• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2003년도 추계총회 및 연구발표회 초록집
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• pp.62.1-62
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• 2003

• 한국정밀공학회지
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• 제26권5호
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• pp.48-56
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• 2009

In this paper, laser-assisted machining(LAM) has been employed to machine hot isostatically pressed (HIPed) Si3N4 work pieces. Due to little residual flaws and porosity, HIPed $Si_3N_4$ work pieces are more difficult to machine compared to normally sintered $Si_3N_4$ workpieces. In LAM, the intense energy of laser was used to enhance machinability by locally heating the workpiece and thus reducing yield strength. In experiments, the laser power ranges from 200W to 800W and the diameter of work pieces is 16mm. While machining, the surface temperature was kept nearly constant by laser heating except for a short period of rise time of max. 58 seconds. Results showed as feed rate increases the surface temperature of $Si_3N_4$ workpieces decreases slightly, whereas the effect of depth of cut is disregardable. With a laser power of 800W, achievable maximal depth of cut as 0.7mm and feed rate was 0.03mm/rev.

• Journal of Welding and Joining
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• 제28권6호
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• pp.40-44
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• 2010

Laser assisted machining (LAM) has been researched in order to machine the silicon nitride ceramics economically and effectively. LAM is an effective machining method by local heating of the cutting part to the softening temperature of the silicon nitride using laser beam. When silicon nitride ceramics is heated using a laser beam, the surface of silicon nitride ceramic is softened, oxidized and decomposed. And then surface hardness is decreased. Through machining in low viscosity and hardness conditions, silicon nitride was machined effectively and the life span of tool was increased. The plastic deformation was occurred due to softening of amorphous YSiAlON above $ 1,000^{\circ}C$. Transgranular fracture of ${\beta}-Si_3N_4$ was occurred when YSiAlON was not softened, but mostly intergranular fracture was occurred by the plastic deformation of softened YSiAlON.

• 한국재료학회지
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• 제10권1호
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• pp.83-89
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• 2000

$Si_3N_4$에 2wt% $Al_2O_3$와 6wt% $Y_2O_3$을 첨가한 분말을 가스압 소결 방법으로 시편을 제조하였다. 이때 소결시 시간변화에 따른 공기 중에서 마모 특성을 비교하였다. 소결 시간에 따른 마모 특성의 변화는 기계적 성질, 즉, 파괴인성 등이 영향을 주는 것으로 나타났다. 소결 시간이 길어지면 큰 elongated 입자의 과잉성장에 따라 곡강도 및 파괴인성이 낮아져 이 결과 마모가 증가되었다. 이때 나타난 결과에 의하면 공기 중에서 질화규소의 마모특성에 영향을 주는 인자는 여러 가지 기계적 특성 중에서 파괴인성 및 곡강도가 미치는 영향이 크게 나타났다.

• 한국세라믹학회지
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• 제36권2호
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• pp.210-219
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• 1999

Alcohols, hydrocarbons, ketones 그리고 ethers와 같은 다양한 유기용매에서 질화규소 및 소결첨가제로 사용되는 AlN, Nd2O3 입자의 분산특성을 연구하였다. 분산안정화기구 및 유기공정첨가제와의 상호작용에 관한 연구를 수행하여 비수계 시스템에서 세라믹 입자의 분산성을 규명하였다. 현탁액의 물성특성은 산술된 Hamaker 상수 뿐 아니라 electrokinetic sonic amplitude 측정 및 유동학적 결과로부터 얻어진 흐름곡선을 이용하여 평가하였다. 유기용매 내에서 Si3N4, AlN 그리고 Nd2O3 분산안정화에 기여하는 정전기적 척력은 예상보다 컸으며, 이것은 유기용매의 물리화학적 특성에 의존함을 알 수 있었다.

• 한국세라믹학회지
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• 제35권7호
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• pp.659-664
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• 1998

구조재료용 요업체로 널리 쓰이는 질화규소 요업체를 2단계 가스압 소결 방식에 의해 치밀화시켰을 때의 효과를 상압조절, 단순 가스압소결 또는 HIP 처리시와 비교하였다. 상압 소결시에는 $1800^{\circ}C$ 이상에서 분해가 일어나지만 질소 가스에 의한 가스압 소결시에는 소결 온도를 더 높일 수 있어서 ${\beta}-Si_3N_4$ 침상 조직의 발달을 이룰 수 있었다. 질소 가스압이 2MPa 정도이면 $1890^{\circ}C$까지도 상압소결시에 비해 분해가 현저히 억제될 수 있어서, 폐기공이 형성될 수 있는 단계까지는 분해만 억제시킬 수 있는 정도의 비교적 낮은 압력으로 치밀화시키고, 이어서 10MPa의 높은 압력을 가하는 소위 2단계 가스압 소결시 경도와 인성이 증진되는 것을 확인할 수 있었다.

• 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.

• 한국정밀공학회지
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• 제26권4호
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• pp.47-54
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• 2009

In the last few years, lasers have found new applications as tools for ceramic machining which is laser-assisted machining(LAM). LAM process for the machining of difficult-to-machine materials such as structural ceramics, has recently been studied on silicon nitride workpiece for a wide range of operating condition. However, there have been few studies on rake angle in LAM process. In this paper we analyzed difference of machinability between positive and negative rake angle in tools. We have obtained interesting results that we could eliminate chattering, lower specific cutting and cutting ratio in case of positive rake angle. The results suggest that positive rake angled tools can make more plastic deformation and stable cutting of silicon nitride in comparison with negative rake angled one.

• 대한기계학회논문집
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• 제17권6호
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• pp.1441-1455
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• 1993

본 연구에서는 최신기법에 의해서 제조된 HIP제 질화규소와 지르코니아를 실험재료로 하여 무윤활하에서의 미끄럼마찰·마멸실험을 수행하여 마찰·마멸특성을 규명하고, SEM을 이용한 마멸면의 미시적 관찰을 통해서 세라믹의 마멸기구를 조사하 여 세라믹마멸기구의 마멸모델을 제시하고자 한다. 제시된 마멸모델에서 파괴역학을 도입하여 이론해석과 고찰을 수행하여 보다 실용적인 세라믹의 마멸율울 평가할 수 있 는 새로운 무차원 파라메터를 제안하고자 한다.

• Journal of Welding and Joining
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• 제28권4호
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• pp.61-66
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• 2010

Silicon nitride is widely used as an engineering ceramics because it has high strength, abrasion resistance and corrosion resistance even at high temperature. However, machining of silicon nitride is difficult due to its high hardness and brittleness. Laser assisted machining(LAM) allows effective cutting using CBN tool by locally heating the cutting part to the softening temperature of YSiAlON using the laser beam. The effect of preheating depending on process parameters were studied to find out the oxidation mechanism. If silicon nitride is sufficiently preheated, the surface is oxidized and $N_2$ gas is formed and escapes from the material, thereby making the cutting process more advantageous. During laser preheating process before machining, high temperature results in strong oxidation which makes the bloating, silicate layers and micro cracks. Using the results of these experiments, preheating characteristics and oxidation behavior were found out.