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Page : 112 - 117
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- Enhancement of the Corrosion Resistance of CrN Film Deposited by Inductively Coupled Plasma Magnetron Sputtering
- Inductively coupled plasma magnetron sputtering (ICPMS) has the advantage of being able to dramatically improve coating properties by increasing the plasma ionization rate and the ion bombardment effect during deposition. Thus, this paper presents the comparative results of CrN films deposited by direct current magnetron sputtering (dcMS) and ICPMS systems. The structure, microstructure, and mechanical and corrosive properties of the CrN coatings were investigated by X-ray diffractometry, scanning electron microscopy, nanoindentation, and corrosion-resistance measurements. The as-deposited CrN films by ICPMS grew preferentially on a 200 plane compared to dcMS on a 111 plane. As a result, the films deposited by ICPMS had a very compact microstructure with high hardness. The nanoindentation hardness reached 19.8 GPa, and 13.5 GPa by dcMS. The corrosion current density of CrN film prepared by ICPMS was about 9.8 × 10-6 mA/cm2, which was 1/470 of 4.6 × 10-3 mA/cm2, the corrosion current density of CrN film prepared by dcMS.
- KEYWORDs : Corrosion resistance, CrN, Films, Inductively coupled plasma, Sputtering
- AUTHORs : Sung-Yong Chun and Seong-Jong Kim†
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Page : 118 - 128
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- A way Analyzing Oxide Layer on an Irradiated CANDU-PHWR Pressure Tube Using an EPMA and X-ray Image Mapping
- The oxide layer in samples taken from an irradiated Zr-2.5Nb pressure tube from a CANDU-PHWR reactor was analyzed using electron probe microanalysis (EPMA). The examined tube had been exposed to temperatures ranging from 264 to 306 oC and a neutron fluence of 8.9 × 1021 n/cm2 (E > 1 MeV) for the maximum 10 effective full-power years in a nuclear power plant. Measuring oxide layer thickness generally employs optical microscopy. However, in this study, analysis of the oxide layer from the irradiated pressure tube components was undertaken through X-ray image mapping obtained using EPMA. The oxide layer characteristics were analyzed by X-ray image mapping with 256 × 256 pixels using EPMA. In addition,the slope of the oxide layer was measured for each location. A particular advantage of this study was that backscattered electrons and X-ray image mapping were obtained at a magnification of 9,000 when 20 kV volts and 30 uA of current were applied to radiation-shielded EPMA. The results of this study should usefully contribute to the study of the oxide layer properties of various types of metallic materials irradiated by high radiation in nuclear power plants.
- KEYWORDs : Irradiated Zr-2.5Nb, CANDU-PHWR, Pressure tube, Oxide properties, EPMA
- AUTHORs : Yang Hong Jung† and Hee Moon Kim
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Page : 129 - 142
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- Effects of Inhibitors on Corrosion Resistance of Steel in CaCl2 Solution Based on Response Surface Analysis
- Effects of corrosion inhibitors (i.e., sodium nitrite, sodium hexametaphosphate, trimethylamine (TEA), sugar, and urea) on the corrosion resistance of carbon steel in CaCl2 solution were investigated. The test solution was designed with response surface methodology of design of experiments (DOE) in the range of 0 ~ 50 ppm for NaNO2, 0 ~ 200 ppm for (NaPO3)6, 0 ~ 2000 ppm for TEA, 0 ~ 3000 ppm for sugar, 0 ~ 200 ppm for urea with 3 wt% CaCl2. The corrosion potential and the corrosion rate were measured with potentiodynamic polarization tests and analyzed statistically to find main effects of inhibitor concentrations and interactions between them. As a result, hexametaphosphate was the most effective compound in reducing the corrosion rate. Sugar also reduced the corrosion rate significantly possibly because it covered the surface effectively with a high molecular weight. The inhibiting action of sugar was found to be enhanced by adding trimethylamine into the solution. Nevertheless, trimethylamine did not appear to be effective in inhibiting corrosion by itself. However, urea and sodium nitrite showed almost no inhibition on corrosion resistance of steel.
