• Journal of Powder Materials
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• v.24 no.6
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• pp.494-507
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• 2017

A three-dimensional physical part can be fabricated from a three-dimensional digital model in a layer-wise manner via additive manufacturing (AM) technology, which is different from the conventional subtractive manufacturing technology. Numerous studies have been conducted to take advantage of the AM opportunities to penetrate bespoke custom product markets, functional engineering part markets, volatile low-volume markets, and spare part markets. Nevertheless, materials issues, machines issues, product issues, and qualification/certification issues still prevent the AM technology from being extensively adopted in industries. The present study briefly reviews the standard classification, technological structures, industrial applications, technological advances, and qualification/certification activities of the AM technology. The economics, productivity, quality, and reliability of the AM technology should be further improved to pass through the technology adoption lifecycle of innovation technology. The AM technology is continuously evolving through the introduction of PM materials, hybridization of AM and conventional manufacturing technologies, adoption of process diagnostics and control systems, and enhanced standardization of the whole lifecycle qualification and certification methodology.

• Korean Journal of Materials Research
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• v.7 no.6
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• pp.460-463
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• 1997

에폭시 수지 계의 경화반응 속도를 증가시키고 기계적 물성을 향상시키기 위해 합성 pheny1 glycidy1 ether(PGE)-acetamide(AcAm)를 diglycidy1 ether of bispenol A(DGEBA)/4,4'-methylene dianiline(MDA)계에 도입하였다. PGE와 AcAm을 2:1의 몰비로 혼합한 후 18$0^{\circ}C$에서 1시간 반응시켜서 PGE-AcAm을 합성하였다. 5phr의 PGE-AcAm이 첨가되었을 때 인장강도가 15% 개선되었으며, 그 이후로는 PGE-AcAm을 합성하였다. 5phr의 PGE-AcAm이 첨가되었을 때 인장강도가 15% 개선되었으며, 그 이후로는 PGE-AcAm의 함량에 관계없이 거의 비슷한 값을 나타내었다. 반면에유리전이 온도(Tg)와 충격강도는 PGE-AcAm의 함량이 증가함에 따라 감소하였다. 파단면은 PGE-AcAm이 첨가됨으로써 더 복잡한 형상을 나타내었다.

• Korean Journal of Materials Research
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• v.8 no.9
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• pp.797-801
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• 1998

The cure kinetics for diglycidyl ether of bisphenol A(DGEBA)/4, 4'-methylene dianiline(MDA) system with or without lOphr of phenyl glycidyl ether(PGE)-acetamide(AcAm) was studied by autocatalytic cure expression. On the dynamic DSC curves, the exothermic peak temperature and the onset temperature of reaction decreased with the addition of PGE-AcAm. Regardless of the addition of PGE-AcAm, the shape of the conversion curve showed sigmoid, and this meant that DGEBA/MDA and DGEBA/MDA/PGE-AcAm systems followed autocatalytic cure reaction. When PGE-AcAm was added to DGEBA/MDA system, the cure rate increased about 1.2~1.4 times due to the catalytic role of hydroxyl groups in PGE-AcAm.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.924-929
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• 2002

We have developed the novel liquid crystal materials with a difluoromethyleneoxy (CF2O) moiety as a linkage group in order to satisfy the diversified various requirements for AM-LCDs. These novel CF2O LC materials have excellent physical properties that are high dielectric anisotropy, low viscosity and wide nematic temperature ranges. Physical properties measurement results that mixtures containing CF2O LC materials have suitable for characteristics for AM-LCDs. The CF2O LC materials are excellent compound for quick response and low driving voltage application.

• Korean Journal of Materials Research
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• v.22 no.10
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• pp.499-503
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• 2012

The present study is intended to comparatively investigate the changes in microstructure and tensile properties at room and elevated temperatures in commercial AM50(Mg-5%Al-0.3%Mn) and 0.3 wt%CaO added ECO-AM50 alloys produced by permanent mould casting. The typical microstructure of AM50 alloy was distinctively characterized using two intermetallic compounds, ${\beta}(Mg_{17}Al_{12})$ and $Al_8Mn_5$, along with ${\alpha}$-(Mg) matrix in an as-cast state. The addition of a small amount of CaO played a role in reducing dendrite cell size and quantity of the ${\beta}$ phase in the AM50 alloy. It is interesting to note that the added CaO introduced a small amount of $Al_2Ca$ adjacent to the ${\beta}$ compounds, and that inhomogeneous enrichment of elemental Ca was observed within the ${\beta}$ phase. The ECO-AM50 alloy showed higher hardness and better YS and UTS at room temperature than did the AM50 alloy, which characteristics can be mainly ascribed to the finer-grained microstructure that originated from the CaO addition. At $175^{\circ}C$, higher levels of YS and UTS and higher elongation were obtained for the ECO-AM50 alloy, demonstrating that even 0.3 wt%CaO addition can be beneficial in promoting the heat resistance of the AM50 alloy. The combinational contributions of enhanced thermal stability of the Ca-containing ${\beta}$ phase and the introduction of a stable $Al_2Ca$ phase with high melting point are thought to be responsible for the improvement of the high temperature tensile properties in the ECO-AM50 alloy.

