• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.4
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• pp.425-431
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• 2007

[ $Al_2O_3/SiC$ ]composite ceramics were sintered to evaluate the bending strength and elastic wave characteristics. The three-point bending test was carried out under room temperature. The elastic wave was detected by fracture wave detector. The crack healing behavior was investigated from 1373 K to 1723 K. The bending strength of $Al_2O_3/SiC$ composite by nanocomposite is higher than that of $Al_2O_3$ monolithic. Crack-healing behavior depended on an amount of additive powder $Y_2O_3$. In $Al_2O_3/SiC$ composite ceramics with 3 wt. % $Y_2O_3$ for additive powder, the bending strength at 1573 K is about 100% increase than that of the smooth specimens. From the result of wavelet analysis of elastic wave signal, the smooth specimen and heat treated specimen of $Al_2O_3$ monolithic and $Al_2O_3/SiC$ composite ceramics showed characteristics of frequency about 58 kHz. The strength of $Al_2O_3/SiC$ composite ceramics was a little higher than those of $Al_2O_3$ monolithic. The dominant frequencies were high with increasing of $Y_2O_3$ for additive powder. The dominant frequencies had direct connection with the bending strength.

• Journal of the Korean Ceramic Society
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• v.30 no.4
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• pp.316-324
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• 1993

Three types of dispersed, coated and mechanically mixed SiC reinforced Al2O3 composite powders were used to investigate the effect of composite powder type on sintering characteristics and properties of Al2O3-SiC composites. Sinterability of coated type composite powders was superior to that of other composite powders when they were pressureless sintered at 1500~1$700^{\circ}C$ for 2h in Ar atmosphere. However, sinterabilities (>98% TD) of each type of composite powders were similar when they were hot pressed at 180$0^{\circ}C$ for 1h under 30MPa in N2 atmosphere. SiC powders were randomly distributed in the specimen prepared from dispersed type composite powders, whereas homogeneously distributed for coated type specimens. It was found that SiC powders inhibited the grain growth of Al2O3, and fracture toughness was increased by the increment of crack growth resistance due to residual stress by secondary SiC particles within Al2O3 grains.

• Journal of Powder Materials
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• v.10 no.5
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• pp.337-343
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• 2003

Nanostructured Cu-$Al_2O_3$ composite powders were synthesized by thermochemical process. The synthesis procedures are 1) preparation of precursor powder by spray drying of solution made from water-soluble copper and aluminum nitrates, 2) air heat treatments to evaporate volatile components in the precursor powder and synthesis of nano-structured CuO + $Al_2O_3$, and 3) CuO reduction by hydrogen into pure Cu. The suggested procedures stimulated the formation of the gamma-$Al_2O_3$, and different alumina formation behaviors appeared with various heat treating temperatures. The mean particle size of the final Cu/$Al_2O_3$ composite powders produced was 20 nm, and the electrical conductivity and hardness in the hot-extruded bulk were competitive with Cu/$Al_2O_3$ composite by the conventional internal oxidation process.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.3 s.36
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• pp.259-265
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• 2005

Characteristics of electroplated Ni films and $Ni-Al_2O_3$ composite films, such as yield strength, fracture elongation, and $Al_2O_3$ content, were evaluated as a function of electroplating current density. $Al_2O_3$ content was $11.48\~11.64\;vol\%$ for $Ni-Al_2O_3$ composite films electroplated at $5\~20\;mA/cm^2$, and decreased to $8.41\;vol\%$ at $30\;mA/cm^2$ $Ni-Al_2O_3$ possessed yield strengths higher than those of Ni films. Especially, $Ni-Al_2O_3$ fabricated at $5\;mA/cm^2$ exhibited $50\%$ improved yield strength. Fracture elongations of Ni and $Ni-Al_2O_3$ decreased with increasing the electroplating current density. $Ni-Al_2O_3$ electroplated at $5\;mA/cm^2$ exhibited more uniform dispersion of $Al_2O_3$ and higher yield strength and larger fracture elongation than the composite films processed at other current densities.

• Journal of the Korean Ceramic Society
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• v.34 no.5
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• pp.483-490
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• 1997

Al2O3/metal composites were fabricated by oxidation and reaction of molten Al-alloy into two types of commercial Al2O3-SiO2 fibrous insulation board. The growth rate, composition and microstructure of these materials were described. An AlZnMg(7075) alloy was selected as a parent alloy. Mixed polycrystalline fiber and glass phase fiber were used as a filler. The growth surface of an alloy was covered with and without SiO2. SiO2 powder was employed as a surface dopant to aid initial oxidation of Al-alloy. Al-alloy, SiO2, fiber block and growth inhibitor CaSiO3 were packed sequentially in a alumina crucible and oxidized in air at temperature range 90$0^{\circ}C$ to 120$0^{\circ}C$. The growth rate of composite layer was calculated by measuring the mass increasement(g) per unit surface($\textrm{cm}^2$). XRD and optical microscope were used to investigate the composition and phase of composites. The composite grown at 120$0^{\circ}C$ and with SiO2 dopant showed rapid growth rate. The growth behavior differed a little depending on the types of fiber used. The composites consist of $\alpha$-Al2O3, Al, Si and pore. The composite grown at 100$0^{\circ}C$ exhibited better microstructure compared to that grown at 120$0^{\circ}C$.

