• 한국표면공학회지
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• 제51권1호
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• pp.34-39
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• 2018

Steel crucible used for molten Al has a problem of very limited lifetime because of the interaction between Fe and molten Al. This study was performed to improve the lifetime of steel crucible for molten Al by coating metallic Al and by further anodizing treatment to form thick and uniform anodic oxide films. The lifetime of the steel crucible was improved slightly by Al coating from 30 to 40 hours by metallic Al coating and largely to 120 hours by coating the surface with anodic oxide film. The improved lifetime was attributed to blocking of the reaction between Fe and molten Al with the help of anodic oxide layer with more than 20 um thickness on the crucible surface. The failure of the steel crucible arises from the formation of intermetallic compounds and pores at the steel/Al interface.

• 연구논문집
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• 통권28호
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• pp.183-192
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• 1998

The wear and oxidation resistance of two phase nickel aluminides was investigated. Wear tests of various heat-treated specimens at room temperature and at $500^{\circ}C$ were performed under no lubricant condition in air by using a ball-on-disk type tribotester. Isothermal oxidation tests were made at $1100^{\circ}C$ in air flowing at the rate of 70cc/min and at $1000^{\circ}C$ in air by using TGA. Experimental results from wear tests showed that nickel aluminide with a higher content of Al had an improved wear resistance at both temperatures. Also the examination of the wear tracks after wear test at both room temperature and $500^{\circ}C$ indicated that regardless of the alloy compositions the wear tracks of the two phase nickel aluminides showed an abrasive type wear The improved oxidation resistance observed in the Ni-34at%Al alloy could to be attributed to the microstructural difference between the aluminides. An accelerated oxidation along the thin layer of $Ni_3AL$ along the grain boundary observed in the microstructure of the Ni-32at%Al aluminide could be attributed to the poor oxidation resistance.

• 열처리공학회지
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• 제34권6호
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• pp.309-314
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• 2021

Due to the superior corrosion resistance and mechanical properties of TiAl alloy at high temperature, it has been utilized as a turbine wheel of a turbocharger. The dissimilar metallic bonding is usually applied to combine the TiAl turbine wheel with the SCM440 structural steel which is used as a driving shaft. In this study, the TiAl and SCM440 joint were fabricated by using a friction welding technique. During bonding process, to suppress the martensitic transformation and the formation of cracks, which might reduce a strength of the joints, Cu was used as an insert metal to relieve stress. As a result, the intermetallic compounds (IMCs) layer was observed at TiAl/Cu interface while no IMC formation was formed at SCM440/Cu interface. Since understanding of the IMCs effects on the mechanical performance of welded joint is also essential for ensuring the reliability and integrity of the turbocharger system, we estimated the nanohardness of welded joint region through nanoindentation. The relation between the microstructural feature and its mechanical property is discussed in detail.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1999년도 춘계학술대회 및 발표대회 강연 및 발표논문 초록집
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• pp.5-5
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• 1999

The Principal deficiency of the existing notion about the sintering-mixtures consists in the fact that almost no attention is focused on the Phenomenon of alloy formation during sintering, its connection with dimensional changes of powder bodies, and no correct ideas on the driving force for the sintering process in the stage of establishing chemical equilibrium in a system are available as well. Another disadvantage of the classical sintering theory is an erroneous conception on the dissolution mechanism of solid in liquid. The two-particle model widely used in the literature to describe the sintering phenomenon in solid state disregards the nature of the neighbouring surrounding particles, the presence of pores between them, and the rise of so called arch effect. In this presentation, new basic scientific principles of the driving forces for the sintering process of a two-component powder body, of a diffusion mechanism of the interaction between solid and liquid phases, of stresses and deformation arising in the diffusion zone have been developed. The major driving force for sintering the mixture from components capable of forming solid solutions and intermetallic compounds is attributed to the alloy formation rather than the reduction of the free surface area until the chemical equilibrium is achieved in a system. The lecture considers a multiparticle model of the mixed powder-body and the nature of its volume changes during solid-state and liquid-phase sintering. It explains the discovered S-and V-type concentration dependencies of the change in the compact volume during solid-state sintering. It is supposed in the literature that the dissolution of solid in liquid is realised due to the removal of atoms from the surface of the solid phase into the melt and then their diffusicn transfer from the solid-liquid interface into the bulk of liquid. It has been shown in our experimental studies that the mechanism of the interaction between two components, one of them being liquid, consist in diffusion of the solvent atoms from the liquid into the solid phase until the concentration of solid solutions or an intermetallic compound in the surface layer enables them to pass into the liquid by means of melting. The lecture discusses peculimities of liquid phase formation in systems with intermediate compounds and the role of the liquid phase in bringing about the exothermic effect. At the frist stage of liquid phase sintering the diffusion of atoms from the melt into the solid causes the powder body to grow. At the second stage the diminution of particles in size as a result of their dissolution in the liquid draws their centres closer to each other and makes the compact to shrink Analytical equations were derived to describe quantitatively the porosity and volume changes of compacts as a result of alloy formation during liquid phase sinteIing. Selection criteria for an additive, its concentration and the temperature regime of sintering to control the density the structure of sintered alloys are given.