• Journal of Powder Materials
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• v.27 no.3
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• pp.256-267
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• 2020

Metal additive manufacturing (AM) technologies are classified into two groups according to the consolidation mechanisms and densification degrees of the as-built parts. Densified parts are obtained via a single-step process such as powder bed fusion, directed energy deposition, and sheet lamination AM technologies. Conversely, green bodies are consolidated with the aid of binder phases in multi-step processes such as binder jetting and material extrusion AM. Green-body part shapes are sustained by binder phases, which are removed for the debinding process. Chemical and/or thermal debinding processes are usually devised to enhance debinding kinetics. The pathways to final densification of the green parts are sintering and/or molten metal infiltration. With respect to innovation types, the multi-step metal AM process allows conventional powder metallurgy manufacturing to be innovated continuously. Eliminating cost/time-consuming molds, enlarged 3D design freedom, and wide material selectivity create opportunities for the industrial adoption of multi-step AM technologies. In addition, knowledge of powders and powder metallurgy fuel advances of multi-step AM technologies. In the present study, multi-step AM technologies are briefly introduced from the viewpoint of the entire manufacturing lifecycle.

• Journal of Microbiology and Biotechnology
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• v.21 no.1
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• pp.28-36
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• 2011

Diblock copolymers composed of poly(${\varepsilon}$-caprolactone) (PCL) and poly(N,N-dimethylamino-2-ethyl methacrylate) (PDMAEMA), or methoxy polyethylene glycol(PEG), were synthesized via a combination of ring-opening polymerization and atom-transfer radical polymerization in order to prepare polymeric nanoparticles as an antifungal drug carrier. Amphotericin B (AmB), a natural antibiotic, was incorporated into the polymeric nanoparticles. The physical properties of AmB-incorporated polymeric nanoparticles with PCL-b-PDMAEMA and PCL-b-PEG were studied in relation to morphology and particle size. In the aggregation state study, AmB-incorporated PCL-b- PDMAEMA nanoparticles exhibited a monomeric state pattern of free AmB, whereas AmB-incorporated PCL-b- PEG nanoparticles displayed an aggregated pattern. In in vitro hemolysis tests with human red blood cells, AmBincorporated PCL-b-PDMAEMA nanoparticles were seen to be 10 times less cytotoxic than free AmB (5 ${\mu}g$/ml). In addition, an improved antifungal activity of AmBincorporated polymeric nanoparticles was observed through antifungal activity tests using Candida albicans, whereas polymeric nanoparticles themselves were seen not to affect activity. Finally, in vitro AmB release studies were conducted, proving the potential of AmB-incorporated PCL-b-PDMAEMA nanoparticles as a new formulation candidate for AmB.

• Korean Journal of Materials Research
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• v.19 no.6
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• pp.305-312
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• 2009

The effects of Quenching and Partitioning (Q&P) and Annealed Martensite (AM) heat treatment on the microstructure and tensile properties were investigated for 0.24C-0.5Si-1.5Mn-1Al steels. The Q&P steels were annealed at a single phase ($\gamma$) or a dual phase (${\gamma}+{\alpha}$), followed by quenching to a temperature between $M_s$ and $M_f$. Then, enriching carbon was conducted to stabilize the austenite through the partitioning, followed by water quenching. The AM steels were intercritically annealed at a dual phase (${\gamma}+{\alpha}$) temperature and austempered at $M_s$ and $M_s{\pm}50^{\circ}C$, followed by cooling in oil quenching. The dual phase Q&P steels showed lower tensile strength and yieldyield strength than those of the single phase Q&P steels, and tThe elongation for the dual phase Q&P steel was partitioning 100s higher than that of that for the single phase Q&P steels as the partitioning time was less than 100s up to partitioning 100s. For AM steels, the tensile/yield strength decreased and the total elongation increased as the austempering temperature increased. The stability of the retained austenite controlled the elongation for Q&P steels and the volume fraction of the retained austenite controlled the elongation for AM steels.

• Korean Journal of Materials Research
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• v.6 no.6
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• pp.644-650
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• 1996

Diglycidy1 ether of bisphenol A (DGEBA)/4,4'-methylene dianiline(MDA)계의 경화반응 속도에 미치는 pheny1 glycidy1 ether (PGE)-acetamide(AcAm)의 영향을 연구하였다. 반응성 첨가제로 사용된 PGE-AcAm는 PGE와 acetamide를 2:1의 몰 비로 혼합한 후 18$0^{\circ}C$에서 1시간 반응시켜서 합성하였으며, PGE의 에폭사이드기와 AcAm의 아민기가 반응함으로써 수산기를 형성함에 의해 진행되었다. 이 때 생성된 수산기는 DGEBA와 MDA의 반응에서 촉매로 작용하여 반응속도를 크게 활성화 에너지는 11.11 Kcal/mol이었고, 30 phr의 PGE-AcAm이 첨가된 계의 활성화 에너지는 7.91Kcal/mol이었다.

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.180-180
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• 1994