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$Al_2O_3$/5vo1%Cu 나노복합재료의 제조 및 기계적특성
오승탁,이재성,Koichi Niihara 한국분말야금학회 2000 한국분말재료학회지 (KPMI) Vol.7 No.4
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.
Characterization of 3YSZ/LaPO4 composites coatings made by an atmospheric plasma spraying method
김성호,ZhenbgYi Fu,Koichi Niihara,이수완 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.2
3YSZ/LaPO4 composites applied for thermal barrier coatings (TBC) were deposited by an atmospheric plasma spraying (APS)method. The residual stresses and thermal conductivity of 3YSZ/LaPO4 composite coating samples were investigated. The thickness of the APS coating layer on the substrate metal was about 115 to 130 μm. Residual stresses of APS coating samples were observed to be both compressive and tensile. Residual stresses of APS coating samples were changed by the amount of LaPO4. As the amount of LaPO4 increased, the compressive residual stresses of APS coating samples were increased. The differences of the residual stress of APS coating samples were increased from 49.44MPa of 3YSZ/10 vol% LaPO4 to 305.9 MPa of 3YSZ/40 vol% LaPO4. The thermal conductivity of the 3YSZ/LaPO4 composite coating layer was calculated by utilizing APS coating layer on the substrate metal. The calculated value of the thermal conductivity of coating layers ranges from 0.11to 0.19 W/m·K.
Multifunctionality in Ceramic/Metal Nanocomposites
Sekino, Tohru,Kondo, Hiroki,Niihara, Koichi The Korean Powder Metallurgy Institute 2001 한국분말재료학회지 (KPMI) Vol.8 No.3
Several fabrication processes, corresponding nanostructural features and multifunctionality as well has been investigated for oxide ceramic based nanocomposites with metal nanodispersion (i.e., ceramic/metal nanocomposites). Transition metal (Ni, Co, etc) dispersed alumina and zirconia based nanocomposites have been synthesized by reducing and hot-press sintering of ceramic and metal oxide mixtures prepared by several method. Improved fracture strength (1.1 and 1.9 GPa for $Al_2O_3/Ni$ and $ZrO_2/Ni$ nanocomposites, respectively) of these composites have been achieved according to their nanostructures. In addition, ferromagnetic characteristic has been kept. The variation of magnetization with an applied stress has found to be more sensitive as smaller as the magnetic metal dispersion is. This result thus suggests the possibility of fracture and/or stress sensing of the composites by simple magnetic measurement.
PECVD법에 의한 3C-SiC막 증착(II): Nanoindentation 방법을 이용한 SiC 막의 기계적성질
김광호,윤석영,서지윤,김창열,Koichi Niihara 한국세라믹학회 2001 한국세라믹학회지 Vol.38 No.4
플라즈마 화학증착법(PECVD)에 의해 실리콘 (100) 기판 위에 3C-SiC막을 증착하였다. 증착반응시 유입가스비, R$_{x}$[=CH$_4$/(CH$_4$+H$_2$)]에 따른 증착막의 결정성에 대해 검토하였다. 증착된 3C-SiC막의 결정성은 R$_{x}$ 값이 감소할수록 더욱 향상되었으며, 형성된 결정상은 (111) 면으로 최대의 우선배향성을 가졌다. Nanoindentation 방법을 이용하여 3C-SiC막의 압입깊이에 따른 경도 및 탄성계수를 측정하였으며, 유입가스비(R$_{x}$)의 변화에 따라서 막의 경도 및 탄성계수가 뚜렷이 변화하였다.
김성호,ZhengYi Fu,Koichi Niihara,이수완 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.3
To apply a thermal barrier coating, the coating materials must satisfy the basic requirements. This paper explains composite powder processing and the characterization of sintered materials. The composite powders were prepared by two types of method: conventional ball-milling and chemical precipitation. The morphology of the powder differed with the processing method. In chemically precipitated powder, the surface of zirconia was coated with LaPO4. The samples were fabricated from these powders, using the PECSed method. The flexural strength of the nanocomposites was decreased with an increase in the amount of LaPO4 due to its poor mechanical properties. However, the thermal properties, such as thermal conductivity and high temperature stability, were lower and more stable than that of the monolith.