• Journal of Welding and Joining
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• 제14권4호
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• pp.99-108
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• 1996

The microstructure and bond strength are examined on the SiC/SiC and SiC/mild steel joints brazed by the Ag-Ti based alloys with different Ti contents. In the SiC/SiC brazed joints, the thickness of the reaction layers at the bond interface and the Ti particles in the brazing alloy matrices increase with Ti contents. When Ti is added up to 9 at% in the brazing alloy. $Ti_3SiC_2$ phase in addition to TiC and $Ti_5Si_3$ phase is newly created at the bond interface and TiAg phase is produced from peritectic reaction in the brazing alloy matrix. In the SiC/mild steel joints brazed with different Ti contents, the microstructure at the bond interface and in the brazing alloy matrix near SiC varies similarly to the case of SiC/SiC brazed joints. But, in the brazing alloy matrix near the mild steel, Fe-Ti intermetallic compounds are produced and increased with Ti contents. The bond strengths of the SiC/SiC and SiC/mild steel brazed joints are independent on Ti contents in the brazing alloy. There are no large differences of the bond strength between SiC/SiC and SiC/mild steel brazed joints. In the SiC/mild steel brazed joints, Fe dissolved from the mild steel does not affect on the bond strength of the joints. Thermal contraction of the mild steel has nearly no effects on the bond strength due to the wide brazing gap of specimens used in the four-point bend test. The brazed joints has the average bond strength of about 200 MPa independently on Ti contents, Fe dissolution and joint type. Fracture in four-point bend test initiates at the interface between SiC and TiC reaction layer and propagates through SiC bulk. The adhesive strength between SiC and TiC reaction layer seems to mainly control the bond strength of the brazed joints.

• 마이크로전자및패키징학회지
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• 제15권3호
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• pp.27-33
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• 2008

PDA, 핸드폰과 같은 포터블 제품의 사용이 급증함에 따른 전자 제품의 사용 환경의 변화는 제품의 솔더 조인트 신뢰성을 더욱 필요로 하게 되었다. 무전해 니켈/금 도금 표면 처리는 솔더링 특성이 우수하고, 표면처리 두께가 균일하며 패키징 공정에서 사용되는 광학설비에서 인식이 잘되기 때문에 미세피치 SMT 디바이스와 BGA 기판에 폭넓게 사용되고 있다. 그러나 무전해 니켈/금 도금 표면과 솔더 계면에서 발생되는 취성 파괴가 문제점으로 지적되고 있다. 솔더의 취성 파괴는 솔더링시 금속간 화합물과 무전해 니켈층 사이에 형성된 P-rich 영역의 갈바닉 니켈 부식에 의한 black pad 현상에 기인한다. 이론적으로 평탄한 무전해 Ni표면은 무전해 금도금 과정 중 도금액의 균일하게 순환되기 때문에 black pad 발생을 억제하는 장점을 가지고 있다. 그러나 이러한 장점에도 불구하고 무전해 Ni층의 표면형상을 어떻게 제어 할지에 대한 연구는 충분히 이루어 지지 않고 있다. 본 연구에서는 Cu 하지층의 표면 형상이 무전해 Ni층의 표면 형상에 미치는 영향에 대하여 분석하였다. 이를 위해 Cu 에칭액과 Cu에칭 처리 횟수를 변화시켜 Cu 하지층의 표면 형상을 다양하게 변화시켰다.

