• Journal of the Korean Ceramic Society
• /
• v.28 no.6
• /
• pp.478-482
• /
• 1991

Numerous researchers have observed the bubble formation from C/C composite at high temperature (1300$^{\circ}C$∼1700$^{\circ}C$). According to thermodynamic calculation, the bubble can be formed at the temperatures above 1500$^{\circ}C$ in the case of SiC coated C/C composite. However, the bubble below 1500$^{\circ}C$ could not be explained. Therfore, in an effort to explain the low temperature bubble formation, the effects of inhibitors such as B, Al, Zr and Si were thermodynamically investigated along with hydrogen and water vapor impurities resolved in C/C composite and SiC coating layer.

• Journal of the Korean Ceramic Society
• /
• v.55 no.5
• /
• pp.440-445
• /
• 2018

To control the electrical properties of a SiC heating element, we sintered $SiC-ZrB_2$composites by using the spark plasma sintering method. The addition of $ZrB_2$ particles with lower electrical conductivity to the SiC matrices with comparatively higher electrical resistivity lowers the electrical resistivities of the composite material. The $ZrB_2$ particles aggregate to form large particles and 3-1, 3-2, and 3-3 networks, i.e., conduction paths. In our study, about $1-{\mu}m$-sized $ZrB_2$ powders start to form the conduction path at about 10 vol.% of addition, namely the threshold volume. The Joule heating experiment shows that 20 vol.% $ZrB_2$-added SiC heating element has outstanding heating efficiency.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1080-1081
• /
• 2006

In this investigation, $B_4C$ based ceramic composites were fabricated by in-situ reaction hot pressing using $B_4C$, TiC SiC powder as starting materials. The reaction synthesized composites by hot pressing at $1950^{\circ}C$ was found to posses very high relative density. The reaction synthesized $B_4C$ composites comprise $B_4C$, $TiB_2$, SiC and graphite by the reaction between TiC and $B_4C$. The newly formed $TiB_2$ and graphite was embedded both inside grain and at grain boundary $B_4C$. The mechanical properties of reaction synthesized $B_4C-TiB_2-SiC$-graphite composites were more enhanced compared to those of monolithic $B_4C$.

• Korean Journal of Materials Research
• /
• v.32 no.12
• /
• pp.553-559
• /
• 2022

In this work, the ablation behavior of monolith ZrB₂-30 vol%SiC (Z30S) composites were studied under various oxy-acetylene flame angles. Typical oxidized microstructures (SiO₂/SiC-depleted/ZrB₂-SiC) were observed when the flame to Z30S was arranged vertically. However, formation of the outmost glassy SiO₂ layer was hindered when the Z30S was tilted. The SiC-depleted region was fully exposed to air with reduced thickness when highly tilted. Traces of the ablated and island type SiO₂ were observed at intermediate flame angles, which clearly verified the effect of flame angle on the ablation of the SiO₂ layer. Furthermore, the observed maximum surface temperature of the Z30S gradually increased up to 2,200 ℃ proving that surface amorphous silica was continuously removed while monoclinic ZrO₂ phase began to be exposed. A proposed ablation mechanism with respect to flame angles is discussed. This observation is expected to contribute to the design of complex-shaped UHTC applications for hypersonic vehicles and re-entry projectiles.

• Journal of the Korean Magnetics Society
• /
• v.17 no.5
• /
• pp.198-204
• /
• 2007

