• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.453-460
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• 2019

To reduce residual pores of composites and obtain a dense matrix, SiC_f/SiC composites were fabricated by chemical vapor deposition (CVI) using SiC nanorods. SiC nanorods were uniformly grown in the thickness direction of the composite preform when the reaction pressure was maintained at 50 torr or 100 torr at 1,100℃. When SiC nanorods were grown, the densities of the composites were 2.57 ~ 2.65 g/㎤, higher than that of the composite density of 2.47 g/㎤ for non-growing of SiC nanorods under the same conditions; grown nanorods had uniform microstructure with reduced large pores between bundles. The flexural strength, fracture toughness and thermal conductivity (room temperature) of the SiC nanorod grown composites were 412 ~ 432 MPa, 13.79 ~ 14.94 MPa·m^1/2 and 11.51 ~11.89 W/m·K, which were increases of 30%, 25%, and 25% compared to the untreated composite, respectively.

• Journal of Powder Materials
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• v.20 no.5
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• pp.345-349
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• 2013

Carbon nanotube-dispersed bismuth telluride matrix (CNT/$Bi_2Te_3$) nanopowders were synthesized by chemical routes followed by a ball-milling process. The microstructures of the synthesized CNT/$Bi_2Te_3$ nanopowders showed the characteristic microstructure of CNTs dispersed among disc-shaped $Bi_2Te_3$ nanopowders with as an average size of 500 nm in-plane and a few tens of nm in thickness. The prepared nanopowders were sintered into composites with a homogeneous dispersion of CNTs in a $Bi_2Te_3$ matrix. The dimensionless figure-of-merit of the composite showed an enhanced value compared to that of pure $Bi_2Te_3$ at the room temperature due to the reduced thermal conductivity and increased electrical conductivity with the addition of CNTs.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.390-394
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• 1999

Al2O3 particles were dispersed into carbon fiber reinforced epoxy composites to fabricate hybrid epoxy based composites. Interface behavior and mechanical properties of these hybrid composites were studied at room and liquid nitrogen temperature and liquid nitrogen temperature and the results were compared with the those of carbon fiber reinforced composites to investigate their applicability at room and cryogenic temperature. Young's modulus in-perpendicular to fiber direction and interlaminar shear strength at room temperature and the thermal contraction down to cryhogenic temperature were improved significantly by the addition of AL2O3 filler into the epoxy matrix. The effect of Al2O3 particle addition on mechanical properties were discussed.

• The Korean Journal of Ceramics
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• v.3 no.3
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• pp.169-172
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• 1997

Sintered diamond/(WC-Co) composites were prepared by spark plasma sintering technique. Tribological properties were measured at temperatures from RT to $500^{\circ}C$ in sliding tests with alumina ball. They show coefficient of friction of 0.1 and below at RT and wear of the diamond composites is hardly detected. Effects of diamond grit size, diamond content and test temperature on the coefficient of friction and the wear are discussed. The wear scars were analyzed.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.378-383
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• 2013

Continuous fiber-reinforced ceramic matrix composites (CFCCs) have a complex distribution of porosity, consisting of interfiber micro pores and interbundle/interply macro pores. Owing to the complex geometry of the pores and fiber architecture, it is difficult to obtain representative microstructural features throughout the specimen volume with conventional, destructive ceramographic approaches. In this study, we introduce X-ray computed microtomography (X-ray ${\mu}CT$) to nondestructively analyze the microstructures of disk shaped and tubular $SiC_f$/SiC composites fabricated by the chemical vapor infiltration (CVI) method. The disk specimen made by stacking plain-woven SiC fabrics exhibited periodic, large fluctuation of porosity in the stacking direction but much less variation of porosity perpendicular to the fabric planes. The X-ray ${\mu}CT$ evaluation of the microstructure was also effectively utilized to improve the fabrication process of the triple-layered tubular SiC composite.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.6
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• pp.3-9
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• 2013

Aluminum Oxide($Al_2O_3$) ceramics are excellent candidates for such applications due to their outstanding mechanical, thermal, and tribological properties. However, they are difficult to machine using conventional mechanical methods. Carbon fillers, such as carbon nanotubes(CNT) and graphene nanoplatelets(GNP)can be dispersed in a ceramic matrix to improve the mechanical and electrical properties. In this study, CNT and Graphene reinforced hybrid ceramic composites were fabricated using the spark plasma sintering method at a temperature of $1,500^{\circ}C$, pressure of 40 MPa, and soaking time of 10min. Besides this, the material properties such as microstructure, crystal structure, hardness, and electrical conductivity were analyzed using FE-SEM, XRD, Vickers, and the 4-point probe method. A micro machining test was carried out to compare the effects of the material properties and the machining performance for CNT and Graphene reinforced ceramic composites.

