• Analytical Science and Technology
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• v.8 no.3
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• pp.351-358
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• 1995

Oxidation behavior on the surface of Nd-Fe-B ribbon alloy has been studied by X-ray Photoelectron Spectroscopy. In the incipient stage of oxidation on the surface of "as-received" ribbon Nd-oxide film was formed from the fast oxidation of Nd and Fe was metal state in bulk. In process of oxidation time Fe was more abundant in the outmost surface of ribbon from the defused Fe through Nd-oxide film and layer structure of oxidation film was formed.

• Journal of Korea Foundry Society
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• v.29 no.5
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• pp.225-232
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• 2009

For comprehensive understanding of the formation behavior of $\beta-Al_5FeSi$ phase in Al-Si-Cu alloys with the existence of Fe element, microstructure characterizations were performed using combined analysis of OM, SEM-EDS, XRD. Especially, experimental and predictive works on solidification events of $\beta-Al_5FeSi$ phase as well as other phases formed together with $\beta-Al_5FeSi$ have been carried out by using DSC analysis and Java-based Materials Properties software (J. Mat. Pro.). Primary and eutectic $\beta-Al_5FeSi$ phases were able to distinguish from each other on microstructures by their morphological features. Primary $\beta-Al_5FeSi$ phase was seen to have rough surface perpendicular to growth direction, indicating free attachment of solute atoms in liquid state. On the other hand, the eutectic $\beta-Al_5FeSi$ phase was formed with plain and straight surface during eutectic reaction together with $\alpha$-Al phase. The eutectic reaction of $\beta-Al_5FeSi$ and $\alpha$-Al phases was seen to be able to separate into each formation depending on cooling rate.

• Korean Journal of Materials Research
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• v.11 no.9
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• pp.733-739
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• 2001

In Al-25Nb binary system, it was observed only formation of $D0_{22}$ $Al_3Nb$ intermetallic compound after 5hr milling but it was not observed formation of meta stable phase like L1$_2$ phase. In this state, $D0_{22}$ $Al_3Nb$ fabricated had nano sized grain of approximately 20nm. Ternary systems, transition metals such as Cr, Cu, Fe, Mn were added 6~12at.% as substitution of Al, showed formation of $D0_{22}$ $Al_3Nb$ like Al-25Nb binary system. In Al- l2Cu-25Nb system, it was observed that broad XRD pattern like amorphization of Al and not observed formation of $D0_{22}$ $Al_3Nb$ after 5hr milling. But there was mixed phase of a lot of amorphous Al and little $D0_{22}$ $Al_3Nb$ through TEM. In the states of unalloyed, 5~7hr milling time, those showed exothermic reaction at 35$0^{\circ}C$, which was formation of $D0_{22}$ $Al_3Nb$ like Al-25Nb binary system. With increasing milling time to 10hr, $D0_{22}$ $Al_3Nb$ was transformed to mixed phase of amorphous and nanocryatlline, having approximately 10nm grain but the meta stable $Al_3Nb$ was not fabricated by adding transition metals.

• Korean Journal of Materials Research
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• v.24 no.8
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• pp.393-400
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• 2014

NiO catalysts were successfully coated onto FeCrAl metal alloy foam as a catalyst support via a dip-coating method. To demonstrate the optimum amount of NiO catalyst on the FeCrAl metal alloy foam, the molar concentration of the Ni precursor in a coating solution was controlled, with five different amounts of 0.4 M, 0.6 M, 0.8 M, 1.0 M, and 1.2 M for a dip-coating process. The structural, morphological, and chemical bonding properties of the NiO-catalyst-coated FeCrAl metal alloy foam samples were assessed by means of field-emission scanning electron microscopy(FESEM), scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS). In particular, when the FeCrAl metal alloy foam samples were coated using a coating solution with a 0.8 M Ni precursor, well-dispersed NiO catalysts on the FeCrAl metal alloy foam compared to the other samples were confirmed. Also, the XPS results exhibited the chemical bonding states of the NiO phases and the FeCrAl metal alloy foam. The results showed that a dip-coating method is one of best ways to coat well-dispersed NiO catalysts onto FeCrAl metal alloy foam.

• Transactions of Materials Processing
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• v.24 no.1
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• pp.37-43
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• 2015

The purpose of the current study is to improve the clinching joint strength of aluminum and fiber metal laminates (FMLs) comprised of three layers. The joining of FML and Al 5052 by a conventional clinching joint has some disadvantages such as necking of the upper sheet, lack of interlocking, defects caused by the vertical load, and especially loss of strength of the composite material due to the low ductility. In the current study, a tapered-hole clinching method is proposed as an alternative for the joining of Al 5052 and FMLs. A hole with a tapered shape is formed before the joining process. The design parameters were evaluated using the Taguchi method for the geometry of the tapered hole in order to determine the maximum separation load. The diameter of the punch corner, clearance, punch stroke and the tapered length were used as the main variables in the Taguchi method. In conclusion, the contribution ratio for each of the fours variable examined was 35.07%, 22.44%, 21.32% and 14.11%, respectively. In addition, the appropriate combination of the design parameters can make a 5% improvement in the vertical direction joint strength.

