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Page : 129 - 137
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- 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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Page : 138 - 145
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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†
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Page : 147 - 153
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- Corrosion of Copper in Anoxic Ground Water in the Presence of SRB
- Copper is used in various applications in environments favoring and enabling formation of biofilms by naturally occurring microbes. Copper is also the chosen corrosion barrier for nuclear waste in Finland. The copper canisters should have lifetimes of 100,000 years. Copper is commonly considered to be resistant to corrosion in oxygen-free water. This is an important argument for using copper as a corrosion protection in the planned canisters for spent nuclear-fuel encapsulation. However, microbial biofilm formation on metal surfaces can increase corrosion in various conditions and provide conditions where corrosion would not otherwise occur. Microbes can alter pH and redox potential, excrete corrosion-inducing metabolites, directly or indirectly reduce or oxidize the corrosion products, and form biofilms that create corrosive microenvironments. Microbial metabolites are known to initiate, facilitate, or accelerate general or localized corrosion, galvanic corrosion, and intergranular corrosion, as well as enable stress-corrosion cracking. Sulfate-reducing bacteria (SRB) are present in the repository environment. Sulfide is known to be a corrosive agent for copper. Here we show results from corrosion of copper in anoxic simulated ground water in the presence of SRB enriched from the planned disposal site.
- KEYWORDs : Copper, Repository, Sulfate reducing bacteria, Anoxic ground water, Corrosion
- AUTHORs : L. Carp?n†, P. Rajala, and M. Bomberg
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Page : 154 - 165
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- Effects of Sulfuric Acid Concentration and Alloying Elements on the Corrosion Resistance of Cu-bearing low Alloy Steels
- During the process of sulfur dioxide removal, flue gas desulfurization equipment provides a serious internal corrosion environment in creating sulfuric acid dew point corrosion. Therefore, the utilities must use the excellent corrosion resistance of steel desulfurization facilities in the atmosphere. Until now, the trend in developing anti-sulfuric acid steels was essentially the addition of Cu, in order to improve the corrosion resistance. The experimental alloy used in this study is Fe-0.03C-1.0Mn?0.3Si-0.15Ni-0.31Cu alloys to which Ru, Zn and Ta were added. In order to investigate the effect of H2SO4 concentration and the alloying elements, chemical and electrochemical corrosion tests were performed. In a low concentration of H2SO4 solution, the major factor affecting the corrosion rate of low alloy steels was the exchange current density for H+/H2 reaction, while in a high concentration of H2SO4 solution, the major factors were the thin and dense passive film and resulting passivation behavior. The alloying elements reducing the exchange current density in low concentration of H2SO4, and the alloying elements decreasing the passive current density in high concentration of H2SO4, together play an important role in determining the corrosion rate of Cu-bearing low alloy steels in a wide range of H2SO4 solution.
- KEYWORDs : Cu-bearing low alloy steel, Sulfuric acid, Exchange current density, Passivation
- AUTHORs : Ki Tae Kim and Young Sik Kim†
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Page : 166 - 175
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- 적층가공된 티타늄 합금의 전기화학적 특성에 미치는 불산의 영향
- In this study, the electrochemical properties of CP-Ti (commercially pure titanium) and Ti-64 (Ti-6Al-4V) were evaluated and the effect of hydrofluoric acid on corrosion resistance and electrochemical properties was elucidated. Additive manufactured materials were made by DMT (Directed Metal Tooling) method.
Samples were heat-treated for 1 hour at 760 oC and then air cooled. Surface morphologies were studied by optical microscope and SEM. Electrochemical properties were evaluated by anodic polarization method and AC-impedance measurement. The oxide film formed on the surface was analyzed using an XPS. The addition of HF led to an increase in the passive current density and critical current
density and decreased the polarization resistance regardless of the alloys employed. Based on the composition of the oxide film, the compositional difference observed by the addition of HF was little, regardless of the nature of alloys. The Warburg impedance obtained by AC-impedance measurement indicates the dissolution of the constituents of CP-Ti and Ti-64 through a porous oxide film. - KEYWORDs : Additive manufacture (3D printing), CP-Ti, Ti-6Al-4V, Hydrofluoric acid, Electrochemical properties
- AUTHORs : 김기태?조현우?장현영?김영식†
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Page : 176 - 182
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- 잔류 염소가 포함된 해수에서의 Cu-Ni 합금의 부식 거동 연구
- Corrosion of the Cu alloy with 10wt% Ni in stagnant seawater with residual free chlorine was investigated. Despite that fact that Cu alloys are widely used for seawater applications due to their stubborn resistance to chloride attack, not much is known as to how the residual free chlorine in seawater affects corrosion of Cu and its alloys. In this work, immersion tests were conducted in the presence of different levels of chlorine for 90-10 Cu-Ni samples, one of the most frequently used Cu alloys for seawater application, mostly in shipbuilding. The results revealed no evidence for accelerated corrosion of the Cu-Ni alloy even in the presence of 5 ppm residual chlorine in seawater, signifying that the Cu-Ni alloy can be more tolerant to residual chlorine that has been commonly cited by the shipbuilding industry. However, comparison of polarization behavior of the alloy samples in the presence of different electrolytes with different concentrations of residual chlorine suggests that higher concentration of chlorine could increase the corrosion rate of the Cu-Ni alloy. Furthermore, it is suggested that microorganisms in the seawater could increase the corrosion rate of the Cu-Ni alloy by encouraging exfoliation of the corrosion product
