• Carbon letters
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• 제2권1호
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• pp.27-36
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• 2001

The pack-cementation process is the method which is formed SiC coating layer to improve weak oxidation properties of CFRCs (carbon fiber-reinforced carbons). This method develops the anti-oxidation coating layer having no dimensional changes and good wetting properties. In this study to improve the oxidative resistance of the prepared 4D CFRCs, the surface of CFRCs is coated by SiC using pack cementation method. The mechanical properties of SiC-coated 4D CFRCs are measured by the 3-point bending test, and their ablation properties are investigated by the arc torch plasma test. From the results, it is found that both mechanical and ablation properties of SiC-coated 4D CFRCs are much better than bare CFRCs.

• International Journal of Concrete Structures and Materials
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• 제2권2호
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• pp.99-105
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• 2008

Southern exposure test specimens were used to evaluate corrosion performance of epoxy-coated reinforcing bars in chloride contaminated concrete by electrochemical impedance spectroscopy method. The test specimens with conventional bars, epoxy-coated bars and corrosion inhibitors were subjected 48 weekly cycles of ponding with sodium chloride solution and drying. The polarization resistance obtained from the Nyquist plot was the key parameter to characterize the degree of reinforcement corrosion. The impedance spectra of specimens with epoxy-coated bars are mainly governed by the arc of the interfacial film and the resistance against the charge transfer through the coating is an order of magnitude higher than that of the reference steel bars. Test results show good performance of epoxy-coated bars, although the coatings had holes simulating partial damage, and the effectiveness of corrosion-inhibiting additives. The corrosion rate obtained from the impedance spectroscopy method is equivalent to those determined by the linear polarization method for estimating the rate of corrosion of reinforcing steel in concrete structures.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(1)
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• pp.393-396
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• 2001

In this paper, a new type of linearizer using a parallel diode with a bias feed resistance has been studied. It has positive gain and negative phase deviations because of a nonlinearity of the diode and movement of bias point cause by a voltage drop at the bias feed resistance. This predistortion linearizer consists of the little component and miniaturizes circuit design. The characteristics of this linearizer can be easily tuned using input bias voltage. In fabricated linearizer, maximum gain and Phase deviation of the linearizer is 1dB, 21$^{\circ}$ respectively. By applying its characteristics to the power amplifier, it will be linearized power amplifier.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2007년 추계학술발표대회 개요집
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• pp.363-365
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• 2007

Titanium and its alloys have excellent corrosion resistance, high strength to weight ratios and high temperature creep properties, which make them using many various fields of application. Responding to these needs, welding processes for titanium are also being used including TIG, MIG, resistance welding, plasma arc welding, diffusion welding, electron beam welding and laser welding. In this study, It is possible to get sound beads without humping bead and spatter with the decrease of peak power according to increase of pulse width and change of welding speed for heat input control at pulsed Nd:YAG laser welding of titanium plates for Lap welding.

• 한국표면공학회지
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• 제25권6호
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• pp.299-308
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• 1992

Titanium nitride(TiN) has been synthesized by nitrogen ion irradiation onto the Ti thin film deposited on STD11 and SKH9 tool materials. The effect of irradiation flux and substrate temperature on the formation behavior and mechanical properaties of TiN were investigated through X-ray diffraction analysis, hardness and pin-on-disc wear testings. Nitrogen ion irradiation onto arc evaporated Ti thin film produced TiN of < 200> orientation at elevated temperature and thereby enhancing surface microhardness by 50% at maximum. Wear resistance was also improved by nitrogen irradiation at most process conditions. The enhancement of wear resistance appeared to be more effective for the nitrogen irradiated conditions at room temperature than at elevated temperature.

• 열처리공학회지
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• 제37권4호
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• pp.172-181
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• 2024

In this study, the effect of addition of Ti and Co elements on microstructural evolution and characteristics of vacuum-casted Cu-25%Cr electrical contact material was investigated. The coarse and insoluble Cr phases with an average size of 300 ㎛ in commercial Cu-25%Cr alloy were reduced to tens of micrometers in vacuum casted Cu-25%Cr-X(X=Ti, Co) alloy, which can be interpreted as result controlling coarsening and the work-frame structure of the insoluble Cr phase by the formation of intermetallic compounds such as Cr₂Ti or Cr_0.5Co_1.5Ti around the Cr phase As a result, the electrical properties such as weight loss and fusion resistance against the repeated arc generation of the electrical contact material as well as the mechanical properties were greatly improved.

