The effect of solidification rate on micro-segregation in investment casting of IN738LC superalloy was studied. In Ni-based superalloys, the micro-segregation of solute atoms is formed due to limited diffusion during cast and solidification. The microstructure of cast Ni-based superalloys is largely divided into dendrite core of initial solidification and interdendrite of final solidification. In particular, mosaic shaped eutectic γ/γ’ and carbides are formed in the interdendrite of the final solidification region in some cases. The micro-segregation phenomena formed in regions of dendrite core and interdendrite including eutectic γ/γ’ and carbides were analyzed using OM, SEM/EDS and micro Vickers hardness. As a result of analysis, the lack of (Cr, W) and the accumulation of Ti were measured in the eutectic γ/γ’, and the accumulation of (Cr, Mo) and the lack of Ti were measured in the interdendrite between dendrite and eutectic. Carbides formed in interdendritic region were composed of (Ti, W, Mo, C). The segregation applied to each microstructure is mainly due to the formation of γ’ with Ni3(Al,Ti) composition. The Ni accumulation accompanied by Cr depletion, and the Ti accumulated in the eutectic region as a γ’ forming elements. The Mo tends to diffuse out from the dendrite core to the interdendrite, and the W diffuse out from the interdendrite to the dendrite core. Therefore, the accumulation of Mo in the interdendrite and the deficiency of W occur in the eutectic region located in the interdendrite. Heat treatment makes the degree of the micro-segregation decrease due to the diffusion during solid solution. This study could be applied to the heat treatment technology for the micro-segregation control in cast Ni-based superalloys.

신종코로나바이러스감염증(코로나19)의 확산과 거리두기와 같은 방역 정책의 시행은 도심의 생활인구 분포에 상당한 변화를 가져왔다. 그러나 이러한 변화의 양상은 서울시 안에서도 상권의 유형과 주거인구의 특성에 따라 다르게 나타나며, 외국인 밀집지역 간에도 해당 지역에 주로 거주하는 외국인의 체류 기간과 이주 목적 등에 따라 상당한 차이를 보일 수 있다. 본 연구에서는 서울의 대표적인 중국인 밀집지역인 가리봉동과 대림2동을 사례로, 두 지역에서 코로나19 확산 이후 내외국인의 분리 수준이 어떻게 변화했는지 살펴볼 것이다. 내외국인의 공간적 분포는 서울 생활인구 데이터를 통해 확인하였으며, 분리 수준의 측정에는 커널 밀도 기반의 측도인 S를 사용하였다. 본 연구 결과는 코로나19가 중국인 밀집지역에 미친 영향을 실증적으로 파악하고, 지역의 특성에 따라 이러한 영향이 차별적으로 나타날 수 있음을 밝혔다는 점에서 의미가 있다.

PURPOSES: The objective of this study is to evaluate of the effect of thermal segregation reduction in asphalt paving using material transfer vehicles (MTVs). METHODS: Asphalt paving using MTVs was carried out, and the paved surface temperature was measured using an infrared camera. The amount of thermal segregation was estimated from temperature variations. RESULTS : The transportation of hot mix asphalt (HMA) using dump trucks caused temperature segregation that persisted in the paving surface if an MTV was not used. The average temperature variation was 8.58% in paved surfaces where an MTV was not used. However, the temperature variation was 3.10%, 2.86%, and 4.53% for the base layer, inter-layer, and surface layer, respectively, when an MTV was used. CONCLUSIONS: The use of an MTV in asphalt paving reduces thermal segregation approximately 2.3 times in an asphalt mat via a remixing process and also allows for a smoother work process because the paver never needs to stop to receive HMA. However, MTV equipment without pre-heating devices requires careful temperature control during the warm up process at the MTV during construction in the winter.