Microstructural characteristics and film properties of diamond-like carbon coatings grown by PECVD
Won Jae Yang,Koichi Niihara,Keun Ho Auh 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.3
Diamond-like carbon (DLC) films were deposited by plasma decomposition of CH4/H2 gas mixtures in a RF glow discharge reactor. The chemical structure of diamond-like carbon films deposited at different bias voltages and CH4 flow contents was investigated by Fourier Transform Infrared (FT-IR) and Raman spectroscopy. An indirect evaluation on the sp3-bonded carbon in the DLC films was made based on the structural information on the sp2-bonded carbon obtained from Raman measurements. The mechanical properties of DLC films deposited at different CH4 flow contents are discussed in terms of Raman parameters such as the position, width and integrated intensities of Raman D and G peaks. The friction coefficient of DLC films was obtained and their frictional behavior was investigated.
Optical, Mechanical and Tribological Properties of Boronnitride Dispersed Silicon Nitride Ceramics
Joshi, Bhupendra,Fu, Zhengyi,Niihara, Koichi,Lee, Soo-Wohn Materials Research Society of Korea 2010 한국재료학회지 Vol.20 No.8
Transparent ceramics are used in new technology because of their excellent mechanical properties over glasses. Transparent ceramics are nowadays widely used in armor, laser windows, and in high temperature applications. Silicon nitride ceramics have excellent mechanical properties and if transparent silicon nitride is fabricated, it can be widely used. h-BN has a lubricating property and is ductile. Therefore, adding h-BN to silicon nitride ceramics gives a lubricating property and is also machinable. Translucent silicon nitride was fabricated by hot-press sintering (HPS) and 57% transmittance was observed in the near infrared region. A higher wt. % of h-BN in silicon nitride ceramics does not favor transparency. The optical, mechanical, and tribological properties of BN dispersed polycrystalline $Si_3N_4$ ceramics were affected by the density, ${\alpha}:{\beta}$-phase ratio, and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of $\alpha-Si_3N_4$, AlN, MgO, and h-BN at $1850^{\circ}C$. The composite contained from 0.25 to 2 wt. % BN powder with sintering aids (9% AlN + 3% MgO). A maximum transmittance of 57% was achieved for the 0.25 wt. % BN doped $Si_3N_4$ ceramics. Fracture toughness increased and wear volume and the friction coefficient decreased with an increase in BN content. The properties such as transmittance, density, hardness, and flexural strength decreased with an increase in content of h-BN in silicon nitride ceramics.
Oxidation behavior of a silicon boride composite
Jun-ichi Matsushita,심광보,Koichi Niihara,Akiko Kitajima,Satoshi Okuhata,Keun Ho Auh 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.2
The oxidation resistance of a silicon hexaboride (SiB6) composite at high temperature was investigated in order to determine the possibility of its use as an advanced high temperature structural material. Fortunately, monolithic SiB6 and its composites were known to be chemically stable up to high temperatures. To date, there have been few reports regarding the properties of SiB6 ceramics. In this study, the oxidation resistance at high temperature of a dense SiB6 composite prepared from SiB6 with the addition of 10 mass% C as starting powders has been studied. The samples were oxidized at room temperature up to 1173 K for 25 h in air. The weight changes were measured to estimate the oxidation resistance. The oxidation of samples oxidized for a short oxidation time of 5 minutes started at 973 K, and the weight gain increased with increasing oxidation temperature. On the other hand, at oxidation times of above 1 h, a maximum weight gain value at 973 K was observed. After that a SiB6 composite oxidized at 973 to 1073 K for 25 h exhibited increased weight gain with increasing oxidation temperature; the oxidation changed in accordance with the parabolic law during the initial oxidation stage. However, even if the oxidation temperature was increased only a slight additional weight change occurred. The weight gain of the sample oxidized at 1173 K for 25 h was approximately 2.5%. Finally, the SiB6 composite showed a good oxidation resistance at high temperature, because the surface oxide film formed by oxidation acted as an oxidation-resistant layer.
Processing and Mechanical/Electronical Properties of Oxide Based Nanocomposites
Choa,Yong-Ho,Niihara,Koichi 국립경상대학교 공과대학 부설 첨단소재연구소 1997 尖端素材 Vol.7 No.-
Application of Nanocomposites .Micro / Nano-type: Inter type, Intra type Structural Ceramic Materials; Alumina/SiC, MgO/SiC, Silicon Nitride/SiC etc. Electronic Ceramic Materials; Zirconia/SiC, ZnO/NiO, BaTiO₃/NiO or SiC Magnetic Materials; Alumina/Ni, Alumina/Co,Alumina/SmCo? MgO/PbTiO₃etc. .Nano / Nano-Type: Superplastic Materials; Silicon Nitride/SiC, Zirconia/Alumina etc. Electronic Ceramic Materials; Ag/ZnO?? Magnetic Materials; Ag /Fe₂O₃ as a Functional Materials