• Journal of Powder Materials
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• v.7 no.1
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• pp.35-41
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• 2000

Al2O3$.$SiC particle was prepared was prepared by the self-propagting high temperature sYthesis(SHS) process from a mixture of SiO2, Al and C powders, The fabricated Al2O3$.$SiC particle was applied to 2024Al/(Al2O3$.$SiC)pcomposite as a reinforcement. Aluminum matix composites were fabricares by the powder extrusion method using the synthesized Al2O3$.$SiC particle and commercial 2024Al powder. Theoptimum preparation conditions for Al2O3$.$SiC partticle by SHS process were described. The influence of the Al2O3$.$SiC voiume fraction on the mechanical was composite was also discussed. Despite adiabatic temperature was about 2367K, SHs reaction was completed not by itself, but by using pre-heating. Mean particle size of final particle synthesized was 0.73 ${\mu}$m and most of the particle was smaller than 2${\mu}$m. Elastic modulus and tensile strength of the composite increased with increase the volume fraction of reinforcement but, tensile strength depreciated at 30 vol% of reinforcement.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.6
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• pp.239-245
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• 2001

$Al/Al_2O_3$composites were prepared from the reaction of mullite preforms and amorphous silica in aluminum melt at $1100^{\circ}C$ for 5 hrs. The chemical reaction between mullite preform and aluminum melt has formed the interconnected microstructure. The metal content of $Al/Al_2O_3$composite was controlled with the variable of the apparent porosity according to the sintering temperature of mullite preforms; $1600^{\circ}C$,$ 1625^{\circ}C$, $1650^{\circ}C$ and $1700^{\circ}C$, the mechanical properties of $Al/Al_2O_3$composite were investigated upon the content of Al. The mullite preform sintered above $1600^{\circ}C$ showed the chemical reaction with the penetrated Al melt, but the mullite sintered at $1600^{\circ}C$ didnt react with aluminum melt owing to the non-wetting of Al melt/mullite preform. The influences of penetration direction on the mechanical properties of composites were considered with the two different models of the perpendicular pattern and the parallel pattern to the direction of Al melt penetration. With the increase of Al metal penetration content, the fracture strength of $Al/Al_2O_3$composite decreased and the fracture toughness of composite increased. The microstructure of $Al/Al_2O_3$composite was determined by the direction of metal penetration, but the fracture strength and fracture toughness of composite didnt show the dependence on metal penetration direction.

• Journal of the Korean Ceramic Society
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• v.52 no.4
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• pp.273-278
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• 2015

${\alpha}-Al_2O_3$ was synthesized by solvothermal synthesis using ${\alpha}-Al_2O_3$ seed, precursor of fine boehmite (Al(OOH)) or gibbsite ($Al(OH)_3$), and 1, 4-butanediol solvent. The seed content and precursor type were selected as variables in order to synthesize ${\alpha}-Al_2O_3$. The formation time of ${\alpha}-Al_2O_3$ was reduced and the size of the particles was decreased with addition of the seed. When the seed content was increased, the size of the synthesized ${\alpha}-Al_2O_3$ was reduced. Morphologies of the as-synthesized ${\alpha}-Al_2O_3$ with ${\alpha}-Al_2O_3$ seed were polyhedron-shaped, while the shape was plate-like or polyhedral without the seed, depending on the additives or the average particle size of the boehmite precursor. The aggregation of as-synthesized ${\alpha}-Al_2O_3$ from boehmite was smaller than that from gibbsite. As-synthesized ${\alpha}-Al_2O_3$, with 140 nm size, was obtained by using the seed and boehmite precursor.

• Journal of the Korean Ceramic Society
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• v.30 no.2
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• pp.123-130
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• 1993

Dispersed type Al2O3-SiC composite powders were synthesized from Al-isopropoxide (Al(i-OC3H7)3) and Si(OC2H5)4 precursors by hydrolysis of mixed alkoxides and carbothermal reaction method. The characteristics of the synthesized (dispersed type) Al2O3-SiC composite powders were investigated using XRD, SEM, TEM, BET and particle size analyzer. Carbothermal reaction to produce Al2O3-SiC composite was completed in 10h at 135$0^{\circ}C$ on 3~4㎤/s (0.21~0.28cm/s) of H2 flow rate and about 1/1 of carbon/oxides(=SiO2＋Al2O3) molar ratio. The synthesized powders were observed to have the mean particle size range of 0.4~1.26${\mu}{\textrm}{m}$ and showed finer particle size with increasing SiC content.

• Journal of the Korean Ceramic Society
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• v.30 no.3
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• pp.243-249
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• 1993

Coated type Al2O3-SiC composite powders were synthesized by surface modification method. Transformation temperature to $\alpha$-Al2O3 of Al2O3 monolith was 115$0^{\circ}C$ whereas increased to 1200, 1250, 130$0^{\circ}C$ with increment of SiC content to 5, 15, 25wt%. Transformation temperature to $\alpha$-Al2O3 was lowered by $\alpha$-Al2O3 seeding. FTIR data analysis and electron micrographs showed that Al2O3 particles were effectively coated on SiC particles.