• Carbon letters
• /
• 제1권3_4호
• /
• pp.138-142
• /
• 2001

The effect of electrochemical surface treatments in KOH chemical solution on microstructures of carbon blacks was investigated in terms of surface functional values and XRD measurements. And their mechanical interfacial properties of the carbon blacks/rubber composites were studied by the composite tearing energy ($G_{IIIC}$). It was found that the development of basic-surface functional groups lead to the significant physical changes of carbon blacks, such as, decrease of the interlayer spacing ($d_{002}$), increase of the crystalline size along c-axis ($L_c$), and increase of degree of crystalline (${\chi}_c$). This treatment is possibly suitable for carbon blacks to be incorporated in a hydrocarbon rubber matrix, resulting in improving the hardness and tearing energy of the resulting composites.

• 센서학회지
• /
• 제15권2호
• /
• pp.148-152
• /
• 2006

This paper describes the fabrication of SiCN microstructures for super-high temperature MEMS using photopolymerization of pre-ceramic polymer. In this work, polysilazane liquide as a precursor was deposited on Si wafers by spin coating, microstructured and solidificated by UV lithography, and removed from the substrate. The resulting solid polymer microstructures were cross-linked under HIP process and pyrolyzed to form a ceramic of withstanding over $1400^{\circ}C$. Finally, the fabricated SiCN microstructures were annealed at $1400^{\circ}C$ in a nitrogen atmosphere. Mechanical characteristics of the SiCN microstructure with different fabrication process conditions were evaluated. The elastic modules, hardness and tensile strength of the SiC microstructure implemented under optimum process condtions are 94.5 GPa, 10.5 GPa and 11.7 N/min, respectively. Consequently, the SiCN microstructure proposed in this work is very suitable for super-high temperature MEMS application due to very simple fabrication process and the potential possiblity of sophisticated mulitlayer or 3D microstructures as well as its good mechanical properties.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
• /
• pp.392-393
• /
• 2006

This paper describes the fabrication of SiCN microstructures for super-high temperature MEMS using photopolymerization of pre-ceramic polymer. In this work. polysilazane liquide as a precursor was deposited on Si wafers by spin coating. microstructured and solidificated by UV lithography. and removed from the substrate. The resulting solid polymer microstructures were cross-linked under HIP process and pyrolyzed to form a ceramic of withstanding over $1400^{\circ}C$. Finally, the fabricated SiCN microstructures were annealed at $1400^{\circ}C$ in a nitrogen atmosphere. Mechanical characteristics of the SiCN microstructure with different fabrication process conditions were evaluated. The elastic modules. hardness and tensile strength of the SiC microstructure implemented under optimum process conditions are 94.5 GPa, 10.5 GPa and 11.7 N/min, respectively. Consequently, the SiCN microstructure proposed in this work is very suitable for super-high temperature MEMS application due to very simple fabrication process and the potential possiblity of sophisticated multlayer or 3D microstructures as well as its good mechanical properties.

• 대한기계학회논문집A
• /
• 제26권4호
• /
• pp.609-616
• /
• 2002

The characteristics of mechanical behavior are investigated for Ti-6Al-4V alloy. Four kinds of the specimens are prepared under different heat treatments in order to produce different microstructures. In the present investigations, impact, tensile and fatigue crack growth tests are performed for each test specimen. The results obtained through the investigations are compared. Additionally fr actal dimensions of crack pass are obtained using the box counting method. The results are, 1) the microstructures shows as equiaxed, bimodal and Widmanstatten microstructures respectively, 2) the impact energy and elongation are superior fur the bimodal microstructure, and the hardness and tensile strength are superior fur the Widmanstatten microstructure, 3) the fatigue crack growth rate is similar to all microstructures in low ΔK region while that of equiaxed microstructure is the largest, and that of Widmanstatten microstructure is the lowest in high ΔK region respectively, 4) the fractal dimension D of Widmanstatten microstructure shows higher value than that of the equiaxed and bimodal microstructures under 200 magnification view of the SEM micrographs.

• 한국분말재료학회지
• /
• 제26권2호
• /
• pp.138-145
• /
• 2019

In this study, Al-Si-Mg alloys are additively manufactured using a selective laser melting (SLM) process from AlSi10Mg powders prepared from a gas-atomization process. The processing parameters such as laser scan speed and laser power are investigated for 3D printing of Al-Si-Mg alloys. The laser scan speeds vary from 100 to 2000 mm/s at the laser power of 180 and 270 W, respectively, to achieve optimized densification of the Al-Si-Mg alloy. It is observed that the relative density of the Al-Si-Mg alloy reaches a peak value of 99% at 1600 mm/s for 180 W and at 2000 mm/s for 270W. The surface morphologies of the both Al-Si-Mg alloy samples at these conditions show significantly reduced porosities compared to those of other samples. The increase in hardness of as-built Al-Si-Mg alloy with increasing scan speed and laser power is analyzed due to high relative density. Furthermore, it was found that cooling conditions after the heat-treatment for homogenization results in the change of dispersion status of Si phases in the Al-Si matrix but also affects tensile behaviors of Al-Si-Mg alloys. These results indicate that combination between SLM processing parameters and post-heat treatment should be considered a key factor to achieve optimized Al-Si alloy performance.