• 한국산학기술학회논문지
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• 제13권10호
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• pp.4365-4370
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• 2012

MAO 법을 이용하여 전류밀도 4A/$cm^2$조건에서 3종류의 전해액과 코팅시간에 따라 AZ31 마그네슘 합금을 산화피막 처리하였다. 코팅시간이 길어짐에 따라 코팅층의 표면형상은 기공이 더욱 커지고, 표면에 균열이 발생하기도 하였다. 또한 코팅시간이 길어짐에 따라 코팅층의 두께와 경도(HV)값은 증가하였다. AZ31합금의 코팅층 상들은 MgO, $Mg_2SiO_4$ 그리고 $MgAl_2O_4$ 산화물로 이루어졌다. 산화코팅된 AZ31합금을 5% NaCl 용액에서 168시간동안 염수분무실험결과 우수한 내식성을 나타냈다.

• 한국방재학회 논문집
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• 제1권1호
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• pp.127-138
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• 2001

CFRCs는 고온에서의 우수한 물성에도 불구하고, 연소에 대한 취약한 성질로 인하여 많은 분야에서 사용에 제약을 받고 있다. 그러므로 EFRCs의 연소저항성을 향상시키기 위해서 수 많은 연구가 수행되어지고 있다. 본 연구에서는 고온에서 보다 개선된 물성과 높은 연소저항성을 부여하고, 다른 도포물질과 비교해서 낮은 열팽창계수의 차이를 보이는 탄화규소를 Pack-Cementation 방법으로 4방향성 CFRCs에 도포하였다. 제작된 탄화규소로 도포된 CFRCs는 광학현미경의 관찰을 통하여 도포 메카니즘을 추정하였으며, TGA 시험을 통하여 개선된 연소저항성을 조사하였다. Arc plasma torch 시험을 통하여 고온 연소특성과 거동을 연구하였다. 그 결과로부터 탄화규소로 코팅된 CFRCs의 기계적 강도와 고온 연소특성이 순수한 4방향성 CFRCs에 비해서 개선되었다는 것을 알았다.

• Corrosion Science and Technology
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• 제2권6호
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• pp.289-295
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• 2003

The corrosion behavior of Cr-N coated steels with different phases (${\alpha}-Cr$, CrN and $Cr_2N$) deposited by cathodic arc deposition on Hl3 steel was investigated in 3.5% NaCl solution at ambient temperature. Potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were the techniques applied to characterize the corrosion behavior. It was found that the CrN coating had a lower current density from potentiodynamic polarization test than others. The porosity, corresponding to the ratio of the polarization resistance of the uncoated and the coated substrate, was higher in the $Cr_2N$ coating than in the other Cr-N coated steels. EIS measurements showed, for the most of Cr-N coated steels, that the Bode plot presented two time constants. Also, the $Cr_2N$ coating represents the characteristic of Warburg behavior after 72hr of immersion. The coating morphologies were examined in planar view and cross-section by SEM analyses and the results were compared with those of the electrochemical measurement. The CrN coating had a dense, columnar grain-sized microstructure with minor intergranular porosity. From the above results, the CrN coating provided a better corrosion protection than the other Cr-N coated steels.

• 한국압력기기공학회 논문집
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• 제19권2호
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• pp.84-92
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• 2023

As temporary storage facilities for spent nuclear fuels in domestic nuclear power plants are expected to be saturated, external intermediate storage facilities would be required in the future. Spent nuclear fuels are stored in metal canisters and then placed in a dry environment within concrete or metal casing for operation. In the United States, the dry storage method for spent nuclear fuels has been operated for an extended period. Based on the corrosion experiences of dry storage canisters in chloride environments, numerous studies have been conducted to reduce corrosion in welds. With the construction of intermediate storage facilities in Korea for spent nuclear fuels expected near coastal areas adjacent to nuclear power plants, there is a need for research on the corrosion occurrence of welds and mitigation methods for canisters in chloride environments. In this paper, we measured and compared the residual stresses in the Heat-Affected Zones (HAZ) after electron beam welding (EBW) and gas tungsten arc welding (GTAW) processes for candidate materials such as 304L, 316L, and duplex stainless steel(DSS). We investigated the possibility of microstructure control through the application of surface modification processes using friction stir processing (FSP). Corrosion tests on each welded specimen revealed a higher corrosion rate in EBW welds compared to GTAW. Furthermore, it was confirmed that corrosion resistance improved due to phase refinement and redistribution of precipitates when FSP was applied.