• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2009.10a
• /
• pp.105-106
• /
• 2009

AZ31 (3% Al, 1% Zn) Mg 판재의 내식성 향상을 위해 Ti/Zr/Polymer 복합계의 Cr-free 화성처리 방법을 이용하였다. 염수분무시험을 통해 최고 72시간 ($5{\sim}10%$ 발청) 내식성이 나타남을 확인하였다. 화성피막의 내식성은 그 피막이 가진 성분, 균일도, 치밀도, 형상 및 두께에 의해 좌우되는 만큼 TEM, SEM을 통해 화성피막 구조가 내식성과 어떠한 관련이 있는지 조사하였다. 또한, 화성처리 전 단계 공정인 탈지와 산세 및 중화 공정의 변수 조절을 통해 전처리 공정이 최종 화성피막의 물성에 어떠한 영향을 미치는지 조사하였다. 탈지조건을 $35{\sim}40^{\circ}C$, 5분에서 $50{\sim}80^{\circ}C$, $10{\sim}20$분으로 변경 시 좀 더 균일한 외관을 얻을 수 있었고, 적절한 중화제 선택을 통해 화성피막을 균일하게 형성시킬 수 있었다. 투과전자현미경 결과로 미루어 화성피막의 두께보다 균일도와 치밀도가 내식성에 결정적인 영향을 미치는 것을 확인할 수 있었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.04a
• /
• pp.298-302
• /
• 2011

티타늄 용접부는 수소취성과 잔류응력에 대한 영향을 최소화 하기 위해 용접 후 잔류응력 제거 열처리 작업을 수행하고 있다. 하지만, 현재 항공 분야에 널리 사용하고 있는 규격에 따라 열처리 온도가 다양하게 설정되어 있어 현장에 적용하기에는 어려움이 있다. 이에 규격 별로 대표하고 있는 열처리 조건을 선정하여 열처리 조건에 따른 용접부에 대한 잔류응력, 잔류수소량을 확인하였고, 용접부에 대한 강도와 충격 인성을 확인하였다.

• Journal of the Korean Society for Heat Treatment
• /
• v.34 no.6
• /
• pp.281-286
• /
• 2021

Arc ion plating (AIP), laser cladding, and nitriding are methods that can prevent mold damage or repair and create cracks and breakages on the die surface. The dissolution and soldering behavior of coated SKD61 by using arc ion plating, laser cladding, and nitriding was investigated. The structure of the coating was investigated as a function of deposition conditions by X-ray diffraction and the crystallographic orientation was determined using the texture factor. The TiAlN film deposited with AIP showed excellent corrosion resistance in the molten aluminum alloy at 680℃. In this paper, we have detailed the corrosion and mass loss phenomena associated with these steel-cast metal interactions.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.6
• /
• pp.707-712
• /
• 2012

Very high cycle fatigue (VHCF) behavior of aerospace components has emerged much attention due to their long service life. In this study, a piezoelectric ultrasonic fatigue testing (UFT) system has been developed by Mbrosiatec Co., Ltd. to study the high cycle fatigue (HCF) strength of Ti-6Al-4V alloy. Hourglass-shaped specimens have been investigated in the range from $10^6$ to $10^9$ cycles at room temperature under completely reversed R = -1 loading conditions,. Scanning electron microscopy (SEM) analysis revealed that failures occurred in the entire range up to the gigacycle regime, and the fractures have beenfound to be initiated from the surface, unlike in steels. However, it was found from the SEM microgprahs that microcracks transformed into intergranular fractures. Thus, it can be concluded from according to the results that this test method can be applicable to commercialized automotive and railroad parts that require high cycle fatigue strength.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.6
• /
• pp.591-598
• /
• 2012

In this study, the cutting characteristics of bulk metallic glass (BMG) cut using a computer numerically controlled (CNC) lathe were investigated for different insert tool materials and cutting speeds. The surface roughness, chip morphology, cutting forces, and tool wear during turning of $Zr_{50}Cu_{40}Al_{10}$ BMG alloy were examined. Four kinds of tool materials were used to cut an 8-mm-diameter BMG. The examination of the surface roughnesses of the BMG specimens machined at each cutting speed showed that the surface roughness became better as the cutting speed increased, and the tool materials also influenced the surface roughness. The chip morphology investigations showed that the unoxidized BMG chips had serrated curled chips with adiabatic shear bands, while the oxidized chips exhibited local melting and tangling rather than the usual spiral-shaped chips. The cutting force induced during machining of the Zr-based BMG was the largest for the TiN-WC tool, followed by the polycrystalline diamond (PCD) tool. The cermet tool exerted the smallest cutting force.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.9
• /
• pp.778-782
• /
• 2007

In the present study, design and forming process of fabricating titianium lightweight components are developed with applicaton of superplastic forming and diffusion bonding technology. SPF/DB(Superplastic forming/Diffusion bonding) technology is one of the advanced technologies to reduce production cost and weight and currently applied to aircrafts and space launchers in foreign countries. The present study constructs an analysis model to predict superplastic forming behavior of titanium alloy, which is well known for its resistance to deform. The experimental results show the forming of titanium lightweight sandwich structure is successfully performed from 3 sheets of Ti-6Al-4V. The results demonstrate that the developed technology to process design of SPF/DB by the finite element method can be applied to various types of components.

