Journal of Powder Materials

Volume 33(2); April 2026 Cover PDF Issue information PDF

Research Articles

[English]
Ultrasonic Nanocrystal Surface Modification of 3D Interconnected Heterostructured Complex Concentrated Alloys Produced by Liquid Metal Dealloying: Microstructural Evolution and Wear Behavior: Jumi Choi, Yeji Kim, Munsu Choi, Jae Hyuk Lee, Dong Jun Lee, Auezhan Amanov, Soo-Hyun Joo, Hyoung Seop Kim; J Powder Mater. 2026;33(2):91-103. Published online April 30, 2026; DOI: https://doi.org/10.4150/jpm.2026.00045

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Abstract PDF: This study investigates the effects of ultrasonic nanocrystal surface modification (UNSM) on the microstructural evolution and tribological performance of a three-dimensional interconnected heterostructured compositionally complex alloy fabricated by liquid metal dealloying (LMD). The as-LMD microstructure comprises an interconnected Cu-rich phase and a CoCrFe-rich ligament phase. Electron backscatter diffraction reveals pronounced severe plastic deformation near the surface after UNSM, characterized by subgrain formation and increased intragranular misorientation. The kernel average misorientation distribution reveals a pronounced depth-dependent deformation gradient, with dislocations preferentially accumulating at the interphase boundaries. Vickers hardness increases from approximately 100–120 HV in the as-LMD condition to greater than 270 HV at the surface after UNSM, and the hardening effect remains detectable to a depth of approximately 500 μm. Compressive residual stresses are concentrated within the surface-adjacent ~50 μm. The solid ligament phase exhibits higher compressive residual stress than the Cu-rich phase, reflecting phase-dependent deformation accommodation and stress partitioning. Reciprocating wear tests show a narrower wear track, a markedly reduced wear depth, and a lower and more stable friction coefficient after UNSM. Microscopy shows oxide-layer cracking and delamination in the as-LMD condition, whereas the UNSM-treated surface exhibits minor abrasive wear of the tribo-film without delamination.

[English]
Influence of Cobalt Content on Phase Formation and Morphology in Co-Zn-O Oxides: Deukhyeon Nam, Sungdo Yun, Bo Eun Choi, Chan Woong Na, Yoon Myung; J Powder Mater. 2026;33(2):104-112. Published online April 30, 2026; DOI: https://doi.org/10.4150/jpm.2026.00052

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Abstract PDF: Co–Zn–O–based materials have attracted attention for applications in energy storage and catalysis. In this study, the effects of cobalt incorporation on the crystal phase and particle morphology of Co–Zn–O oxides were investigated. ZnO-based oxides were synthesized using a reflux method, and the influence of cobalt content on phase formation and morphology was systematically evaluated. As the cobalt precursor concentration increased, scanning electron microscopy–energy dispersive X-ray spectroscopy confirmed higher cobalt incorporation. This compositional variation was accompanied by changes in particle morphology, including nanoparticles, disk-like structures, and occasional rod-like features. X-ray diffraction and Raman spectroscopy showed that samples with low cobalt content retained the wurtzite ZnO phase, whereas higher cobalt concentrations led to formation of a ZnO/ZnCo2O4 composite. X-ray photoelectron spectroscopy revealed comparable binding energies among samples, while differences in peak width suggested variations in the local coordination environment of cobalt. These results indicate that cobalt content significantly influences phase composition and particle morphology in Co–Zn–O oxides synthesized under reflux conditions.

[Korean]
Effect of Powder Preparation Method on the Microstructural Characteristics of Sintered W-7Ni-3Cu Heavy Alloy: Youngmin Kim, Ji Young Kim, Minju Son, Wonyong Kwon, Eui Seon Lee, Sung-Tag Oh; J Powder Mater. 2026;33(2):113-118. Published online April 30, 2026; DOI: https://doi.org/10.4150/jpm.2026.00038

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Abstract PDF: The effect of powder characteristics and sintering temperature on the properties of W-7Ni-3Cu is investigated. The heavy alloy powders were prepared by ball milling and hydrogen reduction of elemental metal or metal oxide powders. Microstructural analysis revealed that the powder mixtures reduced by hydrogen at 800oC consist of a trace amount of Ni4W phase along with the metal W phase and Ni-Cu solid solution. Additionally, compared to metal powder, the powder mixture using oxide as raw material exhibited a relatively fine particle size. The W-7Ni-3Cu alloys sintered using oxide powders had relative density of over 99%, whereas the specimens using metal powders as a raw material showed relatively low values of 87.8~98.2%. The Vickers hardness of the sintered specimens using oxide powder was 3.34–3.92 GPa, which was higher than that of 2.39–3.22 GPa measured when using metal powders. The observed results can be attributed to the relatively high density and the reduced grain size.

