• Journal of the Korean Society for Heat Treatment
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• v.34 no.2
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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.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.244.2-244.2
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• 2011

We introduce a novel and robust method for the preparation of nanocomposite multilayers, which allows the excellent photoluminescent (PL) properties as well as the accurate control over the composition and dimensions of multilayers. By exchanging the oleic acid stabilizers of CdSe@ZnS quantum dots (QDs) synthesized in organic solvent with 2-bromo-2-methylpropionic acid (BMPA) in the same solvent, these nanoparticles were be alternately deposited by nucleophilic substitution reaction with highly branched poly(amidoamine) dendrimer (PAMA) through layer-by-layer (LbL) assembly process. Our approach does not need to be transformed into the water-dispersible nanoparticles with electrostatic or hydrogen-bonding groups, which can deteriorate their inherent properties, for the built-up of multilayers. The nanocomposite multilayers including QDs exhibited the strong PL properties achieving densely packed surface coverage as well as long-term PL stability under atmospheric conditions in comparison with those of conventional LbL multilayers based on electrostatic interaction. Furthermore, we demonstrate that the flexible multilayer films with optical properties can be easily prepared using nucleophilic substitution reaction between bromo and amino groups in organic media. This robust and tailored method opens a new route for the design of functional film devices based on nanocomposite multilayers.

• Korean Journal of Materials Research
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• v.16 no.1
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• pp.30-36
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• 2006

A novel method was proposed to grow an epitaxial $CoSi_2$ on (100)Si substrate. A $CoN_x$ interlayer was deposited by reactive sputtering of Co in an Ar+$N_2$ flow. From the Ti/Co/$CoN_x$/Si structure, a uniform and thin $CoSi_2$ layer was epitaxially grown on (100)Si by annealing above $700^{\circ}C$. Two amorphous layers were found at the $CoN_x$/Si interface, where the top layer has a silicon nitride (Si-N) bonding state with some Co content and the bottom layer has a Co-Si intermixing state. The SiNx amorphous layer seems to play a critical role of suppressing the diffusion of Co into Si substrate for the direct formation of epitaxial $CoSi_2$.

• Journal of Korea Foundry Society
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• v.17 no.4
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• pp.371-378
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• 1997

The study for direct synthesis of TaC carbide which was a reaction product of tantalum and carbon in the cast iron was performed. Cast iron which has hypo-eutectic composition was cast bonded in the metal mold with tantalum thin sheet of thickness of $100{\mu}m$. The contents of carbon and silicon of cast iron matrix was controlled to have constant carbon equivalent of 3.6. The chracteristics of microstructure and the formation mechanism of TaC carbide in the interfacial reaction layer in the cast iron/tantalum thin sheet heat treated isothermally at $950^{\circ}C$ for various time were examined. TaC carbide reaction layer was grown to the dendritic morphology in the cast iron/tantalum thin sheet interface by the isothermal heat treatment. The composition of TaC carbide was 48.5 at.% $Ti{\sim}48.6$ at.% C-2.8 at.% Fe. The hardness of reaction layer was MHV $1100{\sim}1200$. The thickness of reaction layer linearly increased with increasing the total content of carbon in the cast iron matrix and isothermal heat treating time. The growth constant for TaC reaction layer was proportional to the log[C] of the matrix. The formation mechanism of TaC reaction layer at the interface of cast iron/tantalum thin sheet was proved to be the interfacial reaction.

• Journal of the Korean institute of surface engineering
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• v.20 no.2
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• pp.49-59
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• 1987

The properties of $Cr_2O_3-Al_2O_3-SiO_2$ composite oxide coatings on steel surface were investigated. The results obtained were as follows: The microhardness of oxide coating layer increased with increasing heat-treatment temperature and $Cr_2O_3$ content in coating layer. The hardness showed the highest value (850Hv) treated at 700$^{\circ}C$ for $SiO_2:Al_2O_3:Cr_2O_3$=1:1:4. Increasing heat-treatment temperature, corrosion current density became lower and coating layer became denser. The corrosion current density showed the lowest value $(6.5{\times}10^{-5}\;Acm^2)$ treated at 750$^{\circ}C\;for\;SiO_2:Al_2O_3:Cr_2O_3$=1:1:3. These results were explained by protective layer which was formed during heat-treatment. The bonding between matrix and coating layer is expected to be made mechanically and chemically by the inter diffusion of Ni and Fe. The composite oxide coating was formed by softening of the binder with increasing heat-treatment temperature. The strengthening of coating layer is to be resulted from the dispersion of major oxide particles.

