• Korean Journal of Metals and Materials
• /
• v.48 no.11
• /
• pp.1003-1008
• /
• 2010

In this study, the effect of the reinforcement on the wear behaviour and mechanical properties of hypereutectic Al-Si alloys was investigated. The Gas atomized hypereutectic Al-20Si alloy powders were mixed with 1, 3, and 5 wt.% AlN and TiC ceramic particles and consolidated by hotpress. The Al-20Si powder has both finely dispersed primary Si phases and eutectic structures. The Al-20Si-AlN, TiC composites showed that the reinforcements were distributed along the boundary of the Al-20Si alloy. The UTS increased with increasing the AlN, TiC contents. At a lower load, with an increasing weight fraction of reinforcements, the wear rate decreased in both composites and the wear mechanism was adhesive wear. At a higher load, the shape of the debris changes the mechanism of the AlN composites to abrasive-adhesion wear and this resulted in an increase of the wear rate.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1301-1302
• /
• 2006

Sintered composites of Al-8wt%Cu-10vol%SiCp were deformed by repressing or equal channel angular pressing(ECAP) at room temperature, $500^{\circ}C$ and $600^{\circ}C$. Repressing produced more densification than ECAP but resulted in much lower transverse rupture strengths. In both cases, deformation at room temperature and $500^{\circ}C$, resulted in much lower strengths than deformation at $600^{\circ}C$, and also caused the fracturing of some SiC particles. The higher bend strengths and less SiC fracturing at $600^{\circ}C$ are attributable to the presence of an Al-Cu liquid phase during deformation. The employment of copper coated SiC instead of bare SiC particles for preparing the composites was found not improving the properties.

• Journal of Korea Foundry Society
• /
• v.10 no.1
• /
• pp.43-49
• /
• 1990

The influences of Cu and Mg addition on wear properties of SiC particulate reinforced Al-Si metal(alloy) matrix composites were investigated. Metal matrix composites were prepared by combination of compocasting and hot pressing techniques. The main results obtained are as follows : 1) The composite with Mg addition exhibits letter wear resistance than that with Cu addition. It is considered that Mg addition improved wettability of matal matrix composite by the strong segregation to the SiC / Al matrix interface. 2) After homogenization treatment, it was found that the interfacial segregation of Mg was predominant, while that of Cu was not detected. 3) The SiC / Al-11Si eutectic composite exhibits better wear resistance than the SiC / Al-6Si hypoeutectic composite does. 4) It seems that the increase in the amount of Mg addition affects on the uniform dispersion of SiC particulates, on the refinement of microstructure and on age hardening and these effects cause wear resistance improvement of composites.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.1
• /
• pp.122-131
• /
• 1995

The research trends for metal matrix composites have been on basic mechanical properties, fatigue behavior after aging and fractographic observations. In this study, the fatigue crack initiation as well as the fatigue crack growth behavior and the fracture mechanism were investigated through observations of the fracture surface on silicon carbide particles reinforced aluminum metal matrix composites(SiCp/Al). Based on the fractographic study done by scanning electron microscope and replica, crack growth path model and fracture mechanism are presented. The mechanical properties, such as the tensile strength, yield strength and elongation of SiCp/Al composites are improved in a longitudinal direction, however, the fatigue life is shorter than the basic Al6061 alloys. From fractographic observations, it is found that the failure mode is ductile in basic Ai6061 alloys. And because some SiC particles were pulled out from the matrix and a few SiC particles could be seen on the fracture surface of SiCp/Al, crack growth paths are believed to follow the interface of the matrix and its particles.

• Journal of Powder Materials
• /
• v.9 no.1
• /
• pp.11-18
• /
• 2002

The 6061 Al alloy based composites reinforced with 10 vol% SiC whiskers were prepared by powder metallurgy with the powders having the different sizes, i.e. < $30{\mu}m$ and > $30{\mu}m$ The composites were subjected to equal channel angular pressing (ECAP) at various conditions and the microstructural changes during ECAP were examined In the composites SiC whiskers were clustered and randomly aligned. The clusters were relatively well distributed in the composite with the smaller initial powder size. After ECAP, the clusters were aligned parallel to flow direction and became smaller. In addition, the shape of clusters was changed from irregular to round. The microstructure of the ECAPed samples were compared with those of the conventionally hot-extruded composites. The uniform microstructure and enhanced microhardness could be obtained by using the powders having the smaller size, decreasing ECAP temperature and repeating ECAP.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.50 no.11
• /
• pp.544-549
• /
• 2001

The mechanical and electrical properties of the hot-pressed and pressureless annealed SiC-39vo1.%TiB$_2$electroconductive ceramic composites were investigated as functions of the liquid additives of $Al_2O_3+Y_2O_3$ and the sintering temperature. The result of phase analysis for the SiC-39vo1.%TiB$_2$ composites by XRD revealed $\alpha -SiC(6H),\; TiB_2,\; and YAG(Al_5Y_3O_{12})$ crystal phase. The relative density of SiC-39vo1.% $TiB_2$ composites was increased with increased $Al_2O_3+Y_2O_3$ contents. The fracture toughness showed the highest value of $7.8 MPa.m_{1/2}$ for composites added with 12 wt% $Al_2O_3+Y_2O_3$additives at $1750^{\circk}C$. The electrical resistivity of the SiC-39vo1.%$TiB_2$composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $25S^{\circ}C \;to\; 700^{\circ}C$.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.53 no.7
• /
• pp.352-357
• /
• 2004

