• Journal of the Korean institute of surface engineering
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• v.42 no.6
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• pp.280-286
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• 2009

In this study, the corrosion property of copper alloy tubes in seawater has been investigated. Three copper alloys of nominal composition Cu-20Zn-2Al(Al-Brass), Cu-30Ni(CN70/30) and Cu-10Ni(CN90/10) were considered. The samples were immersed in 3%NaCl flowing solution at $90^{\circ}C$ for 30, 50 and 80 days. Corrosion rate of copper alloy tubes in 3%NaCl flowing solution was investigated by weight-loss measurements and electrochemical test. The CN70/30 showed lowest corrosion rate among three copper alloy tubes. Because of passive films formation, corrosion rates of three types of copper tubes were decrease with time. Surface characteristics of copper alloy tubes were analyzed by optical micrograph(OM), scanning electronic microscopy (SEM), energy dispersive X-ray analysis(EDAX) and X-ray diffraction patterns(XRD). CN70/30 showed partly pitting problem on the surface owing to high Fe content, even though having high resistant against corrosion. Cracks appeared on the surface of CN90/10 and CN70/30 after more than 50 days immersion, which could be derived from high nickel contents.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.1
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• pp.23-32
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• 2020

The intermittent characteristics of renewable energy complicates the process of balancing supply with demand. Electrolysis technology can provide flexibility to grid management by converting electricity to hydrogen. Alkaline electrolysis has been recognized as established technology and utilized in industry for over 100 years. However, high overpotential of oxygen evolution reaction in alkaline water electrolysis reduces the overall efficiency and therefore requires the development of anode catalyst. In this study, Raney Ni-Zn-Fe electrode was prepared by electroplating and the electrode characteristics was studied by varying electroplating parameters like electrodeposition time, current density and substrate. The prepared Raney Ni-Zn-Fe electrode was electrochemically evaluated using linear sweep voltammetry. Physical and chemical analysis were conducted by scanning electron microscope, energy dispersive spectrometer, and X-ray diffraction. The plating time did not changed the morphology and composition of the electrode surface and showed a little effect on overpotential reduction. As the plating current density increased, Fe content on the surface increased and cauliflower-like structure appeared on the electrode surface. In particular, the overpotential of the electrode, which was prepared at the plating current density of 320 mA/㎠, has showed the lowest value of 268 mV at 50 mA/㎠. There was no distinguishable overpotential difference between the type of substrate for the electrodes prepared at 80 mA/㎠.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2000.11a
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• pp.57-57
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• 2000

Brazing characteristics of the LTCC(Low Temperature Co-fired Ceramics)/ Kovar(Fe-Ni-Co alloy) was investigated. Kovar is one of the typical material for the lid of MCM and packages. In case of alumina package, Brazing process is done by higher temperature profile than 800 $^{\circ}C$ and Ag-Cu alloy. But, LTCC has sintering temperature near 850 $^{\circ}C$. So, it is difficult to use the same process as alumina brazing. The adhesion strength of the brazed part is affected by brazing alloy and metallization properties between conductor pattern and LTCC material. We investigated brazing characteristics of the LTCC/Kovar using various brazing alloys(Ag-Cu, Au-Sn) and process conditions. And, we examined the influence of the glass contents in conductor on the brazing characteristics of the LTCC/Kovar.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1997.04a
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• pp.34-34
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• 1997