• Journal of the Korean Electrochemical Society
• /
• v.7 no.2
• /
• pp.108-123
• /
• 2004

Imaging of surfaces and structures by near-field scanning optical microscopy (NSOM) has matured and is routinely used for studies ranging from biology to materials science. Of interest in this review paper is a versatility of modified or multi-functional NSOM (mf-NSOM) to enable high resolution imaging in several modes: (1) Concurrent fluorescence and Topographical Imaging (gases) (2) Microspectroscopy (gases) (3) Concurrent Scanning Electrochemical and Topographical Imaging (SECM) (liquids) (4) Concurrent Photoelectrochemical and Topographical Imaging (PEM) (liquids) The present study will summarize some of the recent advances in mf-NSOM work confirmed and supported by the results from several other imaging techniques of optical, fluorescence, electron and electrochemical microscopy. The studies are directed at providing local information on pitting precursor sites and vulnerable areas on metal and semiconductor surfaces, and at reactive sites on heterogeneous, catalytic substrates, especially on Al 2024 alloy and polycrystalline Ti. In addition, we will introduce some results related to the laser-induced nanometal (Ag) synthesis using mf-NSOM.

• Korean Journal of Metals and Materials
• /
• v.47 no.4
• /
• pp.242-247
• /
• 2009

On the Transient Liquid Phase Bonding (TLPB) phenomenon with the MBF-50 insert metal at narrow gap (under 100), it takes long time for the bonding and the homogenizing. Typically, isothermal solidification is controlled by the diffusion of depressed element of B and Si. However, the amount of B and Si in the MBF-50 filler metal is large. This is reason of the long bonding time. Also, the MBF-50 filler metal did not contained Al and Ti which are ${\gamma}^{\prime}$ phases former. This is reason of the long homogenizing time. From the bonding phenomenon with the MBF-50 insert metal, we search main factors on the bonding mechanism and select several insert-metals for using the wide-gap TLPB. New insert-metals contained Al and Ti which are ${\gamma}^{\prime}$ phases former and decrease the B then the MBF-50. When the new insert-metal was used on the TLPB, the bonding time was decreased about 1/10 times and homogenizing heat treatment was no needed. In spite of the without homogenizing, the volume fraction of ${\gamma}^{\prime}$ phases in the boned interlayer was equal to homogenizing heat treated specimen which was TLPB with the MBF-50. Finally, the new insert metal named WG1 for the wide-gap TLPB is more efficient then the MBF-50 filler metal without decreasing the bonding characteristic.

• Journal of Korea Foundry Society
• /
• v.41 no.6
• /
• pp.543-549
• /
• 2021

Aluminum cast iron has excellent oxidation resistance and good resistance to sulfide and corrosion. Compared to Ti and Ni alloys, it is expected to be a substitute material for structural materials and stainless steels because it is relatively inexpensive to use Fe, which is a non-strategic element. This results in a weight reduction effect of about 30% as compared to the use of stainless steel. With regard to aluminum as an alloying material, it is an element that has been widely used for the alloying of cast iron in recent years. Practical use has been delayed owing to the resulting lack of ductility at room temperature and the sharp decrease in the strength above 600℃ of this alloy, however. The cause of the weak room temperature ductility is known to be environmental embrittlement by hydrogen, and the addition of various alloying elements has been attempted in order to mitigate these shortcomings. Although alloying elements such as vanadium, chromium, and manganese are mainly used to increase the hardness and wear resistance of gray cast iron, the price of finished products containing these elements and the problems associated with alloys with this material impose many limitations.

• Journal of Welding and Joining
• /
• v.28 no.3
• /
• pp.92-98
• /
• 2010

Ferritic stainless steels, which have relatively small thermal expansion coefficient and excellent corrosion resistance, are increasingly being used in vehicle manufacturing, in order to increase the lifetime of exhaust manifold parts. But, there are limits on use because of the problem related to cosmetic resistance, corrosions of condensation and high temperature salt etc. So, Aluminum-coated stainless steel instead of ferritic stainless steel are utilized in these parts due to the improved properties. In this investigation, Al-8wt% Si alloy coated 409L ferritic stainless steel was used as the base metal during Gas Tungsten Arc(GTA) welding. The effects of coated layer on the microstructure and hardness were investigated. Full penetration was obtained, when the welding current was higher than 90A and the welding speed was lower than 0.52m/min. Grain size was the largest in fusion zone and decreased from near HAZ to base metal. As welding speed increased, grain size of fusion zone decreased, and there was no big change in HAZ. Hardness had a peak value in the fusion zone and decreased from the bond line to the base metal. The highest hardness in the fusion zone resulted from the fine re-precipitation of the coarse TiN and Ti(C, N) existed in the base metal during melting and solidification process and the presence of fine $Al_2O_3$ and $SiO_2$ formed by the migration of the elements, Al and Si, from the melted coating layer into the fusion zone.