• 한국결정성장학회지
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• 제13권6호
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• pp.309-314
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• 2003

방전 플라즈마 소결법을 적용하여 $Al_2O_3$-SiC 나노 복합체를 150$0^{\circ}C$ 이하의 온도에서 완전치밀화를 이루었다. 제조된 $Al_2O_3$-SiC 복합체는 이상 결정립 성장 없이 매우 균질한 미세구조를 형성하고 있는데, 첨가된 SiC 입자는 주로 결정립 내 및 결정립계에 존재하면서 $Al_2O_3$기지상에서 결정립 성장을 억제하는데 매우 유호하였음을 확인 할 수 있다. 한편, SiC 입자의 첨가는 크랙 회절 및 브릿징 등에 의해서 유도된 재료 강도 및 인성 강화 기구에 의해서 $Al_2O_3$-SiC 복합체의 기계적 물성을 크게 향상시켰다.

• 한국표면공학회지
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• 제54권5호
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• pp.230-237
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• 2021

In this study, the influence of silicon contents on the microstructure, mechanical and tribological properties of Ti-Al-Si-N coatings were systematically investigated for application of cutting tools. The composition of the Ti-Al-Si-N coatings were controlled by different combinations of TiAl₂ and Ti₄Si composite target powers using an arc ion plating technique in a reactive gas mixture of high purity Ar and N₂ during depositions. Ti-Al-Si-N films were nanocomposite consisting of nanosized (Ti,Al,Si)N crystallites embedded in an amorphous Si₃N₄/SiO₂ matrix. The instrumental analyses revealed that the synthesized Ti-Al-Si-N film with Si content of 5.63 at.% was a nanocomposites consisting of nano-sized crystallites (5-7 nm in dia.) and a three dimensional thin layer of amorphous Si₃N₄ phase. The hardness of the Ti-Al-Si-N coatings also exhibited the maximum hardness value of about 47 GPa at a silicon content of ~5.63 at.% due to the microstructural change to a nanocomposite as well as the solid-solution hardening. The coating has a low friction coefficient of 0.55 at room temperature against an Inconel alloy ball. These excellent mechanical and tribological properties of the Ti-Al-Si-N coatings could help to improve the performance of machining and cutting tool applications.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.134-134
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• 2016

CMC(Ceramic Matrix Composites)는 $1500^{\circ}C$ 이상의 고온에서 내열성, 내산화성, 내식성이 우수하여, 초음속 비행체, 가스터빈 엔진 및 원자로용 초고온 부품 등에 수요가 증가하고 있다. 하지만 이러한 특성은 비산소 환경에 국한되는 것으로 약 $400^{\circ}C$ 이상의 산화 분위기에는 탄소섬유가 산화되는 문제로 인하여 적용의 한계를 가지고 있다. 따라서 CMC의 적용범위 확대를 위하여 내산화 코팅으로 CMC의 초고온 산화특성을 개선하는 것이 필수적이며, 장시간 초고온 산화환경 분위기에서 사용되기 위하여 안정적인 코팅기술이 최근 기술개발의 핵심현안으로 부각되고 있다. 본 연구에서는 pack cementation 공정을 이용하여 내산화성이 우수한 SiC 코팅층을 제조하였다. Pack cementation 공정에 사용된 코팅 분말은 57wt.% SiC, 30wt.% Si, 3wt.% B, 10wt.% Al2O3의 비율로 혼합된 것이다. 실험은 3D 직조된 CMC 모재를 혼합분말 내에 침적한 후, Ar 분위기에서 $1600^{\circ}C$, 4~12시간 반응시켜 수 마이크론 두께의 SiC 코팅층을 형성하였다. 더 우수한 산화 특성을 부여하기 위하여 pack 처리된 CMC 표면에 초고온 세라믹인 TaC 소재를 진공플라즈마 코팅 공정으로 적층시켰다. 제조된 코팅층을 SEM, XRD를 이용하여 미세구조 및 결정구조를 분석하였으며, pack cementation에 따른 내산화 특성을 비교 분석하고자 $2000^{\circ}C$에서 산화 실험을 진행하였다. 산화 실험 이후 미세구조 및 결정구조 분석으로 산화거동을 규명하고자 하였다.