The effect of alloying mode and porosity on the axial tension-tension fatigue behavior of a P/M steel of nominal composition Fe-4w/o Ni-1.5w/o Cu-O.5w/o Mo-O.5w/o C has been evaluated. Alloying modes utilized were elemental powder mixing, partial alloying(distaloy) and prealloying by water atomization; in each case the carbon was introduced as graphite prior to sintering. Powder compacts were sintered($1120{\circ}C$/30 min.) in 7Sv/o $H_2$/25v/o $N_2$ to densities in the range 6.77-7.2 g/$cm^3$. The dependence of fatigue limit response on alloying mode and porosity was interpreted in terms of the constituent phases and the pore and fracture morphologies associated with the three alloying modes. For the same nominal composition, the three alloying modes resulted in different sintered microstructures. In the elemental mix alloy and the distaloy, the major constituent was coarse and fine pearlite, with regions of Ni-rich ferrite, Ni-rich martensite and Ni-rich areas. In contrast, the prealloy consisted primarily of martensite by with some Ni-rich areas. From an examination of the fracture surfaces following fatigue testing it was concluded that essentially all of the fracture surfaces exhibited dimpled rupture, characteristic of tensile overload. Thus, the extent of growth of any fatigue cracks prior to overload was small. The stress amplitude for the three alloying modes at 2x$l0^6$ was used for the comparison of fatigue strengths. For load cycles <3x$l0^5$, the prealloy exhibited optimum fatigue response followed by the distaloy and elemental mix alloy, respectively. At load cycles >2x$l0^6$, similar fatigue limits were exhibited by the three alloys. It was concluded that fatigue cracks propagate primarily through pores, rather than through the constituent phases of the microstructure. A decrease in pore SIze improved the S-N behavior of the sintered steel.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.64-70
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• 2012

Samples of pure Mg, 76.5 wt%Mg-23.5 wt%Ni, and 71.5 wt%Mg-23.5 wt%Ni-5 wt%$Fe_2O_3$ were prepared by reactive mechanical grinding and their hydriding and dehydriding properties were then investigated. The reactive mechanical grinding of Mg with Ni is considered to facilitate nucleation and to shorten diffusion distances of hydrogen atoms. After hydriding-dehydriding cycling, the 76.5 wt%Mg-23.5 wt%Ni and 71.5 wt%Mg-23.5 wt%Ni-5 wt%$Fe_2O_3$ samples contained $Mg_2Ni$ phase. In addition to the effects of the creation of defects and the decrease in particle size, the addition of Ni increases the hydriding and dehydriding rates by the formation of $Mg_2Ni$. Expansion and contraction of the hydride-forming materials (Mg and $Mg_2Ni$) with the hydriding and dehydriding reactions are also considered to increase the hydriding and dehydriding rates of the mixture by forming defects and cracks leading to the fragmentation of particles. The reactive mechanical grinding of Mg-Ni alloy with $Fe_2O_3$ is considered to decrease the particle size.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.6
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• pp.87-93
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• 2004

An experimental is carried out to investigate the characteristics of blanking for nickel alloy Alloy42 (t=0.203mm), a kind of IC lead frame material. By varying clearance between die and punch the shapes of shear profile are examined. Finite element analysis with element deletion algorithm for ductile fracture mode is also carried out to study the effect of clearance theoretically and to compare with experimental results. The rectangular shape specimen with four different comer radius is used to study the characteristics of blanking for straight side and comer region simultaneously. As the result the ratios measured k(m experiment of roll over, burnish and fracture zone based on initial blank thickness are compared with those of FE analysis. Both experiment and FE analysis show that the amount of mil over and fracture is increased as the clearance increases. When the radius of comer is less than thickness of blank it has been found that larger clearance is required than that of straight region in order to maintain same quality of shear profile at the comer region.

• Transactions of the Korean hydrogen and new energy society
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• v.5 no.1
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• pp.1-8
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• 1994

Lattice structure, hydrogen absorption characteristics, discharge capacity and cycle life of $V_{22}Ti_{16}Zr_{16}Ni_{39}X_7$(X= Cr, Co, Fe, Mn, Al) alloys were investigated. The matrix phases of these alloys were the C14 Laves phase. Chromium-containing alloy had a vanadium-rich phase in addition to the Laves phase. The chromium, maganese, or aluminum-containing alloys had lower hydrogen equilibrium pressure and larger hydrogen absorption content than the cobalt or iron-containing alloys. The discharge capacities of these alloys were 270~330mAh/g. The discharge capacity according to the alloying element X decreased in the order of Mn>Cr>Co, Al)Fe. The charge/discharge cycle lives of the chromium, cobalt or iron-containing alloys were longer than those of maganese or aluminum-containing alloys due to the lower vanadium dissolution rate.

