Journal of Powder Materials

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

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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.

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

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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.

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

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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.

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

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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

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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.

Fabrication of Equiatomic CoCrFeMnNi High-Entropy Alloy by Metal Injection Molding Process Using Coarse-Sized Powders: Eun Seong Kim, Jae Man Park, Ji Sun Lee, Jungho Choe, Soung Yeoul Ahn, Sang Guk Jeong, Do Won Lee, Seong Jin Park, Hyoung Seop Kim; J Powder Mater. 2023;30(1):1-6. Published online February 1, 2023; DOI: https://doi.org/10.4150/KPMI.2023.30.1.1

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Abstract PDF: High-entropy alloys (HEAs) are attracting attention because of their excellent properties and functions; however, they are relatively expensive compared with commercial alloys. Therefore, various efforts have been made to reduce the cost of raw materials. In this study, MIM is attempted using coarse equiatomic CoCrFeMnNi HEA powders. The mixing ratio (powder:binder) for HEA feedstock preparation is explored using torque rheometer. The block-shaped green parts are fabricated through a metal injection molding process using feedstock. The thermal debinding conditions are explored by thermogravimetric analysis, and solvent and thermal debinding are performed. It is densified under various sintering conditions considering the melting point of the HEA. The final product, which contains a small amount of non-FCC phase, is manufactured at a sintering temperature of 1250°C.

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

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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.

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

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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

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Combinatorial Experiment for Al-6061 and Al-12Si alloy Based on Directed Energy Deposition (DED) Process: Seoyeon Jeon, Suwon Park, Yongwook Song, Jiwon Park, Hyunyoung Park, Boram Lee, Hyunjoo Choi; J Powder Mater. 2023;30(6):463-469. Published online December 1, 2023; DOI: https://doi.org/10.4150/KPMI.2023.30.6.463

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Abstract PDF: Aluminum alloys, known for their high strength-to-weight ratios and impressive electrical and thermal conductivities, are extensively used in numerous engineering sectors, such as aerospace, automotive, and construction. Recently, significant efforts have been made to develop novel aluminum alloys specifically tailored for additive manufacturing. These new alloys aim to provide an optimal balance between mechanical properties and thermal/ electrical conductivities. In this study, nine combinatorial samples with various alloy compositions were fabricated using direct energy deposition (DED) additive manufacturing by adjusting the feeding speeds of Al6061 alloy and Al-12Si alloy powders. The effects of the alloying elements on the microstructure, electrical conductivity, and hardness were investigated. Generally, as the Si and Cu contents decreased, electrical conductivity increased and hardness decreased, exhibiting trade-off characteristics. However, electrical conductivity and hardness showed an optimal combination when the Si content was adjusted to below 4.5 wt%, which can sufficiently suppress the grain boundary segregation of the α- Si precipitates, and the Cu content was controlled to induce the formation of Al₂Cu precipitates.

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

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Hydrogen Reduction Behavior of NCM-based Lithium-ion Battery Cathode Materials: So-Yeong Lee, So-Yeon Lee, Dae-Hyeon Lee, Ho-Sang Sohn; J Powder Mater. 2024;31(2):163-168. Published online April 30, 2024; DOI: https://doi.org/10.4150/jpm.2024.00017

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Abstract PDF: As the demand for lithium-ion batteries for electric vehicles is increasing, it is important to recover valuable metals from waste lithium-ion batteries. In this study, the effects of gas flow rate and hydrogen partial pressure on hydrogen reduction of NCM-based lithium-ion battery cathode materials were investigated. As the gas flow rate and hydrogen partial pressure increased, the weight loss rate increased significantly from the beginning of the reaction due to the reduction of NiO and CoO by hydrogen. At 700 °C and hydrogen partial pressure above 0.5 atm, Ni and Li2O were produced by hydrogen reduction. From the reduction product and Li recovery rate, the hydrogen reduction of NCM-based cathode materials was significantly affected by hydrogen partial pressure. The Li compounds recovered from the solution after water leaching of the reduction products were LiOH, LiOH·H2O, and Li2CO3, with about 0.02 wt% Al as an impurity.

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

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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

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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 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

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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.

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