Kyung Man Moon

Mechanical Properties of Carbon/PEEK Composites According to the Fiber Ply Orientation and Sizing Removal of Carbon Fiber for Artificial Hip Joint

The purpose of this study is to determine the correct estimation of the mechanical property between epoxy resin and PEEK sheet as the composites and its validity has been tested with the alternative materials of the metal-based materials for artificial hip joint. Moreover, this work evaluated the mechanical properties according to the temperature of heat treatments for sizing removal of carbon fiber and the fractured surfaces of Carbon/Epoxy and Carbon/PEEK composites were also evaluated. First, the sizing removal of carbon fiber were conducted at 300°C for 4 hours and 400°C for 2 hours. The fractured surface in the specimen of tensile test made from PEEK and epoxy resin was observed by SEM. the fracture surface of the tensile test specimen of the Carbon/Epoxy composites heat-treated to 400°C showed that the resin did not bury nearly in the fiber surface and pull out was observed. It is shown that 400°C is suitable for the sizing removal of the carbon fiber. The mechanical test result showed that there was no significant differences in short beam strength. However, the tensile strength and compressive strength of the Carbon/PEEK composites was higher than those of the Carbon/Epoxy composites in the case of the Vacuum Bag process. In addition, this result showed that the sizing material did not have a significant effect on the strength of the Carbon/PEEK composites.

Glass Fiber Permeability Using the VARTM Process

This study investigated a flow rate control system for the vacuum-assisted resin transfer molding (VARTM) process. Using Darcy’s equation, the permeability of multiaxial glass fiber composites is predicted and experimentally confirmed. The resin velocity vector is inversely proportional to the fiber mat length and resin viscosity, but proportional to the fiber mat permeability. In this study, the permeability of the preform and viscosity of the epoxy resin were measured using multiaxial glass fiber by VARTM. The permeability and time for impregnation differed according to the fiber direction in the VARTM process. The results indicated the need for further study of reinforcement fiber permeability in VARTM processing design.

The Characteristics of Multilayer Thin Films Deposited with Metal Thin Films (Ag, Al, Cu)

In order to study the characteristics of multilayer thin films with a ZnO/ metal/ ZnO structure the manufacture of the thin films was performed by a dc (direct current) magnetron sputtering system on slide glass substrates. The ZnO thin films were manufactured with the thicknesses of 30 nm and 50 nm. Three kinds of metals (Ag, Al and Cu) were deposited with the thicknesses of 4 nm, 8 nm, 12 nm and 16 nm. The electrical and optical properties of the manufactured thin films were then observed. As a result, the multilayer thin films with an Ag layer represented the most excellent electrical conductivity. This is due to the difference in the fundamental electrical properties of each of the metals. The structures of the metal particles deposited on the ZnO thin films were observed by an SEM (scanning electron microscope). The thin films exhibited a continuous structure with regular spaces between the metal particles. This resulted in an increase of transmittance. This is considered by the decrease of scattering and of light absorption on thin films with a continuous structure.

Difference of Corrosion Characteristics of the Welding Zone between Laser and TIG Welding

Two kinds of welding methods were performed on 22APU stainless steel: laser welding and TIG welding. In this case, the differences of the corrosion characteristics of the welded zones between the two welding methods mentioned above were investigated with electrochemical methods such as the measurement of corrosion potential, polarization curves, cyclic voltammogram, etc. The Vickers hardness of all welded zones (WM:Weld Metal, HAZ:Heat-Affected Zone, BM:Base Metal) was relatively higher for the laser welding than for the TIG welding. Furthermore, the laser welding method’s corrosion current densities in all welding zones were also observed to have a lower value compared to TIG welding. In particular, the corrosion current density of BM, regardless of the welding method, was the lowest value among all other welding zones. Intergranular corrosion was not observed at the corroded surface of all laser-welded welding zones; however, it was observed at the TIG-welded WM and HAZ welding zones, which suggests that chromium depletion due to the formation of chromium carbide occurs on the WM and HAZ which are in the range of sensitization temperatures, therefore the zones can easily be corroded with a more active anode. Consequently, we can see that corrosion resistance of all welding zones of 22APU stainless steel may be improved by the use of laser welding. Keywords: Laser welding, TIG welding, Corrosion potential, Weld metal, Heat affected zone, Polarization curves, Chromium depletion1.Introduction In recent years, use of austenitic stainless steel, which has a high corrosion resistance, has been increasing due to the development of industries, such as atomic energy, aerospace, petro chemical, etc. When stainless steel was welded for numerous kinds of structures, intergranular corrosion would often be observed at the area surrounding the welding zone due to chromium depletion; in addition, there are numerous papers which have investigated both general corrosion and intergranular corrosion[1-6]. However, there are few experimental results on the effect of corrosion control at the welding zones when laser or TIG welding are used for the purpose of constructing heat exchangers with 22 APU stainless steel. Although laser welding is more expensive than TIG welding, laser welding is often used instead of TIG welding for the production of heat exchangers. Consequently, it has been suggested that, from a long-term point of view, laser welding is more economic than TIG welding. In this study, when TIG and laser welding are performed on the stainless steel, the differences of the corrosion characteristics in the welding zone was investigated with electrochemical methods. The experimental results are therefore expected to provide useful reference data for the appreciation of mechanical and corrosion characteristics in the welding zones.

