• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.405-406
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• 2006

Raw materials from different sources, produced by a given process and having equal chemical composition, are supposed to be equivalent. The differences in sintering behavior have been investigated on P/M steels obtained from four diffusion-bonded powders (Fe + Ni + Cu + Mo) on atomized iron base, at the same alloy contents. Two levels of carbon and two sintering conditions have been investigated. Dimensional changes, C content, hardness, microhardness pattern, universal hardness, fractal analysis, pore features, microstructure features, and rupture strength have been compared to characterize different raw materials. The results show that the claimed equivalence is not confirmed by experimental data.

• Journal of the Korean Society for Heat Treatment
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• v.8 no.2
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• pp.127-136
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• 1995

The simultaneous addition of Al and Cr to the surface of Ni-and Fe-base alloy provides enhanced resistance to oxidation and corrosion in high temperatures. However, because of the large differences in thermodynamic stabilities of the volatile halides of Al and Cr, the codeposition of Al and Cr by halideactivated pack cementation is only possible for very specific, limited combinations of conditions. In this study, the experiments on the combinations of various metallic source powders and activators were conducted in order to obtain codeposition layers of Al and Cr on Ni with adequate composition by pack cementation. When Cr-Al masteralloy was used as a source powder, it was not easy to control Al and Cr content sensitively in the coating layers. On the other hand, when pure Cr and Al powder was used, ${\beta}$-NiAl layer containing about 20wt % Cr was obtained.

• Journal of Korea Foundry Society
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• v.19 no.6
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• pp.493-500
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• 1999

Squeeze casting was used for fabricating a light metal base composite having high strength and wearresistance. Reactive sintering was used to prepare the preform of Squeeze casting. To utilize Fe-Al intermetallic compounds and SiC particle as a reinforcement, there needs to prepare Fe-Al mixed powder at 50, 60, 70at.%Al, and add SiC powder to the above mixture at 4, 7, 16, 24wt.%. The prepared mixture with SiC was reactive sintered in a tube furnace at $660^{\circ}C$ to get a porous hybrid preform of intermetallic compound and SiC. The preform prepared above was placed in a metal mold, preheated at $660^{\circ}C$ AC4C matrix was injected into the mold with the temperature of the melt at $610^{\circ}C$ After these processes, 66MPa was applied to the mold for 5 minute to finish the whole procedure. The maximum reaction temperature was increased with the increased Al amount, but decreased with the increased SiC amount. The density of the preform was decreased with SiC amount increase in the compacts due to swelling of the preform. An optical microscope was applied to observe the micro structure and the dispersion of the reinforcements. To analyze phases, We utilized XRD, EDS. Hardness test were chosen to get the information of mechanical properties. There were no significant changes in micro structure between the composite and preform. However, it was shown that uniform dispersion of the reinforcers and complete infiltration of the melt into the preform were achieved through the procedure of the squeeze casting. It was observed that the hardness of the composite is decreased with increased SiC amount, resulting from the volumetric expansion of the preform.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.213-213
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• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7NO1 spot-welded by pulse Nd: YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed: center line crack($C_{C}$), diagonal crack($C_{D}$), and U shape crack($C_{U}$). Also, HAZ crack($C_{H}$), was observed in the HAZ region, furthermore, mixing crack($C_{M}$), consisting of diagonal crack and HAZ crack was observed.White film was formed at the hot crack region in the fractured surface after it was immersed to 10%NaOH water. In the case of A5083 alloy, white films in C crack and $C_D crack region were composed of low melting phases, Fe₂Si$Al_8$ and eutectic phases, Mg₂Al₃ and Mg₂Si. Such films observed near HAZ crack were also consist of eutectic Mg₂Al₃. In the case of A7N01 alloy, eutectic phases of CuAl₂, $Mg_{32}$ (Al,Zn) ₃, MgZn₂, Al₂CuMg and Mg₂Si were observed in the whitely etched films near $C_{C}$ crack and $C_{D}$ crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Si in the case of A7N01 aooly, respectively.The $C_{D}$ and $C_{C}$ cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of $C_{M}$ crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The $C_{U}$ crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification. (Received October 7, 1999)

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.129-129
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• 2018

Hard coating application is effective way of cutting tool for hard-to-machine materials such as Inconel, Ti and composite materials focused on high-tech industries which are widely employed in aerospace, automobile and the medical device industry also Information Technology. In cutting tool for hard-to-machine materials, high hardness is one of necessary condition along with high temperature stability and wear resistance. In recent years, high-entropy alloys (HEAs) which consist of five or more principal elements having an equi-atomic percentage were reported by Yeh. The main features of novel HEAs reveal thermodynamically stable, high strength, corrosion resistance and wear resistance by four characteristic features called high entropy, sluggish diffusion, several-lattice distortion and cocktail effect. It can be possible to significantly extend the field of application such as cutting tool for difficult-to-machine materials in extreme conditions. Base on this understanding, surface coatings using HEAs more recently have been developed with considerable interest due to their useful properties such as high hardness and phase transformation stability of high temperature. In present study, the nanocomposite coating layers with high hardness on WC substrate are investigated using high entropy alloy target made a powder metallurgy. Among the many surface coating methods, reactive magnetron sputtering is considered to be a proper process because of homogeneity of microstructure, improvement of productivity and simplicity of independent control for several critical deposition parameters. The N2 is applied to reactive gas to make nitride system with transition metals which is much harder than only alloy systems. The acceleration voltage from 100W to 300W is controlled by direct current power with various deposition times. The coating layers are systemically investigated by structural identification (XRD), evaluation of microstructure (FE-SEM, TEM) and mechanical properties (Nano-indenter).