• Journal of Welding and Joining
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• v.25 no.5
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• pp.45-50
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• 2007

The Ni-base superalloy GTD111 DS is used in the first stage blade of high power land-based gas turbines. Advanced repair technologies of the blade have been introduced to the gas turbine industry over recent years. The effect of the filler metal powder on Transient Liquid Phase bonding phenomenon and tensile mechanical properties was investigated on the GTD111 DS superalloy. At the filler metal powder N series, the base metal powders fully melted at the initial time and a large amount of the base metal near the bonded interlayer was dissolved by liquid inter metal. Liquid filler metal powder was eliminated by isothermal solidification which was controlled by the diffusion of B into the base metal. The solids in the bonded interlayer grew from the base metal near the bonded interlayer inward the insert metal during the isothermal solidification. The bond strength of N series filler metal powder was over 1000 MPa. and ${\gamma}'$ phase size of N series TLP bonded region was similar with base metal by influence of Ti, Al elements. At the insert metal powder M series, the Si element fluidity of the filler metal was good but microstructure irregularity on bonded region because of excessive Si element. Nuclear of solids formed not only from the base metal near the bonded interlayer but also from the remained filler metal powder in the bonded interlayer. When the isothermal solidification was finished, the content of the elements in the boned interlayer was approximately equal to that of the base metal. But boride and silicide formed in the base metal near the bonded interlayer. And these boride decreased with the increasing of holding time. The bond strength of M series filler metal powder was about 400 MPa.

• Membrane Journal
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• v.28 no.5
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• pp.297-306
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• 2018

This review focused carbon-free hydrogen productions from ammonia decomposition including inorganic membranes, catalysts and the presently studied reactor configurations. It also contains general information about hydrogen productions from hydrocarbons as hydrogen carriers. A Pd-based membrane (e.g. a porous ceramic or porous metallic support with a thin selective layer of Pd alloy) shows its efficiency to produce the high purity hydrogen. Ru-based catalysts consisted of Ru, support, and promoter are the efficient catalysts for ammonia decomposition. Packed bed membrane reactor (PBMR), Fluidized bed membrane reactor (FBMR), and membrane micro-reactor have been studied mainly for the optimization and the improvement of mass transfer limitation. Various types of reactors, which contain various combinations of hydrogen-selective membranes (i.e. Pd-based membranes) and catalysts (i.e. Ru-based catalysts) including catalytic membrane reactor, have been studied for carbon-free hydrogen production to achieve high ammonia conversion and high hydrogen flux and purity.

• Journal of Welding and Joining
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• v.35 no.3
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• pp.68-74
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• 2017

Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E71T-1C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, Intragranular polygonal ferrite and grainboundary ferrite were formed only in first layer of weld metal. Another layers consisted of acicular ferrite and $Widmannst{\ddot{a}}tten$ ferrite. The amount of acicular ferrite was increased with decreasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered martensite and lower bainite. Lower and upper bainite were formed in heat affected zone of carbon steel. Tensile strengths of dissimilar metal welds decreased with increasing heat inputs. Dissimilar metal welds showed a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals welds showed that the weight loss rate by corrosion below 170 hours was decreased with increasing heat inputs due to the increase of the amount of acicular ferrite.

• Journal of Technologic Dentistry
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• v.23 no.1
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• pp.31-43
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• 2001

This study was performed to observe the micro-structure change of surface, behavior of oxide change of element, the component transformation of the alloy and the bonding strength between the porcelain interface in order to investigate effects of indium, tin on interfacial properties of porcelain fused to low gold alloy. Hardness of castings was measured with a micro-Vicker's hardness tester. The compositional change of the surface of heat-treated specimen was analyzed with an EDS and an EPMA. The interfacial shear bonding strength between alloy specimen and fused porcelain was measured with a mechanical testing system(MTS 858.20). The results were as follows: 1) The hardness value of alloy increased as increasing amount of indium addition. 2) The formation of oxidation increased as increasing indium and tin contents after heat treatment. 3) Diffusion of indium and tin elements increased as increasing indium and tin contents in metal-porcelain surface after porcelain fused to metal firing. 4) The most interfacial shear bonding strength was increased as increasing a composition of adding elements, and a heat-treatment time, and an oxygen partial pressure. From the results of this study it was found that the addition of alloying elements such as indium and tin increase hardness of as-cast alloy, produce surface oxide layer of adding elements by heat-treatment which may improve interfacial bonding strength between alloy and porcelain.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.5
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• pp.625-633
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• 2011

Characteristics of a commercial metal hydride (MH) hydrogen supply system have been investigated and an operating strategy was developed based on the experimental data. As a prior step, charging/discharging capacity, thermal properties such as heat capacity, heat of reaction of MH system were experimentally measured. And then P-C-T data for various operating conditions were collected and a correlation between P, C and T predicting the behavior of MH was derived. Based on the basic experimental data, an operating strategy of MH system was developed, in which the hot water temperature supplied into the water jacket of MH was controlled depending on the pressure of MH, thereby the pressure of MH could be maintained at a suitable range. By adjusting the temperature of hot water from $40^{\circ}C$ to $60^{\circ}C$, the maximum discharging capacity of hydrogen could be increased by 4.7%, and consequently more stable hydrogen supply and longer operation time of fuel cell system could be achieved.