• Journal of the Korean Ceramic Society
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• v.40 no.3
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• pp.301-308
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• 2003

Glass-infiltrated alumina, which can be used as an all-ceramic dental crown, was prepared. The glasses in the system of SiO$_2$-B$_2$O$_3$-Al$_2$O$_3$-CaO-La$_2$O$_3$with various amount of $Al_2$O$_3$infiltrated into a porous sintered alumina. The effect of $Al_2$O$_3$on the infiltration characteristics and its mechanical strength were studied. The corrosion of the sintered alumina by infiltrated glasses was prevented by increasing the amount of $Al_2$O$_3$in the glass batches, this increased the bending strength of the glass infiltrated alumina composite. The crack like voids in the sintered alumina was a cause of the deteriorating the mechanical strength of the composite, and this can be eliminated by sintering the alumina at 130$0^{\circ}C$. Glass infiltration under the vacuum atmosphere enhanced the hording strength of the composite up to 453$\pm$31 MPa.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05c
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• pp.15-18
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• 2001

The composites were fabricated 61 vol% $\beta$-SiC and $39vol%TiB_2$ powders with the liquid forming additives of 8, 12, 16wt% $Al_2O_3+Y_2O_3$ by hot pressing at $1730^{\circ}C$ and subsequent pressed annealing and pressureless annealing at $1750^{\circ}C$ for 4 hours to form YAG. The result of phase analysis of composites by XRD revealed $\alpha$-SiC(6H), $TiB_2$, and YAG($Al_5Y_3O_{12}$) crystal phase. The relative density of composites were increased with increasing $Al_2O_3+Y_2O_3$ contents. The fracture toughness showed the highest value of $7.77MPa{\cdot}m^{1/2}$ for composites added with 12wt% $Al_2O_3+Y_2O_3$ additives at room temperature. The electrical resistivity and the resistance temperature coefficient showed the lowest of $7.3{\times}10^{-4}{\Omega}{\cdot}cm$ and $3.8{\times}10^{-3}/^{\circ}C$, respectively, for composite added with 12wt% $Al_2O_3+Y_2O_3$ additives at room temperature. The electrical resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $25^{\circ}C$ to $700^{\circ}C$.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.105.1-105.1
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• 2012

고온가압소결으로 제조된 SiCf/SiC 복합체는 부식과 침식에 강하고 우수한 열적 성질과 고온에서의 높은 기계적 강도를 유지하는 장점을 가진 복합체다. 복합체의 파괴인성은 섬유와 기지 사이에 존재하는 열분해탄소 (PyC) 계면층에 의해 큰 영향을 받는데, 고온가압소결중 첨가되는 소결조제 ($Y_2O_3$, MgO, $Al_2O_3$)와 반응하여 계면이 손상되어 복합체의 기계적 특성치가 낮아지는 결과를 보였다. 본 연구에서는 계면의 손상을 보호하고자 PyC 계면상 위에 SiC 층을 증착하였는데 계면층과 SiC 층의 증착은 화학기상 증착법(CVD)을, 기지채움 공정은 전기영동법(EPD)과 고온가압소결방법(Hot Pressing)을 이용하여 복합체를 제조하였다. Tyranno-SA 섬유에 소스가스인 메탄을 열분해 하여 200nm 두께로 PyC 계면상을 증착하고, 두께를 달리하여 보호층으로써의 SiC 층을 single 과 double layer로 증착하였다. SiC 나노분말과 소결 첨가제인 $Y_2O_3$, $Al_2O_3$, MgO를 첨가한 슬러리를 전기영동법(EPD)을 이용하여 섬유내부에 슬러리를 함침시켰고, 이러한 프리폼을 $1750^{\circ}C$/20MPa의 조건으로 고온 가압소결 하여 $SiC_f$/SiC 복합체를 제조하였다. 이렇게 single layer와 double layer로 제조된 $SiC_f$/SiC 복합체에 대해 밀도와 미세구조를 관찰하였고, 기계적 특성을 비교하여 보호층으로써의 SiC 증착효과를 고찰하고자 하였다.

• Journal of Korea Foundry Society
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• v.16 no.2
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• pp.132-140
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• 1996

Both cast and extruded composites of SiC whisker reinforced 6061 Al alloy matrix were fabricated by high pressure infiltration of the alloy melt into the SiC preform and subsequent hot extrusion of the composite ingots. The micro structures, age hardening behavior and mechanical properties have been examined on the both cast and extruded composites of SiCw/6061. The cast composites of SiCw/6061 were obtained in which SiC whiskers were randomly oriented. Hot extrusion of these cast composites lead to alignment of the whisker in the direction of extrusion. Strengthening effect of whisker in the extruded composites is lower than that of the cast composites. The cast composites of SiCw/6061 showed higher thensile strength and lower elongation than extruded composites of SiCw/6061 at all testing temperatures. Lower tensile strength and higher elongation of the extruded composites were attributable to fine grain structures in which grain boundary sliding occruued preferentially at elevated temperatures.