off the metal surface. - KEYWORDs : MIC, Chlorination, Cu alloy, Residual chlorine, Seawater corrosion
- AUTHORs : 정 근 수†·윤 병 영·임 채 선
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Page : 183 - 192
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- 스테인리스강 입계부식
- Stainless steel can be classified into three categories depending on the microstructure as austenitic stainless steel, ferritic stainless steel and martensitic stainless steel. Generally, stainless steel is extremely resistant to corrosion as the name implies. However, under specific environments, susceptibility to localized corrosion such as pitting, intergranular corrosion and stress corrosion cracking increases. This paper reviewed the state of arts on intergranular corrosion mechanisms, countermeasures on intergranular corrosion and intergranular corrosion test methods. Intergranular corrosion is mostly related with chromium depletion at the grain boundary and sometimes with segregation of electroactive elements in solution
annealed stainless steel. Countermeasures on intergranular corrosion include avoiding chromium depletion by heat treatment and the addition of alloying elements. Sensitization evaluation of stainless steel was performed either through acid immersion test or electrochemical test. The methods were standardized in (Japanese Industrial Standards) . Even though are useful in evaluating the degree of sensitization for industrial purpose but do not provide detailed information about sensitization mechanism, cause and chromium profile. - KEYWORDs : Intergranular corrosion, Sensitization, Stainless steel, Chromium depletion, Grain boundary
- AUTHORs : 김 홍 표†·김 동 진
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Page : 193 - 201
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- 자동차 강재의 수소취성 연구에 대한 고찰
- In order to suppress CO2 emission and protect passengers in case of vehicle collision, continuous efforts are being made to increase the application ratio and tensile strength of advanced high strength steels used in the manufacturing of automotive body. Simultaneously, hydrogen embrittlement which was not a concern in the past has currently become a major issue due to microstructure that is sensitive
to hydrogen uptake. The sensitivity increases with residual stress and hydrogen uptake content. Many automotive OEM companies and mill makers are setting specifications to control hydrogen embrittlement. The factors which lead to hydrogen embrittlement are material sensitivity, residual stress, and hydrogen concentration; researches are in progress to develop countermeasures. To reduce material sensitivity, mill makers add high energy trap elements or microstructure refinement elements. Automotive OEM companies design the car parts not to concentrate local stress. And they manage the levels to not to exceed critical hydrogen concentration. In this article, we have reviewed hydrogen embrittlement evaluation methods and corresponding solutions that are being studied in automobile manufacturing
industries and mill makers. - KEYWORDs : Automotives, CO2 emission, Advanced high strength steel, Hydrogen embrittlement
- AUTHORs : 양 원 석,†·서 지 원·안 승 호
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Page : 203 - 210
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- Study of Chloride Corrosion Organic Inhibitors in Alkaline Pore Solution
- This paper compares the inhibition properties of aspartic and lactic acid salts with nitrite ions and their effect on critical chloride concentration. The tests were carried employing carbon steel specimens in saturated lime solution with varying pH in the range between13 to 13.6. The critical chloride concentration was estimated through multiple specimen potentiostatic tests at potentials in the usual range for passive rebar in the alkaline concrete of atmospheric structures. During tests, chloride salt
was added every 48 h until all the specimens showed localized attacks. The cumulative distribution curves, i.e. the number of corroded specimens as a function of the chlorides concentration was obtained. Furthermore, IR spectra were recorded for the evaluation of the presence of the organic inhibitors on the passivity film. The results confirmed the inhibitory effect of 0.1M aspartate comparable with nitrite ions, at a similar concentration. Addition of calcium lactate did not result in an increase in
the critical chloride concentration. However, the formation of a massive scale containing the substance that could reduce the corrosion propagation was observed. - KEYWORDs : Rebar, Localized corrosion, Corrosion inhibitors, Chloride, Pore solution
- AUTHORs : M. Cabrini†, S. Lorenzi, T. Pastore, and S. Pellegrini
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Page : 211 - 217
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- Corrosion Performance of Cu Bonded Grounding-Electrode by Accelerated Corrosion Test
- Natural degradation of grounding-electrode in soil environment should be monitored for several decades to predict the lifetime of the grounding electrode for efficient application and management. However, long-term studies for such electrodes have many practical limitations. The conventional accelerated corrosion test is unsuitable for such studies because simulated soil corrosion process cannot represent the actual soil environment. A preliminary experiment of accelerated corrosion test was conducted using existing test standards. The accelerated corrosion test that reflects the actual soil environment has been developed to evaluate corrosion performances of grounding-electrodes in a short period. Several test conditions with different chamber temperatures and salt spray were used to imitate actual field conditions based on ASTM B162, ASTM B117, and ISO 14993 standards. Accelerated degradation specimens of copper-bonded electrodes were made by the facile method and their corrosion performances were investigated. Their corrosion rates were calculated to 0.042 μm/day, 0.316 μm/day, and 0.11 μm/day, respectively. These results indicate that accelerated deterioration of grounding materials can
be determined in a short period by using cyclic test condition with salt spray temperature of 50 °C. - KEYWORDs : Corrosion accelerated test, Soil corrosion, Grounding rods, Copper-bonded electrode, Life cycle estimation
- AUTHORs : Sun Kyu Choi† and Kyung Chul Kim
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