• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.106.1-106.1
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• 2012

EBSD(Electron BackScattered Diffraction)분석은 주사전자현미경에서 관찰되는 비교적 넓은 영역의 결정 방위를 측정하여 집합조직을 해석하는 동시에 결정 방위의 변화를 기준으로 결정립계를 구분 지어 미세조직의 정량 분석도 가능하기 때문에 많은 연구자들이 사용하고 있다. 그러나 EBSD의 Kikuchi 패턴은 시편 표면으로부터 30~50nm 깊이 범위의 표면층으로부터 방출되기 때문에 EBSD 분석 결과는 시편의 표면 처리 상태에 크게 영향을 받아 적절한 시편준비법이 요구된다. 시편 준비 과정 중에 생기는 변형층, 산화층이나 오염층이 10nm 이내로 제어되지 못하면 명확한 패턴을 얻지 못하여 분석이 어려운 경우가 많으므로, 시료의 절단과 연마 과정 중에 변형층을 되도록 적게 만들고 표면의 산화나 오염을 최대한 방지해야 한다. 또한 EBSD 분석 특성상 시편을 70도로 기울이기 때문에 시편의 요철이 심하면 볼록한 영역에 의해 오목한 영역의 패턴이 가려져 결정방위 정보를 얻기 힘들다. 이런 이유로 시편을 최대한 평평하게 하고 요철이 생기지 않게 시편 준비를 하는 것이 관건이다. 금속재료의 EBSD 시편준비법으로는 일반적으로 기계적 연마법과 전해연마법이 주로 쓰인다. 경한 석출물이나 개재물이 연한 기지에 분산되어 있는 시편이나 이종 소재 접합재의 경우는 전해연마법을 사용하면 특정 상(혹은 합금)이 먼저 연마되어 큰 단차가 생기거나 석출물에 의해 요철이 심해져서 정량적인 EBSD 분석이 어렵게 된다. 이 연구에서는 시편 준비가 어렵다고 알려진 다상 금속재료에서의 EBSD 분석 사례를 소개한다. Ti-6Al-4Fe-0.25Si 시효처리합금, 알루미늄 기지 복합재료, 마찰교반용접한 알루미늄-타이타늄합금의 EBSD 시편준비법과 그 분석 결과를 고찰한다.

• 한국주조공학회지
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• 제29권4호
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• pp.176-180
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• 2009

Effect of matrix microstructure on creep behaviors of squeeze cast magnesium matrix composites was investigated. Aluminum borate whisker was used as reinforcement and AZ31, AS52 and Sr added AS52 Mg alloys were used for matrix alloys. The reinforcement was distributed homogeneously and defect-free composite was manufactured. Creep tests were carried out at the temperature of $150^{\circ}C$ under the applied stress of 50 and 100 MPa for Mg alloys and Mg MMCs, respectively. The creep resistance of Mg MMCs was in this order: AS52-Sr > AS52 AZ31 MMCs. Void initiation during creep mainly occurred at $Mg/Mg_{17}Al_{12}$ interface and propagation went along grain boundaries. On the other hand, $Mg_2Si$ phase was not attributed to the creep void initiation.

• 한국전기전자재료학회논문지
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• 제31권7호
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• pp.496-501
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• 2018

In this study, we prepared 40, 45, 50, 55, 60, 65, and 70 wt% content composites filled in epoxy matrix for two micro silica and three micro alumina types for use as a GIS heavy electric machine. As a filler type of epoxy composite, micro silica composites showed excellent AC breakdown strength properties compared to micro alumina composites in the case of electrical properties of micro silica and alumina. The electrical breakdown properties of micro silica composites increased with increasing filler content, whereas those of micro alumina decreased with increasing filler content. In the case of mechanical properties, the micro silica composite showed improved tensile strength and flexural strength compared with the micro alumina composite. In addition, mechanical properties such as tensile strength and flexural strength of micro silica and alumina composites decreased with increasing filler content. This is probably because O-H groups are present on the surface of silica in the case of micro silica but are not present on the surface of alumina in the case of micro alumina.