[English]
Influence of Ta Addition on Austenite Stability and Strain-Induced Martensite Transformation in Sintered Fe-7Mn Alloy: Seunghyeok Choi, Sungjin Kim, Junho Lee, Seok-Jae Lee; J Powder Mater. 2026;33(2):119-129. Published online April 30, 2026; DOI: https://doi.org/10.4150/jpm.2026.00066

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Abstract PDF: This study examines the effect of Ta addition on austenite stability and strain-induced martensitic transformation behavior in Fe–7Mn alloys fabricated by powder metallurgy. Fe–7Mn–xTa alloys (x = 0, 1, and 1.5 wt.%) were produced via mechanical alloying followed by spark plasma sintering, achieving nearly full relative density for all compositions. With increasing Ta content, the initial retained austenite fraction significantly increased, reaching 80.55 vol.% in the Fe–7Mn–1.5Ta alloy. EBSD analysis revealed a grain coarsening tendency with Ta addition, indicating that the increase in retained austenite fraction could not be explained solely by grain refinement. Compression tests up to 20% strain showed strain-induced martensitic transformation in all alloys, with substantially more pronounced transformation observed in the Fe–7Mn–1.5Ta alloy. The Burke–Matsumura–Tsuchida model showed that the austenite stability parameter (k), where higher values indicate lower stability, increased from 3.89 to 10.62 with Ta addition. Ta thus exhibits a dual effect: promoting retained austenite after sintering while reducing its deformation stability. The hardening efficiency per unit martensite fraction decreased with Ta content, and a preliminary correlation between k and hardening efficiency suggests that austenite stability governs the mechanical response of Fe–Mn-based alloys.

[English]
Analysis of Sintering Behavior and Microstructure of Mo-Ta Alloy under Different Sintering Conditions: Byungheon Oh, Geon Kim, Jio Yoon, Dongju Lee; J Powder Mater. 2026;33(2):130-136. Published online April 30, 2026; DOI: https://doi.org/10.4150/jpm.2026.00080

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Abstract PDF: Molybdenum-tantalum (Mo-Ta) alloy sputtering targets are widely used in electronic applications owing to their excellent corrosion resistance, high thermal and electrical conductivity, and low electrical impedance. In this study, the sintering behavior and microstructural evolution of Mo-Ta alloys fabricated by spark plasma sintering (SPS) were investigated as a function of sintering temperature in the range of 1650-1800 °C. X-ray diffraction and microstructural analyses indicate that densification and alloying of the mixed Mo and Ta powders occur simultaneously during the SPS process. Increasing the sintering temperatures significantly enhances densification, and the compact sintered at 1750 °C achieves a relative density exceeding 99%, which is essential for high-quality sputtering target applications. The sintered alloys exhibit a clear temperature-dependent grain growth behavior together with a homogeneous microstructure and randomly oriented grains. These results demonstrate that appropriate control of sintering temperature enables the fabrication of dense and microstructurally uniform Mo-Ta alloys, providing valuable guidelines for optimizing sputtering target performance.

[English]
Effect of Compositional Trade-off Between Cr and Mo on the Corrosion Resistance of Additively Manufactured Co-Cr-Fe-Ni-Mo High-Entropy Alloys: Jeongmin Lee, Yeonghwan Song, Jae Hyuk Lee, Sung-Jae Jo, Minho Shin, Hyunbin Lim, Soon-Jik Hong, Soo-Hyun Joo; J Powder Mater. 2026;33(2):137-144. Published online April 30, 2026; DOI: https://doi.org/10.4150/jpm.2026.00087

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Abstract PDF: In this study, the corrosion behavior of Co-Cr-Fe-Ni-Mo high-entropy alloys additively manufactured via direct energy deposition was investigated according to the compositional trade-off between Cr and Mo elements. Two distinct alloy compositions were fabricated by adjusting the feeding rate of two powders with different chemical compositions through a dual nozzle. Electrochemical testing in a 3.5 wt% NaCl solution revealed that the Cr-rich and Mo-lean alloy exhibited inferior corrosion resistance compared to the Cr-lean and Mo-rich alloy. Specifically, the corrosion potential of the Cr-rich and Mo-lean alloy shifted negatively by approximately 200 mV compared to the Cr-lean and Mo-rich alloy, accompanied by an increase in corrosion current density and the pronounced initiation of localized pitting. This deterioration is attributed to a lack of passivation caused by the small amount of Mo in the Cr-rich and Mo-lean alloy. The passive film of the Cr-lean and Mo-rich alloy was more robust, characterized by a higher concentration of Mo, which effectively inhibited pit propagation through repassivation. These findings demonstrate that maintaining a critical Cr-Mo balance is more vital for the electrochemical stability of additively manufactured high-entropy alloys than unilateral Cr enrichment.

Critical Review

[English]
X-Ray Imaging of Solid-State Sintering and Laser Powder Bed Fusion: A Review of Process Monitoring and Defect Evolution: Wonjun Cho, Woobin Cho, Seongheon Park, Donghwan Son, Insung Han; J Powder Mater. 2026;33(2):145-158. Published online April 30, 2026; DOI: https://doi.org/10.4150/jpm.2025.00479

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Abstract PDF: X-ray imaging has become essential for understanding powder-based metal processing. In solid-state sintering, synchrotron tomography reveals particle rearrangement, neck growth, and pore evolution, clarifying how packing heterogeneity and particle-size distribution govern densification. In laser powder bed fusion, high-speed radiography captures microsecond-scale melt-pool behavior, including keyhole dynamics, vapor-jet entrainment, spatter formation, and bubble-mediated porosity, thereby enabling mechanistic links between processing conditions and defect generation. Nonetheless, current X-ray methods face trade-offs between spatial and temporal resolution and often remain qualitative. Integrating operando imaging with physics-based simulations and machine-learning models offers a path toward quantitative prediction and real-time control. This review summarizes recent progress and highlights key challenges and opportunities for advancing operando characterization of powder-based metal processes.

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