Eco-Materials Processing & Design VI

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Authors: Y. Kim, Soo Ryong Kim, Hee Song, Hyeon Yoon
Abstract: The hydrothermal hot pressing (HHP) technique is a method by which hard solid bodies of powders can be produced in a short time and at a relatively low temperature under saturated vapor pressure. In this study, the hydrothermal hot pressing (HHP) technique is used for preparing porous hydroxyapatite/TCP block having a high mechanical strength. The SEM result of the sample shows that all the pores are interconnected from 200µm to 300µm in sizes. The observed X-ray powder diffraction pattern of the sample after sintering at 1200oC is composed of hydroxyapatite and tricalciumphosphste.
Authors: Shae K. Kim, Young Jig Kim
Abstract: To comply with the growing demand for life cycle environmental effect, life cycle assessment (LCA) was carried out for producing A356 aluminum alloy and AZ91D magnesium alloy diecastings. The main emphasis was placed on the improvement assessment for aluminum and magnesium diecasting processes and the comparison between the two competitive processes. The process evaluated was based on yields of finished parts relative to the metal input. This is important both from the environmental point of view and the commercial point of view because the environmental data are sensitive to the design of cast parts and the efficiency of the diecasting operation.
Authors: Seong Jong Kim, Seok Ki Jang, Jeong Il Kim
Abstract: The effects of the duration of potentiostatic anodizing on the corrosion resistance and surface morphology of anodic oxide films formed on Mg-Al alloy (AZ91) in 1 M NaOH were investigated. With the formation of an anodic film, the current density decreased gradually, started to stabilize at 300 s, and was relatively constant at 600 s. These results may be related to the increased time for catalysis of the active dissolution reaction, which not only enlarges the area covered by the anodic film, but also produces a more coherent, thicker film. The reference corrosion potentials of the anodic oxide film for AZ91 shifted in the noble direction with time. In general, the corrosion resistance characteristics were improved with anodizing time.
Authors: Seong Jong Kim, Jeong Il Kim, Masazumi Okido
Abstract: The effects of sealing solutions on the corrosion resistance of anodized Mg-Al alloys were investigated. As the proportion of Mg(OH)2 increases with the increase in the NaOH concentration, the corrosion potential improves. The sealing effects were further improved by increasing the temperature of distilled water, the pH of solutions, and the proportion of Mg(OH)2 present in the anodic film.
Authors: Seong Jong Kim, Seok Ki Jang, Jeong Il Kim
Abstract: The electrochemical and mechanical properties of welded high-strength steel were investigated using the slow strain rate test method with a constant applied cathodic potential. No correlations were found with the maximum tensile strength, yield strength, stress at failure, or hydrogen embrittlement. However, the elongation, time-to-fracture, and strain-to-failure ratio decreased as the potential became more negative. These parameters were greatest when the potential was -770mV, regardless of the post-weld heat treatment conditions. The elongation and time-to-fracture increased with PWHT.
Authors: Gyung Guk Kim, Ji Hui Kim, Kwon Yeong Lee, Seon Jin Kim, Deok Hyun Lee, Do Haeng Hur, Myung Sik Choi, Jung Ho Han
Abstract: Wear damage of steam generator tubes of nuclear power plants can cause leakage of radioactive substances. So the evaluation of tubes’ integrity is very important from the viewpoint of nuclear ecocide. In the present study, sliding wear behaviors of Inconel 600 and 690 steam generator tube materials mated with 409 stainless steel commonly used as the support plate were investigated at room temperature in an air environment. For more precise prediction of wear behaviors of steam generator tubes, Archard equation was modified, and the modified wear coefficients were estimated as a function of sliding distance. When using the modified Archard equation, the reliabilities for prediction of wear behavior of Inconel 600 and 690 mated with 409 stainless steel increased from 71.8% to 83.8% and from 60.2% to 85.2%, respectively.
Authors: Jai Won Byeon, N. Mu, J. Liu, Yong Ho Sohn
Abstract: Microstructures and residual stress of long-term oxidized nickel aluminide coating on superalloy were evaluated by photostimulated luminescence spectroscopy (PSLS). CMSX-4 superalloy coupons coated with single phase b-NiAl were oxidized in air at 788, 871, 954 and 1010°C for up to 10000 hours. The photoluminescence technique was applied for the analysis of the phase constituents and the residual stress of the thermally grown oxide (TGO) scale formed on the^coating, together with transmission electron microscopy. According to the PSLS analysis, TGO consisted of both stable a-Al2O3 and metastable Al2O3 phases in specimens oxidized at 788°C and 871°C. At higher temperatures, the TGO scale primarily consisted of equilibrium a-Al2O3. The compressive residual stress within TGO increased up to about 3GPa with increasing oxidation temperature and time until local spallation, after which a decrease as well as large standard deviation of residual stress was observed owing to the stress-relief associated with TGO scale spallation.
Authors: Jai Won Byeon, B. Jayaraj, Yong Ho Sohn
Abstract: Electrochemical impedance spectroscopy was employed to examine ZrO2-8wt.%Y2O3 (yttria stabilized zirconia, YSZ) thermal barrier coating (TBC) as a function of isothermal exposure time at 1121°C. Electrochemical impedance response (resistance and capacitance of YSZ and thermally grown oxide (TGO)) of TBC specimens was analyzed with an alternative current equivalent circuit based on the multi-layered micro-constituents of TBC, and the impedance response was correlated with microstructural changes attributed to isothermal oxidation. The resistance of YSZ was observed to increase initially and then decrease with thermal exposure. The initial increase was related to the high temperature sintering of YSZ, and the subsequent decrease was discussed in terms of microcrack initiation and electrolyte penetration. The TGO thickness was linearly correlated to the capacitance of TGO.
Authors: Jai Won Byeon, S. Laxman, Yong Ho Sohn
Abstract: The growth and microstructure of the thermally grown oxide (TGO) underneath the electron beam physical vapor deposited (EB-PVD) yttria stabilized zirconia (YSZ) topcoat were examined after short-term isothermal oxidation (1100 °C, up to 50 hours) for the as-coated and gritblasted (Ni,Pt)Al bondcoats. Microstructural analysis was carried out by a high resolution scanning transmission electron microscope equipped with bright/dark field imaging, high angle annular dark field imaging, and nano-spot energy dispersive spectroscopy. Presence of mixed oxide zone (MOZ) and a continuous Al2O3 oxide zone (COZ) was observed on the thermal barrier coating (TBC) with the as-coated (Ni,Pt)Al bondcoat. However, on the TBC with grit-blasted bondcoat, only the continuous-columnar Al2O3 scale was observed. For the as-coated type bondcoat, numerous voids were observed near the interface between MOZ and COZ after isothermal oxidation. On the other hand, COZ showed parabolic growth without any formation of voids for the grit-blasted specimens.
Authors: Jong Gwan Ahn, Dong Jin Kim, Hoang Tri Hai, Jae Ryeong Lee, Hun Saeng Chung, Chong Oh Kim
Abstract: Ni-diamond composite powders with nickel layer of round-top type on the surface of synthetic diamond (140/170 mesh) were coated with semi-batch reactor by an electroless plating method (EN). The effect of nickel concentration and feeding rate of reductant, temperature, reaction time, and stirring speed on the weight percentage of deposited Ni and morphology, mean particle size, and specific surface area of the composite powders were investigated by AAS, FE-SEM, PSA and BET. The weight percentage of Ni in the composite powder increased with time and temperature but decreased with stirring speed, and the weight percentage was 55% at 150 min., 200 rpm and 70oC.

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