• Journal of Surface Science and Engineering
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• v.52 no.6
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• pp.364-370
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• 2019

Fe-Mn-Si-Ni-Cr-TiC alloys have a shape memory property, recovering initial shape by heating. With an aim to improve a durability and stability of building and infrastructure, this Fe-based shape memory alloy (FSMA) can be employed to reinforce concrete structure with creation of compressive residual stress. In this work, corrosion resistance of FSMA was compared with general rebar and S400 carbon steel to evaluate the stability in concrete environment. Potentiodynamic polarization test in de-ionized water, tap-water and 3.5 wt.% NaCl solution with variations of pH was used to compare the corrosion resistance. FSMA shows better corrosion resistance than rebar and S400 in tested solutions. However, Cl-containing solution is critical to significantly reduce the corrosion resistance of FSMA. Therefore, though FSMA can be a promising candidate to replace the rebar and S400 for the reinforcement of concrete structure, serious cautions are required in marine environments.

• 연구논문집
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• s.27
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• pp.201-208
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• 1997

To improve the joining characteristics of metallic converter substrate for exhaust gas cleaning, high temperature brazing process has been studied. In this study, the effect of chemical composition of brazing filler metal on the oxidation behavior of brazed joints was investigated closely. Brazing was carried out at $1200^\circC$ in vacuum furnace using nickel-based filler metals : BNi-5 powder(Ni-Cr-Si base alloy) and MBF-50 foil(Ni-Cr-Si-B). The MBF-50 containing 1-1.5 wt%B showed relatively poor oxidation resistance of the brazed joints compared to BNi-5, because of the faster invasion of oxygen through the Kirkendal voids along the interface of mother alloy/filler metal.

• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.107-112
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• 2009

Corrosion of nickel-base alloys (Hastelloy C-276, Inconel 625, and Inconel X-750) in $500^{\circ}C$, 25MPa supercritical water (with 10 wppb oxygen) was investigated to evaluate the suitability of these alloys for use in supercritical water reactors. Oxide scales formed on the samples were characterized by gravimetry, scanning electron microscopy/energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results indicate that, during the 1000h exposure, a dense spinel oxide layer, mainly consisting of a fine Cr-rich inner layer ($NiCr_{2}O_{4}$) underneath a coarse Fe-rich outer layer ($NiFe_{2}O_{4}$), developed on each alloy. Besides general corrosion, nodular corrosion occurred on alloy 625 possibly resulting from local attack of ${\gamma}$" clusters in the matrix. The mass gains for all alloys were small, while alloy X -750 exhibited the highest oxidation rate, probably due to the absence of Mo.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.3
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• pp.177-182
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• 2005

The steady state cyclic mechanism, and the behaviour of Nicoseal(Fe-29Ni-17Co) have been examined under the condition of square wave stress cyclic tension creep test at the temperature, stress and frequency range of $430{\sim}470^{\circ}C$($0.41{\sim}0.43T_m$), 353~383 MPa, and 3 cpm, respectively. Also, the relationship between cyclic creep and static creep have been examined. The stress exponents(n) for the static creep deformation of this alloy were 11.6, 10.0, 8.4 and 7.9 at the temperature of 430, 445, 460 and $470^{\circ}C$, respectively. The apparent activation energies (Q) for the static creep deformation were 54.2, 51.8, 49.7 and 46.8 kcal/mole for the stress of 353, 363, 373 and 383 MPa, From the above results, it could be considered that the cyclic creep accelaration phenomena was obtained and that the cyclic deformation for Nicoseal seemed to be controlled by dislocation climb over the range of experimental conditions. Nicoseal alloy under the cyclic creep conditions was obtained as P=(T+460)(logt+17). The failure plane observed by SEM showed up transgranular fracture at all range.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.2
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• pp.88-95
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• 1994

In order to compare mechanical properties of ausformed martensite with those of marformed martemsite in Fe-30%Ni-0.1%C alloy and to investigate their strengthening mechanisms, ausformed martensite and marformed martensite were prepared by ausforming treatment and marforming treatment respectively. The microstructures were observed and the quantities of retained austenite, hardness, yield strength, ultimate tensile strength and elongation were examined. The strength of ausformed martensite was mainly increased because of the lattice defects inherited from austenite. The ductility of ausformed martensite was constant at the rate of 7-8% by ductile matrix formation of the retained austenite in spite of the increase in strength. The strength of marformed martensite was increased by the increment in dislocation density, the crossing of transformation twin with deformation twin and the mutual crossing of deformation twin. The ductility of mar formed martensite was slightly lower than that of ausformed martensite, but the strength of mar formed martensite was prominently higher.

• Korean Journal of Materials Research
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• v.12 no.8
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• pp.624-633
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• 2002

