- Microstructural Wear Mechanism of Al_2O_3-5 vol% SiC nanocomposite and Si_3N_4Ceramics
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Doh-Hyung Riu, Yoon-Ho Kim, Soo-Wohn Lee, Niihara Koichi
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J Korean Powder Metall Inst. 2001;8(3):179-185.
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- Through the observation of wear scar of two ceramic materials, microstructural wear mechanisms was investigated. As for the Al_2O_3-5 vol% SiC nanocomposite, the grain boundary fracture was suppressed by the presence of SiC nano-particles. The intragranular SiC particles have inhibited the extension of plastic deformation through the whole grain. Part of plastic deformation was accommodated around SiC particles, which made a cavity at the interface between SiC and matrix alumina. On the other hand, gas-pressure sintered silicon nitride showed extensive grain boundary fracture due to the thermal fatigue. The lamination of wear scar was initiated by the dissolution of grain boundary phase. These two extreme cases showed the importance of microstructures in wear behavior.
- Preparation and Mechanical Properties of Al_2O_3/5vo1%Cu Nanocomposites
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Niihara Koichi
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J Korean Powder Metall Inst. 2000;7(4):212-217.
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- An optimum route to fabricate the Al_2O_3/Cu nanocomposites with sound microstructure and improved mechanical properties was investigated. Microstructural investigations for the composites prepared using Al_2O_3/Cu-nitrate showed that fine Cu particles with average size of 150 nm were homogeneously distributed within the Al_2O_3 matrix grains and at the grain boundaries. Fracture strength of 953 MPa and toughness of 4.8 Mpa(equation omitted)m were measured for the composite. The strengthening and toughening of the composites are explained by the refinement of the microstructure and the crack bridging/deflection, respectively.
- Microstructure and Properties of Nano-Sized Ni-Co Particulate Dispersed Al_2O_3 Matrix Nanocomposites
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Sung-Tag Oh, Sando Mutsuo, Niihara Koichi
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J Korean Powder Metall Inst. 1998;5(4):334-339.
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- In purpose of introducing the inverse magnetostrictive properties into the structural ceramics, Al_2O_3 based nanocomposites dispersed with nano-sized Ni-Co particles were studied. The composites were fabricated by the hydrogen reduction and hot-pressing of Al_2O_3 and NiO-CoO mixed powders. The mixtures were prepared by using Ni- and Co-nitrate (Ni(NO_3)_2;cdot;6H_2O;and;Co(NO_3)_2;cdot6H_2O) as source materials for the Ni-Co particles. Microstructural observations revealed that nano-sized Ni-Co particles were dispersed homogeneously at Al_2O_3 grain boundaries. High strength above 1 GPa was obtained for the Al_2O_3/10 wt% Ni-Co nanocomposite fabricated by a controlled powder preparation process. The inverse magnetostrictive response to applied stress was obtained due to the presence of dispersed Ni-Co particles, which indicates a possibility to incorporate new functions into the structural ceramics without loosing the mechanical properties.
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