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.

Although the Ti–6Al–4V alloy has been used in the aircraft industry owing to its excellent mechanical properties and low density, the low formability of the alloy hinders broadening its applications. Recently, laser-powder bed fusion (L-PBF) has become a novel process for overcoming the limitations of the alloy (i.e., low formability), owing to the high degree of design freedom for the geometry of products having outstanding performance used in hightech applications. In this study, to investigate the effect of bulk shape on the microstructure and mechanical properties of L-PBFed Ti-6Al-4V alloys, two types of samples are fabricated using L-PBF: thick and thin samples. The thick sample exhibits lower strength and higher ductility than the thin sample owing to the larger grain size and lower residual dislocation density of the thick sample because of the heat input during the L-PBF process.

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• 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
  journal of Korean Powder Metallurgy Institute.2024; 31(1): 8.     CrossRef
• 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
  journal of Korean Powder Metallurgy Institute.2024; 31(1): 1.     CrossRef
• 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
  journal of Korean Powder Metallurgy Institute.2024; 31(2): 137.     CrossRef
• High-speed manufacturing-driven strength-ductility improvement of H13 tool steel fabricated by selective laser melting
  Yeon Woo Kim, Haeum Park, Young Seong Eom, Dong Gill Ahn, Kyung Tae Kim, Ji-hun Yu, Yoon Suk Choi, Jeong Min Park
  Powder Metallurgy.2023; 66(5): 582.     CrossRef

Because magnets fabricated using Nd-Fe-B exhibit excellent magnetic properties, this novel material is used in various high-tech industries. However, because of the brittleness and low formability of Nd-Fe-B magnets, the design freedom of shapes for improving the performance is limited based on conventional tooling and postprocessing. Laserpowder bed fusion (L-PBF), the most famous additive manufacturing (AM) technique, has recently emerged as a novel process for producing geometrically complex shapes of Nd-Fe-B parts owing to its high precision and good spatial resolution. However, because of the repeated thermal shock applied to the materials during L-PBF, it is difficult to fabricate a dense Nd-Fe-B magnet. In this study, a high-density (>96%) Nd-Fe-B magnet is successfully fabricated by minimizing the thermal residual stress caused by substrate heating during L-PBF.

The CoCrFeMnNi high-entropy alloy (HEA), which is the most widely known HEA with a single facecentered cubic structure, has attracted significant academic attention over the past decade owing to its outstanding multifunctional performance. Recent studies have suggested that CoCrFeMnNi-type HEAs exhibit excellent printability for selective laser melting (SLM) under a wide range of process conditions. Moreover, it has been suggested that SLM can not only provide great topological freedom of design but also exhibit excellent mechanical properties by overcoming the strength–ductility trade-off via producing a hierarchical heterogeneous microstructure. In this regard, the SLM-processed CoCrFeMnNi HEA has been extensively studied to comprehensively understand the mechanisms of microstructural evolution and resulting changes in mechanical properties. In this review, recent studies on CoCrFeMnNi-type HEAs produced using SLM are discussed with respect to process-induced microstructural evolution and the relationship between hierarchical heterogeneous microstructure and mechanical properties.

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• Investigation of effects of process parameters on microstructure and fracture toughness of SLM CoCrFeMnNi
  Joseph Agyapong, Diego Mateos, Aleksander Czekanski, Solomon Boakye-Yiadom
  Journal of Alloys and Compounds.2024; 987: 173998.     CrossRef
• 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
  journal of Korean Powder Metallurgy Institute.2024; 31(1): 8.     CrossRef
• 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
  journal of Korean Powder Metallurgy Institute.2024; 31(2): 137.     CrossRef
• High-speed manufacturing-driven strength-ductility improvement of H13 tool steel fabricated by selective laser melting
  Yeon Woo Kim, Haeum Park, Young Seong Eom, Dong Gill Ahn, Kyung Tae Kim, Ji-hun Yu, Yoon Suk Choi, Jeong Min Park
  Powder Metallurgy.2023; 66(5): 582.     CrossRef

Selective laser melting (SLM), a type of additive manufacturing (AM) technology, leads a global manufacturing trend by enabling the design of geometrically complex products with topology optimization for optimized performance. Using this method, three-dimensional (3D) computer-aided design (CAD) data components can be built up directly in a layer-by-layer fashion using a high-energy laser beam for the selective melting and rapid solidification of thin layers of metallic powders. Although there are considerable expectations that this novel process will overcome many traditional manufacturing process limits, some issues still exist in applying the SLM process to diverse metallic materials, particularly regarding the formation of porosity. This is a major processing-induced phenomenon, and frequently observed in almost all SLM-processed metallic components. In this study, we investigate the mechanical anisotropy of SLM-produced 316L stainless steel based on microstructural factors and highly-oriented porosity. Tensile tests are performed to investigate the microstructure and porosity effects on mechanical anisotropy in terms of both strength and ductility.

