• 한국주조공학회지
• /
• 제11권3호
• /
• pp.208-216
• /
• 1991

The solidification behavior of the squeeze cast composites of aluminum alloys reinforced with boron fiber($100{\mu}m$) and silicon carbide fibers($140{\mu}m$ and $15{\mu}m$) were investigated. Al-4.5wt%Cu and Al-l0wt%Mg were chosen for the matrix phase of the composites. In the squeeze cast specimen with high thermal difference between fiber and melt, the average secondary dendrite arm spacing(DAS) in reinforced alloy is smaller than that in unreinforced alloy. It was also observed that primary ${\alpha}$ and non-equilibrium eutectic, which seems to be penetrated and solidified at the final stage of the solidification of the matrix, are irregularly distributed around fibers. It is considered that cold fibers serve as heterogeneous nucleation site. While in the remelted and resolidified specimen without temperature difference, the DAS was not changed with reinforcement and microstructure reveals non-equilibrium eutectic with relatively uniform thickness around fibers. It might be evident the nucleation starts at interfiber region. Microsegregation decreases with the decrease in cooling rate and with reinforcement in the as-squeeze cast specimen. Al-10wt% Mg alloy shows less microsegregation than Al-4.5wt%Cu alloy.

• 한국세라믹학회지
• /
• 제55권4호
• /
• pp.392-399
• /
• 2018

$C_f/SiC$ composites were prepared via a process combining chemical vapor infiltration (CVI) and precursor infiltration pyrolysis (PIP), wherein silicon carbide matrices were infiltrated into 2.5D carbon preforms. The obtained composites exhibited porosities of 20 vol % and achieved strengths of 244 MPa in air at room temperature and 423 MPa at $1300^{\circ}C$ under an Ar atmosphere. Carbon fiber pull-out was rarely observed in the fractured surfaces, although intermediate layers of pyrolytic carbon of 150 nm thickness were deposited between the fiber and matrix. Fatigue fracture was observed after 1380 cycles under 45 MPa stress at $1000^{\circ}C$. The fractured samples were analyzed by transmission electron microscopy to observe the distributed phases.

• Composites Research
• /
• 제33권5호
• /
• pp.247-250
• /
• 2020

본 연구에서는 액상가압성형 공정을 이용하여 SiC 연속섬유가 강화된 마그네슘 복합재료의 제조 가능성을 검토하였다. 액상가압성형 공정을 이용하여 SiC 섬유가 균일 분산된 AZ91 복합재료를 제조하였으며 열처리를 통하여 석출상을 제어하였다. SiC 섬유와 기지합금의 계면에 연속적인 Mg₂Si상이 형성되면서 계면 결합력이 향상되었고, 제조된 복합재료의 상온 인장강도는 479 MPa로 우수한 기계적 특성을 나타내었다.

• Composites Research
• /
• 제30권2호
• /
• pp.116-125
• /
• 2017

본 연구의 목적은 고온 산화성 분위기하에서 기계적물성이 우수한 탄화규소섬유(SiC Fiber)를 파일롯-규모로의 생산 제조공정을 개발하는 것이다. 프리세라믹 전구체로서 폴리카보실란(PCS)을 사용하여 탄화규소섬유를 제조하였다. 연속성의 PCS 섬유는 $300{\sim}350^{\circ}C$에서 PCS를 용융한 후에 용융방사로부터 얻었다. 열처리 전에 섬유의 불융화를 위하여 공기 분위기하에서 경화를하였다. 경화 전, 후에 측정한 FT-IR 스펙트라 피크로 부터 경화도를 계산하였다. 탄화규소섬유의 물성은 경화도에 따라 크게 영향을 받았다. 본 개발에서 열처리 중 섬유의 장력 조절로 우수한 물성을 갖는 탄화규소섬유를 얻었다. 탄화규소섬유의 화학조성과 기계적물성은 안정화섬유의 열처리시의 이송속도에 영향을 받았다. 탄화규소섬유를 공기분위기하 $1000^{\circ}C$에서 1분부터 50시간까지 노출한 후에 인장시험을 수행하였다. 그 결과 인장강도는 약 60%까지 감소함을 보여주었다. 장시간 노출시험시 낮은 인장 강도값을 나타내는 섬유는 화학성분 분석시 섬유의 표면에 많은 탄소량을 함유하고 있었다.

• 한국세라믹학회지
• /
• 제47권6호
• /
• pp.485-490
• /
• 2010

In our previous studies, continuous SiC fiber-reinforced SiC-matrix composites ($SiC_f$/SiC) had been fabricated by two different slurry infiltration methods: vacuum infiltration and electrophoretic deposition (EPD). 12 wt% of $Al_2O_3-Y_2O_3$-MgO with respect to SiC powder was used as additives for liquid-phase assisted sintering. After hot pressing at $1750^{\circ}C$ under 20 MPa for 2 h in Ar atmosphere, a high composite density could be achieved for both cases, whereas the problems such as large grain size and non-uniform distribution of liquid phase were observed, which was resulted in the relatively poor mechanical properties of composites. Therefore, efforts have been made to reduce the grain growth during the sintering, including the optimization for hot pressing condition and utilization of spark plasma sintering using a SiC monolith. Based on the results, spark plasma sintering was found to be effective method in decreasing the amount of sintering additive, time and grain growth, which will be explained in comparison to the results of hot pressing in this paper.

