• Advanced Composite Materials
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• 제18권4호
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• pp.339-350
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• 2009

Al-Fe-V-Si alloys reinforced with SiC particles were prepared by multi-layer spray deposition technique. Both microstructures and mechanical properties including hardness and tensile properties development during hot exposure process of Al-8.5Fe-1.3V-1.7Si, Al-8.5Fe-1.3V-1.7Si/15 vol% $SiC_P$ and Al-10.0Fe-1.3V-2Si/15 vol% $SiC_P$ were investigated. The experimental results showed that an amorphous interface of about 3 nm in thickness formed between SiC particles and the matrix. SiC particles injected silicon into the matrix; thus an elevated silicon concentration was found around $\alpha-Al_{12}(Fe,\;V)_3Si$ dispersoids, which subsequently inhibited the coarsening and decomposition of $\alpha-Al_{12}(Fe,\;V)_3Si$ dispersoids and enhanced the thermostability of the alloy matrix. Moreover, the thermostability of microstructure and mechanical properties of Al-10.0Fe-1.3V-2Si/15 vol% $SiC_P$ are of higher quality than those of Al-8.5Fe-1.3V-1.7Si/15 vol% $SiC_P$.

• 생명과학회지
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• 제16권2호
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• pp.225-230
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• 2006

생육온도가 느타리버섯 자실체의 생육 및 조직에 미치는 영향을 검토하기 위하여 온도를 $7^{\circ}C,\;15^{\circ}C,\;23^{\circ}C$로 달리하여 생육시키고, 자실체의 특성 및 조직의 미세구조 변화를 관찰 한 결과, 생육온도가 높을수록 갓의 두께는 얇아지고, 대의 두께 및 대의 길이는 길어졌으며, 버섯의 갓 색깔이 백색에 가깝게 변화하였다. 생육온도에 따른 자실체의 미세구조변화는 생육온도가 높아질수록 주름에 있어서 담자포자의 비산이 빠르고, 노화현상이 두드러졌다. 생육온도별로 느타리버섯 대부위의 물리적 특성을 조사한 결과 생육온도가 높을수록 경도는 낮아졌는데 이는 세포의 노화 및 균사의 밀도가 낮았기 때문으로 생각된다. 또한 대의 세포학적인 특정으로 액포화가 두드러져 생육온도가 높을수록 생육일수는 빨라지나 그만큼 노화가 쉽게 일어남을 확인하였다.

• 한국세라믹학회지
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• 제35권9호
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• pp.939-944
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• 1998

실리콘함유 고분자(Polysiloxane)의 세라믹변환과정에서의 부피수축효과를 조절하기 위하여 활성화금속으로 중석을 첨가하여 열분해 및 합성반응을 통해 신 세라믹 복합체를 개발하고 이의 세라믹화 과정이나 물성을 조사하였다. 제조된 시편의 미세조직은 고분자로부터 야기된 $S_{1}$-O-C게열의 Glass기지상과, 분해잔여물(고상,기상)등과 활성화금속과의 반응르로 생성된 고경도의 탄호물로 이루어져 있어 향후 내마모재료로서의 응용을 기대할 수 있을 것이다. 제조된 복합체의 물성은 반응조건에 많이 의존함을 알 수 있었다. 1400~$1500^{\circ}C$에서 열분해 시켜 제조한 복합체의 밀도는 95% 이상의 상대밀도와, 경도 값은 7~8GPa 정도이고 탄성률은 220~230 GPa, 파괴인성응ㄴ 6~6.8$MPam^{1/2}$, 파괴강도는 380~470 MPs정도의 값을 나타내었다.