A Study on Galvanic Current Variation of Zn Sacrificial Anode Made by Including of Additive in Solutions with Various Conductivities

There have been two cathodic protection methods to inhibit corrosion of the structural steel piles which are being immerged under seawater, or to control corrosion of a hull part of the ship exposed to sea water. One of them is a sacrificial anode cathodic protection method that the steel pile can be protected with galvanic current by potential difference between sacrificial anode and corrosive structural steel. And, the sacrificial anode cathodic protection method have generally merits compared to impressed current method because it can be easily applied to everywhere which is not connected with electricity. However, when the steel piles are being submerged in low conductivity solution mixed with fresh water and sea water, the structural steel piles mentioned above have not been protected occasionally perfectively due to decreasing of galvanic current of zinc anode caused by deposited with oxide film on the surface of anode. In this study, four types of zinc anodes samples which are included with three types of additives such as NaCl, KCl, and ZnCl2 were prepared, and galvanic currents, the polarization characteristics of these anodes was investigated using electrochemical methods such as polarization curves, impedance, cyclic voltammogtam and galvanic current in order to evaluate the effect of additive affecting to quality of zinc anode. The sample added with NaCl indicated the highest value of galvanic current density compared to other samples in the case of lower and higher conductivity solutions such as 0.32 and 2.97mS respectively, and the sample added with KCl revealed the smallest galvanic current density in middle value of conductivities such as 1.53 and 2.27 mS. Moreover, Zn sample no added with additive exhibited the smallest value of galvanic current density in the lowest conductivities such as 0.32 and 0.98 mS. Therefore, it is considered that the galvanic current of the sacrificial anode can be increased by adding of additive when the anode is submerged in low conductivity solution mixed with fresh water and sea water.

Effect of Osmotic Pressure by Salt Concentration on Corrosion Resistance of Anti-Corrosive Paint

Recently, many types of constructional steels have been often exposed to severely corrosive environments due to acid rain with increasing environmental contamination. To control corrosion problems, a painting protection method has been widely applied to numerous constructional steels on land as well as offshore. Therefore, development of anti-corrosive paint with good quality of corrosion resistance is very important from an economical perspective. In this study, four types of anti-corrosive paint were coated to test specimens, and then, were immersed in various salt solutions (0.1, 3 and 9% NaCl solution) for 11 days. Corrosion resistance of these samples by effect of osmotic pressure with various salt concentration was investigated with electrochemical methods such as measurement of corrosion potential, impedance and corrosion current density. Corrosion current density of these samples submerged in 0.1% NaCl solution exhibited highest value than those immersed in 3% and 9% NaCl solutions because water, dissolved oxygen and chloride ion etc. is easily to invade towards inner side of coating film due to increasing osmotic pressure compared to 3% and 9% NaCl solutions. However, corrosion current densities of all samples in the case of submerged in 9% NaCl solution exhibited higher values compared to 3% NaCl solution.Thus, a large amount of chloride ion dissolved in 9% NaCl solution plays a more critical role in corrosion behavior of coated steel rather than osmotic pressure. Consequently, the corrosion mechanism between coated steel and bare steel plates is different from each other because of presence of osmotic pressure between salt solution and coating film of coated steel plate. As a result, corrosion resistance of tcoated steel plate may be depend on the osmotic pressure as well as salt concentration

Corrosion Behaviors for Galvanizing, Galvalume and Chromate Treated Steels in 1% NaOH Solution

The galvanized steel structures may be inevitably corroded rapidly in the case of exposed to corrosive environments for long time, and these corrosive environments has been accelerated with increasing the environmental contamination due to the rapid development of industrial society. However, since the galvanizing method have the various merits compared to surface coating treatment in economical point of view, the galvanized steel have been extensively used to the numerous constructional steels such as a guard rail of high way, various types of structural steel for manufacturing ship and various industrial fields etc.. Therefore, it has been made an effort to improve the corrosion resistance of the galvanizing film through various methods such as variation of chemical composition of galvanizing bath, chromate treatment and coating treatment etc.. In this study, comparison evaluation on the corrosion resistance of three types of the test specimens, that is, three samples of pure galvanizing, galvalume and chromate treatment were investigated using electrochemical methods in 1% NaOH solution. The samples of chromate treatment and of galvalume exhibited the lowest and highest corrosion current density respectively in 1% NaOHsolution. In addition, the sample of chromate treatment revealed the highest impedance at 0.01Hz, which is considered that the oxide film by chromate treatment is deposited on the surface of pure galvanizing sample. After drawing polarization curves, the corroded surface of the pure galvanizing specimen indicated pattern like as localized corrosion, moreover, the large amount of corrosive products was observed on the surface of galvalume sample. However, the smooth pattern nearly similar to general corrosion was observed at the corroded surface of the sample of chromate treatment. Consequently, it is considered that the chromate treatment is an optimum method compared to pure galvanizing and, galvalume treatment to improve corrosion resistance in 1% NaOH solution.

