• 동력기계공학회지
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• 제18권5호
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• pp.115-121
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• 2014

Alloy 617 is the one of the leading candidate materials for intermediate heat exchangers(IHX) of a very high temperature reactor(VHTR) system. Some of the components are joined by many welding techniques and therefore the welded joints are inevitable in the construction of systems. In the present paper, the low cycle fatigue(LCF) behaviors of Alloy 617 base metal(BM) and the gas tungsten arc welded (GTAWed) weld joints(WJ) are investigated experimentally under strain controlled LCF tests. Fully axial total-strain controlled tests have been conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. The weld joints have shown a lower fatigue lives compared with base metals at all the testing conditions. The weld joints have shown a higher cyclic stress response behavior than base metal. Both BM and WJ exhibited cyclic strain hardening behavior, depending on the total strain range. In addition, the strain-life parameters for BM and WJ were determined, based on Coffin-Manson equations.

• 한국수소및신에너지학회논문집
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• 제3권2호
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• pp.9-15
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• 1992

Electroless copper plating method using an alkaline bath have been employed in copper coating of the (LM)Ni4.5Co0.1MnO.2A10.2 hydrogen storage alloy powders for electrode preparation. The plating were conducted without any pretreatment of alloy powders. For the preparation of the electrodes, about 0.12g of the copper coated alloy powder (copper to alloy ratio 1/3 by weight) was compacted with pressure of 6 tons/cm2 at room temperature. The disk-type compacts had a diameter of 10mm and thickness of about 0.24mm. The electrode characteristics were examined through SEM observations and electrochemical measurements in a half cell. The electrochemical measurement showed that the maximum discharge capacity of the electrodes prepared by using alkaline bath were 245mAh per gram of coated alloy (327mAh per gram of alloy) and appeared a considerable degradation with increasing number of cycles. The decrease of the discharge capacity after 100 cycles was about 30% It can be suggested that, with a slight of improvement, this electroless copper plating method could be applied to the preparation of the rare earth-nickel based alloy electrode.

• 한국수소및신에너지학회논문집
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• 제17권1호
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• pp.31-38
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• 2006

There are two types of metal hydride electrodes as a negative electrode in a Ni-MH battery, $AB_2$ Zr-based Laves phases and $AB_5$ LM(La-rich mischmetal)-based alloys. The $AB_5$ alloy electrodes have characteristic properties such as a large discharge capacity per volume, easiness in activation, long cycle life and a low cost of alloy. However they have a relatively small discharge capacity per weight. The $AB_2$alloy electrodes have a much higher discharge capacity per weight than $AB_5$ alloy electrodes, however they have some disadvantages of poor activation behavior and cycle life. Therefore, in order to improve the discharge capacity of the $AB_5$ alloy electrode the Zr, Ti and V which are the alloying elements of the $AB_2$ alloys were added to the $LaNi_{3.6}Ai_{0.4}Co_{0.7}Mn_{0.3}$ alloy which was chosen as a $AB_5$ alloy with a high capacity. The addition of Zr, Ti and V to $LaNi_{3.6}Ai_{0.4}Co_{0.7}Mn_{0.3}$ alloy improved the activation to be completed in two cycles. The discharge capacities of Zr 0.02, Ti 0.02 and V 0.1 alloys in $LaNi_{3.6}Ai_{0.4}Co_{0.7}Mn_{0.3}M_y$ (M = Zr, Ti, V) were respectively 346, 348 and 366 mAh/g alloy. The alloy electrodes, Zr 0.02, Ti 0.05 and V 0.1 in $LaNi_{3.6}Ai_{0.4}Co_{0.7}Mn_{0.3}M_y$ (M = Zr, Ti, V), have shown good cycle property after 200 cycles. The rate capability of the $LaNi_{3.6}Ai_{0.4}Co_{0.7}Mn_{0.3}M_y$ (M = Zr, Ti, V) alloy electrodes were very good until 0.6 C rate and the alloys, Zr 0.02, Ti 0.05 and V 0.1, have shown the best result as 92 % at 2.4 C rate. The charge retention property of the $LaNi_{3.6}Ai_{0.4}Co_{0.7}Mn_{0.3}M_y$ (M = Zr, Ti, V) alloys was not good and the alloys with M content from 0.02 to 0.05 showed better charge retention properties.

• 한국표면공학회지
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• 제39권1호
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• pp.25-34
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• 2006

Al-Mg alloy, an open rack vaporizer(ORV) material was reported to be corroded in seawater environments though the ORV material was coupled to thermally sprayed Al-Zn alloy functioning a sacrificial anode. In addition, the corrosion behavior based on the calculated corrosion potential did not match the observed corrosion behavior. Hence, the goal of this study is to get better understanding on Al or Al-Mg alloy coupled to Al-Zn alloy and to provide the calculated corrosion potential representing the corrosion behavior of the ORV material by immersion test, electrochemical tests, and calculation of corrosion and galvanic potential. The corrosion potentials of Al and Al alloys also depended on alloying element as well as surface defects. The corrosion potentials of Al and Al-Mg alloy were changed with time. In the meantime, the corrosion potentials of Al-Zn alloys were not. The corrosion rates of Al-Zn alloys were exponentially increased with zinc contents. The phenomena were explained with the stability of passive film proved by passive current density depending on pH and confirmed by the model proposed by McCafferty. Dissimilar material crevice corrosion (DMCC) test shows that higher content of zinc caused Al-Mg alloy corroded more rapidly, which was due to the fact that higher corrosion rate of Al-Zn makes [$H^+$] and [$Cl^-$] more concentrated within pit solution to corrode Al-Mg alloy. Considering electrochemical reactions within pit as well as bulk in the calculation gives better prediction on the corrosion behavior of Al and Al-Mg alloy as well as the capability of Al-Zn alloy for corrosion protection.

