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Page : 206 - 211
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- Superhard SiC Thin Films with a Microstructure of Nanocolumnar Crystalline Grains and an Amorphous Intergranular Phase
- Silicon carbide (SiC) thin films become superhard when they have microstructures of nanocolumnar crystalline grains (NCCG) with an intergranular amorphous SiC matrix. We investigated the role of ion bombardment and deposition temperature in forming the NCCG in SiC thin films. A direct-current (DC) unbalanced magnetron sputtering method was used with pure Ar as sputtering gas to deposit the SiC thin films at fixed target power of 200 W and chamber pressure of 0.4 Pa. The Ar ion bombardment of the deposited films was conducted by applying a negative DC bias voltage 0-100 V to the substrate during deposition. The deposition temperature was varied between room temperature and 450°C. Above a critical bias voltage of -80 V, the NCCG formed, whereas, below it, the SiC films were amorphous. Additionally, a minimum thermal energy (corresponding to a deposition temperature of 450°C in this study) was required for the NCCG formation. Transmission electron microscopy, Raman spectroscopy, and glancing angle X-ray diffraction analysis (GAXRD) were conducted to probe the samples’ structural characteristics. Of those methods, Raman spectroscopy was a particularly efficient non-destructive tool to analyze the formation of the SiC NCCG in the film, whereas GAXRD was insufficiently sensitive.
- KEYWORDs : Silicon carbide, Nanocomposite structure, Hardness, Nanocolumnar crystalline grain, Amorphous matrix phase
- AUTHORs : Kwan-Won Lim, Yong-Sub Sim, Joo-Youl Huh, Jong-Keuk Park, Wook-Seong Lee, and Young-Joon Baik†
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Page : 212 - 219
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- Composite PEO-Coatings as Defence Against Corrosion and Wear: A Review
- This paper reviews recent approaches to develop composite polymer-containing coatings by plasma electrolytic oxidation (PEO) using various low-molecular fractions of superdispersed polytetrafluoroethylene (SPTFE). The features of the unique approaches to form the composite polymer-containing coating on the surface of MA8 magnesium alloy were summarized. Improvement in the corrosion and tribological behavior of the polymer-containing coating can be attributed to the morphology and insulating properties of the surface layers and solid lubrication effect of the SPTFE particles. Such multifunctional coatings have high corrosion resistance (Rp = 3.0×107 Ω cm2) and low friction coefficient (0.13) under dry wear conditions. The effect of dispersity and x-potential of the nanoscale materials (ZrO2 and SiO2) used as electrolyte components for the plasma electrolytic oxidation on the composition and properties of the coatings was investigated. Improvement in the protective properties of the coatings with the incorporated nanoparticles was explained by the greater thickness of the protective layer, relatively low porosity, and the presence of narrow non-through pores. The impedance modulus measured at low frequency for the zirconia-containing layer (|Z|f=0.01 Hz = 1.8×106 Ω·cm2) was more than one order of magnitude higher than that of the PEO-coating formed in
the nanoparticles-free electrolyte (|Z|f=0.01 Hz = 5.4×104 Ω·cm2). - KEYWORDs : Protective coating, Plasma electrolytic oxidation, Nanoparticles
- AUTHORs : S. V. Gnedenkov†, S. L. Sinebryukhov, V. I. Sergienko, and A. S. Gnedenkov
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Page : 221 - 227
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- Sulphate Reducing Bacteria and Methanogenic Archaea Driving Corrosion of Steel in Deep Anoxic Ground Water
- During the operation, maintenance and decommissioning of nuclear power plant radioactive contaminated waste is produced. This waste is stored in an underground repository 60-100 meters below the surface. The metallic portion of this waste comprises mostly carbon and stainless steel. A long-term field exposure
showed high corrosion rates, general corrosion up to 29 μm a-1 and localized corrosion even higher. High corrosion rate is possible if microbes produce corrosive products, or alter the local microenvironment to favor corrosion. The bacterial and archaeal composition of biofilm formed on the surface of carbon steel was studied using 16S rRNA gene targeting sequencing, followed by phylogenetic analyses of the microbial community. The functional potential of the microbial communities in biofilm was studied by functional gene targeting quantitative PCR. The corrosion rate was calculated from weight loss measurements and the deposits on the surfaces were analyzed with SEM/EDS and XRD. Our results demonstrate that microbial
diversity on the surface of carbon steel and their functionality is vast. Our results suggest that in these nutrient poor conditions the role of methanogenic archaea in corrosive biofilm, in addition to sulphate reducing bacteria, could be greater than previously suspected. - KEYWORDs : MIC, Steel, SRB, Methanogenic archaea
- AUTHORs : P. Rajala†, M. Raulio, and L. Carp?n
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Page : 228 - 231
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- Fabrication of Superhydrophobic Aluminum Alloy Surface with Hierarchical Pore Nanostructure for Anti-Corrosion
- Aluminum and its alloys have been widely used in various fields because of low weight, high strength, good conductivity, and low price. It is well known that aluminum alloys that cause natural oxide film can inhibit corrosion in wet, salty environments. However, these oxides are so thin that corrosion occurs in a variety of environments. To prevent this problem, an electrochemical anodizing technique was applied to the aluminum alloy surface to form a thick layer of oxide and a unique oxide shape, such as a hierarchical pore structure simultaneously combining large and small pores. The shape of the structures was implemented using stepwise anodization voltages such as 40 V for mild anodizing and 80 V for hard anodizing, respectively. To maximize water repellency, it is crucial to the role of surface structures shape. And a hydrophobic thin film was coated by 1H, 1H, 2H, 2H-Perfluorodecyltrichlorosilane (FDTS) to minimize surface energy of the structure surface. Thus, such nanoengineered superhydrophobic surface exhibited a high water contact angle and excellent corrosion resistance such as low corrosion current density and inhibition efficiency.
