• 한국자기학회지
• /
• 제21권5호
• /
• pp.185-192
• /
• 2011

박막제조 기술은 과학 기술의 기초가 되는 분야로 양질의 박막을 제조하기 위한 다양한 노력이 경주되고 있다. 박막제조는 표면개질과 함께 표면처리 기술의 한 분야이며 이중 진공증착으로 알려진 물리증착법과 화학증착법은 현대의 과학기술 연구는 물론 산업적으로 폭넓게 이용되는 박막제조 기술 중의 하나이다. 진공증착을 이용한 박막제조 기술은 나노 기술의 등장과 함께 비약적인 발전을 이루었으며 자연모사와 완전화 박막의 제조, 융복합 공정을 이용한 기능성 코팅과 Engineered Structure 구현 그리고 초고속 증착과 원가 저감 기술의 실현이 주요 이슈로 등장하고 있다. 본 논문에서는 물리증착법과 화학증착법을 중심으로 박막제조 기술의 종류와 원리를 설명하고 박막제조 기술의 최신 동향과 기술적 이슈 및 향후 전망에 대해 기술한다.

• Journal of Magnetics
• /
• 제18권3호
• /
• pp.245-249
• /
• 2013

A finite element model was built for MnBi/${\alpha}$-Fe nanocomposite permanent magnets, and the demagnetization curves of the magnets were simulated by micro-magnetic calculation. The microstructure of the cubic model is composed of 64 irregular grains with an average grain size of 20 nm. With the volume fraction of soft magnetic phase (t vol. %) ranged from 5 to 20 vol. %, both isotropic and anisotropic nanocomposite magnets show typical single-phase permanent magnets behavior in their demagnetization curves, illustrating good intergranular exchange coupling effect between soft and hard magnetic phases. With the increase of volume fraction of soft magnetic phase in both isotropic and anisotropic magnets, the coercive force of the magnets decreases monotonically, while the remanence rises at first to a peak value, then decreases. The optimal values of maximum energy products of isotropic and anisotropic magnets are 84 and $200kJ/m^3$, respectively. Our simulation shows that the MnBi/${\alpha}$-Fe nanocomposite permanent magnets own excellent magnetic properties and therefore good potential for practical applications.

• Smart Structures and Systems
• /
• 제19권1호
• /
• pp.105-113
• /
• 2017

A microstructure-dependent dynamic model for silicon nanobeams with axial motion is developed by considering the effects of nonlocal elasticity and surface energy. The nanobeam is considered to subject to both transverse and longitudinal loads arising from nanostructural surface effect and all positive directions of physical quantities are defined clearly prior to modeling so as to clarify the confusions of sign in governing equations of previous work. The nonlocal and surface effects are taken into consideration in the dynamic behaviors of silicon nanobeams with axial motion including circular natural frequency, vibration mode, transverse displacement and critical speed. Various supporting conditions are presented to investigate the circular frequencies by a numerical method and the effects of many variables such as nonlocal nanoscale, axial velocity and external loads on non-dimensional circular frequencies are addressed. It is found that both nonlocal and surface effects play remarkable roles on the dynamics of nanobeams with axial motion and cause the frequencies and critical speed to decrease compared with the classical continuum results. The comparisons of the non-dimensional calculation values by present and previous studies validate the correctness of the present work. Additionally, numerical examples for silicon nanobeams with axial motion are addressed to show the nonlocal and surface effects on circular frequencies intuitively. Results obtained in this paper are helpful for the design and optimization of nanobeam-like microstructures based sensors and oscillators at nanoscale with desired dynamic mechanical properties.

• 한국방재학회 논문집
• /
• 제11권2호
• /
• pp.39-44
• /
• 2011

마이크로 스케일에서 다결정 재료의 소성 거동을 살펴볼 때, 결정의 geometrically necessary dislocation(GND) 효과에 의한 소성 구배(plastic gradient)를 고려하는 것은 재료의 소성 거동에 큰 영향을 줄 수 있다. 이러한 영향을 확인하기 위하여, 본 연구에서는 소성 구배의 영향을 고려한 다결정 고체(polycrystalline solids)의 거동을 유한요소해석을 이용하여 살펴보았다. 소성 구배의 영향을 살펴보기 위해 구배 경화 계수(gradient hardness coefficient)와 먼 거리 변형률에 대한 재료 길이 변수 (material length parameter)가 사용되었다. 재료 길이 변수에 의한 영향을 확인하기 위해, 재료 길이 변수의 차이에 따른 다결정 고체의 거동을 분석하였다. 또한 소성 구배 효과의 고려 및 재료 길이 변수에 따른 다결정 고체 내부에 위치한 단결정이 받는 영향을 살펴보았다. 재료 길이 변수에 따라 결정이 받는 영향을 비교하여, GND에 의한 다결정 고체 거동의 영향을 확인하였다.