The composites were fabricated, respectively, using 61vol.% SiC - 39vol.% TiB$_2$ and using 61vo1.% SiC - 39vo1.% WC powders with the liquid forming additives of 12wt% $Al_2$O$_3$＋Y$_2$O$_3$ by pressureless annealing at 180$0^{\circ}C$ for 4 hours. Reactions between SiC and transition metal TiB$_2$, WC were not observed in this microstructure. The result of phase analysis of composites by XRD revealed SiC(6H), TiB$_2$ and YAG(Al$_{5}$Y$_3$O$_{12}$) crystal phase on the SiC-TiB$_2$, and SiC(2H), WC and YAG(Al$_{5}$Y$_3$O$_{12}$) crystal phase on the SiC-WC composites. $\beta$\$\longrightarrow$$\alpha$-SiC phase transformation was ocurred on the SiC-TiB$_2$, but $\alpha$\$\longrightarrow$$\beta$-SiC reverse transformation was not occurred on the SiC-WC composites. The relative density, the vicker's hardness, the flexural strength and the fracture toughness showed respectively value of 96.2%, 13.34GPa, 310.19Mpa and 5.53Mpaㆍml/2 in SiC-WC composites. The electrical resistivity of the SiC-TiB$_2$ and the SiC-WC composites is all positive temperature coefficient resistance(PTCR) in the temperature ranges from $25^{\circ}C$ to 50$0^{\circ}C$. 2.64${\times}$10-2/$^{\circ}C$ of PTCR of SiC-WC was higher than 1.645${\times}$10-3/$^{\circ}C$ of SiC-TiB$_2$ composites.posites.

• Proceedings of the KIEE Conference
• /
• 1998.11c
• /
• pp.847-849
• /
• 1998

The effect of $Al_{2}O_{3}$ additives on the microstructure, mechanical and electrical properties of ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composites by pressureless sintering were investigated. The ${\beta}$-SiC+39vol.%$ZrB_2$ ceramic composites were pressureless sintered by adding 4, 8, 12wt.% $Al_{2}O_{3}$ powder as a liquid forming additives at $1950^{\circ}C$ for 1h. Phase analysis of composites by XRD revealed mostly of $\alpha$-SiC(6H), $ZrB_2$ and weakly $\alpha$-SiC(4H), $\beta$-SiC(15R) phase. The relative density of composites was lowered by gaseous products of the result of reaction between $\beta$-SiC and $Al_{2}O_{3}$ therefore, porosity was increased with increased $Al_{2}O_{3}$ contents. The fracture toughness of composites was decreased with increased $Al_{2}O_{3}$ contents, and showed the maximum value of $1.4197MPa{\cdot}m^{1/2}$ for composite added with 4wt.% $Al_{2}O_{3}$ additives. The electrical resistivity of ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composite was increased with increased $Al_{2}O_{3}$ contents, and showed positive temperature coefficient resistance (PTCR) in the temperature from $25^{\circ}C$ to $700^{\circ}C$.

• Journal of Korea Foundry Society
• /
• v.20 no.4
• /
• pp.254-259
• /
• 2000

Metal matrix composites(MMCs) reinforced with hard particles have many potential application in aerospace structures, auto parts, semiconductor package, heat resistant panels, wear resistant materials and so on. In this work, the effect of SiC partioel sizes(50 and 100 ${\mu}m$) and additional elements such as Si, Cu and Ti on the microstructure and the wear property of $Al-5Mg-X(Si,Cu,Ti)/SiC_p$ composites produced by pressureless infiltration method have been investigated using optical microscopy, scanning eletron microcopy(SEM) with EDS(energy dispersive spectrometry), hardness test, X-ray diffractometer(XRD) and wear test. In present study, the sound $Al-5Mg-X(Si,Cu,Ti)/SiC_p$(50 and 100 ${\mu}m$) composites were fabricated by pressureless infiltration method. The $Al-5Mg-0.3Si-O.1Cu-O.1Ti/SiC_p$ composite with $50 {\mu}m$ size of SiC particle has higher hardness and better wear property than any other composite with $100{\mu}m$ size of SiC particle produced by pressureless infiltration method. The hardness and wear property of $Al-5Mg/SiC_p$(50 and 100 ${\mu}m$) composites were enhanced by the addition of Si, Cu and Ti in Al-5%Mg matrix alloy.

• Proceedings of the KIEE Conference
• /
• 2008.07a
• /
• pp.1230-1231
• /
• 2008

The effect of content of $Al_2O_3+Y_2O_3$ sintering additives on the densification behavior, mechanical and electrical properties of the pressureless-sintered $SiC-ZrB_2$ electroconductive ceramic composites was investigated. The $SiC-ZrB_2$ electroconductive ceramic composites were pressureless-sintered for 2 hours at 1,700[$^{\circ}C$] temperatures with an addition of $Al_2O_3+Y_2O_3$(6:4 mixture of $Al_2O_3$ and $Y_2O_3$) as a sintering aid in the range of 8${\sim}$20[wt%]. Phase analysis of $SiC-ZrB_2$ composites by XRD revealed mostly of ${\alpha}$-SiC(6H), $ZrB_2$ and In Situ YAG($Al_5Y_3O_{12}$). The relative density, flexural strength, Young's modulus and vicker's hardness showed the highest value of 89.01[%], 81.58[Mpa], 31.437[GPa] and 1.34[GPa] for $SiC-ZrB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature respectively. Abnormal grain growth takes place during phase transformation from ${\beta}$-SiC into ${\alpha}$-SiC was correlated with In Situ YAG phase by reaction between $Al_2O_3$ and $Y_2O_3$ additive during sintering. Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites. In this paper, it is convinced that ${\beta}$-SiC based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.