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Effects of Sintering Conditions on the Properties of Sintered Molybdenum
Kadokura Takanori,Hiraoka Yutaka,Nakabayashi Seiji,Yamamoto Yoshiharu 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Effects of sintering conditions such as sintering temperature and heating rate on oxygen content, density, microstructure and toughness of sintered Mo were investigated. The oxygen content of the sintered Mo significantly depended on the sintering conditions. The oxygen content of the primary sintered(below 1673 K) Mo influenced the densifications. The number of pores at grain boundaries of the secondary sintered(at 2073 K)Mo depended on the oxygen content of the primary sintered Mo. Grain growth of the secondary sintered Mo was inhibited by the existence of pores at the grain boundaries. The secondary sintered Mo having larger number of pore and smaller grain size demonstrated higher strength.
Flow visualization and numerical analysis of a new mixing equipment with vibratory fins
Yoshihito Kato,이영세,Setsuro Hiraoka,Shogo Fukumoto,Yutaka Tada,Yuichiro Nagatsu,Ryushin Ohmasa,Sung Tae Koh 한국화학공학회 2010 Korean Journal of Chemical Engineering Vol.27 No.1
The mixing performance of a new type of mixing equipment which has several fin oscillators on a pair of shafts with a vibrating motor was investigated. This mixing equipment, which is mainly used for industrial plating processes, was usually operated at a vibrating frequency of about 40 Hz with the amplitude 1mm. The flow visualization in this equipment showed that the flow in the vessel at laminar flow region was vertically divided into two distinct symmetric regions. The numerical simulation of the flow and the mixing patterns agreed well with the visualization result at laminar flow region.
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.
몰리브덴 선재의 상온연성 및 non-sag 성질에 미치는 미세조직의 영향
최주,유명기,평강유,최종술 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.10
To understand the dependency of microstructures on non-sag property and ductility in molybdenum wire, five different specimens were prepared through sintering, swaging and drawing processes. Each specimen was doped with K₂O and SiO₂ in various amounts, i.e., 0, 0.028, 0.14, 0.28 and 0.49(K+Si) by weight percents, and isochronally annealed at various temperatures for 30 minutes. The microvickers hardness was measured as a function of annealing temperature and then optical micrographs were taken with each specimen annealed at 1400℃ and 2000℃. Each specimen annealed at 1000℃ and 2000℃ underwent. 90˚ repetition bending until crack occurred to evaluate its ductility. Non-Sag values were measured in temperature range from 1000℃ to 2340℃(0.9Tm) under load of 250g, and then some fractured surfaces were observed by scanning electron microscopy. The specimen doped with 0.28(K+Si) weight percent was completely recrystallized at a temperature between 1800℃ and 2000℃ and its grain structure consisted of elongated and interwoven shape grains, including many small bubbles at grain boundary, of which aspect ratio(length/width) was about 30. This grain structure showed a good ductility after recrystallization and an excellent non-sag property over 0.5T_m. When the microstructures were not fully recrystallized, however, the sagging-resistance was increased with the doping amount of K₂O and SiO₃, and the ductility was inversely decreased. Especially, when the bubbles grew, the fracture occurred easily due to a sagging phenomenon assisted by the reduction of effective area supporting the load.
K2O 및 SiO2 를 도핑한 몰리브덴에서 기포형성물질 관찰
최주,유명기,평강유 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.10
To identify bubble formation substance in molybdenum doped with K₂O and SiO₂ two kinds of specimens were prepared; first, solid potassium disilicate was intentionally implanted in molybdenum powder followed by compacting at 300MPa. Then the compact was sintered at 2200℃. Secondly, molybdenum powder doped with potassium disilicate was produced from the hydrogen reduction of molybdenum trioxide, MoO₃, doped with potassium disilicate in acqueous solution. The doped powder was compacted and sintered at the same conditions as the former specimen. The sintered ingot was swaged and drawn to 1mm diameter wire. To analyze the bubble formation substance during sintering, hot isostatic pressing (HIPing) at 1900℃ under 190MPa was applied to transform bubbles into solid particles and to collapse pores induced by sintering. And to analyze the entrapped substance in the bubble of molybdenum wire, HIPing was performed at 2000℃ under 190MPa after annealing at 2000℃ for 30minutes. Scanning electron micrographs were taken and bubble formation substance was analyzed by using EDX (energy dispersive X-ray spectroscopy) and WDX(wave dispersive X-ray spectroscopy). It was analyzed that the evolution of bubble was due to the vaporization of K-Si oxide during sintering and Al-K-Si complex oxide during annealing of wire. Al-oxide participated in bubble formation for wire was exidsted as separate one from K-Si oxide in sintered ingot. The substructure of as-drawn state was observed by using TEM(transmission electron microscopy) to understand the reaction of Al-oxide with K-Si oxide during wire making process. It was cautiously concluded that the participation of Al in bubble formation should be assisted by the deformation processes such as swaging and drawing inducing the distribution of bubble formation substance along the tangled dislocation cell boundaries.
몰리브덴 판재의 두께 방향에서 CaO , MgO 의 조성차가 재결정과 결정립성장에 미치는 영향
유명기(Myoung Ki Yoo),평강 유(Yutaka Hiraoka),최주(Ju Choi) 대한금속재료학회(구 대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.1
Preparation of double-layered grain structure was stuided in molybdenum (Mo) sheet. Mo powder doped with CaO and MgO (D-layer) and pure Mo powder (P-layer) were compacted at 300MPa in sequence of P-D-P and D-P-D. The compacts were sintered at 1850℃ and straight rolled by 70% reduction in thickness. Microstructures in thickness direction were observed by optical, scanning electron and transmission electron microscopies. Pole intensities were also calculated for a specific [hkl] orientation. To understand the role of dopants, i.e, CaO and MgO during annealing, P-D-P and D-P-D specimens were annealed at 1200℃ for 10hrs, at 1776℃ for 2hrs and at 1950℃ for 2hr under hydrogen atmosphere. D-layers at the surface of D-P-D specimen revealed smaller grain size than D-layer at the center of P-D-P specimen in the range of primary recrystallization (l200℃), At 1776℃, both P-D-P and D-P-D specimens showed secondary recrystallization phenomenon from the surface of specimen, At 1950℃, double-layered grain structure developed in D-P-D specimen while coarse grains formed in P-D-P specimen.
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.
Nakahara Takayuki,Okamoto Yoshihisa,Nagae Masahiro,Yoshio Tetsuo,Kurishita Hiroaki,Takada Jun,Hiraoka Yutaka,Takida Tomohiro 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
In order to overcome the recrystallization embrittlement and irradiation embrittlement of Mo, which are major problems for its fusion applications, internally nitrided Mo alloys were prepared by a novel multi-step internal nitriding. Neutron irradiation was performed in the Japan Material Testing Reactor (JMTR). After irradiation, nitrided Mo alloys exhibited ower ductile-brittle transition temperature than irradiated TZM. These results suggested that multi-step internal nitriding was effective to the improvement in the embrittlement by irradiation. Transmission electron microscope observation revealed that TiN particles precipitated by nitriding acted as a sink for irradiation-induced defects.