• 공업화학
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• 제4권3호
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• pp.497-504
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• 1993

본 연구는 고온 구조재료 및 전자재료로 주목받고 있는 복합산화물인 mullite($3Al_2O_3${\cdot}2SiO_2$)를 금속알콕사이드에 의한 졸-겔법으로 합성함에 있어서 재활용품으로서의 aluminium foil을 aluminium 금속원으로 사용하여 알루미늄 알콕사이드를 제조하고 $Si(OC_2H_5)_4$와 혼합하여 가수분해 단계에서 건조조절화학첨가제(Drying Control Chemical Additives, DCCA)를 첨가함으로써 건조시간을 단축시키려는 시도를 하였으며 이러한 DCCA가 mullite 물성에 어떠한 영향을 주는지 검토하고자 하였다. 이때 DCCA로 N, N-dimethyl formamide (DMF), Glycerol, 1, 4-Dioxane과 Oxalic acid가 첨가되었으며 건조된 겔을 각 온도별로 소성하여 TG-DTA, FT-IR, XRD 및 SEM을 사용하여 결정의 전이과정 및 각 소성온도에서의 결정상태 등을 관찰하였다. DCCA를 첨가하여 건조시킨 결과 0.1mole의 DMF를 첨가하였을 경우 DCCA를 첨가하지 않았을 때보다 건조시간이 1/2 정도 단축되었으며 분석결과 mullite의 결정형성에 큰 영향을 미치지 않았음을 확인하였다.

• 한국재료학회지
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• 제9권1호
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• pp.35-41
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• 1999

In this study we investigated the effects of process variables on the bond strength, and its dependency upon the interfacial chemistry when the joined $ZrO_2$ toughened $Na\beta$"-alumina to $\alpha$-alumina using B$_2$$O_3$-$SiO_2$-Al$_2$$O_3$-CaO glass sealant. We observed that bond strength is mainly determined by the strength of the glass, which, in turn, depends on the glass composition established after joining reaction. Joining at $950^{\circ}C$ for 15min yielded the highest average bond strength of 66MPa. Different types of interfacial reaction seem to occur at each interface. After joining at $950^{\circ}C$ for 15min we found that Ca and Si diffuse much deeper(~15$\mu\textrm{m}$) into the $\beta$"-alumina composite than into the $\alpha$-alumina(<1$\mu\textrm{m}$) as a result of ion exchange reaction and more effective grain boundary diffusion. Thermal expansion coefficient of the glass was found to have changed more closely to those of the $\beta$"-alumina composite and $\alpha$-alumina, which put the glass under a slight compressive stress.ressive stress.

• 한국분말재료학회지
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• 제16권5호
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• pp.316-325
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• 2009

Fe based (Fe$_{68.2}$C$_{5.9}$Si$_{3.5}$B$_{6.7}$P$_{9.6}$Cr$_{2.1}$Mo$_{2.0}$Al$_{2.0}$) amorphous powder, which is a composition of iron blast cast slag, were produced by a gas atomization process, and sequently mixed with ductile Cu powder by a mechanical ball milling process. The experiment results show that the as-prepared Fe amorphous powders less than 90 $\mu$m in size has a fully amorphous phase and its weight fraction was about 73.7%. The as-atomized amorphous Fe powders had a complete spherical shape with very clean surface. Differential scanning calorimetric results of the as-atomized Fe powders less than 90 $\mu$m showed that the glass transition, T$_g$, onset crystallization, T$_x$, and super-cooled liquid range $\Delta$T=T$_x$-T$_g$ were 512, 548 and 36$^{\circ}C$, respectively. Fe amorphous powders were mixed and deformed well with 10 wt.% Cu by using AGO-2 high energy ball mill under 500 rpm.

• 한국분말재료학회지
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• 제16권5호
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• pp.326-335
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• 2009

Fe based (Fe$_{68.2}$C$_{5.9}$Si$_{3.5}$B$_{6.7}$P$_{9.6}$Cr$_{2.1}$Mo$_{2.0}$Al$_{2.0}$) amorphous powder, which is a composition of iron blast cast slag, were produced by a gas atomization process, and sequently mixed with ductile Cu powder by a mechanical ball milling process. The Fe-based amorphous powders and the Fe-Cu composite powders were compacted by a spark plasma sintering (SPS) process. Densification of the Fe amorphous-Cu composited powders by spark plasma sintering of was occurred through a plastic deformation of the each amorphous powder and Cu phase. The SPS samples milled by AGO-2 under 500 rpm had the best homogeneity of Cu phase and showed the smallest Cu pool size. Micro-Vickers hardness of the as-SPSed specimens was changed with the milling processes.