Evaluation on the Addition of Inhibitor and Surface Treatment to Corrosion Behavior of the Reinforced Steel Bar Embedded in Mortar Specimen

In this study, seven types of mortar test specimens were manufactured with parameters, that is, the surface of the reinforced steel bar was treated with hot dip galvanizing (Zn) and the surface of the test specimen was coated with underwater paint, and four types of inhibitors (DAW, MCI, DCI, and Silcon) were added in mortars respectively. And, the seven types of mortar test specimens were immersed in seawater for 4 years. The corrosion properties of the reinforced steel bars embedded in mortar test specimens were investigated using electrochemical methods. The corrosion potentials of the test specimens with painting on the surface of the specimen and Zn coating on the surface of the steel bar exhibited the noblest and lowest values respectively after one year, however, after 4 years, the specimens of underwater painting and of addition of Silcon inhibitor indicated the noblest and lowest values of corrosion potentials respectively. Furthermore, the painting specimen exhibited the smallest values of corrosion probability as welll as of the corrosion current density, while, addition of MCI inhibitor showed the highest values of both corrosion probability and corrosion current density. Moreover, the painting specimen showed the smallest value of neutralization degree among all the specimens, and the largest value of neutralization degree was observed at the specimen of natural condition (no adding of inhibitor, no painting and no Zn coating). As a result, it is considered that the addition of inhibitors, coating with hot dip galvanizing (Zn), and painting on the surface have the effects not only to inhibit the neutralization degree but also to increase the corrosion resistance of the embedded steel bar.

Evaluation on the Mechanical and Corrosion Resistance of ALDC 12 Al Alloy by Three Types of Heat Treatments

Al is a active metal. However, it has a generally fine oxide film with thin and protective barrier, which is stable in air and neutral aqueous solution. Thus, Al alloys have been widely used in architectural trim, cold & hot-water storage vessels and piping. However, Al and most of their alloys may be easy to be corroded with various patterns of corrosion such as pitting, intergranular and galvanic corrosion etc. in the case of exposure to various industrial and marine corrosive environments. Therefore, an optimum evaluation of corrosion resistance for Al and Al alloys may be more important in a economical point of view. In this study, characteristics evaluation for ALDC 12 Al alloy by solution, normalizing, and aging (natural and artificial) heat treatments was carried out using electrochemical methods etc.. We can see that the hardness of ALDC 12 Al alloy were decreased by solution and aging heat treatments, in particular, the solution and natural aging (SNA) heat treatments indicated the lowest value of hardness. However, the lower hardness by heat treatment, the better corrosion resistance, for instance, the solution and natural aging (SNA) heat treatment exhibited the best corrosion resistance with showing the lowest hardness. Furthermore, the highest hardness was observed after normalizing and artificial aging (NAA) heat treatments. Therefore, it is considered that if improvement of the hardness as well as the corrosion resistance were to be required together, the normalizing and artificial aging (NAA) heat treatment should be performed. On the other hand, the solution and natural aging (SNA) heat treatment is thought to be an optimum heat treatment method for only corrosion resistance improvement.

Evaluation on the Corrosion and Wear Resistance of Welding Zone Welded with Plasma Transferred Arc Welding Method

There are many welding methods which have been currently performed to prolong the life time of exhaust valve of marine engine from an economic point of view. In this study, one of these welding methods, plasma transferred arc (PTA) welding was performed at the base metal of Nimonic 80A which would be used as the material of exhaust valve with three kinds of filler metals such as Stellite 6, Inconel 625 and Inconel 718. The mechanical and corrosion characteristics were investigated with electrochemical and wear loss test methods. The Nimonic 80A as the base metal had a better corrosion resistance than those of the weld metals welded with three types of the filler metals. However, after post weld heat treatment, all these weld metals mentioned above exhibited better corrosion resistance compared to the base metal, shifting the corrosion potential to the noble direction, and pitting corrosion was more or less observed at the surface of Nimonic 80A after post weld heat treatment. In particular, Inconel 625 showed the best corrosion resistance among the filler metals after heat treatment. The wear ratio of Stellite 6 showed the lowest value due to its highest hardness among the filler metals, however, its ratio by cavitation test exhibited the highest value. It is considered that increasing of embrittlement with increasing the hardness was resulted in increasing the wear loss by cavitation test.