• Journal of the Korean Ceramic Society
• /
• v.56 no.2
• /
• pp.191-196
• /
• 2019

This study assessed the feasibility of a Ti₃AlC₂ MAX phase as an Al-source for the formation of a mullite bond in the fabrication of porous SiC tubes with high strength. The as-received Ti₃AlC₂ was partially oxidized at 1200℃ for 30 min before using to minimize the abrupt volume expansion caused by oxidation during sintering. Thermal treatment at 1100-1400℃ for 3 h in air led to the formation of Al₂O₃ by the decomposition of Ti₃AlC₂, which reacted further with oxidation-derived SiO₂ on the SiC surface to form a mullite phase. The fabricated porous SiC tubes with a relative density of 48 - 62 % exhibited mechanical strengths of 80 - 200 MPa, which were much higher than those with the Al₂O₃ filler material. The high mechanical strength of the Ti₃AlC₂-added porous SiC was explained by the rigid mullite neck formation along with the retained Ti₃AlC₂ with good mechanical properties.

• Journal of the Korean Ceramic Society
• /
• v.31 no.8
• /
• pp.849-860
• /
• 1994

The microstructural evolution and crystalline phases of this infiltration of Ti+Al liquids in TiC, SiC, TiC+C, and SiC+C preforms have been investigated. As the Ti and Al mixing ratio in Ti+Al infiltrated liquid changes, the newly formed reaction products, which were reacted from the Ti+Al liquid with preforms, consisted of three major phases as Ti3AlC, Al2Ti4C2 or Al4C3. The TiC grain shape was changed to spheroid, when Ti3AlC was formed. In case of Al2Ti4C2 formation, the platelet grain was formed from the original TiC grain. When Al4C3 was formed, nodular or intergranular fine-grained Al4C3 was formed around the TiC grain, while the original TiC grain shape was not changed.

• Journal of the Korean Ceramic Society
• /
• v.37 no.4
• /
• pp.359-367
• /
• 2000

Particulate composites of Al2O3/SiC, Al2O3/ZrO2 and Al2O3/ZrO2/SiC have been fabricated to investigate their R-curve behaviors and toughening mechanisms. Al2O3 containing 30 vol% SiC particles of 3${\mu}{\textrm}{m}$ showed rising R-curve behavior owing to the strong crack bridging by SiC particles. The fracture toughness reached 9.1 MPa {{{{ SQRT {m} }} at the crack length of 1000${\mu}{\textrm}{m}$. On the other hand, ZrO2-toughened Al2O3 had a high flat R-curve since it rose steeply in the short crack region due to the well known transformation toughening. For Al2O3/ZrO2/SiC composites, the R-curve behavior was similar to that of Al2O3/SiC but with slightly higher toughness. The SiC particles in this composite decreased the amount of transformable tetragonal phase to reduce the effect of transformation toughening by 50%. It was also found that the fracture toughness of this composite with two different toughening mechanisms was markedly lower than that estimated by the simple addition of two contributions.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.85-86
• /
• 2006

A theoretical model is applied to the analysis of thermomechanical properties of $Al-SiC_p$ FGMs in this study. Functionally graded $Al-SiC_p$ composites ($Al-SiC_p$ FGMs) consisted with 10 layers gradually changing volume fractions of Al and $SiC_p$ were fabricated using the pressureless infiltration technique. $Al-SiC_p$ FGMs plates of total thickness of 3mm, 5mm and 7mm with fairly uniform distribution and compositional gradient of $SiC_p$ reinforcement in the Al matrix throughout the thickness was successfully fabricated. The curvature of $Al-SiC_p$ FGM plates was measured to check the internal stress distribution predicted via a theoretical model for the analysis of thermo-mechanical deformation. The evolution of curvature and also internal stresses in response to temperature variations could be predicted for the different combinations of geometric thickness of FGM plates. Theoretical prediction of thermally induced stress distribution makes it possible to design FGM structures without any critical failure during the usage of them.

