• 한국분말재료학회지
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• 제1권2호
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• pp.153-158
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• 1994

The effect of the role of alloyed components on the densification of two kind of high speed steel (mixed and prealloyed powder), which were sintered at 1403~ 1573 K for 7.2 ks in vacuum, was investigated. The results obtained were as follows. (1) Without the presence of Vanadium (V), the relative density of sintered compacts (Ds) could not reached the density of 100% regardless of the. elements in the compacts. (2) The addition of V up to 2 mass% did not result In the complete densification when the carbon content was fixed at 2% in the compact. (3) With the fixed amount of V of 7%, Ds decreased with the increase of the carbon content. (4) The addition of mixed fine powder to the prealloyed powder in the range of 20 to 40% provided the complete densification and carbide panicles of 1~2 $\mu\textrm{m}$ through the solid phase sintering. (5) The V element played important role in controlling the complete or incomplete densification of the sintered compacts in the alloyed component because of its formation of stable oxide and carbide as well as the low equilibrium pressure of CO gas.

• 한국세라믹학회지
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• 제49권1호
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• pp.124-129
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• 2012

An M-shaped SiC gas igniter was fabricated by a reaction sintering followed by nitrogen doping. The igniter showed both resistivity at room temperature and NTC to PTC transition temperature values that were lower than those of commercial igniters. It was deduced that the doped nitrogen reduces the electrical resistivity at room temperature, while, at high temperature, the doped nitrogen and a trace of $Si_3N_4$ phase work as scattering centers against electron transfer, resulting in a lowered NTC-to-PTC transition point (below $650^{\circ}C$). Such characteristics were correlated to the fast heating speed (as compared to the commercial models) and to the prevention of the high temperature overshooting of the nitrogen-doped SiC igniter.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.898-901
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• 2000

It is known that Si3N4 ceramic insert has less hardness than Al2O3 ceramic insert. But Si3N4 ceramic insert has not only high toughness and strength but also low thermal expansion coefficient, which makes it has longer tool life under thermal stress condition. In this study, commercial Si3N4 ceramic insert and home-made SiC-Si3N4 ceramic insert which has different sintering time and chemical composition is tested under various cutting conditions. The experimental result is compared in terms of tool life and cutting force. Generally, As the cutting speed and the feed rate increased, the cutting force and the flank wear increased too. The performance of SiC-Si3N4 ceramic insert shows the possibility to be a new ceramic tool.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 추계학술대회논문집 - 한국공작기계학회
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• pp.386-391
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• 2000

It is known that Si$_3$N$_4$ceramic insert has less hardness than A1$_2$O$_3$ceramic insert. But Si$_3$N$_4$ceramic insert has not only high toughness and strength but also low thermal expansion coefficient, which makes it has longer tool life under thermal stress condition. In this study, commercial Si$_3$N$_4$ ceramic insert and home-made SiC-Si$_3$N$_4$ceramic insert which has different sintering time and chemical composition is tested under various cutting conditions. The experimental result is compared in terms of tool life and cutting force. Generally, As the cutting speed and the feed rate increased, the cutting force and the flank wear increased too. The performance of SiC-Si$_3$N$_4$ceramic insert shows the possibility to be a new ceramic tool.

• 한국세라믹학회지
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• 제31권3호
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• pp.265-274
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• 1994

Intermetallic Ti-Si system ceramics were synthesized from stochiometric mixtures of titanium and silicone powders in vacuum by Self-propagating High-temperature Synthesis(SHS). In each cases of Ti5Si3, Ti5Si4 and TiSi, and TiSi2 synthesis, 20wt% product dilution, direct ignition and SHS chemical furnace method were employed. The combustion modes, which were observed during the synthesis process by using the high speed camera, of Ti5Si3, Ti5Si4, TiSi, and TiSi2 exhibit spin, osciallatory, steady-state, and spin combustion, respectively. With increasing Ti/Si molar ratio an decrease of combustion velocities was found. From the results on the measurement of the flexural strength, the specimen hot pressed at 135$0^{\circ}C$ for 30 min using synthesized Ti5Si4 powders showed the highest flexural strength at 215 MPa.

• 한국재료학회지
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• 제12권8호
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• pp.656-660
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• 2002

It was investigated that $Al_2$$O_3$/Cu nanocomposite powder could be optimally prepared by dispersion and reduction of Cu oxide, and suitably consolidated by employing pulse electric current sintering (PECS) process. $\alpha$-$Al_2$$O_3$ and CuO powders were used as elemental powders. In order to obtain $Al_2$O$_3$ embedded by finely and homogeneously dispersed CuO particles, the elemental powders were high energy ball milled at the rotating speed of 900 rpm, with the milling time varying up to 10 h. The milled powders were heat treated at $350^{\circ}C$ in H$_2$ atmosphere for 30 min to reduce CuO into Cu. The reduced powders were subsequently sintered by employing PECS process. The composites sintered at $1250^{\circ}C$ for 5 min showed the relative density of above 98%. The fracture toughness of the $Al_2$$O_3$/Cu nanocomposite was as high as 4.9MPa.$m^{1}$2//, being 1.3 times the value of pure $Al_2$$O_3$ sintered under the same condition.