- KEYWORDs : Stepwise anodizing, Hierarchical pore nanostructures, Superhydrophobic coating, Anti-corrosion
- AUTHORs : Hyejeong Ji, Chanyoung Jeong†
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Page : 232 - 242
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- Analysis of PVDF Coating Properties with Addition of Hydrophobically Modified Fumed Silica
- In this study, hydrophobically modified fumed silica was added to the PVDF coating to improve corrosion protection performance. Two types of silane modifiers, trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ), were used for hydrophobic modification of the fumed silica. The composition of modified fumed
silica was analyzed by Fourier transform infrared, X-ray photoelectron spectroscopy, and elemental analysis. The dispersion of modified fumed silica in the PVDF coating was observed by the transmission electron microscopy, and the hydrophobicity of PVDF coating was analyzed by the water contact angle. Surface
properties were examined by the field emission scanning electron microscopy and scanning probe microscopy. Potentiodynamic polarization was conducted to confirm corrosion protection performance of PVDF coating in terms of hydrophobically-modified fumed silica contents. As a result, the average surface roughness and
the water contact angle of the PVDF coating increased with modifier contents. The results of the potentiodynamic polarization test showed an increase of the Ecorr values with increase of the hydrophobicity of PVDF coating. Thus, it clearly indicates that the corrosion protection performance of PVDF coating improved with the addition of the hydrophobic-modified fumed silica that prevents the penetration of moisture into the PVDF coating. - KEYWORDs : Polyvinylidene fluoride, Hydrophobic modification, Fumed silica
- AUTHORs : Nam Kyu Lee, Young Hoon Kim, Tae Gyu Im, Dong Uk Lee, MinYoung Shon, and Myung Jun Moon†
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Page : 243 - 252
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- Corrosion Behavior and Inhibition Studies of AZ31B Magnesium Alloy With and Without Cl- in the Alkaline Electrolytes in Addition with Various Inhibitor and Without Cl- in the Alkaline Electrolytes in Addition with Various Inhibitor Additives
- The pitting corrosion and inhibition studies of AZ31B magnesium alloy were investigated in the alkaline solution (pH12) with chloride and inhibitors. The corrosion behavior of passive film with/without Cl- in the alkaline electrolyte were conducted by polarization curve and immersion tests in the presence of various
additives (inhibitors) to clarify the inhibition efficiency of pitting corrosion at higher potential region. Critical concentration of pitting corrosion for Mg alloy was evaluated with 0.005 M NaCl in 0.01 M NaOH on the anodic polarization behavior. Critical pitting of AZ31B Mg alloy in 0.01 M NaOH is a function of chlorides; Epit = - 1.36 ? 0.2 log [Cl?]. When the Sodium Benzoate (SB) was only used as an inhibitor,
a few metastable pits developed on the Mg surface by an immersion test despite no pitting corrosion on the polarization curve meaning that adsorption of SB on the surface is insufficient protection from pitting corrosion in the presence of chloride. The role of SB and Sodium Dodecylbenzenesulfonate (SDBS) inhibitors for the Mg alloy surface in the presence of chloride was suppressed from pitting corrosion to co-adsorb on the Mg alloy surface with strong formation of passive film preventing pitting corrosion. - KEYWORDs : Magnesium alloy, Corrosion inhibitor
- AUTHORs : Yoonji Shin and Kyehyun Cho†
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Page : 253 - 257
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- Deep Learning Based Real-Time Painting Surface Inspection Algorithm for Autonomous Inspection Drone
- A deep learning based real-time painting surface inspection algorithm is proposed herein, designed for developing an autonomous inspection drone. The painting surface inspection is usually conducted manually. However, the manual inspection has a limitation in obtaining accurate data for correct judgement on the surface because of human error and deviation of individual inspection experiences. The best method to replace manual surface inspection is the vision-based inspection method with a camera, using various image processing algorithms. Nevertheless, the visual inspection is difficult to apply to surface inspection due to diverse appearances
of material, hue, and lightning effects. To overcome technical limitations, a deep learning-based pattern recognition algorithm is proposed, which is specialized for painting surface inspections. The proposed algorithm functions in real time on the embedded board mounted on an autonomous inspection drone. The inspection
results data are stored in the database and used for training the deep learning algorithm to improve performance. The various experiments for pre-inspection of painting processes are performed to verify real-time performance of the proposed deep learning algorithm. - KEYWORDs : Surface inspection, Deep learning, Inspection drone, Real-time inspection