• Journal of Powder Materials
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• v.26 no.5
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• pp.383-388
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• 2019

To improve the mechanical properties of aluminum, graphene has been used as a reinforcing material, yielding graphene-reinforced aluminum matrix composites (GRAMCs). Dispersion of graphene materials is an important factor that affects the properties of GRAMCs, which are mainly manufactured by mechanical mixing methods such as ball milling. However, the use of only mechanical mixing process is limited to achieve homogeneous dispersion of graphene. To overcome this problem, in this study, we have prepared composite materials by coating aluminum particles with graphene by a self-assembly reaction using poly vinylalcohol and ethylene diamine as coupling agents. The scanning electron microscopy and Fourier-transform infrared spectroscopy results confirm the coating of graphene on the Al surface. Bulk density of the sintered composites by spark plasma sintering achieved a relative density of over 99% up to 0.5 wt.% graphene oxide content.

• Journal of Mechanical Science and Technology
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• v.20 no.7
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• pp.1002-1011
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• 2006

In this study, we describe the conventional hot pressing (CHP) of layered $Al-B_4C$ composites and their characterization. The matrix alloy Al-5 wt.%Cu was prepared from elemental powder mixtures. The metal and B4C powders were mixed to produce either $Al-Cu-10vol.%B_4C$ or $Al-Cu-30vol.%B_4C$ combinations. Then, these powder mixtures were stacked as layers in the hot pressing die to form a two-layered composite. Hot pressing was carried out under nitrogen atmosphere to produce $30\times40\times5mm$ specimens. Microstructural features and age hardening characteristics of composites were determined by specimens cut longitudinally. The flexural strength of both layered composites and their monolithic counterparts were investigated via three point bending tests. In the case of layered specimens of both $10vol.%B_4C$ and $30vol.%B_4C$ containing layers were loaded for three-point test. The results show that a homogeneous distribution of $B_4C$ particles in the matrix alloy which is free of pores, can be obtained by CHP method. The ageing behavior of the composites was found to be influenced by the reinforced materials, i.e. higher hardness values were reached in 8 hrs for the composites than that for the matrix alloy. Flexural strength test showed that two-layered composites exhibited improved damage tolerance depending on layer arrangement. Microstructural investigation of the fracture surfaces of the bending specimens was performed by means of scanning electron microscope (SEM). While layer with lower reinforcement content exhibited large plastic deformation under loading, the other with higher reinforcement content exhibited less plastic deformation.

• Journal of Korea Foundry Society
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• v.21 no.1
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• pp.7-14
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• 2001

The research on new DRA(discontinuous reinforced alloy) and CRA(continous reinforced alloy) composites has been carried out to improve the properties of ceramic fiber and particle reinforced metal matrix composites(MMCs). Effects of alloying elements and aging conditions on the microstructures and aging behavior of Al-Si-Cu-Mg-(Ni)-SiCp composite have been examined. The specimens used in this study were manufactured by duplex process. The first squeeze casting is the process to make precomposite and the second squeeze casting is the process to make final composite. The hardening behavior was accelerated with decreasing the size of SiCp particle in the composites. It is considered that the dislocation density increased with increasing SiCp size, due to the different thermal deformation between Al matrix and SiCp during quenching after the solution treatment. Peak aging time to obtain the maximum hardness in 3 ${\mu}m$ SiCp reinforced Al composite was reduced than that in large size(5, 10 ${\mu}m$) of SiCp because of difference in dislocation density. Aging hardening responce(${\Delta}H$ = $H_{Max}.-H_{S.T}$) of composites was greater than that of unreinforced Al alloy because of higher density of second phases in matrix.

• Journal of the Korean Ceramic Society
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• v.38 no.1
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• pp.52-55
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• 2001

Polyacrylonitrile(PAN)-based 탄소섬유와 epoxy resin matrix 내에 장착된 PAN-based 탄소섬유의 전기저항을 탄소섬유와 파괴될 때까지 인장강도를 증가시키며 측정하였다. 탄소섬유가 끊어져 측정 계기가 open-circuit을 나타내기 전까지 탄소섬유의 전기저항 값은 strain이 증가할수록 증가하였으며, epoxy resin은 탄소섬유의 저항값 측정에 거의 영향을 미치지 않았다. 탄소섬유의 저항값 변화는 strain에 대해 정확도 1% 이내로 예측(calibrate)할 수 있었으며 재현성 또한 우수하였다. 따라서 탄소섬유는 재료의 기계적 강도를 증가시키기 위해 사용될 수 있을 뿐만 아니라 구조재료의 파괴를 예측할 수 있는 스마트 센서로서도 사용할 수 있다는 가능성을 확인하였다.