• Journal of Welding and Joining
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• 제34권2호
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• pp.46-53
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• 2016

Effect of heating rate on microstructure of brazed joints with STS 304 Printed Circuit Heat Exchanger (PCHE),which was manufactured as large-scale($1170(L){\times}520(W)){\times}100(T)$, mm), have been studied to compare bonding phenomenon. The specimens using MBF 20 was bonded at $1080^{\circ}C$ for 1hr with $0.38^{\circ}C/min$ and $20^{\circ}C/min$ heating rate, respectively. In case of a heating rate of $20^{\circ}C/min$, overflow of filler metal was observed at the edge of a brazed joints showing the height of filler metal was decreased from $100{\mu}m$ to $68{\mu}m$. At the center of the joints, CrB and high Ni contents of ${\gamma}$-Ni was existed. For the joints brazed at a heating rate of $0.38^{\circ}C/min$, the height of filler was decreased from $100{\mu}m$ to $86{\mu}m$ showing the overflow of filler was not appeared. At the center of the joints, only ${\gamma}$-Ni was detected gradating the Ni contents from center. This phenomenon was driven from a diffusion amount of Boron in filler metal. With a fast heating rate $20^{\circ}C/min$, diffusion amount of B was so small that liquid state of filler metal and base metal were reacted. But, for a slow heating rate $0.38^{\circ}C/min$, solid state of filler metal due to low diffusion amount of B reacted with base metal as a solid diffusion bonding.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.393-395
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• 2005

The bonding for Aluminum and Copper in the air is investigated in this study. This bonding method does not include the special process of removing aluminum oxide films. In case of this bending, each metal Is heated at bonding temperature where is above eutectic temperature of Al-Cu system and below melting point of Aluminum. The liquefaction around the bonding surface occurs after the diffusion at solid state of each metal. This phenomenon is predicted by the temperature range above eutectic temperature of Al-Cu equilibrium phase diagram.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1995년도 특별강연 및 추계학술발표 개요집
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• pp.208-211
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• 1995

Five cast gamma titanium aluminides, Ti-45~48%Al-2%Nb-2%Cr (nominal composition in at. %), were laser welded and their weld cracking susceptibilities were evaluated. Laser power, traversing rate and preheat temperature were systematically varied to generate a series of welds exhibiting a wide range of cooling rate ($100^{\circ}C/s-10,000^{\circ}C/s$). As Al content increased and the weld cooling rate decreased, solidification cracking susceptibility increased while solid-state cracking susceptibility decreased. Through laser beam energy input control and preheat, it was determined possible to produce high quality laser welds.

• 한국분말재료학회지
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• 제22권3호
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• pp.181-186
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• 2015

In this study, the effect of the friction stir welding (FSW) was compared with that of the gas tungsten arc welding (GTAW) on the microstructure and microhardness of Cu-Ni alloy weldment. The weldment of 10 mm thickness was fabricated by FSW and GTAW, respectively. Both weldments were compared with each other by optical microstructure, microhardness test and grain size measurement. Results of this study suggest that the microhardness decreased from the base metal (BM) to the heat affected zone (HAZ) and increased at fusion zone (FZ) of GTAW and stir zone (SZ) of FSW. the minimum Hv value of both weldment was obtained at HAZ, respectively, which represents the softening zone, whereas Hv value of FSW weldment was little higher than that of GTAW weldment. These phenomena can be explained by the grain size difference between HAZs of each weldment. Grain size was increased at the HAZ during FSW and GTAW. Because FSW is a solid-state joining process obtaining the lower heat-input generated by rotating shoulder than heat generated in the arc of GTAW.

• Journal of Welding and Joining
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• 제32권5호
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• pp.72-79
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• 2014

Shaped charge(SC) ammunition is a weapon that penetrates directly the target by made jet from metal liner on impacting at a target. In SC, the liner occupies significantly important role causing an explosion and penetration of the target. The Al-Ni composite coating was deposited on copper liner in a solid state via kinetic spraying to improve the explosive force. The mechanical properties, reactivity and microstructure were investigated to confirm the possibility of kinetic sprayed Al/Ni composite coating as a reactive liner material. Reactive liner using Al/Ni composite exhibited much enhanced reactivity than pure copper liner due to Self-propagating High-temperature Synthesis (SHS) reaction with significantly improved adhesive bond strength. Especially, among the Al/Ni composite coatings, AN11 (the Al versus Ni atomic percent ratio is 1:1) showed the greatest reactivity due to its widest reaction area between deposited Al and Ni.

