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Fabrication of Alumina Free-standing Objects by Electrophoretic Deposition
Uchikoshi Tetsuo,Furumi Seiichi,Suzuki Tohru S.,Sakka Yoshio 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
The coating of conductive polypyrrole (Ppy) on nonconductive ceramic substrates was performed by polymerization of pyrrole (Py) in an aqueous solution. The Ppy film was characterized by scanning electron microscopy and conductivity measurements. Electrophoretic deposition of bimodal alumina suspension prepared with a phosphate ester was performed using Ppy film as a cathode. Fabrication of alumina ceramics with irregular shapes or complicated patterns were also attempted by sintering the deposits together with the Ppy coated substrates in air.
Multi-step Internal Nitriding of Tungsten-titanium Alloys
Nagae Masahiro,Yoshio Tetsuo,Takada Jun,Hiraoka Yutaka,Takida Tomohiro 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Internally nitrided dilute W-Ti alloy specimens having a heavily deformed surface microstructure were prepared by a multi-step internal nitriding at 1573-2073 K. Primary nitriding below their recrystallization temperature induced a precipitation of ultrafine TiN particles. After secondary and tertiary nitriding, those precipitates grew into rod-like TiN with a length of 20-60 nm. The recrystallization temperature after nitriding was elevated above 2073 K. The yield strength at 1773 K obtained from nitrided W-0.5 mass% Ti alloy was about 5 times as large as that of the recrystallized specimen. DBTT of the nitrided alloys was about 373 K.
Bending Strength of Textured Alumina Prepared by Slip Casting in a Strong Magnetic Field
Suzuki Tohru S.,Uchikoshi Tetsuo,Morita Koji,Hirage Keijiro,Sakka Yoshio 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
The mechanical properties of ceramics materials can be tailored by designing their microstructures. We have reported that development of texture can be controlled by slip casting in a strong magnetic field followed by heating even for diamagnetic ceramics such as alumina. A strong magnetic field of 12T was applied to the suspension indcuding alumina powder to rotate each particle during slip casting. The sintering was conducted at the desired temperature in air without a magnetic field. C-axis of alumina was parallel to the magnetic field. Bending strength of textured alumina depended on the direction of oriented microstructure.
Carbon Monoxide Gas Carburization Behavior of Molybdenum Materials
Hieda Koji,Nagae Masahiro,Yoshio Tetsuo,Takada Jun,Hiraoka Yutaka,Takida Tomohiro 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
For pure Molybdenum carburized in mixed gases of argon and carbon monoxide, microstructural observations were carried out. X-ray diffraction analysis for carburized specimens revealed that brittle - layer hardly formed in the case of low carbon monoxide concentration. Fracture strength of the specimen carburized at 1673 K for 16 h is about 550 MPa higher than that of the un-carburized specimen. SEM observation revealed that with increasing carburizing temperature, the region demonstrating a transgranular fracture mode progressed towards the center of specimen. This result means that the grain boundaries were strengthened by the grain boundary diffusion of carbon and the strength of grain boundaries exceeded that of grain itself.
Toyosima Gouhei,Nagae Masahiro,Yoshio Tetsuo,Takada Jun,Hiraoka Yutaka,Takida Tomohiro 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
TZM alloy having elongated coarse-grain structure was developed by three-step internal nitriding treatment at 1423 to 1873 K in and subsequent recrystallization treatment at 2173 K in vacuum. Some specimens were subjected to re-nitriding treatment at 1873 K for 16 h. After the recrystallization treatment, aspect ratio (L/W) of grains for rolling direction was about 50 at the maximum. Yield stress obtained at 1773 K after re-nitriding treatment was about 6 times as large as that of recrystallized specimen. Re-nitriding was very effective in the improvement in strength of TZM alloy having elongated coarse-grain structure.
Aqueous Processing of Textured Silicon Nitride Ceramics by Slip Casting in a Strong Magnetic Field
Zhu Xinwen,Uchikoshi Tetsuo,Sakka Yoshio 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
This work will report a highly textured β-Si3N4 ceramic by aqueous slip casting in a magnetic field and subsequent pressureless sintering, Effects of the sintering aids, polymer dispersant, pH and stirring time on the stability of the Si3N4 slurries were studied. The textured β-Si3N4 with 97 % relative density could be obtained by slip casting in a magnetic field of 12 T and subsequent sintering at 1800 oC for 1 h. The textured microstructure is featured by the alignment of c-axis of β-Si3N4 crystals perpendicular to the magnetic field, and the Lotgering orientation factor, f, is determined to be 0.8.
Formation Mechanism of Y-type Barium Ferrite Prepared by the Glass-ceramic Method
Hori Chinatsu,Miki Hiroki,Nagae Masahiro,Yoshio Tetsuo 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Y-type barium ferrite was prepared by the glass-ceramic method. Glasses with composition of were prepared, and the precipitation behavior of Y-type ferrite from the glass matrix was investigated by heating glass specimens at various temperature. which is a precursor of M-type ferrite was precipitated at about 813 K and an unknown compound, phase X, was precipitated at about 850 K. M-type ferrite and Y-type ferrite started to form at about 923 K and 1103 K, respectively. The formation of Y-type ferrite was int erpreted as the result of the reaction of M-type ferrite with a melt of phase X.
Miki Hiroki,Hori Chinatsu,Nagae Masahiro,Yoshio Tetsuo 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Y-type barium ferrite ( Me=Zn, Co, Cu) expected as an electromagnetic wave absorber were prepared by the glass-ceramic method. The glasses with composition of were prepared. Single-phase powders of Y type barium ferrite were obtained with the composition . The shape of Y-type crystals depended strongly on the heating temperature and changed from a plate-like hexagon to a complex polyhedron with increasing heating temperature. Correlation was recognized between saturation magnetization and crystal shape. Electromagnetic wave absorption characteristics was affected by the saturation magnetization and crystal shape.