• Aerospace Engineering and Technology
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• v.12 no.1
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• pp.81-86
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• 2013

This article deals with the manufacturing and performance evaluation on the specimen pipes which have large size diameter and thin thickness. This specimen is for LOX main pipe of KSLV-II propulsion feeding system. The material of specimen is alloy 21-6-9. Alloy 21-6-9 has higher strength and better weldability rather than STS-300 class pipes. We found that the specimen using alloy 21-6-9 satisfied the requirement by pressurization tests.

• Nuclear Engineering and Technology
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• v.37 no.4
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• pp.375-384
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• 2005

To investigate the flow-accelerated corrosion (FAC) dependency of carbon steel (A106 Gr. B) and low-alloy steels (1Cr-1/2Mo, 21/4Cr-1Mo) on pH, orifice distance, and material, experiments were carried out. These experiments were performed using a flow velocity of 4 m/sec (partly 9 m/sec) at pH $8.0\~10.0$ in an oxygen-free aqueous solution re-circulated in an Erosion-Corrosion Test Loop at $130^{\circ}\;{\ldots}$ for 500 hours. The weight loss of the carbon steel specimens appeared to be positively dependent on the flow velocity. That of the carbon and low-alloy steel specimens also showed to be distinguishably dependent on the pH. At pH levels of $8.0\~9.5$ it decreased, but increased from 9.5 to 10.0. Utility water chemistry personnel should carefully consider this kind of pH dependency to control the water system pH to mitigate FAC of the piping system material. The weight loss of the specimens located further from the orifice in the distance range of $6.8\~27.2$ mm was shown to be greater, except for 21/4Cr-1Mo, which showed no orifice distance dependency. Low alloy steel specimens exhibited a factor of two times better resistance to FAC than that of the carbon steel. Based on this kind of FAC dependency of the carbon and low-alloy steels on the orifice distance and material, we conclude that it is necessary to alternate the composition of the secondary piping system material of NPPs, using low-alloy steels, such as 21/4Cr-1Mo, particularly when the system piping has to be replaced.

• Journal of the Korean Society of Marine Environment & Safety
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• v.13 no.3
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• pp.223-228
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• 2007

This paper investigated on mechanical characteristic of Al alloy for ship's welded with various welding techniques such as TIG, MIG welding and welding by robot. The yield strength, tensile strength and elongation in TIG welding present 83.9%, 64.6% and 21.9% compare to those in base metal, respectively. The MIG welding is carried out with welding eletrode of ER5183 and ER5356. The mechanical characteristics in ER5356 are improved at approximately 2-4% for ER5183. The mechanical properties of 5083O in welding by robot are better than those of 5456-H116.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.4
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• pp.172-177
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• 2002

The steady-static creep behaviors of Ti-6Al-4V alloy, using the constant stress creep tester, were investigated over the temperature range of $510{\sim}550^{\circ}C$(0.42~0.44Tm) and the stress range of 200~275 MPa($20.41{\sim}28.06kg/mm^2$). The stress exponents(n) for the static creep deformation of this alloy were 9.85, 9.35, 9.24 and 8.85 at the temperature of 510, 525, 535 and $550^{\circ}C$, respectively. The stress exponent(n) decreased with increasing the temperature and became close to about 5. The apparent activation energies(Q) for the static creep deformation were 254.4, 241.8, 234.4 and 221.9 kJ/mole for the stress of 200, 225, 250 and 275MPa, respectively. The activation energy(Q) decreased with increasing the stress. From the above results, it can be concluded that the static creep deformation for Ti-6Al-4V alloy was controlled by the dislocation climb over the ranges of the experimental conditions. Larson-Miller Parameter(P) for the crept specimens of Ti-6Al-4V alloy under the static creep conditions was obtained as $P=(T+460)({\log}\;t_r+21)$. The failure plane observed by SEM showed up dimple phenomenon at all range.

