• E2M - 전기 전자와 첨단 소재
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• 제7권1호
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• pp.1-6
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• 1994

Cordierite based glass ceramics has become an electronic substrate material for electronic circuits and the use of whickers for improving strength and toughness is evident. Pure cordierite containing 15 vol.% silicon nitride were sintered by hot-prossing and it has above 99% density. Especially, it is assumed that toughening increasing at the more high sintering temperature relevants to the glass phase increasing, as showned in the roughness of the fracture surfaces. It was directionally dependent of whisker drirection during processing.

• 한국세라믹학회지
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• 제53권6호
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• pp.575-580
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• 2016

Microstructural design of ceramics has generally focused on information gathered at the micro- and macro-scales and related this to how specific properties could be improved. Ceramic processing serves as the key to optimizes the final microstructure. However, the advent of nano-scale microstructures and highly advanced characterization tools are forcing us to develop new knowledge of what is occurring not just at the micro-scale but also at the atomic level. Thus we are now beginning to be able to address how microstructure is influenced by events at the atomic scale using atomic scale images and data. Theoreticians have joined us in interpreting the mechanisms involved in the "microstructural" evolution at multiple scales and how this can be used to enhance specific properties of ceramics. The focus here is on delving into the various layers the "microstructure" in order understand how atomic-scale events influence the structure and properties of ceramics.

• 한국재료학회지
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• 제7권3호
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• pp.224-228
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• 1997

2종류의 질화규소에 대하여 Ring형시험편을 이용하여 접촉피로시험을 하였다. 질화규소는 금속재료에서와 같은 형태의 피로현상을 나타냈고, 파면해석 및 관찰결과 접촉피로에 있어서 균열의 발생은 고탄소크롬강의 경우와 같이 표면하의 반복전단응력에 의한 것으로 밝혀졌다. 그리고 시험펴 파단면에서 표면하의 Heltz전단응력의 변동이 최대로 되는 깊이의 위치에 다수의 균열이 관찰되었다.

• 한국세라믹학회지
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• 제24권4호
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• pp.364-368
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• 1987

The Si5AION7 specimens containing 20% YAG composition have been sintered and then heat treated to induce the crystallization of the matrix glassy phase. Crystallization of YAG phase during the heat treatment was detected from the X-ray diffraction patterns and the consequent changes in room temperature toughness as well as in microstructures were investigated. Almost all the glassy boundary phase were found to crystallize even after 5 minutes of heat treatment and the KC at room temperature decreased accordingly. The results show that the matrix crystallization can be induced by slow cooling from the sintering temperature.

• 한국결정성장학회지
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• 제8권1호
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• pp.111-116
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• 1998

질화규소는 고경도, 고인성 세라믹 재료이기 때문에, 기계적 가공성은 매우 나쁘며, 또한 질화규소는 높은 전기 저항을 갖는다. 매우 높은 전기저항을 띠는 질화규소에 30wt% 이상의 TiN 분말이 첨가되었을 때 전도성 세라믹 복합체가 된다. 높은 전기 전도도를 가질 때 세라믹을 방전가공방법(EDM)을 이용하여 정밀한 가공을 할 수 있다. 높은 전기 전도도를 갖는 $Si_3N_4-TiN$ 세라믹 복합체는 EDM 방법을 이용하여 금속 가공 tool을 만드는데 이용되며, 이러한 tool 재료들은 산화뿐만 아니라 심각한 마모문제를 갖는다. 상압소결후 post HIP 소결방법으로 $Si_3N_4-TiN$ 복합체를 만들었으며, TiN의 양의 변화에 따른 $Si_3N_4$ 복합체의 마모특성을 상온의 대기중에서 조사하였다. 경도, 파괴인성, 강도값을 마모량과 비교하였다. 마모흔의 SEM 관찰로 $Si_3N_4-TiN$ 복합체의 마모기구를 설명하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제34권7호
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• pp.963-970
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• 2010

This study makes an estimate of the laser-assisted machining (LAM) of an economically viable process for manufacturing precision silicon nitride ceramic parts using a high-power diode laser (HPDL). The surface is locally heated by an intense laser source prior to material removal, and the resulting softening and damage of the workpiece surface simplify the machining of the ceramics. The most important advantage of LAM is its ability to produce much better workpiece surface quality compared to conventional machining. Also important are its larger material removal rates and longer tool life. The cutting force and surface temperature were measured on-line using a pyrometer and a dynamometer, respectively. Tool wear, chips and the surface of the workpiece were measured using optical microscopy, and the surface and fractured cross-section of $Si_3N_4$ were measured by SEM. During the LAM process, the cutting force and tool wear were reduced and oxidation of the machined surface was increased according to the increase in the laser power. Moreover, the more the feed rate increased, the more the cutting force and tool wear increased.

