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김병천,장영원,이성학,류길열 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.6
In this study, a direct in-situ observation of fracture and crack tip deformation behavior under a wedge loading has been carried out in a scanning electron microscope (SEM) using an HSLA steel and an AISI 4340 steel. A specially designed wedge loading stage was adapted in an SEM for the observation of crack propagation on the surface of small double cantilever beam (DCB) specimens. The results for the HSLA steel with simulated microstructures of the heat affected zone of welding show that the formation of shear bands is primarily responsible for the initiation of microcrack at notch tip and crack propagation. A fracture mechanism for the local brittle zone (LBZ) phenomena has also been identified as the initiation of microvoids by the interfacial decohesion between the ferrite matrix and martensite islands. For the 4340 steel, voids were first observed to form around the large MnS inclusions and the plastic deformation became localized into intense shear bands between these voids as they grew. The failure eventually occurred along these shear bands, although fine microvoids would form around alloy carbides within the shear hands. This in-situ SEM technique has been found very useful for studying the microstructural aspects of crack initiation and crack growth behavior on the surface
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투과전자현미경과 전자후방산란회절을 이용한 AlN의 미세구조 분석
주영준,박청호,정주진,강승민,류길열,강성,김철진,Joo, Young Jun,Park, Cheong Ho,Jeong, Joo Jin,Kang, Seung Min,Ryu, Gil Yeol,Kang, Sung,Kim, Cheol Jin 한국결정성장학회 2015 한국결정성장학회지 Vol.25 No.4
AlN 단결정은 넓은 밴드갭(6.2 eV), 높은 열 전도도($285W/m{\cdot}K$), 높은 비저항(${\geq}10^{14}{\Omega}{\cdot}cm$), 그리고 높은 기계적 강도와 같은 장점들 때문에 차세대 반도체 적용을 위한 많은 흥미를 끈다. 벌크 AlN 단결정 또는 박막 템플릿(template)들은 주로 PVT(Physical vapor transport)법, 플럭스(flux)법, 용액 성장(solution growth)법, 그리고 증기 액상 증착(HVPE)법에 의해 성장된다. 단결정이 성장하는 동안에 발생하는 결함들 때문에 상업적으로 어려움을 갖게 된 이후로 결함들 분석을 통한 결정 품질 향상은 필수적이다. 격자결함 밀도(EPD)분석은 AlN 표면에 입자간 방위차와 결함이 존재하고 있는 것을 보여준다. 투과전자현미경(TEM)과 전자후방산란회절(EBSD)분석은 전체적인 결정 퀄리티와 다양한 결함의 종류들을 연구하는데 사용된다. 투과전자현미경(TEM)관찰로 AlN의 형태가 적층 결함, 전위, 이차상 등에 의해 크게 영향을 받는 것을 알 수 있었다. 또한 전자후방산란회절(EBSD)분석은 전위의 생성을 유도하는 성장 결함으로서 AlN의 zinc blende 폴리모프(polymorph)가 존재하고 있는 것을 나타내고 있었다. Aluminum nitride (AlN) single crystals have attracted much attention for a next-generation semiconductor application because of wide bandgap (6.2 eV), high thermal conductivity ($285W/m{\cdot}K$), high electrical resistivity (${\geq}10^{14}{\Omega}{\cdot}cm$), and high mechanical strength. The bulk AlN single crystals or thin film templates have been mainly grown by PVT (sublimation) method, flux method, solution growth method, and hydride vapor phase epitaxy (HVPE) method. Since AlN suffers difficulty in commercialization due to the defects that occur during single crystal growth, crystalline quality improvement via defects analyses is necessary. Etch pit density (EPD) analysis showed that the growth misorientations and the defects in the AlN surface exist. Transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) analyses were employed to investigate the overall crystalline quality and various kinds of defects. TEM studies show that the morphology of the AlN is clearly influenced by stacking fault, dislocation, second phase, etc. In addition EBSD analysis also showed that the zinc blende polymorph of AlN exists as a growth defects resulting in dislocation initiator.
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