• Journal of Korea Foundry Society
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• v.21 no.4
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• pp.239-245
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• 2001

Microstructure and mechanical properties of Sn-3.1 wt.%Ag-6.9 wt.%Bi system solders on Cu-substrate were studied. The Sn3.1 wt.%Ag-6.9 wt.%Bi alloy was designed by phase diagram and chemical properties and was prepared by melting in argon atmosphere. The mechanical properties of solder/Cu joints were examined by shear strength test, and also creep test. The microstructure of Sn-3.1 wt.%Ag-6.9 wt.%Bi alloy consists of Bi-rich phase and $Ag_3Sn$ precipitate in {\beta}-Sn$ matrix phase. The shear strength of the joint was decreased with aging treatment. Crack path under shear test was through the solder. Similar crack path change mode was observed at the creep test of solder/Cu joint. The creep behavior of Sn-3.1 wt.%Ag-6.9 wt.%Bi alloy represented the inverse primary creep behavior at all test condition. It is suggested that the inverse primary creep behavior is induced from Bi solute atoms in Sn-matrix. The creep resistance of Sn-3.1Ag-6.9Bi alloy is better than that of Sn-3.5 wt.%Ag alloy at all test conditions.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.3
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• pp.584-609
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• 1995

The purpose of this study was to evaluate the difference of the galvanic corrosion behaviour of the titanium in contact with gold alloy, silva-palladium alloy, and nickel-chromium alloy using the immersion and electrochemical method. And the effects of galvallit couples between titanium and the dental alloys were assessed for their usefulness as materials for superstructure. The immersion method was performed by measuring the amount of metal elementsreleased by Inductivey coupled plasma emission spectroscopy(ICPES) The specimen of fifteen titanium plates, the five gold alloy, five silver-palladium, five nickel-chromium plates, and twenty acrylic resin plates ware fabricated, and also the specimen of sixty titanium plugs, the thirty gold alloy, thirty silver-palladium, and nickelc-hromium plugs were made. Thereafter, each plug of gold alloy, silver-palladium, and nickel-chromium inserted into the the titanium and acrylic resin plate, and also titanium plug inserted into the acrylic resin plate. The combination specimens uf galvanic couples immersed in 70m1 artificial saliva solution, and also specimens of four type alloy(that is, titanium, gold, silver-palladium and nickel-chromium alloy) plugs were immersed solely in 70m1 artificial sativa solution. The amount of metal elements released was observed during 21 weeks in the interval of each seven week. The electrochemical method was performed using computer-controlled potentiosta(Autostat 251. Sycopel Sicentific Ltd., U.K). The wax patterns(diameter 11.0mm, thickness,in 1.5mm) of four dental casting alloys were casted by centrifugal method and embedded in self-curing acrylic resin to be about $1.0cm^2$ of exposed surface area. Embedded specimens were polished with silicone carbide paper to #2,000, and ultrasonically cleaned. The working electrode is the specimen of four dental casting alloys, the reference electrode is a saturated calmel electrode(SCE) and the ounter electrode is made of platinum plate. In the artificial saliva solution, the potential scanning was carried out starting from-700mV(SCE) TO +1,000mV(SCE) and the scan rate was 75mV/min. Each polarization curve of alloy was recorded automatically on a logrithmic graphic paper by XY recorder. From the polarization curves of each galvanic couple, corrosion potential and corrosion rates, that is, corrosion density were compared and order of corrosion tendency was determined. From the experiments, the following results were obtained : 1. In the case of immersing titanium, gold alloy, silver-palladium alloy, and nickel-chromium alloysolely in the artificial saliva solution(group 1, 2, 3, and 4), the total amount of metal elements released was that group 4 was greater about 2, 3 times than group 3, and about 7.8 times than group 2. In the case of group 1, the amount of titanium released was not found after 8 week(p<0.001). 2. In the case of galvanic couples of titanium in contact with alloy(group 5, 6), the total amount of metal elements released of group 5 and 6 was less than that of group 7, 8, 9, and 10(p<0.05). 3. In the case of galvanic couples of titanium in contact with silver-palladium alloy(group 7, 8), the total amount of metal elements released of group 7 was greater about twice than that of group 5, and that of group 8 was about 14 times than that of group 6(p<0.05). 4. In the case of galvanic couples of titanium in contact with nickel-chromium alloy(group 9, 10), the total amount of metal elements released of group 9 and 10 was greater about 1.8-3.2 times than that of group 7 and 8, and was greater about 4.3~25 times than that of group 5 and 6(p<0.05). 5. In the effect of galvanic corrosion according to the difference of the area ratio of cathode and anode, the total amount of metal elements released was that group 5 was greater about 4 times than group 6, group 8 was greater about twice than group 7, and group 10 was greater about 1.5 times than group 9(p<0.05). 6. In the effect of galvanic corrosion according to the elasped time during 21 week in the interval of each 7 week, the amount of metal elements released was decreased markedly in the case of galvanic couples of the titanium in contact with gold alloy and silver-palladium alloy but the total amount of nickel and beryllium released was not decreased markedly in the case of galvanic couples of the titanium in contact with nickel-chromium alloy(p<0.05). 7. In the case of galvanic couples of titanium in contact with gold alloy, galvanic current was lower than any other galvanic couple. 8. In the case of galvanic couples of titanium in contact with nickel-chromium alloy, galvanic current was highest among other galvanic couples.