- KEYWORDs : Corrosion, Design of Experiment (DOE), Corrosion inhibitor, Steel, Chloride
- AUTHORs : Tae-Jun Park and HeeJin Jang†
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Page : 143 - 151
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- 쇼트피닝이 회주철의 캐비테이션 침식 저항성에 미치는 영향
- In this study, optimal shot peening process conditions were investigated for improving the cavitation erosion resistance of gray cast iron under a marine environment. Shot peening was performed with variables of injection pressure and injection time. The durability was then evaluated through cavitation erosion test which was conducted according to the modified ASTM G-32 standard. The tendency of cavitation erosion damage according to shot peening process condition was investigated through weight loss rate, surface and cross-sectional analysis of the specimen before and after the test. As a result, the shot peening process condition that could minimize cavitation erosion was when the injection pressure was the lowest and when the injection time was the shortest. This was because the flake graphite exposed on the gray cast iron surface could be easily removed under such condition. Therefore, the notch effect can be prevented by surface modification. In addition, the cavitation erosion damage mechanism of gray cast iron was discussed in detail.
- KEYWORDs : Gray cast iron, Cavitation erosion, Flake graphite, Shot peening, Marine environment
- AUTHORs : 박일초†
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Page : 152 - 157
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- 스테인리스 스틸의 표면 산화피막 성장과 내부식성 상관관계
- Stainless steel is a metal that does not generate rust. Due to its excellent workability, economic feasibility, and corrosion resistance, it is used in various industrial fields such as ships, piping, nuclear power, and machinery. However, stainless steel is vulnerable to corrosion in harsh environments. To solve this problem, its corrosion resistance could be improved by electrochemically forming an anodized film on its surface. In this study, 316L stainless steel was anodized at room temperature with ethylene glycol-based 0.1 M NH4F and 0.1M H2O electrolyte to adjust the thickness of the oxide film using different anodic oxidation voltages (30 V, 50 V, and 70 V) with time control. The anodic oxidation experiment was performed by increasing the time from 1 hour to 7 hours at 2-hour intervals. Corrosion resistance according to the thickness of the anodic oxide film was observed. Electrochemical corrosion behavior of oxide films was investigated through polarization experiments.
- KEYWORDs : Stainless steel, Anodization, Oxide thickness, Nanostructure, Corrosion resistance
- AUTHORs : 박영주 · 유진석 · 심성구 · 정찬영†
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Page : 158 - 168
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- 양성자 조사가 316 스테인리스강의 미세조직과 표면산화 특성에 미치는 영향
- Austenitic 316 stainless steel was irradiated with protons accelerated by an energy of 2 MeV at 360 oC, the various defects induced by this proton irradiation were characterized with microscopic equipment. In our observations irradiation defects such as dislocations and micro-voids were clearly revealed. The typical irradiation defects observed differed according to depth, indicating the evolution of irradiation defects follows the characteristics of radiation damage profiles that depend on depth. Surface oxidation tests were conducted under the simulated primary water conditions of a pressurized water reactor (PWR) to understand the role irradiation defects play in surface oxidation behavior and also to investigate the resultant irradiation assisted stress corrosion cracking (IASCC) susceptibility that occurs after exposure to PWR primary water. We found that Cr and Fe became depleted while Ni was enriched at the grain boundary beneath the surface oxidation layer both in the non-irradiated and proton-irradiated specimens. However, the degree of Cr/Fe depletion and Ni enrichment was much higher in the proton-irradiated sample than in the non-irradiated one owing to radiation-induced segregation and the irradiation defects. The microstructural and microchemical changes induced by proton irradiation all appear to significantly increase the susceptibility of austenitic 316 stainless steel to IASCC.
- KEYWORDs : Austenitic 316 stainless steel, Proton irradiation, Irradiation Defects, Surface Oxidation, IASCC
- AUTHORs : 임연수† · 김동진 · 황성식 · 최민재 · 조성환
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Page : 169 - 174
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- Application of High Performance Coatings for Service Life Extension of Steel Bridge Coatings
- In this study, performance tests, a field evaluation, and a life cycle cost (LCC) analysis for high performance coating systems were conducted to prepare a plan to reduce the cost of maintenance coating and contribute to the service life extension of steel bridges by applying high performance coatings to steel bridges that will be constructed in the future. From the deterioration models based on the field evaluation for chlorinated rubber and urethane topcoat systems, which have been applied often, the mean service lives were derived as 20.8 and 26.6 years, respectively. For the other coating systems that have not been applied in practice, the coordination factors were differentially applied with evaluation items. The most durable coating system was predicted to be thermal spray coating (TSC) primer/epoxy intermediate coat/fluoride resin topcoat, with a predicted value as long as 42.2 years. The LCC analysis indicates that partial application of high performance coating, such as TSC and fluoride resin, to specific parts vulnerable to corrosion and ultraviolet ray (UV) is more advantageous than the use of general coating systems.