In order to improve the hydrogen storage capacity and the activation properties of the hydrogen storage alloys, the rare-earth metal alloy series, MmN $i_{4.5}$M $n_{0.5}$Z $r_{x}$(x=0, 0.025, 0.05, 0.1), are prepared by adding excess Zr in MmN $i_{4.5}$M $n_{0.5}$ alloy. The various parts in hydrogen storage vessel consisted of copper pipes reached the setting temperature within 4~5 minutes after heat addition, which indicated that storage vessel had a good heat conductivity required in application. The performance test on storage vessel filled with rare-earth metal alloys of 1000 gr was also conducted after hydrogen charging for 10 min at $18^{\circ}C$ under 10 atm. It showed that the average capacity of discharged hydrogen volume was found to be for $MmNi_{4.5}$ $Mn_{0.5}$ and $MmNi_{4.5}$ $Mn_{x}$ 0.5/$Zr_{samples}$ indicated that the released amount of hydrogen for this $AB_{5}$ type alloys was more than 92 % of theoretic value, and also it was found that the optimum discharging temperature for obtaining an appropriate pressure of 3 atm was determined to be $V^{\circ}C$ for $MmNi_{4.5}$ $Mn_{0.5}$$Zr_{x}$(x=0, 0.025, 0.05, 0.1) hydrogen storage alloys. The released amount of these hydrogen storage samples was 125 $\ell$ , 122.4 $\ell$ and 108.15 $\ell$/kg for $MmNi_{4.5}$ $Mn_{0.5}$ $Zr_{0.025}$ $MmNi_{4.5}$M $n_{0.5}$Z $r_{0.05}$, and MmN $i_{4.5}$ Mn_0.5$Zr_{0}$, at $70^{\circ}C$ respectively. Amount of the 2nd phases increase with increase on Zr contents in $MmNi_{4.5}$$Mn_{0.5}$ $Zr_{ 0.1}$/ alloy. This phenomenon indicates that$ ZrNi_3$ in $MmNi_{4.5}$ $Mn_{0.5}$ $Zr_{x}$ / phase, which shows the maximum storage capacity and the strong resistance to intrinsic degradation, is considered as a proper alloy for hydrogen storage. As the Zr contents increase, the activation time and the plateau pressure decreases and sloping of the plateau pressure increases.creases.eases.s.

• Korean Journal of Metals and Materials
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• v.49 no.2
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• pp.167-173
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• 2011

Nickel cobalt ferrite($Ni_{0.5}Co_{0.5}Fe_2O_4$) powder was prepared through the ceramic route by the calcination of a stoichiometric mixture of NiO, CoO and $Fe_2O_3$ at $1100^{\circ}C$. The pressed pellets of $Ni_{0.5}Co_{0.5}Fe_2O_4$ were isothermally reduced in pure hydrogen at $800{\sim}1100^{\circ}C$. Based on the thermogravimetric analysis, the reduction behavior and the kinetic reaction mechanisms of the synthesized ferrite were studied. The initial ferrite powder and the various reduction products were characterized by X-ray diffraction, scanning electron microscopy, reflected light microscope and vibrating sample magnetometer to reveal the effect of hydrogen reduction on the composition, microstructure and magnetic properties of the produced Fe-Ni-Co alloy. The arrhenius equation with the approved mathematical formulations for the gas solid reaction was applied to calculate the activation energy($E_a$) and detect the controlling reaction mechanisms. In the initial stage of hydrogen reduction, the reduction rate was controlled by the gas diffusion and the interfacial chemical reaction. However, in later stages, the rate was controlled by the interfacial chemical reaction. The nature of the hydrogen reduction and the magnetic property changes for nickel cobalt ferrite were compared with the previous result for nickel ferrite. The microstructural development of the synthesized Fe-Ni-Co alloy with an increase in the reduction temperature improved its soft magnetic properties by increasing the saturation magnetization($M_s$) and by decreasing the coercivity($H_c$). The Fe-Ni-Co alloy showed higher saturation magnetization compared to Fe-Ni alloy.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.6
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• pp.368-374
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• 2009

Nickel titanium shape memory alloys (NiTi) have been investigated for applications in the biomedical industry. However, little is known about the influences of surface modifications on the propertise of these alloys. The effect of electropolishing and heat treatments was found to exhibit significant surface roughness. Change of phase was B2, r-phase and B19' by heat treatments. In this study, effect of the electropolishing conditions on surface roughness is investigated in Ni-Ti alloys (Nitinol). Variation in phases with heat treatment temperature is investigated for a Ni-Ti alloy by X-ray diffraction and DSC. Characteristic of the microstructure have been observed by SEM. Surface roughness have been measured by AFM. The results clearly show that significant different in surface property to heat treated at $500^{\circ}C$ (R-phase). $TiO_2$ phases preciritated all of the specimens. It is not good effect of surface roughness because made to surface relief. The surface roughness appears to be important in the property of Ni-Ti alloys for biomedical applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.8
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• pp.714-719
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• 2005

NiCr thin film was deposited by DC magnetron sputtering on $A;_2O_3$/Si substrate with NiCr (80:20) alloy target. NiCr thin films were annealed at $300^{\circ}C,\;400^{\circ}C,\;500^{\circ}C,\;600^{\circ}C,\;and\;700^{\circ}C$ for 6 hr in $H_2$ after annealing at $500^{\circ}C$ for 6hr in air atmosphere, respectively. To analyze NiCr thin film properties, the changes of its micro structure were Investigated through field emission scanning electron microscope (FESEM). X-ray photoelectron spectroscopy (XPS) was used to analyze a surface of NiCr thin film. Resistance of NiCr thin film was measured by 4-point probe technique. The generated heats were measured by infrared thermometer through the application of DC voltage (5 V/l2 V). NiCr thin film treated by gradational double annealing process had uniform and small grains. Maximum temperature generated heat by NiCr micro heater was $173^{\circ}C$. We expect that our results will be a useful reference in the realization of NiCr micro heater.

• Journal of Korea Foundry Society
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• v.31 no.5
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• pp.262-266
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• 2011

The aim of this study is to investigate aging behavior of A356 alloy for turbo charger part. The specimen was fabricated by investment casting. Solution heat treatment was performed at $525^{\circ}C$ for 8h and followed by aging treated at $160^{\circ}C$, $170^{\circ}C$ for 0.5~20h. And their microstructures and mechanical properties of the aged specimens were analyzed by scanning electron microscope and hardness tester, respectively. All the cast A356 alloy included eutectic Si particles. In the cast A356 alloy, eutectic Si phase mainly was formed along Chinese script phase. Vickers hardness of the cast was improved by aging treatment due to formation of ${\beta}$" phase and ${\beta}$' phase.