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다층원소박판에서 $TiAl_3$의 고온자전합성에 미치는 승온속도의 영향
김연욱,김병관,남태운,허보영,김영직,Kim, Yeon-Uk,Kim, Byeong-Gwan,Nam, Tae-Un,Heo, Bo-Yeong,Kim, Yeong-Jik 한국재료학회 1998 한국재료학회지 Vol.8 No.11
Ti 과 AI의 고순도 원소 박판을 이용하여 열간프레스장치에서 고온자전합성법으로 TiAI계 금속간화합물을 제조하였다. 원소 박판에서 $TiAl_3$ 금속간화합물을 제조하는 데 승온속도, 압력, 온도 등의 변수가 고온자전합성에 영향을 미치는 중요한 인자다. 특히 승온속도는 반응합성온도를 결정하는 인자로서 본 실험에서 DTA 분석을 이용하여 공정변수를 결정하였다. DTA 분석결과에 따르면, Ti와 AI의 계면에서 반응합성은 AI의 용융점 이하와 이상의 온도에서 두 번 발생함을 알 수 있다. 또한 승온속도가 증가할수록 두 반응합성온도는 증가하였다. 10층의 Ti 박판과 9층의 AI 박판을 $20^{\circ}C$/min의 승온속도로 고온자전합성시킨 후, $810^{\circ}C$와 240MPa의 압력에서 4시간 동안 열처리한 결과 $700\mu\textrm{m}$ 두께의 TiAI계 금속간화합물 판재를 제조하였으며, XRD 회절과 SEM으로 확인하였다. Titanium aluminide intermetallic compound was formed from high purity elemental Ti and A1 foils by selfpropagating, high-temperature synthesis(SHS1 in hot press. Formation of $TiAl_3$ intermetallics at the interface between Ti and Al foil was observed to be controlled by temperature, pressure and heating rate. Especially, the heating rate is the most important role to form intermetallic compound by SHS reaction. According to DTA experiment, the SHS reactions appeared at two different temperatures below and above the melting point of Al. It was also observed that both SHS reaction temperatures increased with increasing the heating rate. After the SHS reaction of alternatively layered 10 Ti and 9 A1 foils at the heating rate of $20^{\circ}C$/min, the $700\mu\textrm{m}$ thick titanium aluminide sheet was formed by heat treatment at $810^{\circ}C$ for 4hours.
고 Mole 비 규산소다를 사용한 CO2 주형의 (鑄型) 잔류강도와 (殘留强度) 반응생성물의 성상에 (性狀) 관한 연구
김봉완,남태운,이계완 ( Bong Wan Kim,Tae Woon Nam,Kye Wan Lee ) 한국주조공학회 1988 한국주조공학회지 Vol.8 No.2
N/A The study was carried out to investigate the changes of retained strength and reaction products in the CO₂ sands obtained are as follows. 1) Higher mole-ratio sodium silicates have the lower retained compression strength. 2) Organic liquid additives make a notable decrease in the retained strength and, in case of when use the 2.7 mole-ratio sodium sillicate, the effect is remarkable at the range of temperature to 600℃. 3) Sodium silicate binder forms silica gel with very high bonding force, accompaning an exothemic reaction at the temperatures of around 200℃, and dehydrated brittle silica gel and hydrated sodium silicate glass with sands transformed at the temperature of ahout 600℃. 4) It forms dehydrated glass with sintering of the sand gain surfaces, at the temperatures of around 800℃ and has a value of high retatined strength. 5) The decreases in the retaired strength of CO₂sands are accelerated with the lots of defects resulted from the porosity and cracks in sodium silicate bond films which are caused by the evaporation or combustion of the organic additives.
AISI E 52100 강의 기계적 성질에 미치는 탄화물 크기의 영향
최기윤,김봉완,남태운,이병권 ( K . R . Cho,B . W . Kim,T . W . Nam,B . K . Lee ) 한국열처리공학회 1990 熱處理工學會誌 Vol.3 No.4
A study has been investigated on the effect of mechanical properties (tension strength, rotary bending fatigue strength, wear resistance, hardness) according to the carbide particle size variation by the treatment of 1) quenching tempering, and 2) quenching, subzero treatement and tempering. The material used in this investigation was a typical bearing steel, high C high Cr, AISI E 52100. The result obtained in this study were as follows : (1) Finer the carbide particle size increasing the hardness and retained austenite in same quenching condition. (2) Finer the carbide particle size reduced the tension and rotary bending fatigue which were resulted from austenite grain growth and carbide precipitation on grain boundry that induced by carbide refine heat treatment. (3) Finer the carbide particel size increasing the wear resistance which were resulted by uniform distribution of carbide and increased hardness induced by microstructural uniform hardenability of matrix. (4) When the carbide particles were refinded, subzero treatment is effective only wear resistance and hardness.