• 한국분말재료학회지
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• 제25권4호
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• pp.327-330
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• 2018

This study is conducted as a preliminary research to verify the feasibility of Ti-based Oxide dispersion strengthened (ODS) alloy. Pure-Ti powder is mixed with $Y_2O_3$ powder and subsequently, mechanically alloyed at $-150^{\circ}C$. The Ti-based ODS powder is hot-isostatically pressed and subsequently hot-rolled for recrystallization. The microstructure consists of elongated grains and Y excess fine particles. The oxide particle size is larger than that of the typical Fe-based ODS steel. Tensile test shows that the tensile ductility is approximately 25%, while the strength is significantly higher than that of pure Ti. The high-temperature hardness of the Ti-ODS alloy is also significantly higher than that of pure Ti at all temperatures, while being lower than that of Ti-6Al-4V. The dimple structure is well developed, and no evidence of cleavage fracture surface is observed in the fracture surface of the tensile specimen.

• 한국주조공학회지
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• 제32권4호
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• pp.177-180
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• 2012

Ti-based bulk metallic glasses with high glass forming ability were developed through a systematic alloy design technique. The main alloy design strategy was the selection of alloying elements that may not be toxic in the human body. The $Ti_{45.0}Cu_{40.1}Zr_{12.7}Si_{2.2}$ alloy could be cast into an amorphous rod with the diameter of 3 mm by a suction casting technique using Cu mold. The compressive strength of the amorphous rod was measured as 1826 MPa. Since the Ti-based amorphous alloys consist of non-toxic elements, they can be widely used as bio-materials and eco-materials with unique and beneficial properties.

• 동력기계공학회지
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• 제18권1호
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• pp.106-111
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• 2014

This article describes effect of post heat treatment on wear characteristics of thermally sprayed Co-based self-flux alloy coating. Co-based self-flux alloy coatings were deposited on steel substrates using a flame spray process. Post heat treatments were carried out at 800, 900, 1000 and $1100^{\circ}C$ for 30min in a vacuum chamber. For analysis of effect of post heat treatment on mechanical properties, wear test and hardness test were performed for post heat-treated coating specimen. Microstructures of heat treated coating layer and wear track were examined using SEM and EDS. Wear loss and hardness became lower with increasing post heat treatment temperature.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.9-14
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• 2007

In this paper, a rotating tool clamping device was developed based on a shape memory alloy(SMA) and its feasibility as a tool holder was experimentally explored. The SMA-based device was able to alter clamping to unclamping through temperature control within 1 second. The means and repeatability(${\sigma}$) of the tool clamping force were 185.5N and 6N respectively and its drifts were less than 3% for an hour. Considering the temperature hysteresis of the SMA-based tool clamping device, it is necessary to heat the SMA ring to around $50^{\circ}C$ after tool change to obtain more clamping force.

• 대한치과보철학회지
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• 제44권5호
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• pp.628-641
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• 2006

Statement of problem: Dental magnetic materials have been applied to removable prosthetic appliances, maxillofacial prostheses, obturator and dental implant but they still have some problems such as low corrosion resistance in oral environments. Purpose: To increase the corrosion resistance of dental magnetic materials, surfaces of Sm-Co and Nd-Fe-B based magnetic materials were plated with TiN and sealed with stainless steels. Materials and methods : Surfaces of Sm-Co and Nd-Fe-B based magnetic materials were plated with TiN and sealed with stainless steels, and then three kinds of electrochemical corrosion test were performed in 0.9% NaCl solution; potentiodynamic, potentiostatic, and electrochemical impedance test. From this study, corrosion behavior, amount of elements released, mean average surface roughness values, the changing of retention force, and magnetic force values were measured comparing with control group of non-coated magnetic materials. Results: The values of surface roughness of TiN coated Sm-Co and TiN coated Nd-Fe-B based magnetic materials were lower than those of non coated Sm-Co and Nd-Fe-B alloy. From results of potentiodynamic test, the passive current density of TiN coated Sm-Co alloy were smaller than those of TiN coated Nd-Fe-B alloy and non coated alloys in 0.9% NaCl solution. From results of potentiostatic and electrochemical impedance test, the surface stability of the TiN coated Sm-Co alloy was more drastically increased than that of the TiN coated Nd-Fe-B alloy and non-coated alloy. The retention and magnetic force after and before corrosion test did not change in the case of TiN coated magnetic alloy sealed with stainless steel. Conclusion: It is considered that the corrosion problem and improvement for surface stability of dental magnetic materials could be solved by ion plating with TiN on the surface of dental magnetic materials and by sealing with stainless steels.

• 한국수소및신에너지학회논문집
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• 제21권4호
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• pp.340-345
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• 2010

For the conversion into hydrogen society, not only studying facilities of hydrogen production, storage, transportation and charging system but also developing technique of ensuring safety are essentially needed. Hence, for the first step of that, evaluated the hydrogen embrittlement of Inconel alloy 617, Ni-based super heat-resisting alloy, by small punch test. Prepared the various specimens through changing electrochemical charging time and measured the toughness degradation of the specimens by small-punch test. The analysis of hydrogen embrittlement behavior were carried out by investigating the fractured surface of specimens. This study has significance on revealing mechanism of hydrogen embrittlement behavior and the factor affecting hydrogen embrittlement in the future study.