Browsing by Author "CHUANG, SC"

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ALUMINA-CHROMIUM CARBIDE COMPOSITE THROUGH AN INTERNAL SYNTHESIS METHODS
(1992-11-01)
CHUANG, SC
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KUO, CT
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LEE, CS
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HO, CT
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LI, AK
In situ formation of chromium carbide parlicles, through a solid state reaction between Cr2O3 and SiC, for strengthening Al2O3 has been studied. Three kinds of chromium compound, Cr3Si, Cr3C2 and Cr7C3 and mullite were formed in the alumina matrix. The reaction behaviour during hot pressing depends on heating parameters such as temperature and atmosphere. In a vacuum environment, the Cr3Si particles formed first and was the dominant dispersed phase below 1550-degrees-C, while the Cr7C3 phase was only dominant above 1600-degrees-C. The Cr3C2 phase emerged briefly then diminished at temperature greater-than-or-equal-to 1500-degrees-C. In an argon environment, however, the Cr3C2 phase was the main product component at temperatures ranging from 1450-1550-degrees-C. The mullite phase formed concurrently through the diffusion Of SiO2 phase into the A12O3 matrix, which is a by-product from the reaction between Cr2O3 and SiC. Incorporating chromium carbide or silicide particles into the Al2O3 matrix induces a strengthening effect. However, only when the content of dispersed phases is low and is mainly of Cr3C2 particles, is the strengthening effect significant. For instance, the composite, containing 5 vol % chromium carbide and hot-pressed at 1500-degrees-C in argon, gives a flexural strength and fracture toughness up to 600 M Pa and 6.1 MPa m1/2, respectively.
INSITU REACTED TIB2-REINFORCED ALUMINA
(1992-11-15)
CHUANG, SC
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KUO, CT
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HO, CT
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LI, AK
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機械工程學系
In situ formation of TiB2 in Al2O3 matrix through the reaction of TiO2, boron and carbon has been studied. In hot-pressed samples, in addition to TiB2, TiC and Al2TiO5, were also found to be dispersed phases in Al2O3 matrix. However, in the case of pressureless-sintered samples, pure Al2O3/TiB2 composite with > 99% relative density can be obtained through a preheating step held at 1300-degrees-C for longer than 30 min and then sintering at a temperature above 1500-degrees-C. Pressureless-sintered composite containing 20 vol % TiB2 gives a flexural strength of 580 MPa and a fracture toughness of 7.2 MPa m1/2.
MICROSTRUCTURE DEVELOPMENT AND MECHANICAL-PROPERTIES OF Y2O3-DOPED TETRAGONAL ZRO2 POLYCRYSTALS AND MULLITE COMPOSITES
(1992-08-15)
CHUANG, SC
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KUO, CT
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LI, AK
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機械工程學系
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Department of Mechanical Engineering
Composites containing Y2O3-doped tetragonal ZrO2 polycrystals (Y-TZP) and mullite were prepared by adding Y-TZP powder to a silicon aluminate sol, which is the precursor of the mullite phase. After filtration and drying, the mixed powder was compacted and sintered at 1500-degrees-C in air for various lengths of time. The mullite particles were uniformly distributed in a Y-TZP matrix; energy-dispersive spectroscopy microanalysis indicated that the chemical composition of these particles ranged from 3Al2O3-2SiO2 to 2Al2O3-SiO2. Incorporating mullite particles in a Y-TZP matrix had two evident effects on the composites: first, the ZrO2 grain size was substantially increased; second, the fracture toughness of the composites showed a 50% increase (from 9 to 13.5 MPa m0.5). This increased toughness was due to the enhanced transformability of the tetragonal ZrO2 (t-ZrO2), which resulted mainly from the enlarged grain size and the increased tetragonality of the t-ZrO2.