• Journal of Conservation Science
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• v.35 no.1
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• pp.33-40
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• 2019

During the conservation and maintenance of the birthplace center yard of President Asan Yoon Bosun, four porcelain enamel dishware were excavated from the central yard well. The glaze layer of excavated enamel was severely damaged; hence, the conservation process was done rapidly. In addition, scientific investigation and analysis were conducted to confirm the material properties of the glaze layer. It was confirmed that the outer surface was inverted and dried, while the inner surface was upright and fired during the glazing and drying process by measuring the film thickness. By examining the breakup phenomenon, the breaking up of the white enamel on the colored enamel was confirmed. This indicates that the colored glaze rose to the surface depending on the density of the colored glaze and white glaze. The investigation of the cross-section of the film confirmed that the lower layer formed according to the bonding properties with metal during the glazing process. Analysis of the constituents of the identified lower layer confirmed that there are differences between the specific components of the metal oxide of the lower layer and the surface color development of the upper layer.

• Carbon letters
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• v.7 no.3
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• pp.196-200
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• 2006

Graphite has hexagonal closed packing structure with two bonding characteristics of van der Waals bonding between the carbon layers at c axis, and covalent bonding in the carbon layer at a and b axis. Graphite has high tolerant to the extreme conditions of high temperature and neutron irradiations rather than any other materials of metals and ceramics. However, carbon elements easily react with oxygen at as low as 400C. Considering the increasing production of today of hydrogen and electricity with a nuclear reactor, study of oxidation characteristics of graphite is very important, and essential for the life evaluation and design of the nuclear reactor. Since the oxidation behaviors of graphite are dependent on the shapes of testing specimen, critical care is required for evaluation of nuclear reactor graphite materials. In this work, oxidation rate and amounts of the isotropic graphite (IG-110, Toyo Carbon), currently being used for the Koran nuclear reactor, are investigated at various temperature. Oxidation process or principle of graphite was figured out by measuring the oxidation rate, and relation between oxidation rate and sample shape are understood. In the oxidation process, shape effect of volume, surface area, and surface to volume ratio are investigated at $600^{\circ}C$, based on the sample of ASTM C 1179-91.

• Journal of the Korean Ceramic Society
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• v.27 no.7
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• pp.925-933
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• 1990

The possible use of bioglass,, which is one of the surface active biomaterials, as implants materials has drawn great attention due to their ability to bond to human living tissue. In the present work, the investigation was carried out to find the bonding phenomena between alumina substrate and bioglass(45S5) or fluorine-containing bioglass(45S5$.$4F), and the properties of coated bioglass. The stable bonding between alumina and bioglass was formed when heat-treated at 1150$^{\circ}C$ for 120 minutes or at 1250$^{\circ}C$ for 30 minutes for the 45S5, and at 1150$^{\circ}C$ for 30 minutes for the 45S5$.$4F. When bioglass coated alumina was heat-treated, great amount of Al was diffused into bioglass from alumina substrate. More Al was diffused into fluorine-containing bioglass than into bioglass without fluorine. At early stage of heat-tretment, the diffused alumina content was increased with the square root of time and it was also increased with the thickness of coating layer and heat-treatment temperatures. The alumina content became constant after its saturation for longer heat-treatment time. Coated bioglasses were crystallized to Na2O$.$CaO$.$3SiO2 when heat-treated at lower temperature, and to CaO$.$SiO2 at higher temperature.

• Journal of Welding and Joining
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• v.22 no.2
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• pp.38-45
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• 2004

Ultrasonic signals transmitted through adhesively bonded plates were used to evaluate parameters related to attenuation and frequency in the adhesively bonded joint. The kinds of bonding materials with a different bonding thickness of constant pressure were used. And ultrasonic diagnosis was evaluated by p-wave sensor of 10MHz. FFT has been performed to determine bond-layer parameters such as effective thickness and frequency for adhesively bonded joint of A16061 plates in comparison with measured to theoretical ratios. When variable thickness exists, the ultrasonic spectrum was changed the frequency wave. The more materials thickness and the higher the frequency, the larger shift was observed. Measured ratios for cases of bond thickness and variety bonding materials are then used to determine bond parameters. The results show that the technique can be applied to the characterization of adhesively bonded joint.

• Structural Monitoring and Maintenance
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• v.4 no.3
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• pp.237-253
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• 2017

Among various structural health monitoring technologies, impedance-based damage detection has been recognized as a promising tool for diagnosing critical members of civil structures. Since the piezoelectric transducers used in the impedance-based technique should be bonded to the surface of the structure using bonding layers (e.g., epoxy layer), it is hard to maintain the as-built condition of the bonding layers and to reconfigure the devices if needed. This study presents an experimental investigation by using magnetically attached PZT-interface for the impedance-based damage detection in bolted girder connections. Firstly, the principle of the impedance-based damage detection via the PZT-interface device is outlined. Secondly, a PZT-interface attachment method in which permanent magnets are used to replace the conventional bonding layers is proposed. Finally, the use of the magnetic attraction for the PZT-interface is experimentally evaluated via detecting the bolt-loosening events in a bolted girder connection. Also, the sensitivity of impedance signatures obtained from the PZT-interface is analyzed with regard to the interface's material.