한국부식방식학회

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TiO2 나노튜브 형상에 미치는 NH4F와 H2O의 영향
The aim of this work is the attainment of the TiO2-nanotube photocatalytic-growth condition using anodization, whereby the NH4F–H2O weight ratio is appropriately controlled. We fabricated the TiO2 nanotubes using a two-step anodization (first step is 1 hr; second step is 30 hr) under the ambient pressure and the room temperature at 60 V in ethylene-glycol solutions to investigate the effects of the NH4F(0.1,0.3,0.5wt%) and H2O(1–3wt%) on the TiO2-nanotube geometry and the photocatalytic efficiency. Further, the decomposition efficiency of the methylene blue on the TiO2 nanotubes by the UN radiation depended on the geometrical change of the nanotube geometry, indicating the proportionality of the decomposition efficiency to the surface area that was affected by the NH4F and H2O concentrations. As the NH4F weight was increased, the surface area initially decreased but slightly increased later, and the length consistently increased. As the H2O weight was increased, the surface area and length initially increased, but later decreased with the 3 wt% H2O.
KEYWORDs : TiO2, Nanotube, Photocatalyst, Anodization, Ethylene glycol
AUTHORs : 김건두 · 장상순 · 김희산†

Page : 129 - 137 DOWNLOAD
마이크로 드로플릿 셀 기법과 임계공식온도 측정 기법을 이용한 적층가공 Ti-6Al-4V 합금의 내식성 평가
The resistance to corrosion of additive manufactured (3D printing) Ti-6Al-4V alloys was investigated using micro-electrochemical tests. In terms of corrosion resistance, the acicular martensitic α\\\' phase in such additive manufactured Ti-6Al-4V was the focus of attention, and its behavior was distinct from that of conventional subtractive manufactured Ti-6Al-4V. To order to identify α\\\' phase, XRD tests were performed and micro Vickers hardness was measured for different grains (bright and
dark grains) in the additive manufactured Ti-6Al-4V alloy. Micro-electrochemical tests were performed to measure corrosion resistance of bright and dark grains in the additive manufactured Ti-6Al-4V alloy with specially designed electrochemical micro-droplet cell. Critical pitting temperature (CPT) measurement was performed to evaluate the resistance to pitting corrosion of additive manufactured Ti-6Al-4V alloys with different volumes of α\\\' phase and subtractive manufactured Ti-6Al-4V alloy. The dark grains of the laminated Ti-6Al-4V alloy distributed broader than the bright grains measured with low microhardness. The dark grains of the Ti-6Al-4V alloy, which was rich in martensite α \\\', had lower general corrosion and pitting resistance than bright grains. As the fraction of martensite α \\\'phase increased, the resistance to the pitting corrosion decreased.
KEYWORDs : Additive manufacturing, Ti-6Al-4V, Corrosion Resistance, α', Micro-droplet cell
AUTHORs : 서동일 · 이재봉†

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이온빔을 이용한 표면 미세구조 제어를 통한 발수 표면 제조
The fabrication of a controlled surface is of great interest because it can be applied to various engineering facilities due to the various properties of the surface, such as self-cleaning, anti-bio-fouling, anti-icing, anti-corrosion, and anti-sticking. Controlled surfaces with micro/nano structures were fabricated using an ion beam focused onto a polypropylene (PP) surface with a fluoridation process. We developed a facile method of fabricating hydrophobic surfaces through ion beam treatment with argon and oxygen ions. The fabrication of low surface energy materials can replace the current expensive and complex manufacturing process. The contact angles (CAs) of the sample surface were 106° and 108° degrees using argon and oxygen ions, respectively. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy were used to determine the chemical composition of the surface. The morphology change of the surfaces was observed by scanning electron microscopy (SEM). The change of the surface morphology
using the ion beam was shown to be very effective and provide enhanced optical properties. It is therefore expected that the prepared surface with wear and corrosion resistance might have a considerable potential in large scale industrial applications.
KEYWORDs : Ion beam irradiation, Surface morphology, Hydrophobic, Contact angle
AUTHORs : 김동현 · 이동훈†

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증기발생기 전열관 틈새복합환경(Pb+S+Cl)에서 Alloy 690의 응력부식균열거동
The secondary coolant of a nuclear power plant has small amounts of various impurities (S, Pb, and Cl, etc.) introduced during the initial construction, maintenance, and normal operation. While the concentration of impurities in the feed water is very low, the flow of the cooling water is restricted, so impurities can
accumulate on the Top of Tubesheet (TTS). This environment is chemically very complicated and has a very wide range of pH from acidic to alkaline. In this study, the characteristics of the oxide and the mechanism of stress corrosion cracking (SCC) are investigated for Alloy 690 TT in alkaline solution containing Pb, Cl, and S. Reverse U-bend (RUB) specimens were used to evaluate the SCC resistance. The test solution comprises 3m NaCl + 500ppm Pb + 0.31m Na2SO4 + 0.45m NaOH. Experimental results show that Alloy 690 TT of the crevice environment containing Pb, S, and Cl has significant cracks, indicating that Alloy 690 is vulnerable to stress corrosion cracking under this environment.
KEYWORDs : Lead, SCC, Alloy 690, Corrosion, Crevice Environment
AUTHORs : Jung-Ho Shin†, Sang-Yeop Lim, and Dong-Jin Kim