• 한국산학기술학회논문지
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• 제12권7호
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• pp.2931-2938
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• 2011

2상 복합재에 적용되어오던 수정된 Eshelby 모델(MEM)을 두 종류의 구형 입자를 포함하는 3상 복합재로 확장하여 복합재의 등가열전도계수를 간단히 양함수 형태로 표시한다. 이의 유효성 검증을 위해 이 결과를 미소등가물모델(DEMM)로 구한 결과와 비교하고, 또 참고문헌의 2상 및 3상 복합재의 실험결과와 비교한다. 2상 복합재의 경우 MEM이 충전재의 체적비 0.5 미만에서는 DEMM보다 잘 예측한다. 3상 복합재의 경우 모재 대비 큰 열전도계수비를 갖는 충전재의 체적비가 적은 경우 MEM이 잘 예측하나, 체적비가 증가할수록 DEMM이 잘 예측한다. 이 체적비가 두 모델의 예측결과에 결정적 영향을 주는 인자임이 변수들의 영향 연구를 통해 밝혀졌으며, Molina 등이 제안한 3상 복합재에 대해 MEM과 DEMM은 동등한 예측 수준을 보였다.

• 대한기계학회논문집A
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• 제23권6호
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• pp.1048-1054
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• 1999

It is important to study the shielding effectiveness(SE) of reinforcing material of plastic composite materials against the electromagnetic(EM) waves. In this paper, SE of the shielding material of EM waves was investigated with actual experiments. The materials used in this study were made up of film, fiber and powder of conductive materials - Cu, Al, CF etc. Also, The resin film was used as matrix. The experiment was carried out by using a shielding evaluator(Shielding box) TR17302 with an ADVANTEST spectrum analyzer, model R3361C. It was found from the experimental results that copper, aluminum and carbon fiber were good candidates as a shielding material against the EM waves with increasing the SE as the composite was laminated. The characteristics of the SE against the EM waves depended on a mode of preparation of specimen. The effects of interval of wires on the SE were studied when the orientation and the space of Cu wires were changed. The SE strongly depended on the. orientation and the space of the Cu wire. SE decreased as the space of the Cu wires was increasing.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.95-98
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• 2005

This paper proposes the solutions predicting the coefficient of the thermal expansion changes of composites which include the fiber-like shaped ($a_1$ > ($a_2$ = ($a_3$) and the disk-like shaped (al = a2> a3) inclusions like two dimensional geometries, which has one aspect ratios, ${\alpha}$ = ($a_1$ /($a_3$). The analysis follows the procedure developed for elastic moduli by using the generalized approach of Eshelby’s equivalent tensor. The influences of the aspect ratios, on the effective coefficient of thermal expansion of composites containing aligned isotropic inclusions are examined. This model should be limited to analyze the composites with unidirectionally aligned inclusions and with complete binding to each other of both matrix and inclusions having homogeneous properties. The coefficient of thermal expansion of composites (${\theta}_{11}$,${\theta}_{22}$and ${\theta}_{33}$) are investigated. From material data of the composites with glass fiber in epoxy resin, the thermal expansions along the aspect ratio were obtained and similar to the Chow model. The longitudinal coefficients of thermal expansion ${\theta}_{11}$decrease, as the aspect ratios increase. However, the transverse coefficients of thermal expansion ${\theta}_{22}$increase or decrease, as the aspect ratios increase. And both of them decrease, as the concentration increases.

• Journal of Industrial and Engineering Chemistry
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• 제68권
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• pp.173-179
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• 2018

Electrochemical characterization was conducted on poly(vinyl alcohol) (PVA)-ceramic composite (PVA-CC) separators for supercapacitor applications. The PVA-CC separators were fabricated by mixing various ceramic particles including aluminum oxide ($Al_2O_3$), silicon dioxide ($SiO_2$), and titanium dioxide ($TiO_2$) into a PVA aqueous solution. These ceramic particles help to create amorphous regions in the crystalline structure of the polymer matrix to increase the ionic conductivity of PVA. Supercapacitors were assembled using PVA-CC separators with symmetric activated carbon electrodes and electrochemical characterization showed enhanced specific capacitance, rate capability, cycle life, and ionic conductivity. Supercapacitors using the $PVA-TiO_2$ composite separator showed particularly good electrochemical performance with a 14.4% specific capacitance increase over supercapacitors using the bare PVA separator after 1000 cycles. With regards to safety, PVA becomes plasticized when immersed in 6 M KOH aqueous solution, thus there was no appreciable loss in tear resistance when the ceramic particles were added to PVA. Thus, the enhanced electrochemical properties can be attained without reduction in safety making the addition of ceramic nanoparticles to PVA separators a cost-effective strategy for increasing the ionic conductivity of separator materials for supercapacitor applications.