• 한국방재학회 논문집
• /
• 제11권2호
• /
• pp.31-37
• /
• 2011

다상 재료는 상(phase) 분포의 차이에 따라 재료의 특성이 다르기 때문에 상 분포 상태의 특성을 이해하는 것이 중요하다. 본 연구에서는 확률 분포 함수를 사용하여 미세구조의 상 분포 상태를 나타내고, 이를 사용한 미세구조 재구성 방법을 이용해서 특정 2상 미세구조와 통계적으로 유사한 상 분포를 가진 미세구조를 생성하여 기존의 미세구조와 재구성된 미세구조의 특성을 비교하였다. 그리고 서로 다른 임의의 상 분포를 가진 미세구조들에 유한요소해석 기법을 적용하여 서로 다른 하중 방향에 대한 미세구조의 역학적 거동을 분석하였다. 이를 통해, 미세구조 재구성 방법을 사용하여, 제한된 정보만을 이용해서 통계적으로 유사한 특성을 나타내는 미세구조를 모델링 할 수 있음을 확인하였고, 확률 분포 함수와 미세구조의 역학적 거동이 방향에 따라 동일함을 통하여 재생성 된 재료의 등방성을 확인하였다.

• 소성∙가공
• /
• 제31권6호
• /
• pp.344-350
• /
• 2022

Extruded Mg-Bi binary alloys are known to have an undesirable bimodal grain structure containing a large amount of coarse unrecrystallized grains. Accordingly, to improve the microstructural homogeneity of extruded Mg-Bi alloys, it is necessary to promote the dynamic recrystallization (DRX) behavior during hot extrusion. An effective way to promote DRX is an increase in nucleation sites for DRX through a pre-deformation process before extrusion, such as cold pre-forging and hot pre-compression. However, the application of these pre-deformation processes increases the cost of final extruded Mg products because of an increase in energy consumption and decrease in productivity. Therefore, a low-cost new continuous process with high productivity is required to improve the microstructural homogeneity and mechanical properties of extruded Mg alloys without a drastic increase in the entire process cost. This study proposes a new extrusion method using an extrusion billet with a truncated cone shape (i.e., tapered billet) instead of a conventional extrusion billet with a cylindrical shape. When the hot extrusion of a Mg-5Bi alloy is conducted using the tapered billet, the DRX behavior during extrusion is considerably promoted. The DRX fraction and average grain size of the extruded alloy significantly increase and decrease from 65% to 91% and from 225 ㎛ to 49 ㎛, respectively. Consequently, the extruded Mg-5Bi alloy fabricated using the tapered billet has a finer homogeneous grain structure and higher tensile elongation than the extruded counterpart fabricated using the cylindrical billet.

• Journal of Microbiology and Biotechnology
• /
• 제31권10호
• /
• pp.1401-1408
• /
• 2021

This study examined whether the oral administration of low-molecular-weight collagen peptide (LMCP) containing 3% Gly-Pro-Hyp with >15% tripeptide (Gly-X-Y) content could ameliorate osteoarthritis (OA) progression using a rabbit anterior cruciate ligament transection (ACLT) model of induced OA and chondrocytes isolated from a patient with OA. Oral LMCP administration (100 or 200 mg/kg/day) for 12 weeks ameliorated cartilage damage and reduced the loss of proteoglycan compared to the findings in the ACLT control group, resulting in dose-dependent (p < 0.05) improvements of the OARSI score in hematoxylin & eosin (H&E) and Safranin O staining. In micro-computed tomography analysis, LMCP also significantly (p < 0.05) suppressed the deterioration of the microstructure in tibial subchondral bone during OA progression. The elevation of IL-1β and IL-6 concentrations in synovial fluid following OA induction was dose-dependently (p < 0.05) reduced by LMCP treatment. Furthermore, immunohistochemistry illustrated that LMCP significantly (p < 0.05) upregulated type II collagen and downregulated matrix metalloproteinase-13 in cartilage tissue. Consistent with the in vivo results, LMCP significantly (p < 0.05) increased the mRNA expression of COL2A1 and ACAN in chondrocytes isolated from a patient with OA regardless of the conditions for IL-1β induction. These findings suggest that LMCP has potential as a therapeutic treatment for OA that stimulates cartilage regeneration.