• 한국결정성장학회지
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• 제8권1호
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• pp.111-116
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• 1998

질화규소는 고경도, 고인성 세라믹 재료이기 때문에, 기계적 가공성은 매우 나쁘며, 또한 질화규소는 높은 전기 저항을 갖는다. 매우 높은 전기저항을 띠는 질화규소에 30wt% 이상의 TiN 분말이 첨가되었을 때 전도성 세라믹 복합체가 된다. 높은 전기 전도도를 가질 때 세라믹을 방전가공방법(EDM)을 이용하여 정밀한 가공을 할 수 있다. 높은 전기 전도도를 갖는 $Si_3N_4-TiN$ 세라믹 복합체는 EDM 방법을 이용하여 금속 가공 tool을 만드는데 이용되며, 이러한 tool 재료들은 산화뿐만 아니라 심각한 마모문제를 갖는다. 상압소결후 post HIP 소결방법으로 $Si_3N_4-TiN$ 복합체를 만들었으며, TiN의 양의 변화에 따른 $Si_3N_4$ 복합체의 마모특성을 상온의 대기중에서 조사하였다. 경도, 파괴인성, 강도값을 마모량과 비교하였다. 마모흔의 SEM 관찰로 $Si_3N_4-TiN$ 복합체의 마모기구를 설명하였다.

• Composites Research
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• 제33권5호
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• pp.251-255
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• 2020

본 연구에서는 용융가압함침공정을 이용하여 제조된 TiC 세라믹 입자강화 철강복합재를 제조하고 상용구상흑연주철과 비교를 위하여 미세조직 분석 및 경도 등 기초물성과 선박 해양 분야등의 적용가능성 검토를 위하여 염수환경에서의 부식 특성에 관한 연구를 진행하였다. 염수환경에서의 부식특성 비교 결과 구상흑연주철 대비 부식전위와 부식전류밀도 모두 낮은 값을 나타내었고, 낮은 연간부식률을 통하여 TiC-Fe 금속복합재의 내식성이 더 뛰어난 것을 확인하였다.

• 열처리공학회지
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• 제33권3호
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• pp.99-106
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• 2020

Selective laser melting (SLM) is an additive manufacturing process by melting metallic powders and stacking into layers, and can product complex shapes or near-net-shape (NNS) that are difficult to product by conventional processes. Also, SLM process is able to raise the efficiency of production by creating a streamlined manufacturing process. For manufacturing in SLM process using Ti-6Al-4V powder, analysis of microstructural evolution and evaluation of mechanical properties are essential because of rapid melting and solidification process of powders according to high laser power and rapid scan speed. In addition, it requires a post-processing because the soundness and mechanical properties are degraded by defects such as pore, un-melted powder, lack-of-fusion, etc. In this study, hot isostatic press (HIP) was conducted as a post-processing on SLM-printed Ti-6Al-4V alloy. Microstructure of post-processed Ti-6Al-4V alloy was compared to as-built Ti-6Al-4V, and the evolution of quasi-static (Vickers hardness, room temperature tensile characteristic) and dynamic (high-cycle fatigue characteristic) mechanical properties were analyzed.

• 한국레이저가공학회지
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• 제7권2호
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• pp.1-10
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• 2004

This work was attempted to join SCP sheet and STS304 sheet by using Nd:YAC laser beam. SCP sheet has good formability and low cost, while STS304 has excellent corrosion resistance and mechanical properties in high temp. In this experiment, butt joint type was used to develop the tailored blank welding for dissimilar steel. Sheets which have different thermal properties. Computer simulation was conducted to obtain the off-set position for efficient welding by considering laser power, scanning speed, focal length and basic properties. The result showed that the optimum thermal distribution was obtained when the laser beam was irradiated at $0.05{\sim}0.1$ mm off-set toward the SCP sheet side. The experiment was conducted based on the result of computer simulation to show the same optimum conditions. Optimum conditions were 3KW in laser beam power, 6m/min in scanning speed, -0.5mm in focal position, 0.1mm off-set toward SCP. Microhardness test, tensile test, bulge test, optical microscopy, EDS, and XRD were performed to observe the microstructure around fusion zone and to evaluate the mechanical properties of optimum conditions, The weld zone had high microhardness values by the formation of the martensitic structure. Tensile test measured the strength of welded region by vertical to strain direction and the elongation of welded region by parallel to strain direction. Bulge test showed $52\%$ formability of the original materials. Bead shape, grain size, and martensitic structure were observed by the optical microscopy in the weld zone. Detailed results of EDS, XRD confirmed that the welded region was connected of martensitic structure.