The γ/γ´ two-phases, commonly known as a eutectic structure, are observed in the γ interdendritic region of a Nibase superalloy. However, the growth behavior of the γ/γ´ two-phases, whether it is of eutectic or peritectic nature, has not been decidedly established. Directional solidifications were, thus, performed with the planar interface at a low growth rate of 0.5 μm/s in order to promote macro segregation. Directional solidification started with the γ planar interface and the γ´ phase nucleated on the γ planar interface at the solidification fraction of 0.75. The γ/γ´ two-phases showed the γ´ rod structure as major phase and the γ minor phase between γ´ rods, and the volume fraction of the γ phase changed continuously with an increasing solidification fraction. The two-phase γ/γ´ is seen as the coupled peritectic.

This study was conducted to obtain a growth correlation of basal information from the development of disease resistantFlammulina velutipes cultivars through back-crossing between the strains of wild-type brown monokaryon 4019-20 and thederivative of commercial quality white monokaryons 3. The two strains were selected to back-cross for further enhancing their latentattributes and growth characteristics. The parents of 4019-20×M3 back-crossed to reproduce F1, M3-Sn. Using F1, M3-Sn procuredand isolated into 94 monokaryon strains. Further examination of growth characteristics carried out by back-crossing between M3and BC1F1 from M3-n dikaryon. Monokaryon exhibited an irregular growth pattern and demonstrated to be sluggish development inthe sawdust medium. However BC1F1(M3-n) dikaryon strains confirmed mostly regular growth pattern and demonstrated ordinarygrowth in the sawdust medium. The fruitbody of BC1F1 confirmed as light-brown colour to be the dominant gene. The colourdistributions of fruitbody, BC1F1, resulted as follows; 7% of dark brown, 25% of brown , 27% of light brown, 16% of ivory and 25%of white. The ratio of the other color to white showed 3 to 1 which suggested two major genes were related to fruitbody color.

본 연구는 2005년부터 2007년까지 충북지역 주요 버섯 자생지를 중심으로 채집을 실시하여 이들을 분류 동정하고, 이들 균주를 보존하여 버섯 유전자원 확보 및 자원화 연구의 기초자료로 활용코자 실시한 것으로 그 주요결과는 다음과 같다. 가. 야생버섯 채집균주는 총 79종으로 식용 32종, 약용 3종, 독 15종, 기타(불명) 29종 이었다. 나. 채집된 야생버섯 중 식용 28종에 대한 조직분리를 실시하였고 이중 활력이 좋은 15종의 야생균주를 선발하여 현재 저온보관중이다. 다. 표본제작은 액침표본이 많았으며, 다년생 버섯은 건조표본으로 보관하였고, 자연상태의 자생지에서 채집 균주 79종을 모두 촬영하였다.

Recently warm compaction techniques are focused on and commercialization of one high-density compaction process in the P/M industry. Another development is a new SEGLESS using a developed lubricant that reduces ejection force at room temperature compaction. It is possible to achieve high-density by reducing lubricant amount. In this paper we confirmed that green density was 7.35 g/cm3 at 686MPa of compaction pressure when the new SEGLESS was applied to relatively lower temperature warm compaction process, such as 80℃.

WC/WC interface in VC mono-doped WC-10mass%Co submicro-grained hardmetals of was investigated together with WC/Co interface by using HRTEM and XMA. The thickness of V-rich layer and the analytical value of V at WC/WC interface were almost the same as those at WC/Co interfaces. These results, etc., suggested that the V-rich layers at both interfaces were not generated by an equilibrium segregation mechanism in the sintering stage, but generated by a preferential precipitation mechanism during the solidification of Co liquid phase in the cooling stage. Based on this suggestion, we succeeded in developing a nano-grained hardmetal with 100 nm .

WC-Co와 WC-Co 초경합금중 WC/WC 입계의 구조와 입계 편석상태를 알아볼 목적으로 HRTEM과 EDS를 이용하여 연구하였다. 일부의 입계들은 액상에 의하여 분리된 상태로 관찰되었으나, 상당수는 원자적 상태의 연소계면이었다. 또 연속계면 중 WC-Co 합금에서는 Co 상이 편석되어 있었으며, WC-VC-Co 합금에서는 Co와 V이 동시에 편석되어 있음을 알 수 있었다. 그 편석의 폭은 약6nm이었다. 연속 계면 중 V의 편석은 소결 또는 열처리 시에 일어나는 입계 이동을 억제하는 데 효과적인 역할을 할 것으로 여겨졌다. 동시에 이것은 WC-Co 초경합금에서 VC 첨가에 의한 입성상 억제기구를 설명할 수 있는 것으로 사료되었다.