• 한국정밀공학회지
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• 제16권1호통권94호
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• pp.227-237
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• 1999

As the interface bonding phenomenon between the matrix and the reinforcements has a large effect on the mechanical properties of MMCs, a sugestion of the strength analysis technique considering the residual stress and the interface bonding phenomenon is very important for the design of pans and the estimation of fatigue behavior. In this paper the three dimensional finite element anaysis is performed during the elasto-plastic deformation of the particulate reinforced metal matrix composites. It was analyzed with the volume fractions in view of microscale. Bonding strength. interface separation and matrix void growth between the matrix and the reinforcements will be predicted on deformation under tensile loading. An interface seperation is estimated by the fracture criterion which is a critical value of generalized plastic work per unit volume. The shape of the reinforcement is assumed to be a perfect sphere. And the type of the reinforcement distribution is assumed as FCC array. The thermal residual stress in MMCs is induced by the heat treatment. It is included at the simulation as an initial residual stress. The element birth and death method of the ANSYS program is used for the estimation of the interface bonding strength, void generation and propagation. It is assumed that the fracture in the matrix region begin to occur under the external loading when the plastic work per unit volume is equal to the critical value. The fracture strain will be defined. The experimental data of the extruded $SiC_p$>/606l Al composites are compared with the theoretical results.

• 한국세라믹학회지
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• 제50권1호
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• pp.63-69
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• 2013

Negative-temperature coefficient (NTC) thermistors based on nickel manganite spinel ($NiMn_2O_4$) are widely used for many applications, such as sensors and temperature compensators, due to their good thermistor characteristics and stabilities. However, to achieve thermistors with a high NTC B constant, which is an important figure of merit pertaining to the degree of temperature sensitivity, the activation energy should be high such that high resistivity at ambient temperatures results. To obtain a high B constant and low resistivity, Al and Si modified spinel structured $Ni_{0.6}Si_{0.2}Al_{0.6}Mn_{1.6}O_4$ hybrid thick films with the conducting metal oxide of $LaNiO_3$ were fabricated on a glass substrate by aerosol deposition at room temperature (RT). The NTC-$LaNiO_3$ hybrid thick films showed resistivity as low as < $100k{\Omega}\;cm$ at $90^{\circ}C$, which is one or two orders of magnitude lower than that of the monolithic NTC films, while retaining a high B constant of $NiMn_2O_4$ of over 5500 K when 20 wt% $LaNiO_3$ was added without a post-thermal treatment. These phenomena are explained by the percolation threshold mechanism.

• 한국산학기술학회논문지
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• 제21권7호
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• pp.270-276
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• 2020

3D 프린팅은 고분자, 세라믹, 금속 등 다양한 소재를 대상으로 복합적인 형상을 한 번의 공정으로 제작할 수 있는 적층 기반 제작 기술이다. 최근의 3D 프린팅 기술은 프린팅 속도의 향상과 적용 가능 소재의 지속적인 개발에 의해 양산형 제품 생산이 가능한 수준으로 발전하였다. 본 연구에서는 레이저를 활용한 3D 프린팅 기술을 적용하여 철도 차량용 공기 압축기에 쓰이는 열교환기 제작을 진행하였다. 먼저 3D 프린팅에 적합한 형상으로 경량화 및 컴팩트화를 주안점으로 열교환기의 최적 설계를 진행하였다. 그로부터 도출된 설계안을 기반으로 SLM 기법을 적용하여 AlSi10Mg 합금 소재로 열교환기 시작품을 제작하였다. 다음으로, 제작된 시작품을 기존 공기 압축기에 부착하여, 압축공기의 열교환 성능을 시험하였다. 3D 프린팅 시작품의 시험 결과는 기존 열교환기 대비하여 저압부와 고압부에서 열교환 성능은 각각 약 80% 및 85% 수준을 보였다, 하지만 외부 냉각공기 조건을 기존 열교환기와 유사한 조건으로 가정하였을 때 𝓔-NTU 법을 활용하여 계산한 열전달량은 기존 열교환기 대비하여 유사한 성능을 보여 주었다. 결과적으로, 3D 프린팅 제작 열교환기의 성능 효과 및 경량화 등의 장점을 확인할 수 있었다.