• Korean Journal of Materials Research
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• v.12 no.8
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• pp.608-612
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• 2002

The sliding wear behavior of an iron-base NOREM 02 hardfacing alloy was investigated in the temperature range of $25～250^{\circ}C$ under a contact stress of 103MPa (15ksi). With increasing temperature, the wear loss of Norem 02 in water increased slightly up to $180^{\circ}C$ at which Norem 02 showed the wear loss of 2.1mg. The wear resistance of Norem 02 resulted from the surface hardening due to the strain-induced phase transformation from austenite to $\alpha$'martensite during sliding wear. The wear loss of Norem 02 was smaller in water compared to air at same temperature because the water could be served as a sort of lubricant. The wear mode of NOREM 02 changed abruptly to severe adhesive wear at $190^{\circ}C$ and galling occurred above $200^{\circ}C$. It was caused that the strain- induced phase transformation took place below $180^{\circ}C$ while not above $190^{\circ}C$. Therefore, Norem 02 was considered to be inadequate at high temperature service area.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.500-503
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• 1995

The magnetic properties of ultrathin $Fe_{84}B_{9}Nb_{7}$ nanocrystalline ribbon alloy with the thickness of $7-14\;\mu\textrm{m}$ were investigated. It was found that the effective permeability at the frequency over 100 kHz increased with decreasing ribbon thickness. Moreover the core loss decreased considerably with reduction of the ribbon thickness. The effective permeability at 1 MHz and the core loss at 1 MHz and 0.1 T for $Fe_{84}B_{9}Nb_{7}$ alloy with the thickness of $7\;\mu\textrm{m}$ were 3,700 and 2.7 W/cc, respectively. The reduction of thickness to less than $10\;\mu\textrm{m}$ was found to be very effective in obtaining high permeability and low core loss in the MHz frequency range. It was considered that the improvement of magnetic properties in the high frequency range was due to the reduction of the eddy current.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.110-112
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• 1998

Some recomendations for the manufacturing, operation and maintanance of amorphous alloy core transformer are presented through the operation experiance. Transformers on trouble was taken to pieces and tested from a viewpoint of durability, and low loss characteristics.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1345-1354
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• 2019

Clogging of sump strainers that filter the recirculation water in containment after a loss-of-coolant accident (LOCA) seriously impedes the continued cooling of nuclear reactor cores. In experiments examining the corrosion of aluminium alloy 6061, a common material in containment equipment, in borated solutions simulating the water chemistry of sump water after a LOCA, we found that Fe-bearing intermetallic particles, which were initially buried in the Al matrix, were progressively exposed as corrosion continued. Their cathodic nature $vis-{\grave{a}}-vis$ the Al matrix provoked continuous trenching around them until they were finally released into the test solution. Such particles released from Al alloy components in a reactor containment after a LOCA will be transported to the sump entrance with the recirculation flow and trapped by the debris bed that typically forms on the strainer surface, potentially aggravating strainer clogging. These Fe-bearing intermetallic particles, many of which had a rod or thin strip-like geometry, were identified to be mainly the cubic phase ${\alpha}_c-Al(Fe,Mn)Si$ with an average size of about $2.15{\mu}m$; 11.5 g of particles with a volume of about $3.2cm^3$ would be released with the dissolution of every 1 kg 6061 aluminium alloy.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.5
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• pp.889-898
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• 2022

In this study, sand casting process was applied to manufacture a large aluminum turbo-type fan used for tank powerpack. To apply the sand casting method, the turbo fan was reverse engineered, and after designing three gating systems, the optimal gating system design was selected by performing casting simulation. In the case of the bottom up-gating system, there is a significant temperature loss of the molten alloy during blade filling. When the molten alloy is completely filled into the sand mold, the blade upper tip and front shroud are below the liquidus temperature. In the case of the top down-gating system, molten alloy scattering occurs, but the temperature loss while the blade is filled is smaller than that of the bottom up type. And after the inflow of molten alloy into the mold is completed, the blade upper tip and front shroud are higher than the liquidus temperature. A sand mold was manufactured with the top down-gating system and the casting process was performed. The fan was made perfectly in appearance without any unfilled parts.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.802-803
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• 2006

Recently, there has been a growing demand for soft magnetic materials with high conversion characteristics, due to the trend of electric devices to higher-frequency range. For ruduceing core loss in the high-frequency range, using finely grained and high-resistivity Fe-based alloy powder is most efficient methods. But, conventionally, there's been a compressibility problem for such powder. In this work, Fe-based alloy powder that offers both high resistivity and high compressibility was developed by studyuing composition of the powder, and reduction of core loss of P/M soft magnetic materials in the high frequency range was achieved.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.5
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• pp.218-222
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• 2012

FeNi alloy nanofibers have been prepared by an electrospinning process followed by air-calcination and H2 reduction to develop electromagnetic (EM) wave absorbers in the giga-hertz (GHz) frequency range. The thermal behavior and phase and morphology evolution in the synthetic processes were systematically investigated. Through the heat treatments of calcination and H2 reduction, as-spun PVP/FeNi precursor nanofiber has been stepwise transformed into nickel iron oxide and FeNi phases but the fibrous shape was maintained perfectly. The FeNi alloy nanofiber had the high aspect ratio and the average diameter of approximately 190 nm and primarily composed of FeNi nanocrystals with an average diameter of ~60 nm. The FeNi alloy nanofibers could be used for excellent EM wave absorbing materials in the GHz frequency range because the power loss of the FeNi nanofibers increased up to 20 GHz without a degradation and exhibited the superior EM wave absorption properties compared to commercial FeNi nanoparticles.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1240-1243
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• 2008

The tempering and magnetic annealing are used to improve the soft magnetic properties such as initial permeability coercivity and core loss of the KM35F alloy. The first heat treatmentis performed at the temperature less than the curie temperature of the KM35F alloy to remove the thermal stress for few hours in nitrogen atmosphere. The second stage heat treatment is performed the magnetic annealing at $500{\sim}800^{\circ}C$ for few hours in nitrogen atmosphere, and then quenching to room temperature in absence of oxygen. Finally, magnetic properties of the thermally treated KM35F alloy are investigated for application as a soft magnetic material of the ISO solenoid valve core and plunger.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.143-145
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• 2007

The correlation between crystallization and deformation behavior in the supercooled liquid region (SLR) of a $Cu_{54}Ni_{6}Zr_{22}Ti_{18}$ bulk metallic glass (BMG) alloy is investigated by compression tests, differential scanning calorimetry (DSC), electron energy loss spectrometry (EELS) and high resolution transmission electron microscopy (HRTEM). In the SLR, This BMG alloy was strongly depended on the deformation temperature and the alloy exhibits important change in deformation behavior after a given time which is directly connected to the development of crystallization. Compressive stress impeded decomposition and consequently retarded forming of nano-crystal, which led to enlarge the homogeneous deformation region of the BMG alloy in SLR during compression test.

• Korean Journal of Metals and Materials
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• v.49 no.10
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• pp.747-753
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• 2011

In order to improve the corrosion resistance of Fe-20Cr-1.7C-1Si hardfacing alloy without a loss of wear resistance, the effect of Ni addition was investigated. As expected, the corrosion resistance of the alloy increased with increasing Ni concentration. The wear resistance of the alloy did not decrease, even though the hardness decreased, up to Ni concentration of 5 wt.%. This was attributed to the fact that the decrease in hardness was counterbalanced by the strain-induced martensitic transformation. The wear resistance of the alloy, however, decreased abruptly with increases of the Ni concentration over 5 wt.%.