• 한국주조공학회지
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• 제14권3호
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• pp.274-284
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• 1994

SiC fibers were coated with Cu, Ag and Ni metallic thin films by magnetron sputtering in order to improve wetting properties between Al matrix and SiC fiber. The wetting behavior of metal coated SiC fiber by pure Al has been studied at $670^{\circ}C{\sim}900^{\circ}C$ range for $10{\sim}90min$. under vacuum atmosphere. Besides, the effect of coated film thickness on the wettability has been investigated. The wetting behavior and interfacial reaction between Al and SiC fibers were analysed with optical microscope and SEM (scanning electron microscope). The wetting behavior of the as-received SiC fiber with Al melt was not uniform, indicated by the contact angles from less than $90^{\circ} to more Al melt was appeared in the initial stage of reation. It was considered that the metallic thin film played an important role in reducing the interfacial free energy and breaking down the aluminum oxide film by eutectic reaction with Al melt. However the wettability of Ni coated SiC fiber was not improved as much as that of Cu or Ag coated SiC fiber. The improvement of wettability by coating thickness is clearly showed in $1{\mu}m$ coated SiC fiber compared with $0.25{\mu}m$ coated SiC.

• 대한기계학회논문집A
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• 제20권11호
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• pp.3474-3490
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• 1996

A metal matrix composites(MMCs) for A16061 reinforced with silicon carbide particles is fabricated by melt-stirring method. The primary products of MMCs billets are prepared by volume fractions 5 vol% to 20 vol% and particle size $13\mu m$ to $22\mu m$.This paper will be made to examine the microstructure and mechanical properties of fabricated $SiC_p$/Al 6061 composite by melt-stirring and squeeze casting method. The MMC billets is extruded at $500^{\circ}C$ under the constant extrusion velocity $V_e$=2mm/min using curved shape die. Extrusion force, particle rearrangement, micro structure and mechanical properties of extruded composites will be investigated. The mechanical properties of primary billets manufactured by melt-stirring and squeeze casting method will be compared with extrusion specimen. The effect of volume fraction and size of the reinforcements will be studied. The increase in uniformity of particle dispersion is the major reason for an improvement in reliability due to hot extrusion with optimal shape die. Experimental Young's modulus and 0.2% offset yield strength for the extruded MMCs will be compared with theretical values calculated by the Eshelby method. A method will be proposed for the prediction of Young's modulus and yield strength in $SiC_p$ reinforced MMCs.

• 한국주조공학회지
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• 제23권1호
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• pp.30-39
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• 2003

Porous hybrid preforms were fabricated by reactive sintering using the compacts consisting of SiC particles, Fe and Al powders. Squeeze casting processing was employed to produce the composite in which the matrix phase is Al-Si7Mg. The microstructural change and wear resistance of the composites were investigated in terms of an amount of SiC particles. The wear loss was increased with increasing the contact pressure in the alloy containing SiC particles coated with Cu. The most drastic change was found to the specimen tested at 2.5 MPa of contact pressure. Concerning the alloys containing SiC particles coated with Ni-P, a drastic increase in the wear loss exhibited at 2 MPa of contact pressure in those alloys containing 4 and 8 wt. % of SiC particles coated with Ni-P. In the alloy containing 16 wt. % a proportional increase in wear loss was observed to the change of contact pressure. With respecting to the sliding velocity, the wear loss of the alloy containing SiC particles coated with Cu increased at the initial stage of wear process and then decreased. Similar result was found in the alloys containing SiC particles coated with Ni-P. On the basis of the present results obtained, it was found that wear resistance of the alloys tested was improved to show in the order of the alloy reinforced by coated SiC particles > by uncoated SiC particles > by intermetallic compound without SiC particles.