• Journal of the Korean Ceramic Society
• /
• v.30 no.4
• /
• pp.316-324
• /
• 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 Sensor Science and Technology
• /
• v.16 no.6
• /
• pp.457-461
• /
• 2007

This paper describes the characteristics of poly (polycrystalline) 3C-SiC grown on $SiO_{2}$ and AlN substrates, respectively. The crystallinity and the bonding structure of poly 3C-SiC grown on each substrate were investigated according to various growth temperatures. The crystalline quality of poly 3C-SiC was improved from resulting in decrease of FWHM (full width half maximum) of XRD and FT-IR by increasing the growth temperature. The minimum growth temperature of poly 3C-SiC was $1100^{\circ}C$. The surface chemical composition and the electron mobility of poly 3C-SiC grown on each substrate were investigated by XPS and Hall Effect, respectively. The chemical compositions of surface of poly 3C-SiC films grown on $SiO_{2}$ and AlN were not different. However, their electron mobilities were $7.65{\;}cm^{2}/V.s$ and $14.8{\;}cm^{2}/V.s$, respectively. Therefore, since the electron mobility of poly 3C-SiC films grown on AlN buffer layer was two times higher than that of 3C-SiC/$SiO_{2}$, a AlN film is a suitable material, as buffer layer, for the growth of poly 3C-SiC thin films with excellent properties for M/NEMS applications.

• Korean Journal of Materials Research
• /
• v.11 no.7
• /
• pp.590-598
• /
• 2001

SiCp/pure Al and SiCp/2024Al MMCs were fabricated by in-situ VHP process designed specially just in this study which is composed of the vacuum hot press at range from R.T. to $500^{\circ}C$ and the continuous extrusion without canning process at $520^{\circ}C$. It was investigated the effect of SiC particle size, volume fraction and extrusion ratio on the tensile properties and micro structure in auf composites. In case of the 10:1 extrusion ratio, but SiCp/pure Al and SiCp/2024Al composites were shown a sound appearance and a good micro structure without crack of SiCp as well as uniform distribution of SiCp. However, in case of the 16:1 extrusion ratio, the number of cracked SiC particles more than increased in a higher volume fraction composite and 2024Al matrix composite compared with pure Al matrix one. The tensile strength of the composites reinforced smaller SiCp was higher than that of the bigger SiCp reinforced in same volume fraction and extrusion ratio.

• Korean Journal of Metals and Materials
• /
• v.50 no.11
• /
• pp.839-845
• /
• 2012

The effect of an AlN additive on the thermoelectric properties of SiC ceramics was studied. Porous SiC ceramics with 48-54% relative density were fabricated by sintering the pressed ${\alpha}-SiC$ powder compacts with AlN at $2100-2200^{\circ}C$ for 3 h in an Ar atmosphere. In the undoped specimens, the Seebeck coefficients were positive (p-type semiconducting) possibly due to a dominant effect of the acceptor impurities (Al, Fe) contained in the starting powder. With AlN addition, the reverse phase transformation of 6H-SiC to 4H-SiC was observed during the sintering process. The electrical conductivity of the AlN doped specimen was larger than that of the undoped specimen under the same conditions, which might be due to a reverse phase trans-formation. The Seebeck coefficient of the AlN doped specimen was also larger than that of the undoped specimen. The density of specimen and the amount of addition had significant effects on the thermoelectric properties.

• Journal of Korea Foundry Society
• /
• v.12 no.2
• /
• pp.149-154
• /
• 1992

The wetting behaviour of SiC/Al-Li composite interface has been investigated by using an infiltration method. The critical pressure for melt infiltration into SiC particulate preform has been determined by measuring the melt infiltration distance changes with the variation of applied pressure. The threshold pressure of pure Al, Al-0.2wt%Li, Al-0.5wt%Li for melt infiltration are 3.94, 3.93, $3.7Kg/cm^2$ respectively, which implies a slight improvement in wettability of SiC/Al composite by addition of Li. The threshold pressure for melt infiltration also changes with the variation of other parameters such SiC particulate size, SiC particulate fraction and melt temperature.

• Journal of the Korean Ceramic Society
• /
• v.50 no.6
• /
• pp.372-377
• /
• 2013

Machinable SiC ceramics are prepared with the addition of $Al_2TiO_5$. Ready-to-press SiC and $Al_2TiO_5$ powders are mixed and pressureless sintered at $1750^{\circ}C$ and $1850^{\circ}C$ for 1 h. The weight ratios of the SiC and $Al_2TiO_5$ powders are 100 : 0, 100 : 10, and 100 : 20. After sintering, only SiC peaks are detected in the X-ray diffraction analyses. The density, strength, and grain size of the SiC increase with increases in the $Al_2TiO_5$ content and sintering temperature. The $Al_2TiO_5$-doped specimens are easy to micro-hole machine. Based on the density and strength data, the ceramics sintered at $1850^{\circ}C$ can be used as machinable ceramics.