304 스테인리스강 용접금속의 열처리에 따른 응력부식균열
조대형,김형래,남태운 ( D . H . Cho,H . R . Kim,T . W . Nam ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.1
Austenite stainless steel was produced by arc welding with current 650A, voltage 50V and welding speed 10㎝/min. It was post-welded and then heat treated at 1,050℃ for 120min. And then it was immersed in water or in air. The microstructural changes, ferrite contents, mechanical properties, and stress corrosion cracking(SCC) were investigated. The SCC was studied in 42wt% boiling MgCl₂(140℃) under the constant stress using SCC elongation curve. The results showed that; 1. The as-welded spedimen seemed to increase δ-ferrite content largely, and revealed continuous network of lathy and vermicular type. The post-welded heat treatment changed the morphologies of ferrite from continuous type to island type. 2. The as-welded, air and water quenched specimens had the δ-ferrite content 9.7%, 3.2% and 2.1% respectively. We also showed that ferrite was Cr-rich and Ni-poor by EPMA. 3. The time of failure on the SCC was measured and it was used for corrosion elongation curve. The condition of SCC was investigated under 35㎏f/㎟ load and the results were as follows; 도표 4. The intergranullar cracking by stress corrosion was most distinct in weld metal while the transgranular cracking occurred in the air cooled specimen.
PECVD법에 의한 TiN, TiCN 증착 시 gradient plasma power가 코팅층에 미치는 영향
김동진 ( D. J. Kim ),신창현 ( C. H. Shin ),허정 ( J. Hur ),남태운 ( T. W. Nam ) 한국열처리공학회 2004 熱處理工學會誌 Vol.17 No.4
N/A Effect of plasma power on PECVD process were investigated in this study. TiN and TiCN films were deposited on nitrided STD11 steel with 600W, 1,200W and 1,600W plasma power. As the plasma power was increased, the preferred orientation was reinforced from (200) to (111) and the hardness of films was improved. The low plasma power was, however, effective for improving of adhesion force of films. Regarding above proper-ties, TiN and TiCN films were deposited by gradient plasma power. It was possible to get high hardness as well as adhesion force through gradient plasma power.
스퀴즈캐스팅용 Salt Core 의 제조 및 용탕침투성에 관한 연구
김기배,노상우,이호인,남태운 ( Ki Bae Kim,Sang Woo Noh,Ho In Lee,Tae Woon Nam ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.4
N/A Developing a salt core for squeeze casting process, two different salt cores(pure salt core and mixed salt core) were fabricated and investigated. Pure salt core was composed of 100% NaCl and mixed salt core was made by mixtures of NaCl with MgO(1%), Na₂B₄O_7(2%), and talc(1%) as a binder or a strengthening agent. Salt cores were compacted to various theoretical density, heat treated, and then squeeze-cast with molten Al alloy(AC8A). The compression strength of salt cores were measured and the squeeze-cast products were examined for shape retention, infiltration of molten metal into the cores, and microstructures. The shape of salt core compacted at above 75% of the theoretical density was maintained stably. The higher theoretical density of salt cores gave higher compression strength, and the compression strength of mixed salt core was higher than that of pure salt core. Namely at 90% theoretical density, the compression strength of mixed salt core was 6.3㎏/㎟, compared to 4.6㎏/㎟` for pure salt core. At a squeeze casting pressure of 1000㎏/㎠, molten Al alloy was infiltrated into pure salt core of under 85% of the theoretical density. At squeeze casting pressure of 1000㎏/㎠, only mixed salt core above 90% of the theoretical density were valid, but the shape of the core was altered in the case of pure salt core at 90% of theoretical density. A key factor for developing a salt core for squeeze casting process was estimated as the ultimate compressive strength of salt core.