• 한국정밀공학회지
• /
• 제27권12호
• /
• pp.28-32
• /
• 2010

Technical demands for aspheric glass lens formed in market increases its application from simple camera lens module to fiber optics connection module in optical engineering. WC is often used as a metal core of the aspheric glass lens, but the long life time is issued because it fabricated in high temperature and high pressure environment. High hard thin film coating of lens core increases the core life time critically. Diamond Like Carbon(DLC) thin film coating shows very high hardness and low surface roughness, i.e. low friction between a glass lens and a metal core, and thus draw interests from an optical manufacturing industry. In addition, DLC thin film coating can removed by etching process and deposit the film again, which makes the core renewable. In this study, DLC films were deposited on the SiC ceramic core. The process variable in FVA(Filtered Vacuum Arc) method was the substrate bias-voltage. Deposited thin film was evaluated by raman spectroscopy, AFM and nano indenter and measured its crystal structure, surface roughness, and hardness. After applying optimum thin film condition, the life time and crystal structure transition of DLC thin film was monitored.

• The Korean Journal of Ceramics
• /
• 제4권4호
• /
• pp.382-386
• /
• 1998

titanate and a silicon carbide/zirconium diboride particulate composite have each been blended with thermoplastic of aqueous binders and extruded. The green extrudates have diameters ranging between 50 and 150 ㎛ and polyethylene-base 150 ${\mu}m$ diameter fibers can be drawn down at elevated temperature to approximately 40 ${\mu}m$ diameter. Hollow fibers with 150${\mu}m$ outer and 90 ${\mu}m$ inner diameter can also be fabricated. Green fibers have been processed into chopped fiber felts for use as gas distributors/current collectors in an experimental solid oxide fuel cell (SOFC) and the first attempts at producing simple textile structures have been successful. The fibers, tubes and felts have been successfully debound and sintered and characterization of the sintered PSZ fibers, for example, has revealed a density in excess of 99% and tensile failure stresses up to 1.0 GPa for 78 ${\mu}m$ diameter fibers.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2003년도 춘계학술대회 논문집
• /
• pp.294-299
• /
• 2003

The efficiency of complex slurry preparation route for the development of high performance RS-SiCf/SiC composites has been investigated. The green bodies for RS-SiC and RS-SiCf/SiC composite materials prior to the infiltration of molten silicon were prepared with various C/SiC complex matrix slurries, which associated with both different sizes of starting SiC particles and blending ratios of starting SiC and carbon particles. The reinforcing materials in the composite system were uncoated and C coated Tyranno SA SiC fiber. The characterization of RS-SiC and RS-SiCf/SiC composite materials was examined by means of SEM, EDS and three point bending test. Based on the mechanical property-microstructure correlation, process optimization methodology is discussed.

• 방사선산업학회지
• /
• 제4권3호
• /
• pp.265-269
• /
• 2010

Silicon-based non-oxide ceramic carbide fiber is one of the leading candidate ceramic materials for engineering applications because of its excellent mechanical properties at high temperature and good chemical resistance. In this study, polycarbosilane(PCS) and zirconium butoxide were used as a precursor to prepare polyzirconocarbosilane (PZC) fibers. A polymer solution was prepared by dissolving PCS in zirconium butoxide (50/50 wt%). This solution was heated at $250^{\circ}C$ in a nitrogen atmosphere for 2 hour with stirring, and then dried in a vacuum oven for 48 hour. PZC fibers were fabricated using an electrospinning technique. The fibers were irradiated with an electron beam to induce structural crosslinking. Crosslinked PZC fibers were heat treated at $1,300^{\circ}C$ in a nitrogen atmosphere. The microstructures of PZC fibers were examined by SEM. Chemical structures of PZC fibers were examined by FT-IR and XRD. Thermal stability of PZC fibers was investigated by TGA.

• 한국세라믹학회지
• /
• 제50권6호
• /
• pp.364-371
• /
• 2013

The sintering behavior of monolithic SiC is examined using the binary sintering additive of $Al_2O_3$-rare earth oxide ($RE_2O_3$, where RE = Sc, Nd, Dy, Ho, or Yb). Through hot pressing at 20 MPa and $1750^{\circ}C$ for 1 h in an Ar atmosphere for 52 nm fine ${\beta}$-SiC powder added with 5 wt% sintering additive, a SiC density of > 97% is achieved, which indicates the effectiveness of $Al_2O_3-RE_2O_3$ system as a sintering of additive for SiC. Based on this result, 7 wt% of $Al_2O_3-Sc_2O_3$ is tested as an additive system for the fabrication of a continuous SiC fiber-reinforced SiC-matrix composite ($SiC_f$/SiC). Electrophoretic deposition combined with the application of ultrasonic pulses is used to efficiently infiltrate the matrix phase into the voids of $Tyranno^{TM}$-SA3 fabric. After hot pressing, a composite density of > 97% is obtained, along with a maximum flexural strength of 443 MPa.