun, Young Do Kim; J Powder Mater. 2024;31(1):43-49. Published online February 28, 2024; DOI: https://doi.org/10.4150/KPMI.2024.31.1.43; Funded: Ministry of Trade, Industry and Energy, Korea Planning and Evaluation Institute of Industrial Technology, Ministry of Education, National Research Foundation of Korea

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Fabrication of Bi₂Te_2.5Se_0.5 by Combining Oxide-reduction and Compressive-forming Process and Its Thermoelectric Properties: Young Soo Lim, Gil-Geun Lee; J Powder Mater. 2024;31(1):50-56. Published online February 28, 2024; DOI: https://doi.org/10.4150/KPMI.2024.31.1.50; Funded: Pukyong National University

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Research Trends in Electromagnetic Shielding using MXene-based Composite Materials: Siyeon Kim, Jongmin Byun; J Powder Mater. 2024;31(1):57-76. Published online February 28, 2024; DOI: https://doi.org/10.4150/KPMI.2024.31.1.57; Funded: National Research Foundation of Korea, Ministry of Science and ICT

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Abstract PDF: Recent advancements in electronic devices and wireless communication technologies, particularly the rise of 5G, have raised concerns about the escalating electromagnetic pollution and its potential adverse impacts on human health and electronics. As a result, the demand for effective electromagnetic interference (EMI) shielding materials has grown significantly. Traditional materials face limitations in providing optimal solutions owing to inadequacy and low performance due to small thickness. MXene-based composite materials have emerged as promising candidates in this context owing to their exceptional electrical properties, high conductivity, and superior EMI shielding efficiency across a broad frequency range. This review examines the recent developments and advantages of MXene-based composite materials in EMI shielding applications, emphasizing their potential to address the challenges posed by electromagnetic pollution and to foster advancements in modern electronics systems and vital technologies.

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