• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1994년도 춘계학술대회강연 및 발표대회 강연및 발표논문 초록집
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• pp.6-6
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• 1994

Har dmaterials such as cemented carbides with or without coated layer, cermets, ceramics and diamond or c-BN high pressure sintered compact are used for cutting tools, wear -resistant parts, rock drilling bits and/or high pressure vessels. These hardmaterials contain not only hard phase, but also second consituent as the element for forming ductile phase and/or sintering aid, and the mechanical properties of each material depend on (1) the amount of the second constituent as well as (2) the grain size of the hard phase. The hardness of each material mainly depends on these two factors. The fracture strength, however, largely depends on other microstructur a1 factors as well as the above two factors. For all hardmaterials, the fracture strength is consider ably affected by (3) the size of microstructur a1 defect which acts as the fracture source. In cemented carbides, the following factors which are generated mainly due to the addition of the second constituent are also important; (4) the variation of the carbon content in the normal phase region free from V-phase and graphite phase, (5) the precipitation of $Co_3$ during heating at about $800^{\circ}C$,(6) the domain size of binder phase, and (7) the formation of ${\beta}$-free layer or Co-rich layer near the surface of sintered compacts. For cemented carbides coated with thin hard substance, the important factors are as follows; (8) the kind of coated substance, (9) the formation of ${\eta}$-phase layer at the interface between coated layer and substrate, (10) the type of residual stress (tension or compression) in the coated layer which depends on the kind of coating method (CVD or PVD), and (11) the properties of the substrate, and (12) the combination, coherency and periodicity of multi-layers. In the lecture, the details of these factors and their effect on the strength will be explained.

• 한국세라믹학회지
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• 제29권6호
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• pp.441-450
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• 1992

The microstructur and LPG sensing properties of maghemite (${\gamma}-Fe_2O_3$) ceramics have been studied. The acicular and fine spherical shaped iron oxide particles were sintered at below $900^{\circ}C$. The maghemite ceramics were prepared by reduction-oxidation of sintered iron oxide. With the microstructure of acicular and/or fine grains, the maghemite ceramics have good LPG sensing properties. Increased sintering temperature deteriorates the LPG sensitivity of maghemite ceramics due to the grain growth. The maghemite ceramics prepared from the mixed iron oxide, of a large amount of acicular particles and a small amount of spherical ones, have a lower LPG sensitivity than that of the acicular iron oxide ceramics. But, they seem to be of higher mechanical strength. The optimum working temperature for LPG sensing of the maghemite ceramics was found to be $300~350^{\circ}C$.

• International Journal of Advanced Culture Technology
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• 제3권1호
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• pp.179-187
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• 2015

This study presents the experimental results of the Friction Stir Welding (FSW) of AA6063 aluminum alloy and AISI304 stainless steel butt joint by varying the welding parameters such as the rotating speed and the welding speed. The main results are as follows. The variation of the welding parameters produced various characteristic interfaces and had distinct influences on the joint properties. Increasing the rotating speed and the welding speed decreased the joint tensile strength because it produced the defect on the joint interface. The optimum welding parameter that could produce the sound joint was a rotating speed of 750 rpm and the welding speed of 102 mm/min with the tensile strength of 71 MPa.

• 열처리공학회지
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• 제37권1호
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• pp.23-28
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• 2024

As global warming accelerates, the transportation industry is increasing the use of lightweight materials with the goal of reducing carbon emissions. Magnesium is a suitable material, but its poor formability limits its use, so research is needed to improve it. Rare-earth elements are known to effectively control texture development, but their high cost limits commercial. In this study, changes in microstructure and texture were investigated by adding Pb, which is expected to have a similar effect as rare-earth elements. The material used is Mg-15wt%Pb alloy. Initial specimens were obtained by rolling at 773 K to a rolling reduction of 25% and heat treatment. Afterwards, plane strain compression was performed at 723 K with a strain rate of 5×10^-2s^-1 and a strain of -0.4 to -1.0. As a result, recrystallized grains were formed within the microstructure, and the main component of the texture changed from (0,0) to (30,26). The maximum axial density was initially 10.01, but decreased to 4.23 after compression.

• 한국재료학회지
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• 제6권8호
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• pp.833-840
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• 1996

MPECVD법을 이용하여 다이아몬드 박막을 p형 Si(100)기판 위에 증착하였다. 증착하기에 앞서, 핵생성 밀도를 향상시키기 위하여 40-$60\mu$m 크기의 다이아몬드 분말을 사용하여 6분간 초음파 전처리를 행하였다. 이런 전처리 과정 후, 다이아몬드 박막을 $^900{\circ}C$, 40Torr, 1000W microwave power에서 ${CH}_{4}$와 ${H}_{2}$사용하여 증착하였다. 이렇게 형성된 다이아몬드 박막의 순수도는 Raman spectroscopy로 측정하였으며 박막의 표면은 SEM으로 , 그리고 미세구조와 미세결함은 TEM으로 조사하였다. 반응기체 중 CH4의 농도가 증가함에 따라 다이아몬드의 정형적인 Raman peak와 더불어 다이아몬드가 아닌 제 2상의 peak가 증가하였다. SEM에 의한 박막의 표면은 ${CH}_{4}$가 증가함에 따라 박막의 표면이 뚜렷한 결정형상에서 cauliflower 형태로 변화하였다. 다이아몬드 박막의 결함밀도는 ${CH}_{4}$농도가 증가함에 따라 증가하였으며 결함 중 대부분은 {111}twin이였다. 그리고 MTP(Mulitply Twinned Particle)는 5개의 (111)면으로 형성된 결정으로, 5개의 (111)면은 각각에 대해서 Twin되어 있으며 five-fold symmetry를 나타내었다. 계면에서는 다이아몬드내의 결함들이 핵생성 site를 함유한 작은 지역에서부터 V형재로 퍼져 나갔다.