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• Development of multi-defect diagnosis algorithm for the directed energy deposition (DED) process with in situ melt-pool monitoring
  Hyewon Shin, Jimin Lee, Seung-Kyum Choi, Sang Won Lee
  The International Journal of Advanced Manufacturing Technology.2023; 125(1-2): 357.     CrossRef
• Corrosion Resistance of Laser Powder Bed Fused AISI 316L Stainless Steel and Effect of Direct Annealing
  Kichang Bae, Dongmin Shin, Jonghun Lee, Seohan Kim, Wookjin Lee, Ilguk Jo, Junghoon Lee
  Materials.2022; 15(18): 6336.     CrossRef
• Experimental investigation on the effect of process parameters in additive/subtractive hybrid manufacturing 316L stainless steel
  Chengming Tang, Jibin Zhao, Zhiguo Wang, Yuhui Zhao, Tianran Wang
  The International Journal of Advanced Manufacturing Technology.2022; 121(3-4): 2461.     CrossRef
• Interface characteristics and mechanical behavior of additively manufactured multi-material of stainless steel and Inconel
  Man Jae Sagong, Eun Seong Kim, Jeong Min Park, Gangaraju Manogna Karthik, Byeong-Joo Lee, Jung-Wook Cho, Chong Soo Lee, Takayoshi Nakano, Hyoung Seop Kim
  Materials Science and Engineering: A.2022; 847: 143318.     CrossRef
• Effect of heat treatment on microstructural heterogeneity and mechanical properties of 1%C-CoCrFeMnNi alloy fabricated by selective laser melting
  Jeong Min Park, Eun Seong Kim, Hyeonseok Kwon, Praveen Sathiyamoorthi, Kyung Tae Kim, Ji-Hun Yu, Hyoung Seop Kim
  Additive Manufacturing.2021; 47: 102283.     CrossRef
• Manufacturing Aluminum/Multiwalled Carbon Nanotube Composites via Laser Powder Bed Fusion
  Eo Ryeong Lee, Se Eun Shin, Naoki Takata, Makoto Kobashi, Masaki Kato
  Materials.2020; 13(18): 3927.     CrossRef
• Effects of microstructure and internal defects on mechanical anisotropy and asymmetry of selective laser-melted 316L austenitic stainless steel
  Jin Myoung Jeon, Jeong Min Park, Ji-Hun Yu, Jung Gi Kim, Yujin Seong, Sun Hong Park, Hyoung Seop Kim
  Materials Science and Engineering: A.2019; 763: 138152.     CrossRef
• Microstructural effects on the tensile and fracture behavior of selective laser melted H13 tool steel under varying conditions
  Jungsub Lee, Jungho Choe, Junhyeok Park, Ji-Hun Yu, Sangshik Kim, Im Doo Jung, Hyokyung Sung
  Materials Characterization.2019; 155: 109817.     CrossRef

Nanosized Gd₂O₃:Eu³⁺ red phosphor is prepared using a template method from metal salt impregnated into a crystalline cellulose and is dispersed using a bead mill wet process. The driving force of the surface coating between Gd₂O₃:Eu³⁺ and mica is induced by the Coulomb force. The red phosphor nanosol is effectively coated on mica flakes by the electrostatic interaction between positively charged Gd₂O₃:Eu³⁺ and negatively charged mica above pH 6. To prepare Gd₂O₃:Eu³⁺-coated mica (Gd₂O₃:Eu/mica), the coating conditions are optimized, including the stirring temperature, pH, calcination temperature, and coating amount (wt%) of Gd₂O₃:Eu³⁺. In spite of the low luminescence of the Gd₂O₃:Eu/mica, the luminescent property is recovered after calcination above 600°C and is enhanced by increasing the Gd₂O₃:Eu³⁺ coating amount. The Gd₂O₃:Eu/mica is characterized using X-ray diffraction, field emission scanning electron microscopy, zeta potential measurements, and fluorescence spectrometer analysis.

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• Optimization of dispersed LaPO4:Tb nanosol and their photoluminescence properties
  Mahboob Ullah, Se-Min Ban, Dae-Sung Kim
  Optical Materials.2019; 97: 109366.     CrossRef