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Evaluation of Grooving Corrosion and Electrochemical Properties of H2S Containing Oil/Gas Transportation Pipes Manufactured by Electric Resistance Welding
Electrical Resistance Welding (ERW) on a longitudinal seam-welded pipe has been extensively used in oil and gas pipelines. It is well known that the weld zone commonly suffers from grooving corrosion in ERW pipes. In this paper, the grooving corrosion performances of API X65 grade non-sour service (steel-A) and API X70 grade sour gas resistant (steel-B) steel electrical resistance welding pipelines were evaluated. The microstructure of the bondline is composed of coarse polygonal ferrite grains and several elongated pearlites. The elongated pattern is mainly concentrated in the center of the welded area. The grooving corrosion test and electrochemical polarization test were conducted to study the corrosion behavior of the given materials. A V-shaped corrosion groove was found at the center of the fusion zone in both the steel-A and steel-B ERW pipes, as the corrosion rate of the bondlines is higher than that of the base metal. Furthermore, the higher volume fraction of pearlite at the bondline was responsible for the higher corrosion rate at the bondline of both types of steel.
KEYWORDs : Electrical resistance welding, Grooving corrosion, Seam welding, Bondline, API X65
AUTHORs : Maksudur Rahman, Siva Prasad Murugan, Changwook Ji, Yong Jin Cho, Joo-Yong Cheon, and Yeong-Do Park†

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Effect of Microstructure on the Environmentally Induced Cracking Behavior of Al-Zn-Mg-Cu-Zr Aluminum Alloy
AA7010 is an Al-Zn-Mg-Cu alloy containing Zr, developed as an alternate to traditional AA7075 alloy owing to their high strength combined with better fracture toughness. It is necessary to improve the corrosion resistance and surface properties of the alloy by incorporating plasma electrolytic oxidation (PEO) method. AA7010-T7452 aluminum alloy has been processed through the forging route with
multi-stage working operations, and was coated with 10μm thick Al2O3 ceramic aluminina coating using the plasma electrolytic oxidation (PEO) method. The corrosion, stress corrosion cracking (SCC) and nano-mechanical behaviours were examined by means of potentiodynamic polarization, slow strain rate test (SSRT) and nano-indentation tests. The results indicated that the additional thermomechanical treatment during the forging process caused a fully recrystallized microstructure, which lead to the poor environmental cracking resistance of the alloy in 3.5% NaCl solution, despite the overaging treatment. Although the fabricated PEO coating improved general corrosion resistance, the brittle nature of the coating did not provide any improvement in SCC resistance of the alloy. However, the hardness and elastic modulus of the coating were significantly higher than the base alloy.
KEYWORDs : Aluminum alloys, Potentiodynamic polarization, Stress corrosion cracking (SCC), Nanomechanical
AUTHORs : Rahul Ghosh†, A. Venugopal, Pradeep P I, L. Rama krishna, P. Ramesh Narayanan, Bhanu Pant, and Roy M Cherian

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Anticorrosion Coatings Obtained by Plasma Electrolytic Oxidation on Implant Metals and Alloys
Development of biodegradable implants for treatment of complex bone fractures has recently become one of the priority areas in biomedical materials research. Multifunctional corrosion resistant and bioactive coatings containing hydroxyapatite Ca10(PO4)6(OH)2 and magnesium oxide MgO were obtained on Mg-Mn-Ce magnesium alloy by plasma electrolytic oxidation. The phase and elemental composition, morphology, and anticorrosion properties of the coatings were investigated by scanning electron microscopy, energy dispersive spectroscopy,
potentiodynamic polarization, and electrochemical impedance spectroscopy. The PEO-layers were post-treated using superdispersed polytetrafluoroethylene powder. The duplex treatment considerably reduced the corrosion rate (>4 orders of magnitude) of the magnesium alloy. The use of composite coatings in inducing bioactivity and controlling the corrosion degradation of resorbable Mg implants are considered promising. We also applied the plasma electrolytic oxidation method for the formation of the composite bioinert coatings on the titanium nickelide surface in order to improve its electrochemical properties and to change the morphological
structure. It was shown that formed coatings significantly reduced the quantity of nickel ions released into the organism.
KEYWORDs : Implant alloys, Protective coating, Plasma electrolytic oxidation, Titanium nickelide
AUTHORs : S. L. Sinebryukhov†, S. V. Gnedenkov, O. A. Khrisanfova, A. V. Puz’, V. S. Egorkin, and A. G. Zavidnaya

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