• Journal of Korea Foundry Society
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• v.13 no.3
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• pp.238-247
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• 1993

Microstructure, hardness and wear characteristics of $SiC_p/Al-6.5wt%Si-1.7wt%Mg$ alloy composites fabricated by the method of rheo-compocasting and hot pressing are investigated in this study. The dispersion of SiC particles in the composites is homogeneous and the hardness improves as additional amount increases. The wear amount of the matrix metal increases highly as wear rates increase, for the wear mechanism changes from adhesive wear to melt wear, and the matrix metal was coated on the surface of revolving disc and its weight increases. In the 5vol% composites, Fe is adhered on the surface of specimen by the projection of the dispersed hard SiC particles which have net-work structure and the coating layer is about $300{\mu}m$. But in the composite more than 20vol%, the wear amount of composite decreases because the SiC particles which have superior hardness, wear resistance and heat resistance properties resist wear, the abrasive wear turn out predominant wear mechanism and so the wear amount of revolving disc increases.

• Journal of the Korean Ceramic Society
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• v.30 no.10
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• pp.785-790
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• 1993

Sialon ceramics are presently seen as promising materials with high hardness, strength, fracture toughness and corrosion resistance for friction and wear applications. The objective of present work is to improve of mechanical properties and wear resistance of $\alpha$-Sialon(x=0.4) by addition of SiC whisker. $\alpha$-sialon(x=0.4)/SiC whisker composites were obtained by hot-isostatic pressing at 173$0^{\circ}C$ for 1 hour under 1757Kg/$\textrm{cm}^2$ N2 pressure after pressureless sintering the mixture of Si3N4, Y2O3, AlN at 1780~180$0^{\circ}C$ for 3~5 hours in N2 atmosphere. As the amount of SiC whisker content increased, relative density and hardness were decreased, however fracture toughness, bending strength and tribological properties were improved. Tribological properties of $\alpha$-Sialon/15 vol% SiC whisker composite were improved in spite of its low mechanical properties.

• Composites Research
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• v.16 no.3
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• pp.75-84
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• 2003

The purpose of this study is to investigate the wear properties of Saffil/Al, Saffil/A12O3/Al and Saffil/SiC/Al hybrid metal matrix composites fabricated by squeeze casting method. Wear tests were done on a pin-on-disk friction and wear tester under both dry and lubricated conditions. The wear properties of the three composites were evaluated in many respects. The effects of Saffil fibers, $\textrm{Al}_2\textrm{O}_3$ particles and SiC particles on the wear behavior of the composites were investigated. Wear mechanisms were analyzed by observing the worn surfaces of the composites. The variation of coefficient of friction(COF) during the wear process was recorded by using a computer. Under dry sliding condition, Saffil/SiC/Al showed the best wear resistance under high temperature and high load, while the wear resistances of Saffil/Al and Saffi1/$\textrm{Al}_2\textrm{O}_3$/Al were very similar. Under dry sliding condition, the dominant wear mechanism was abrasive wear under mild load and room temperature, and the dominant wear mechanism changed to adhesive wear as load or temperature increased. Molten wear occurred at high temperature. Compared with the dry sliding condition, all three composites showed excellent wear resistance when lubricated by liquid paraffin. Under lubricated condition, Saffil/Al showed the best wear resistance among them, and its COF value was the smallest. The dominant wear mechanism of the composites under lubricated condition was microploughing, but microcracking also occurred to them to different extents.

• Composites Research
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• v.13 no.5
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• pp.31-36
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• 2000

The effect of several important processing variables was investigated on formation of porous mullite with acicular microstructure. Experimental results demonstrated that microstructure and porosity of porous mullite are depending on concentration of $AlF_3$, holding time at $900^{\circ}C$ and starting material. Acicular mullite was developed by increasing amount of $AlF_3$ and holding time at $900^{\circ}C$. Mullite began to be formed at $1200^{\circ}C$ and the resultant microstructure sintered at this temperature is similar to those at higher temperatures. Porosity increases with increase in amounts of $AlF_3$ and holding time at $900^{\circ}C$ . Therefore, it is found that microstructure of reaction-sintered porous mullite can be controlled by governing the amount of $AlF_3$ and holding time at $900^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.36 no.8
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• pp.799-804
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• 1999

Composites of SiC-Si3N4 consisted of uniformly distributed elongated $\beta$-Si3N4 grains and equiaxed $\beta$-SiC grains were fabricated with $\beta$-SiC,. $\alpha$-Si3N4 Al2O3 and Y2O3 powders. By hot-pressing and subsequent annelaing elongated $\beta$-Si3N4 grains were grown via$\alpha$longrightarrow$\beta$ phase transformation and equiaxed $\beta$-Si3N4 composites increased with increasing the Si3N4 content owing to the reduced defect size and enhanced crack deflection by elongated $\beta$-Si3N4 grains and the grain boundary strengthening by nitrogen incorporation. Typical flexural strength and fracture toughness of SiC-40 wt% Si3N4 composites were 783 MPa and 4.2 MPa.m1/2 respectively.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1061-1062
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• 2006

This paper presents a new approach for analyzing the microstructure of $SiC_p$-reinforced aluminum matrix composites from digital images. Various samples of aluminum matrix composite were fabricated by hot pressing the powder mixtures with certain volume and size combinations of pure Al and SiC particles. Microstructures of the samples were analyzed by computer-based image processing methods. Since the conventional methods are not suitable for separating phases of such complex microstructures, some new algorithms have been developed for the improved recognition and characterization of the particles in the metal matrix composites.