The effects of annealing temperature on electromagnetic wave absorption characteristics in $Fe_{73.5}Cu_1Nb_3Si_{15.5}B_7$ (at%) alloy flakes/polymer composite sheets available for quasi-microwave band have been investigated. The composite sheet including the magnetic flakes annealed at $425{\sim}475^{\circ}C$ for 1 h exhibited highest power loss in the GHz frequency range as compared with the sheets composed of the alloy flakes annealed at higher temperature than $475^{\circ}C$ or in as-milled state. Moreover the imaginary part of complex permeability had largest value in the GHz frequency range for the sheets including the flakes annealed at $425{\sim}475^{\circ}C$. The large value of power loss of the sheets including the magnetic flakes annealed at $425{\sim}475^{\circ}C$ was attributed to the high imaginary part of the complex permeability. However, because of its large transmission parameter $S_{21}$, the composite sheet having the magnetic flakes annealed at $525^{\circ}C$ showed low power loss.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.57 no.11
• /
• pp.2015-2022
• /
• 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 pressurless-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 89.02[%], 81.58[MPa], 31.44[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. The electrical resistivity showed the lowest value of $3.l4{\times}10^{-2}{\Omega}{\cdot}cm$ for $SiC-ZrB_2$ composite added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at 700[$^{\circ}C$]. The electrical resistivity of the $SiC-TiB_2$ and $SiC-ZrB_2$ composite was all negative temperature coefficient resistance (NTCR) in the temperature ranges from room temperature to 700[$^{\circ}C$]. Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.24 no.6
• /
• pp.594-598
• /
• 2015

The effects of Ni on the mechanical properties of WC-Xwt.%Ni-1.5wt.%Si-1.1wt.%$B_4C$ composite (X = 21.6, 23.6, 25.6 and 27.6 wt.%) were investigated in order to replace Co with Ni as the binder metal for hard materials based on WC-Co system. Using X-ray diffraction, optical microscopy, field-emission scanning electron microscopy results, the microstructure, pore distribution and grain size of the composites sintered at $1,150^{\circ}C$ were examined with different fraction (X = 21.6, 23.6, 25.6 and 27.6 wt.%) of binder metal Ni. The average WC grain size of the $WC-Ni-Si-B_4C$ composites was about $1{\mu}m$. The Rockwell hardness : A (HRA) and transverse rupture strength were about 88HRA and $110kgf/mm^2$, respectively. The obtained sample was bonded with SM45C at a temperature of $1,050^{\circ}C$. The thickness and mechanical properties of the bonded area were investigated with different dwell time at a bonding temperature of $1,050^{\circ}C$.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.58 no.4
• /
• pp.770-776
• /
• 2009

The composites were fabricated by adding 0, 15, 30, 45[vol.%] $ZrB_2$ powders as a second phase to SiC matrix. The physical, mechanical and electrical properties of electroconductive SiC ceramic composites by spark plasma sintering(SPS) were investigated. Reactions between ${\beta}$-SiC and $ZrB_2$ were not observed in the XRD and the phase analysis of the electroconductive SiC ceramic composites. The relative density of mono ${\beta}$-SiC, ${\beta}$-SiC+15[vol.%]$ZrB_2$, ${\beta}$-SiC+30[vol.%]$ZrB_2$ and ${\beta}$-SiC+45[vol.%]$ZrB_2$ composites are respectively 99.24[%], 87.53[%], 96.41[%] and 98.11[%] Phase analysis of the electroconductive SiC ceramic composites by XRD revealed mostly of ${\beta}$-SiC, $ZrB_2$ and weakly of $ZrO_2$ phase. The flexural strength showed the lowest of 114.44[MPa] for ${\beta}$-SiC+15[vol.%]$ZrB_2$ powders and showed the highest of 210.75[MPa] for composite no added with $ZrB_2$ powders at room temperature. The trend of the mechanical properties of the electroconductive SiC ceramic composites is accorded with the trend of the relative density. The electrical resistivity of the electroconductive SiC ceramic composites decreased with increased $ZrB_2$ contents. The electrical resistivity of mono ${\beta}$-SiC, ${\beta}$-SiC+15[vol.%]$ZrB_2$, ${\beta}$-SiC+30[vol.%]$ZrB_2$ and ${\beta}$-SiC+45[vol.%]$ZrB_2$ composites are respectively $4.57{\times}10^{-1},\;2.13{\times}10^{-1},\;2.68{\times}10^{-2}\;and\;1.99{\times}10^{-2}[{\Omega}{\cdot}cm]$ at room temperature. The electrical resistivity of mono ${\beta}$-SiC and ${\beta}$-SiC+15[vol.%]$ZrB_2$ are negative temperature coefficient resistance(NTCR) in temperature ranges from $25[^{\circ}C]\;to\; 100[^{\circ}C]$. The electrical resistivity of ${\beta}$-SiC+30[vol.%]$ZrB_2$ and ${\beta}$-SiC+45[vol.%]ZrB_2$ are positive temperature coefficient resistance(PTCR) in temperature ranges from $25[^{\circ}C]\;to\;100[^{\circ}C]$. It is convinced that ${\beta}$-SiC+30[vol.%]$ZrB_2$ composites by SPS for heater or ignitors can be applied.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.7
• /
• pp.1713-1721
• /
• 1994