- KEYWORDs : High performance coating, Steel Bridge, Life cycle cost, Coating life prediction
- AUTHORs : Chan-Young Lee†
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Page : 175 - 182
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- A Study on the Corrosion Behavior of Magnesium Alloy Sealed with Chemical Conversion Coating and Sol-gel Coating
- Magnesium alloy is limited in the industrial field because its standard electrode potential is ?2.363 V vs. NHE (Normal Hydrogen Electrode) at 25 oC. This high electrochemical activity causes magnesium to quickly corrode with oxygen in air; chemical conversion coating prevents corrosion but causes surface defects like cracks and pores. We have examined the anti-corrosion effect of sol-gel coating sealed on the defected conversion coating layer. Sol-gel coatings produced higher voltage current and smaller pore than the chemical conversion coating layer. The conversion coating on magnesium alloy AZ31 was prepared using phosphate-permanganate solution. The sol-gel coating was designed using trimethoxymethylsilane (MTMS) and (3-Glycidyloxypropyl) trimethoxysilane (GPTMS) as precursors, and aluminum acetylacetonate as a ring-opening agent. The thermal shock resistance was tested by exposing specimens at 140 oC in a convection oven; the results showed changes in the magnesium alloy AZ31 surface, such as oxidization and cracking. Scanning electron microscope (FE-SEM) analysis confirmed a sealed sol-gel coating layer on magnesium alloy AZ31. Electrochemical impedance spectroscopy (EIS) measured the differences in corrosion protection properties by sol-gel and conversion coatings in 0.35 wt% NaCl solution, and the potentiodynamic polarization test and confirmed conversion coating with the sol-gel coating show significantly improved resistance by crack sealing.
- KEYWORDs : Sol-gel coating, EIS, Chemical conversion coating, Polarization test, Thermal shock test
- AUTHORs : Dong Uk Lee, Shivshankar Chaudhari, Seung Yong Choi, Myung Jun Moon, and Min Young Shon†
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Page : 183 - 188
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- Electrochemical Characteristics of Synthesized Nb2O5-Li3VO4 Composites as Li Storage Materials
- The increasing demand for energy storage in mobile electronic devices and electric vehicles has emphasized the importance of electrochemical energy storage devices such as Li-ion batteries (LIBs) and supercapacitors. For reversible Li storage, alternative anode materials are actively being developed. In this study, we designed and fabricated an Nb2O5-Li3VO4 composite for use as an anode material in LIBs and hybrid supercapacitors. Nb2O5 powders were dissolved into a solution and the precursors were precipitated onto Li3VO4 through a simple, low-temperature hydrothermal reaction. The annealing process yielded an Nb2O5-Li3VO4 composite that was characterized by X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy. Electrochemical tests revealed that the Nb2O5-Li3VO4 composite electrode demonstrated increased capacities of approximately 350 and 140 mAh g?1 at 0.1 and 5 C, respectively, were maintained up to 1000 cycles. The reversible capacity and rate capability of the composite electrode were enhanced compared to those of pure Nb2O5-based electrodes. These results can be attributed to the microstructure design of the synthesized composite material.
- KEYWORDs : Niobium pentoxide, Li3VO4, Lithium storage, Electrode, Electrochemical properties
- AUTHORs : Youngmo Yang, Hyungeun Seo, and Jae-Hun Kim†
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Page : 189 - 195
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- Failure Evaluation Plan of a Reactor Internal Components of a Decommissioned Plant
- A technology for designing and licensing a dedicated radiation shielding facility needs to be developed for safe and efficient operation an R&D center. Technology development is important for smooth operation of such facilities. Causes of damage to internal structures (such as baffle former bolt (BFB) of pressurized water reactor) of a nuclear power reactor should be analyzed along with prevention and countermeasures for similar cases of other plants. It is important to develop technologies that can comprehensively analyze various characteristics of internal structures of long term operated reactors. In high-temperature, high-pressure operating environment of nuclear power plants, cases of BFB cracks caused by irradiated assisted stress corrosion cracks (IASCC) have been reported overseas. The integrity of a reactor’s internal structure has emerged as an important issue. Identifying the cause of the defect is requested by the Korean regulatory agency. It is also important to secure a foundation for testing technology to demonstrate the operating environment for medium-level irradiated testing materials. The demonstration testing facility can be used for research on material utilization of the plant, which might have highest fluence on the internal structure of a reactor globally.
- KEYWORDs : Nuclear power plant, PWR, Reactor internals, Materials harvesting, IASCC
- AUTHORs : Seong Sik Hwang†, Sung Woo Kim, Min Jae Choi, Sung Hwan Cho, and Dong Jin Kim
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