• Corrosion Science and Technology
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• v.21 no.6
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• pp.495-502
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• 2022

Anodization is a representative electrochemical surface treatment method that can improve both heat resistance and corrosion resistance by forming an anodization film on the surface of the aluminum. However, these properties can be changed after an additional heat treatment process. In this study, Al 6061 was subjected to an anodization process at 60 V for 1 hour, 5 hours, or 9 hours. An additional heat treatment process was performed at 500 ℃ for 30 minutes. Field emission scanning electron microscopy (FE-SEM) analysis revealed that the thickness of the anodized film was increased in proportion to the anodization time. Both pore size and pore diameter of the anodized film was also increased after anodization. After an additional heat treatment process, there were no significant changes in the thickness, pore size, or pore diameter of the anodized film. Heat resistance was confirmed through thermal analysis and chemical resistance was evaluated with a potentiodynamic polarization test.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.1-7
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• 1995

${(Fe_{0.85}Co_{0.15})}_{75}Al_{7}B_{18-x}Nb_{x}(x=2,\;4\;and\;6\;at%)\;and\;{(Fe_{0.85}Co_{0.15})}_{75}Al_{y}B_{21-y}Nb_{4}(y=3,\;5,\;7,\;9\;at%)$ alloys were prepared by a single-roll quenching method. Microstructure and magnetic properties of the alloys such as saturation magnetization, initial permeability, coercive force and power loss have been investigated as functions of composition and armea1ing temperature. Nanocrystallines are obtained by armealing of as-prepared amorphous alloys in all compositions except the alloy of 9 at% AI. Saturation magnetization increases after armea1ing and, decreases with Nb content. However, AI and B affects the saturation magnetization insignificantly. Initial perrreability of nanocrystallized alloy at 50 kHz is improved roore than twice compared to that of the as-prepared alloy. Coercive force and core loss reach less than half after armea1ing.

• Journal of Technologic Dentistry
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• v.9 no.1
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• pp.21-29
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• 1987

The purpose of this investigation was to determine the effect of recasting on the castability and physical properties of the nonprecious metal alloy. Using 2 sorts of the nonprecious metal alloy for production of Crown and Bridge prosthetics, such as 1) sankin C. B 80 metal 2) C & B alloy, the result of experimental research on the castability and hardness according to the recasting, is as followes; 1. The difference of castability between sankin CB80 metal and C & B alloy was statistically significant (p < 0.01) and the difference of castability among the test groups, was statistically significant (p <0.01). 2. In the case of sankin C.B 80 metal, the difference of castability among the New alloy and first mixed alloy and second mixed alloy and old alloy was not significant statistically (p >0.05). 3. In the case of C & B alloy, the difference of castability among the New alloy and mixed alloys and old alloy, was not significant statistically (p >0.05). 4. The difference of hardness between sankin C & B alloy was not significant statistically (p >0.05), but the difference of hardness among the test groups was statistically significant (p <0.01). 5. In the case of Sankin C.B 80 metal, the difference of hardness among the new ally and mixed alloys and old alloy was not significant statistically (p >0.05). 6. In the case of C & B alloy, the difference of hardness between New alloy and mixed alloys was not significant statistically (p >0.05) but the difference of hardness among the old alloy and New alloy and mixed alloys was statistically significant (p <0.01).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.322-327
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• 2020

An Armor Piercing Fin Stabilized Discarding Sabot (APFSDS), which penetrates and sabotages the target by physical energy, consists of a general penetrator using Depleted Uranium (DU) or Tungsten Heavy Alloy (THA) but THA is preferable because of manufacturing and environmental issues. On a THA penetrator, the penetration performance is determined mainly by self-sharpening depending on the hardness and toughness of materials. In particular, the tensile strength and impact strength work as key factors. The correlation coefficient for the penetration performance of the tensile strength was 0.721 and the impact strength was -0.599. The improved penetration performance by additional heat treatment was proven experimentally. Therefore, maintaining elongation over 9 % and tensile strength over 123 kg/㎟ is desirable, and the impact strength should be less than 6.8 kg·m/㎠ for good penetration performance.