• Journal of Korea Foundry Society
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• v.3 no.3
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• pp.174-180
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• 1983

The matrix changes and graphite formation in high manganese cast iron (Fe-12Mn-3.5C) are studied with increasing nickel and silicon content. Also, the decomposition of carbides and graphite precipitation are studied by adequate heat treatment.The results obtained in this work are as follows. 1. In high manganese cast iron, fine flakes graphite appeared by adding 5 wt% nickel and A-type flakes graphite can be obtained by adding 7 wt% nickel. 2. Nodular graphite are obtained by graphite spheroidizing treatment with same melt. 3. In high manganese cast iron containing 7 wt% nickel, full austenitic matrix with nodular graphite can be achieved by water quenching after 10 hours' solution heat treatment at $1050^{\circ}C$ in case of containing 2.0 wt% silicon, and 6 hours' at the same temperature in case of containing 2.5 wt% silicon.

• Nuclear Engineering and Technology
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• v.51 no.2
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• pp.479-489
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• 2019

Low-cycle fatigue (LCF) tests were performed for Alloy 690 and 316 SS in a simulated pressurized water reactor (PWR) environment. Alloy 690 showed about twice longer LCF life than 316 SS at the test condition of 0.4% amplitude at strain rate of 0.004%/s. Observation of the oxide layers formed on the fatigue crack surface showed that Cr and Ni rich oxide was formed for Alloy 690, while Fe and Cr rich oxide for 316 SS as an inner layer. Electrochemical analysis revealed that the oxide layers formed on the LCF crack surface of Alloy 690 had higher impedance and less defect density than those of 316 SS, which resulted in longer LCF life of Alloy 690 than 316 SS in a simulated PWR environment.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.1053-1055
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• 2002

Recently CRT is getting large-sized, Flatness and High Fine Pitched in the meantime the raw material for shadow mask is in rapid progress of thinness, Low Thermal Expansion and high strength.Until now we have used AK(Aluminum Killed) & Invar(Fe-Ni alloy) materials for main raw material of shadow mask component. However recently Nb and Co addition and Nb+Co addition, which has advantage of Low Thermal Expansion and High Strength. has been developed as well as applying in mass production as CRT's trend has become more flat and fine pitch. Among of them, Co addition has been mass production as forming type (Flat CRT) with the beneficial effect of low thermal expansion & high strength for the first time. Since then Nb+Co addition has been used in mass production by the request of much higher strength of shadow mask component. In case of Nb addition, It's thermal expansion coefficient is a little lower than normal Invar and a little higher than Co addition, meanwhile Its Mechanical property is almost similar to Co Addition. The used samples of this experiment are 36%Ni + Fe, 32%Ni + 5%Co + Fe, 32%Ni + 5%Co + 0.3%Nb + Fe, 32%Ni + 0.3%Nb + Fe with heat treatment temperature of 600$^{\circ}C$, 650$^{\circ}C$, 700$^{\circ}C$, 750$^{\circ}C$, 800$^{\circ}C$, 850$^{\circ}C$, 900$^{\circ}C$ respectively under the condition of 15min holding time. After heat treatment, we have observed the change of mechanical property with addition of small elements through mechanical property investigation and metal structure observation as well as transition of thermal expansion coefficient by measuring of thermal expansion coefficient at 850$^{\circ}C$. In conclusion, 5%Co addition indicates that its thermal expansion coefficient is very similar under the condition of at 850$^{\circ}C$ for 15min 's heat treatment. From the experimental result it is suggested that Co addition is mostly suitable for Doming property and Nb addition is mostly suitable for Drop property.