- AUTHORs : Hyung-young Chang, Seung-ryong Han, and Heon-young Lim†
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Page : 258 - 266
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- Study on Corrosion Properties of Additive Manufactured 316L Stainless Steel and Alloy 625 in Seawater
- The objective of this study was to evaluate corrosion resistance of additive manufactured 316L stainless steel and alloy 625 powders widely used in corrosion resistance alloys of marine industry in comparison with cast alloys. Directed Energy Deposition (DED) method was used in this work for sample production.DED parameter adjustment was also studied for optimum manufacturing and for minimizing the influence of defects on corrosion property. Additive manufactured alloys showed lower corrosion resistance in seawater compared to cast alloys. The reason for the degradation of anti-corrosion property was speculated to be due to loss of microstructural integrity intrinsic to the additive manufacturing process. Application of heat treatment with various conditions after DED was attempted. The effect of heat treatments was analyzed with a microstructure study. It was found that 316L and alloy 625 produced by the DED process could recover their expected corrosion resistance when heat treated at 1200 °C.
- KEYWORDs : Additive manufacturing, Corrosion, 3D printing, Nickel alloy, Directed energy deposition(DED)
- AUTHORs : Geun-Su Jung, Yong-Ha Park, Dae-Jung Kim, and Chae-Seon Lim†
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Page : 267 - 276
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- Effect of Heat Treatment Conditions on Corrosion and Hydrogen Diffusion Behaviors of Ultra-Strong Steel Used for Automotive Applications
- The purpose of this study was to examine the influence of conditions for quenching and/or tempering on the corrosion and hydrogen diffusion behavior of ultra-strong automotive steel in terms of the localized plastic strain related to the dislocation density, and the precipitation of iron carbide. In this study, a range of analytical and experimental methods were deployed, such as field emission-scanning electron microscopy, electron back scatter diffraction, electrochemical permeation technique, slow-strain rate test (SSRT), and electrochemical polarization test. The results showed that the hydrogen diffusion parameters involving the diffusion kinetics and hydrogen solubility, obtained from the permeation experiment, could not be directly
indicative of the resistance to hydrogen embrittlement (HE) occurring under the condition with low hydrogen concentration. The SSRT results showed that the partitioning process, leading to decrease in localized plastic strain and dislocation density in the sample, results in a high resistance to HE-induced by aqueous corrosion. Conversely, coarse iron carbide, precipitated during heat treatment, weakened the long-term corrosion resistance. This can also be a controlling factor for the development of ultra-strong steel with superior corrosion and HE resistance. - KEYWORDs : Ultra-strong steel, Heat treatment, Corrosion induced hydrogen diffusion, Residual stress, Carbides
- AUTHORs : Jin-seong Park, Hwan Goo Seong, and Sung Jin Kim†
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Page : 277 - 284
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- Effect of Applied Voltage on the Reliability of Coating Flaw Detection of Pipe with Different Buried Depths
- External corrosion control of buried pipe can be achieved by the combination of barrier coating and cathodic protection. Coating damage and deterioration can be induced by many reasons; damage during handling and laying, enhanced failure at low temperatures, failure during commissioning and operation, disbanding due to inadequate surface cleaning, rock penetration during installation and service etc. This work focused on the effect of survey conditions on the reliability of coating flaw detection of buried pipes. The effects of applied voltage and anode location on the detection reliability of coating flaw of buried pipe in soil with the resistivity of ca. 25.8 kΩ·cm were discussed. Higher applied voltage increased the detection reliability,
regardless of buried depth, but deeper burial depth reduced the reliability. The location of the anode has influenced on the detection reliability. This behaviour may be induced by the variation of current distribution by the applied voltage and buried depth. From the relationship between the applied voltage and reliability, the needed detection potential to get a desire detection reliability can be calculated to get 100% detection reliability using the derived equation. - KEYWORDs : Buried pipe, Coating flaw detection, Buried depth, Detection potential, Reliability
- AUTHORs : B. T. Lim, M. G. Kim, K. T. Kim, H. Y. Chang, and Y. S. Kim†
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