Intermetallic-matrix composites(IMCs) have the potential of combing matrix properties of oxidation resistance and high temperature stability with reinforcement properties of high specific strength and modulus. One of the major limiting factors for successful applications of these composite at high temperatures is the formation of interfacial reactions between matrix and ceramic reinforcement during composite process and during service. The purpose of the present investigation is to develop a better understanding of the nature of creep fracture mechanisms in a $Ni_{3}Al$ composite reinforced with both $TiB_{2}$ and SiC particulates. Emphasis is placed in the roles of the products of the reactions in determining the creep lifetime of the composite. In the present study, creep rupture specimens were tested under constant ranging from 180 to 350 MPa in vacuum at $760^{\cric}C$. The experimental data reveal that the stress exponent for power law creep for the composite is 3.5, a value close to that for unreinforced $Ni_{3}Al$. The microstructural observations reveal that most of the cavities lie on the grain boundaries of the $Ni_{3}Al$ matrix as opposed to the large $TiB_{2}/Ni_{3}Al$ interfaces, suggesting that cavities nucleate at fine carbides that lie in the $Ni_{3}Al$ grain boundaries as a result of the decomposition of the $SiC_{p}$. This observation accounts for the longer rupture times for the monolicthic $Ni_{3}Al$ as compared to those for the $Ni_{3}Al/SiC_{p}/TiB_{2} IMC$. Finally, it is suggested that creep deformation in matrix appears to dominate the rupture process for monolithic $Ni_{3}Al$, whereas growth and coalescence of cavities appears to dominate the rupture process for the composite.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1254_1255
• /
• 2009

The composites were fabricated by adding 30, 35, 40, 45[vol.%] Zirconium Diboride(hereafter, $ZrB_2$) powders as a second phase to Silicon Carbide(hereafter, SiC) matrix. The physical, mechanical and electrical properties of electroconductive SiC ceramic composites by Spark Plasma Sintering(hereafter, SPS) were examined. Reactions between $\beta$-SiC and $ZrB_2$ were not observed in the XRD analysis. The relative density of SiC+30[vol.%]$ZrB_2$, SiC+35[vol.%]$ZrB_2$, SiC+40[vol.%]$ZrB_2$ and SiC+45[vol.%]$ZrB_2$ composites are 88.64[%], 76.80[%], 79.09[%] and 88.12[%], respectively. The XRD phase analysis of the electroconductive SiC ceramic composites reveals high of SiC and $ZrB_2$ and low of $ZrO_2$ phase. The electrical resistivity of SiC+30[vol.%]$ZrB_2$, SiC+35[vol.%]$ZrB_2$, SiC+40[vol.%]$ZrB_2$ and SiC+45[vol.%]$ZrB_2$ composites are $6.74{\times}10^{-4}$, $4.56{\times}10^{-3}$, $1.92{\times}10^{-3}$ and $4.95{\times}10^{-3}[{\Omega}{\cdot}cm]$ at room temperature, respectively. The electrical resistivity of SiC+30[vol.%]$ZrB_2$, SiC+35[vol.%]$ZrB_2$, SiC+40[vol.%]$ZrB_2$ and SiC+45[vol.%]$ZrB_2$ are Positive Temperature Coefficient Resistance(hereafter, PTCR) in temperature ranges from 25[$^{\circ}C$] to 500[$^{\circ}C$]. It is convinced that SiC+40[vol.%]$ZrB_2$ composite by SPS can be applied for heater or electrode.