직경이 각각 4,6,8,12 및 15mm인 순Al 또는 Al-(1,2,3wt%) Cu합금 내부냉금이 95mm ø×200mm H 크기의 흑연주형 중심부에 설치되었다. 이 내부냉금과 같은 조성의 용융금속이 750˚C의 주입온도에서 주형에 주입되었고, 냉각속도, 응고조직 및 성분편석이 분석되었다. 주괴직경/내부냉금직경의 비가 8까지 증가될수록 결정립도, 2차수지상간격 및 성분편석이 현저하게 감소됨이 확인되었다. 그러나 이 비가 8이상이 되면, 미용해 내부냉금이 발생되고, 내부냉금의 효과는 급속히 감소되었다. 순Al 및 Al-(1,2,3wt%)Cu 합금에서 최대 내부냉금 효과를 얻을 수 있는 적정 주괴직경/내부냉금직경의 비는 750˚C주입온도에서는 8이었다.

1시간 주기로 -35˚C에서 +125˚C까지의 온도 변화에 지배되는 Leadless Ceranic Chip Carriers(LLCC'S)의 Solder접합부에서 균열이 계면을 따라 일어났다. 이런 균열이 계면을 취약하게 하는 어떤 불순물에 의한 것이 아닌지를 Scanning Auger Microprobe(SAM)을 이용해 조사했다. 그 결과 계면을 따라 일어나는 균열이 계면의 산화에 의해 일어날 수 있다는 것이 발견되었고, 그에 따라 산화에 취약해진 계면을 따라 일어나는 이런 종류의 피로 파괴현상에 대한 모델을 제시했다.

In mechanical testing of W-Ni-Pe heavy alloys, the cracks nucleate at W/W interface and propagate through W/ Imatrix interface or through matrix phase together with the cleavage of W grains. The mechanical properties can therefore be improved by control of the interfacial strength and area. In this presentation, some experimental result and techniques on this subject will be reviewed and discussed. The hydrogen embrittlement caused by the hydrogen segregation at interfaces during sintering in an hydrogen atmosphere can be removed by an heat-treattnent in vacuum or in an inert atmosphere. The heat-treatment condition can be estimated by using a diffusion equation for a cylindrical shape. The mechanical properties, in particular the impact property, are degraded by the segregation of non-metallic impurities, such as Sand P. The degradation can be prevented by adding a fourth element, such as La or Ca, active with the non-metallic impurities. The cyclic heat-treatment at usual heat-treattnent tempemture causes the penetration of matrix between W/W grain boundaries and results in remarkable increase in impact energy. This is due to an increase in the area of ductile failure during the impact test. The instability of W/matrix interface casued by addition of Mo or Re can be controlled by using W powders of different size. The increase in the interfacial area in found to be related to the presence of non-equilibrium pure W gmins among W(Mo or Re) solid solution gmins.

同-種에서 地理的 隔離에 따른 生理, 形態學的 差異를 알아보기 위하여 全羅南道 海南과 江原道 春域地域의 솔잎혹파리 幼蟲과 成蟲을 재료로 하여 전기영동법, 그리고 走査電子顯徵鏡을 이용하여 比較하였다. 두지역의 3齡 幼蟲에서는 일반 蛋白質의 밴드패턴은 동일하였다. 그러나 同位 酸素 esterase와 MDH는 명확한 차이를 보여주었다. 成蟲에서는 -般環白質과 esterase 밴드패턴에서 부분적으로 명확한 差異를 보여주었다. 두지역 성충 생식절의 外部微細構造를 검토한 결과 産卵管의 들째마디에서 뚜렷한 차이가 관찰되었다.