• 한국정밀공학회지
• /
• 제24권12호
• /
• pp.119-127
• /
• 2007

Recently, microstructures fabricated using microstereolithography technology have been used in the biological, medical and mechanical fields. Microstereolithography can fabricate real 3D microstructures with fine features, although there is presently a limited number of materials available for use in the process. Deformation of the fine features on a fabricated microstructure remains a critical issue for successful part fabrication, and part deformation can occur during rinsing or during fabrication as a result of fluid flow forces that occur during movement of mechanical parts of the system. Deformation can result in failure to fabricate a particular feature by breaking the feature completely, spatial deflection of the feature, or attaching the feature to neighboring microstructures. To improve mechanical strength of fabricated microstructures, a clay nanocomposite can be used. In particular, a high-aspect ratio microstructure can be fabricated without distortion using photocurable liquid resin containing a clay nanocomposite. In this paper, a clay nanocomposite was blended with a photocurable liquid resin to solve the deformation problem that occurs during fabrication and rinsing. An optimal mixture ratio of a clay nanocomposite was found through tensile testing and the minimal allowable distance between microstructures was found through fabrication experimentation. Finally, using these results, high-aspect ratio microstructures were fabricated using a clay nanocomposite resin without distortion.

• 한국전산구조공학회논문집
• /
• 제31권3호
• /
• pp.133-140
• /
• 2018

본 논문은 $Ni-A{\ell}_2O_3$로 구성된 금속-세라믹 이종 입자복합재의 2차원 미세구조(microstructure) 생성과 미세구조 스케일(scale)에 따라 정의되는 계층적 모델들의 역학적 특성 분석에 관한 내용이다. 이종 입자복합재의 미세구조는 수학적인 MDF(random morphology description functions) 모델링기법을 복합재의 2차원 RVE(representative volume element) 영역에 적용하여 생성하였다. 그리고 미세구조 생성에 필요한 가우스 함수들의 개수에 따라 미세구조의 계층적 모델을 정의하였다. 한편 임의 미세구조 내 금속과 세라믹 입자가 차지하는 체적분율(volume fraction)은 RMDF 함수의 레벨을 조정함으로서 설정하였다. RMDF기법에 의한 미세구조들은 가우스 함수들의 개수가 일정할지라도 랜덤하게 생성된다. 이렇게 랜덤하게 생성되는 미세구조들을 2차원 보(beam) 모델에 적용하여 미세구조의 스케일에 따른 수직응력과 전단응력의 계층적 변동을 수치 해석적으로 고찰하였다. 또한, 균열해석을 통해 RMDF의 랜덤성과 가우스 함수들의 개수가 균열선단에서의 응력값에 미치는 영향을 고찰하였다.

• 한국정밀공학회지
• /
• 제27권10호
• /
• pp.93-99
• /
• 2010

A nano-stereolithography is the direct patterning process with a nanoscale resolution using twophoton absorption induced by a femtosecond laser. However, in the majority of the works, the fabrication of 3D microstructures have been done only onto transparent glass due to the use of an oil immersion objective lens for achieving a high resolution. In this work, the coaxial illumination and the auto-focusing system are proposed for the direct patterning of nano-precision patterns on an opaque substrate such as a silicon wafer and a metal substrate. Through this work, 3D polymer structures and metallic patterns are fabricated on a silicon wafer using the developed process.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2005년도 추계학술대회 논문집
• /
• pp.264-267
• /
• 2005

A subregional slicing method (SSM) is proposed to increase the nanofabrication efficiency of a nano-stereolithography (NSL) process based on two-photon polymerization (TPP). The NSL process can be used to fabricate 3D microstructures via the accumulation of layers of uniform thickness; hence, the precision of the final 3D microstructure depends on the layer thickness. The use of a uniform layer thickness means that, to fabricate a precise microstructure, a large number of thin slices is inevitably required. leading to long processing times. In the SSM proposed here, however, the 3D microstructure is divided into several subregions on the basis of the geometric slope, and then each of these subregions is uniformly sliced with a layer thickness determined by the geometric slope characteristics of each subregion. Subregions with gentle slopes are sliced with thin layer thicknesses, whereas subregions with steep slopes are sliced with thick layer thicknesses. Here, we describe the procedure of the SSM based on TPP, and discuss the fabrication efficiency of the method through the fabrication of a 3D microstructure.

• 대한화학회지
• /
• 제49권3호
• /
• pp.292-299
• /
• 2005