• 한국산학기술학회논문지
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• 제9권4호
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• pp.892-898
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• 2008

3차원 쾌속 조형법은 컴퓨터에 저장되어있는 객체 데이터를 이용하여 시제품을 제작하는 기술로써, 기존의 나무나 클레이, 혹은 주조 제작방식과는 달리 원하는 위치에 요구되는 재료를 직접 적층함으로써 원형제품을 제작함을 특징으로 한다. 스테레오리쏘그래피, 용융 점착법, 선택적 레이저 소결법, 판상 제작법 등의 다양한 3차원 쾌속 조형법이 개발되었으나, 그 중에서 잉크젯을 통한 3차원 쾌속 조형법은 잉크화된 조형재료를 통해 구조적으로 기능이 가능한 원형제품의 제작이 가능하다는 특징이 있다. 그러나, 기능성 원형제품의 제작을 위해서는 잉크의 고농도화가 요구되며, 이로 인해 잉크 점도가 상승되어 젯팅 신뢰성이 저하되는 문제점이 있었다. 본 논문에서는 3차원 쾌속 조형법을 위한 최적 젯팅조건을 도출하기 위해 슬러리 타입 세라믹 상변화 잉크의 음파 전달속도 측정과 음파 전달속도가 젯팅에 미치는 영향을 고찰하도록 한다.

• 한국정밀공학회지
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• 제18권9호
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• pp.89-95
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• 2001

Ceramic tool has to equip with not only high toughness and strength but also low thermal expansion and good thermal conductivity which leads to the high thermal shock resistance. These characteristics make it have longer tool life under thermal stress condition. In this study, commercial Si$_3$N$_4$ceramic cutting tool and home-made SiC based ceramic cutting tools which have different sintering time and chemical composition are tested under various cutting speed and the feed rate increase, the cutting force and the flank wear growth ratio increase, too. The performance of home-made SiC based ceramic cutting tool shows the possibility to be a new ceramic tool.

• 한국세라믹학회지
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• 제48권2호
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• pp.152-159
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• 2011

The green and hard machining characteristics of dental ceramics are of great interest to dental industry. The green bodies of TZP/$Al_2O_3$ composites were prepared by the cold isostatic pressing, and machined on the CNC lathe using PCD (polycrystalline diamond) insert under various machining conditions. With increasing nose radius of PCD insert, surface roughness initially increased due to increased cutting resistance, but decreased by the onset of sliding fracture. The lowest surface roughness was obtained at spindle speed of 1,300 rpm and lowest feed rate. Hard bodies were prepared by pressureless sintering the machined green bodies at several temperatures. The grinding test for sintered hard body was conducted using electroplated diamond bur with different grit sizes. During grinding, grain pull out in the composite was occurred due to thermal expansion mismatch between the alumina and zirconia. The strength of the composite decreased with alumina contents, due to increased surface roughness and high monoclinic phase transformed during grinding process. The final polished samples represented high strength by the elimination of a phase transformation layer.

• 구강회복응용과학지
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• 제37권4호
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• pp.177-185
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• 2021

기존의 3 mol%의 이트라아(Y₂O₃)로 안정화된 정방정 지르코니아(3 mol% yttria stabilized tetragonal zirconia polycrystal, 3Y-TZP) 뿐만 아니라 이트리아 함량이 증가된 반투명 지르코니아(translucent zirconia)를 이용한 단일구조 지르코니아 보철물의 사용이 증가하면서 치과용 지르코니아의 광학적 성질에 영향을 미치는 요소에 대한 연구가 지속적으로 이루어지고 있다. 이트리아 함량, 보철물 두께, 소결과정, 연마 및 광택소성 그리고 치과용 시멘트 등과 같은 치과기공실 및 진료실 과정의 처리 방법에 따라 치과용 지르코니아의 광학적 효과가 다르게 나타난다. 이트리아 농도의 증가는 반투명도의 개선과 동시에 차폐효과의 감소를 유발할 수 있으며 수복물 두께가 증가할수록 반투명도는 감소하지만 지르코니아 블록의 물성에 따라 요구되는 두께가 다르므로 주의해야 한다. 고속소결 방식은 제작시간을 단축시키나 경우에 따라 보철물의 반투명도가 감소할 수 있다. 지르코니아의 표면거칠기 및 광택소성 처리에 따라 광학적 결과도 영향을 받을 수 있다. 적절한 유색 시멘트의 사용은 지르코니아의 차폐효과에 도움이 되어 보다 자연스러운 보철치료가 가능하다.