• Journal of Welding and Joining
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• 제25권3호
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• pp.28-36
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• 2007

A bulk amorphous NiTiZrSiSn powder produced using an inert gas atomization was sprayed by kinetic spraying process that is basically a solid-state deposition process onto a mild steel substrate. They were successfully overlaid onto the mild steel substrate. In order to evaluate the tribological behavior of the kinetic sprayed NiTiZrSiSn BMG (Bulk Metallic Glass) coatings, a partially crystallized coating and a fully crystallized coating were prepared by the isothermal heat treatments. Tribological behaviors were investigated in view of friction coefficient, hardness and amorphous phase fraction of coating layer. Surface morphologies and depth in the wear tracks were observed and measured by scanning electron microscope and alpha-step. From the examination of the scratch wear track microstructure, transition from the ductile like deformation (micro cutting) to the brittle deformation (micro fracturing) in the scratch groove was observed with the increase of the crystallinity.

• 한국산학기술학회논문지
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• 제17권7호
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• pp.434-441
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• 2016

마찰교반용접은 소재와 용접 툴 간의 마찰열에 의해 접합되는 고상접합 공정이다. 용접 시 발생하는 입열량에 따라 용접부의 건전성이 결정된다. 과도한 입열량은 산화물 및 기공결함의 원인이 되며, 불충분한 입열량은 터널결함 등의 문제점이 발생한다. 따라서 마찰교반용접부 중심에서의 온도 이력을 파악하는 것은 건전성을 판단하는 데 있어 매우 중요한 연구이다. 본 연구에서는 마그네슘 합금소재에 대한 마찰교반용접부의 온도분포 특성을 평가하였다. 이를 위해 유한요소해석을 통한 마찰교반용접부의 유동장 및 온도분포를 예측하였다. 유한요소해석을 위해 용접 툴 형상 간소화, 마찰 조건 선정 등 선행 해석을 수행하고 최적조건을 도출하였다. 또한, 해석모델의 검증을 위해 마그네슘 합금의 맞대기 마찰교반용접 시 용접부 중앙에서의 온도를 측정하였다. 유한요소해석 결과 마찰교반용접부의 온도에 영향을 미치는 주요변수의 기여도는 회전속도가 이송속도보다 더 높은 것으로 판단된다. 또한, 용접부 중심에서의 실측 온도와 유한요소해석 결과 사이에 5.4% - 7.7% 수준의 오차 내에서 잘 일치하였다.

• 한국공작기계학회논문집
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• 제10권2호
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• pp.73-78
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• 2001

In this study, the friction weldability and properties of inconel alloy(IN738LC) to stainless steel (STS304) was investigat-ed. Upset length increased according to increment of friction pressure and time. The tensile strength of the friction weld-ing reached 85% of the STS304 base metal strength under the conditions of 8 sec friction time, 50MPa friction pressure and 150 MPa upset pressure. From the result of fracture surface analysis, IN738LC section can be joined with STS 304 materials in shape of a convex lens. Also, the temperature of welded interface was measured with k-type thermocouple. Finally the plastic flow confirmed at the welded interface STS304 by micro test.

• 소성∙가공
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• 제15권3호
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• pp.195-205
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• 2006

This paper focuses on a rheo-forming of am part fabricated by electromagnetic stirring system (EMS). This forming process take place under high pressure of high pressure die casting and thin walled casting is possible. Furthermore, the productivity is better than low pressure die casting because of shorter cycle time. The advantages of rheo-forming are performed in the semi solid state with laminar flow and the gas content is low, which makes welding possible. Therefore this research applies for arm part with EMS and has investigated the mechanical properties after T6 and T5 heat-treatment.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.340-343
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• 2005

This paper focuses on an rheo-forming of arm part fabricated by electromagnetic stirring system (EMS). This forming process take place under high pressure of high pressure die casting and thin walled casting is possible. Also the productivity is better than low pressure die casting because of shorter cycle time. The advantages of rheo-forming are performed in the semi solid state with laminar flow and the gas content is low, which makes welding possible. Therefore this research applies for arm part with EMS and has investigated the mechanical propriety after T6 and T5 heat-treatment.