• 한국수소및신에너지학회논문집
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• 제28권6호
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• pp.610-617
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• 2017

This paper presents a study of the effect of thickness of porous Al-Ni electrodes, on the Hydrogen Evolution Reaction (HER) in alkaline media. As varying deposition time at 300 W DC sputtering power, the thickness of the Al-Ni electrodes was controlled from 1 to $20{\mu}m$. The heat treatment was carried out in $610^{\circ}C$, followed by selective leaching of the Al-rich phase. XRD studies confirmed the presence of $Al_3Ni_2$ intermetallic compounds after the heat treatment, indicating the diffusion of Ni from the Ni-rich phase to Al-rich phase. The porous structure of the Al-Ni electrodes after the selective leaching of Al was also confirmed in SEM-EDS analysis. The double layer capacitance ($C_{dl}$) and roughness factor ($R_f$) of the electrodes were increased for the thicker Al-Ni electrodes. As opposed to the general results in above, there were no further improvements of the HER activity in the case of the electrode thickness above $10{\mu}m$. This result may indicate that the $R_f$ is not the primary factor for the HER activity in alkaline media.

• 한국재료학회지
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• 제29권4호
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• pp.258-263
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• 2019

Since the directly bonded interface between TiAl alloy and SCM440 includes lots of cracks and generated intermetallic compounds(IMCs) such as TiC, FeTi, and $Fe_2Ti$, the interfacial strength can be significantly reduced. Therefore, in this study, Cu is selected as an insert metal to improve the lower tensile strength of the joint between TiAl alloy and SCM440 during friction welding. As a result, newly formed IMCs, such as $Cu_2TiAl$, CuTiAl, and $TiCu_2$, are found at the interface between TiAl alloy and Cu layer and the thickness of IMCs layers is found to vary with friction time. In addition, to determine the relationship between the thickness of the IMCs and the strength of the welded interfaces, a tensile test was performed using sub-size specimens obtained from the center to the peripheral region of the friction-welded interface. The results are discussed in terms of changes in the IMCs and the underlying deformation mechanism. Finally, it is found that the friction welding process needs to be idealized because IMCs generated between TiAl alloy and Cu act to not only increase the bonding strength but also form an easy path of fracture propagation.

• 대한금속재료학회지
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• 제47권12호
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• pp.842-851
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• 2009

The long-term reliability of Sn-0.3wt%Ag-0.7wt%Cu solder joints was evaluated and compared with Sn-3.0wt%Ag-0.5wt%Cu under thermal shock conditions. Test vehicles were prepared to use Sn-0.3Ag-0.7Cu and Sn-3.0Ag-0.5Cu solder alloys. To compare the shear strength of the solder joints, 0603, 1005, 1608, 2012, 3216 and 4232 multi-layer ceramic chip capacitors were used. A reflow soldering process was utilized in the preparation of the test vehicles involving a FR-4 material-based printed circuit board (PCB). To compare the shear strength degradation following the thermal shock cycles, a thermal shock test was conducted up to 2,000 cycles at temperatures ranging from $-40^{\circ}C$ to $85^{\circ}C$, with a dwell time of 30 min at each temperature. The shear strength of the solder joints of the chip capacitors was measured at every 500 cycles in each case. The intermetallic compounds (IMCs) of the solder joint interfaces werealso analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results showed that the reliability of Sn-0.3Ag-0.7Cu solder joints was very close to that of Sn-3.0Ag-0.5Cu. Consequently, it was confirmed that Sn-0.3Ag-0.7Cu solder alloy with a low silver content can be replaced with Sn-3.0Ag-0.5Cu.

• 열처리공학회지
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• 제34권2호
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• pp.66-74
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• 2021

Cladding material, which can selectively obtain excellent properties of different metals, is a composite material that combines two or more types of dissimilar metals into one plate. The titanium-copper cladding material between titanium which has excellent corrosion resistance and copper which has high thermal and electrical conductivity, are highly valuable composite materials. It can be used as heat exchangers with high conductivity under severe corrosion conditions. In order to apply the clad plate to the heat exchanger, it must be manufactured in the form of a tube and additional welding is required. It is important to select the cladding material manufacturing process and the welding process. The process of manufacturing the cladding material includes extrusion, rolling, and explosive bonding. Among them, the explosive bonding process is suitable for additional welding because no heat-affected zone is formed. In this study TIG welding of the explosive-bonded dissimilar clad plates was successfully performed by butt welding. The microstructures and bonding interface of the welded part were observed, and the effect of the bonding layer at the welding interface and the intermetallic compounds on the mechanical properties and tensile plastic deformation behaviors were analyzed. And also the integrity of TIG-welded dissimilar part was evaluated.