• Journal of Animal Science and Technology
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• 제62권4호
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• pp.577-586
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• 2020

This study was to investigate the effect of salt alone or in combination with phosphate on physicochemical and textural properties, and chemical interactions of low-fat model sausages. pH, color, expressible moisture (EM), cooking loss (CL), proximate analysis, textural profile analysis and low-vacuum scanning electron microscopy were performed. As salt content increased, color tended to decrease, as did EM and CL parameters, indicating that the ability to retain moisture was improved with increased salt levels (p < 0.05). In addition, textural hardness, gumminess and chewiness all increased with increasing salt (p < 0.05). Sausages with 0.3% salt showed the lowest cohesiveness compared to those with salt levels higher than 0.3% (p < 0.05). Addition of sodium tripolyphosphate (STPP) increased pH of sausages. Increasing salt and STPP did not affect lightness (p > 0.05), but did increase redness and yellowness (p < 0.05). The moisture content was higher when the salt and STPP contents were increased (p < 0.05), but no differences in the fat and protein contents (%) were observed (p > 0.05). EM and CL tended to decrease with increasing salt and STPP. In textural properties, the combination of 1.8% salt and 0.3% STPP was the best among other treatment (p < 0.05). Surface microstructure showed a flat and dense structure with increasing salt and STPP. Since the addition of salt and phosphate improved the functionality, textural and physicochemical properties of meat products in this study, meat products will need to be developed in line with consumer's preference.

• 비파괴검사학회지
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• 제20권3호
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• pp.231-237
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• 2000

공업용 서멧 절삭공구는 다성분계 탄화물과 강자성체(ferromagnetic material)인 철족의 Co, Ni 결합상 금속으로 구성 되어 있다. 본 연구에서는 새로운 시도로서 금속 결합상 량과 소결조건에 따른 TiCN계 서멧의 자기적 특성의 측정에 의한 기계적 성질의 평가방법을 연구하였다. 실험에서는 결합상이 다른 상용 서멧조성의 합금을 분말 야금법에 의해 제조하였다. 소결된 서멧의 자기적 특성은 합금의 조직과 탄소량에 따라 크게 변화하였다. 포화자화(magnetic saturation, $4{\pi}\;{\sigma}$)와 항자력(coercive force, Hc)은 비례하였으며, 고탄소 소결합금에 있어서는 Co-Ni 결합상에서의 W, Mo, Ti등의 용매원자의 농도가 낮아짐에 따라 포화자화는 증가하였다 항자력이 높을수록 경도는 증가하였고, 서멧의 강도 및 인성은 포화자화가 증가할수록 우수하였다. 서멧공구에서 자기적 특성을 측정하여 기계적 성질을 비파괴적으로 평가할 수 있었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1398-1401
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• 2005

The nano/microstructure, the aging response (in T5 heat treatment), and the mechanical/tribological properties of the eutectic regions in squeeze-cast A356 alloy were investigated using nano/micro-indentation and mechanical scratching, combined wit optical microscopy and atomic force microscope(AFM). Most eutectic Si crystals in the A356 alloy showed a modified morphology as fine-fibers. The loading curve for the eutectic region was more irregular than that of the primary Al region due to the presence of various particles of varying strength. In addition, the eutectic region showed lower pile-up and higher elastic recovery than the primary Al region. The aging responses of the eutectic regions in the squeeze-cast A356 alloys aged at $150^{\circ}C$ for different times(0, 2, 4, 8, 10, 16, 24, 36 and 72 h) were investigated. As the aging time increased, acicular Si particles in the eutectic regions gradually came to a fine structure. Both Vickers hardness ($H_V$) and indentation ($H_{IT}$) test results showed almost the same trend of aging curves, and the peak was obtained at the same aging time of 10 h. A remarkable size-dependence of the tests was found. The friction coefficient for the eutectic region was lower than that for the primary Al region.