• 한국기계가공학회지
• /
• 제20권9호
• /
• pp.1-10
• /
• 2021

Recently, the repair and recycling of damaged mechanical parts via metal additive manufacturing processes have been industrial points of interest. This is because the repair and recycling of damaged mechanical parts can reduce energy and resource consumption. The directed energy deposition(DED) process has various advantages such as the possibility of selective deposition, large building space, and a small heat-affected zone. Hence, it is a suitable process for repairing damaged mechanical parts. The shaft is a core component of various mechanical systems. Although there is a high demand for the repair of the shaft, it is difficult to repair with traditional welding processes because of the thermal deformation problem. The objective of this study is to propose a repair procedure for a damaged shaft using the DED process and discuss its applications. Three types of cases, including a small shaft with a damaged surface, a medium-size shaft with a worn bearing joint, and a large shaft with serious damage, were repaired using the proposed procedure. The microstructure and hardness were examined to discuss the characteristics of the repaired component. The efficiency of the repair of the damaged shaft is also discussed.

• The Journal of Advanced Prosthodontics
• /
• 제13권5호
• /
• pp.281-291
• /
• 2021

PURPOSE. To evaluate the wear of computer-aided design/computer-aided manufacturing (CAD-CAM) dental ceramic materials opposed by enamel as a function of increased chewing forces. MATERIALS AND METHODS. The enamel cusps of healthy human third molar teeth (n = 40) opposed by materials from CAD-CAM dental ceramic groups (n = 10), including Vita Enamic^® (ENA), a polymer-infiltrated ceramic network (PICN); GC Cerasmart^® (CERA), a resin nanoceramic; Celtra^® Duo (DUO), a zirconia-reinforced lithium silicate (ZLS) ceramic; and IPS e.max ZirCAD (ZIR), a polycrystalline zirconia, were exposed to chewing simulation (1,200,000 cycles; 120 N load; 1 Hz frequency; 0.7 mm lateral and 2 mm vertical motion). The wear of both enamel cusps and materials was quantified using a 3D laser scanner, and the wear mechanisms were evaluated by scanning electron microscopy (SEM). The results were analysed using Welch ANOVA and Kruskal Wallis test (α = .05). RESULTS. ZIR showed lower volume loss (0.02 ± 0.01 mm³) than ENA, CERA and DUO (P = .001, P = .018 and P = .005, respectively). The wear of cusp/DUO [0.59 mm³ (0.50-1.63 mm³)] was higher than cusp/CERA [0.17 mm³ (0.04-0.41 mm³)] (P = .007). ZIR showed completely different wear mechanism in SEM. CONCLUSION. Composite structured materials such as PICN and ZLS ceramic exhibit more abrasive effect on opposing enamel due to their loss against wear, compared to uniform structured zirconia. The resin nano-ceramic causes the lowest enamel wear thanks to its flexible nano-ceramic microstructure. While zirconia appears to be an enamel-friendly material in wear volume loss, it can cause microstructural defects of enamel.

• Nuclear Engineering and Technology
• /
• 제53권9호
• /
• pp.2982-2989
• /
• 2021

One of the consequences of the 475 ℃ embrittlement of duplex stainless steels is the reduction of the resistance to localized corrosion. Therefore, the detection of this type of embrittlement before the material exhibits significant loss in toughness, and corrosion resistance is important to ensure the structural integrity of critical components under corrosion threats. In this research, conductivity measurements are performed using the alternating current potential drop (ACPD) technique with using a portable four-point probe as a nondestructive evaluation (NDE) method for detecting the embrittlement in a 2507 (UNS S32750) super duplex stainless steel (SDSS) aged at 475 ℃ from as-received condition to 300 h. The electric conductivity results were compared against two electrochemical tests namely double loop electrochemical potentiokinetic reactivation (DL-EPR) and critical pitting temperature (CPT). Mechanical tests and the microstructure characterized using scanning electron microscopy (SEM) imaging are conducted to track the progress of embrittlement. It is shown that the electric conductivity correlates with the changes in impact energy, microhardness, and CPT corrosion tests result demonstrating the feasibility of the four-point probe as a possible field-deployable method for evaluating the 475 ℃ embrittlement of 2507 SDSS.