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.10a
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• pp.292-300
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• 2001

The paper describes spectroscopic characteristics of plasma induces in the pulsed YAG laser welding of alloys containing a large amount of volatile elements. The authors have conducted the spectroscopic analyses of laser induced Al-Mg alloys plasma in the air and argon atmosphere. In the air environment, the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn, and singly ionized Mg lines, as well as the intense molecular spectra of A10 and Mg0 formed by chemical reactions of evaporated Al and Mg atoms from the pool surface with oxygen in the air. In argon atmosphere, Mg0 and AI0 spectra vanished, but AIH spectrum was detected. The hydrogen source was presumably hydrogen dissolved in the base metals, water absorbed on the surface oxide layer, or $H_2$ and $H_2O$ in the shielding gas. The resonant 1ines of Al and Mg were strongly self-absorbed, in particular, self-absorption of the Mg 1ine was predominant. These results show that the laser induced plasma was made of metal1ic vapor with relatively low temperature and high density.

• Journal of Welding and Joining
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• v.25 no.1
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• pp.42-48
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• 2007

For high performance and structural stability, application of high strength steel has continuously increased. However, the change of the base metal gives rise to problems with the accuracy management of the welded structure. It is attributed to the martensite phase transformation of the high strength low alloy steel weldment. The purpose of this study is to establish the predictive equation of transverse shrinkage and residual stress for the HY-100 weldment. In order to do it, high speed quenching dilatometer tests were performed to define a coefficient of thermal expansion(CTE) at the heating and cooling stage of HY-100 with various cooling rates. Uncoupled thermal-mechanical finite element(FE) models with CTE were proposed to evaluate the effect of the martensite phase transformation on transverse shrinkage and residual stresses at the weldment. FEA results were verified by comparing with experimental results. Based on the results of extensive FEA and experiments, the predictive equation of transverse shrinkage and longitudinal shrinkage force at the HY-100 weldment were formulated as the function of welding heat input/in-plane rigidity and welding heat input respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.4
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• pp.339-343
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• 2006

We observed the application possibility of inductive coupler for the underground high-voltage power line communication by means of analysis of signal transmission characteristics and magnetic properties on annealing temperatures for high-permeability Fe-base amorphous alloys. The best electromagnetic and transmission characteristics were shown in nano-crystalline precipitated alloy annealed at temperature $510^{\circ}C$. The transmission characteristics in the low-frequency band depend on permeability of magnetic core materials and its properties of high-frequency band can be improved by impedance matching. Using the high pass filter embedded in the coupler, other noise signal band except for communication signals could be cut off.

• Corrosion Science and Technology
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• v.2 no.6
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• pp.253-259
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• 2003

Zirconium based alloys have been extensively used as a cladding material for fuel rods in nuclear reactors, due to their low thermal neutron absorption cross-section, excellent corrosion resistance and good mechanical properties at high temperatures. However, a cladding material for fuel rods in nuclear reactors was contact water during long time at high-temperature, so it is necessary to improve the wear and corrosion resistance of the fuel cladding, At ambient environment, there are few data or paper on the characteristic of corrosion in chloride solution and acidic solution. The specimens used in this work are pure Zr and Zircaloy-4. Zircaloy-4 is a specific zirconium-based alloy containing, on a weight percent basis, 1.4% Sn, 0.2% Fe, 0.1% Cr. Pitting corrosion resistance of two alloys by ASTM G48 is higher than that of electrochemical method. Passive film formed on Zircaloy-4 is mainly composed of $ZrO_2$, metallic Sn, and iron species regardless of formation environments. Also, passive film formed on Zr alloys shows n-type semiconductic property on the base of Mott-Schottky plot.

• Analytical Science and Technology
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• v.9 no.3
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• pp.302-309
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• 1996

Fe-5.7%AI-1.1%Cr-0.5%Si damping alloys containing 0%C and 0.12%C were heat-treated at $800^{\circ}C$ for an hour and then cooled by using some different methods. The damping behaviors of these alloys were observed by optical microscopy, X-ray diffraction and a specific damping capacity(SDC) test. Effect of cooling method on microstructures and the internal stresses of these alloys were negligible while the damping capacity of these alloys was considerably deteriorated by water quenching. The (200) texture was mainly developed by water quenching while the (110) texture by furnace cooling. These results were interpreted by the magnetization behaviors of the ferromagnetic $\alpha$ ferrite. The easy axis of magnetization in <100> direction means that <100> axis has more $180^{\circ}$ magnetic domain walls than $90^{\circ}$ ones. Thus. $180^{\circ}$ magnetic domain walls were more formed by water quenching, which deteriorated the damping capacity of these alloys. Consequently, the amount of magnetic domain walls giving good damping capacity became less so that the damping capacity was poor in water quenching.