• 대한기계학회논문집
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• 제18권10호
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• pp.2597-2605
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• 1994

The wear behavior of two types of $Si_3N_4$ exposed to high and low humidity was examined at various sliding speeds, using bearing steel as disk material under pin-on-disk type sliding conditions. Higher wear rates were obtained at a high humidity than at a low humidity. As the sliding speed was increased, the wear rates were decreased and the effect of humidity on the wear rates of $Si_3N_4$ was reduced. The result that the $Si_3N_4$ pin showed higher wear rate under the high humidity condition was explained by the decrease in microhardness of $Si_3N_4$ due to the chemisorbed moisture on the pin and plowing action by the hard particles of $Fe_2O_3$ from the disk. An increase in the sliding speed is supposed to reduce the effect of humidity on the wear rate of $Si_3N_4$ by raising the average temperature of the disk surface and the local temperature at pin-disk contact point.

• Tribology and Lubricants
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• 제16권2호
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• pp.121-125
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• 2000

Silicon nitride ceramic has been verified as an excellent rolling bearing material because of its high strength and outstanding rolling fatigue life properties. However under some corrosive circumstances it showed drawbacks such as hardness reduction and severe wear caused by corrosion. In this work, the variations of the rolling wear and hardness of three kinds of ceramics were studied for the specimen aged 15 days in alkali water (90 $\pm$ 2$\^{C}$,25 wt% NaOH ). All of the specimens, ① Si$_3$N$_4$, ② 3Y-TZP and ③ 3Y-TZP alloyed with 5 wt% CeO$_2$, were sintered and post-HIPed, and then polished up to 0.02 $\mu$mRa of surface roughness. Rolling wear tests were conducted by MJ type rolling fatigue life tester under the initial theoretical maximum contact stress of 3.16 GPa and the spindle speed of 1,000 rpm. Spindle oil was used as a lubricant. The specimens were not worn before aging. For the specimen aged in alkali water, Si$_3$N$_4$ and 3Y-TZP were worn by rolling wear tests, and hardness was decreased. While aging the specimens, the phase was transformed from tetragonal to monoclinic in 3Y-TZP and the microstructure change occurred in Si$_2$N$_4$. 3Y-TZP specimens alloyed with 5 wt% CeO$_2$ were not worn after aging and no phase transformation occurred while aging.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.154-159
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• 1999

Silicon nitride ceramic has been verified as an excellent rolling bearing material because of its high strength and outstanding rolling fatigue life properties. However under some corrosive circumstances it showed drawbacks such as hardness reduction and severe wear caused by corrosion. In this work, the variations of the rolling wear and hardness of three kinds of ceramics were studied for the specimen aged 15 days in alkali water (90$\pm$2$^{\circ}C$, 25 wt% NaOH). All of the specimens, \circled1Si$_3$N$_4$, \circled23Y-TZP and \circled33Y-TZP alloyed with 5 wt% CeO$_2$, were sintered and post-Hipped, and then polished up to 0.02 ${\mu}{\textrm}{m}$Ra of surface roughness. Rolling wear tests were conducted by MJ type rolling fatigue life tester under the initial theoretical maximum contact stress or 3.76 Gra and the spindle speed of 1,000 rpm. Spindle oil was used as a lubricant. The specimens were not worn before aging. For the specimen aged in alkali water, Si$_3$N$_4$and 3Y-TZP were worn by rolling wear tests, and hardness was decreased. While aging the specimens, the phase was transformed from tetragonal to monoclinic in 3Y-TZP and the microstructure change occurred in Si$_3$N$_4$. 3Y-TZP alloyed with 5 wt% CeO$_2$specimens were not worn after aging and no phase transformation occurred while aging.

• 한국레이저가공학회지
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• 제9권2호
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• pp.23-30
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• 2006

Silicon Nitride $(Si_3N_4)$, which is widely used in a variety of applications, is hard-to-machine due to its high hardness. At high temperature (e.g. above $1000^{\circ}C)$, however, the machinability can be greatly improved. In this work, we used a $CO_2$ laser with a high absorptivity to $Si_3N_4$ of 0.9 to locally heat the surface of a rotating $Si_3N_4$ rod on a lathe. In order to examine the effects of the laser-assisted heating on hardness, an $Si_3N_4$ rod is heated to temperatures from 900 to $1800^{\circ}C$ and is rotated at speeds from 440-900 rpm in experiments. When the rod is naturally cooled to room temperature, we measured the Vickers hardness (Hv); and observed the surface of HAZ using a scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) was used for ingredient analysis. Results showed that when heated at $1600^{\circ}C$, the hardness of $Si_3N_4$ decreased from 1500 Hv to 1000 Hv. Also, in order to predict the depth of HAZ, we numerically analyzed the laser-assisted heating of $Si_3N_4$.