• 한국표면공학회지
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• 제55권4호
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• pp.236-246
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• 2022

Electropolishing is a surface finishing treatment that compensates for the disadvantages of the mechanical polishing process. It not only has a smooth surface, but also improves corrosion resistance. Therefore, the purpose of this investigation is to examine the corrosion resistance and electrochemical characteristics in seawater of UNS S31603 with electropolishing process time. The roughness improvement rate after electropolishing was improved by about 78% compared to before polishing, indicating that the electropolishing is effective. As a result of potential measuring of mechanical polishing and electropolishing, the potential of electropolishing was nobler than the mechanical polishing condition. As a result of calculating the corrosion current density after potentiodynamic polarization experiment with electropolishing conditions, the corrosion current density of mechanical polishing was about 6.4 times higher than that of electropolishing. After potentiodynamic polarization experiment with electropolishing conditions, the maximum damage depth of mechanical polishing was about 2.2 times higher than that of electropolishing(7 minutes). In addition, the charge transfer resistance of the specimen electropolished for 7 minutes was the highest, indicating improved corrosion resistance.

• Corrosion Science and Technology
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• 제22권4호
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• pp.257-264
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• 2023

Ti-6Al-4V alloys are mainly used as dental materials due to their excellent biocompatibility, corrosion resistance, and chemical stability. However, they have a low bioactivity with bioinertness in the body. Therefore, they could not directly bond with human bone. To improve their applications, their bone bonding ability and bone formation capacity should be improved. Thus, the objective of this study was to improve the bioinert surface of titanium alloy substrate to show bioactive characteristics by performing surface modification using wollastonite powder. Commercial bioactive wollastonite powder was successfully deposited onto Ti-6Al-4V alloy using a room temperature spray process. It was found that wollastonite-coated layer showed homogeneous microstructure and uniform thickness. Corrosion resistance of Ti-6Al-4V alloy was also improved by plasma electrolytic oxidation treatment. Its wettability and bioactivity were also greatly increased by wollastonite coating. Results of this study indicate that both plasma electrolytic oxidation treatment and wollastonite coating by room temperature spray process could be used to improve surface bioactivity of Ti-6Al-4V alloy substrate.

• Corrosion Science and Technology
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• 제22권5호
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• pp.368-376
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• 2023

Dental Ni-Ti files must ensure stability and resistance to fatigue fracture. DLC and ta-C were coated to remove defects on the surface and ensure stability, and the surface characteristics were investigated. When coated with DLC, it was black, and in case of ta-C coating, it was blue-black. Scratches, which are defects caused by mechanical processing, were formed on the surface of the un-coated Ni-Ti file from the end of the file along the direction of processing, with the Pro-file appearing in the vertical direction and the K-file appearing in the file direction. Scratches were reduced on the coated surface, and the surface roughness was greatly reduced after coating compared to before coating. The un-coated Ni-Ti file had the lowest hardness, the DLC-coated file had the highest hardness, and ta-C showed relatively high hardness. The elastic modulus of the DLC coating film was high, and the ta-C elastic modulus was low. The adhesion of the DLC coating film tended to be higher than that of ta-C, and the wear loss amount of DLC coating of taC was lower. The corrosion potential of the ta-C coating increased significantly, and the corrosion current density decreased.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.172-178
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• 2001

Titanium alloys have lightness, high strength and good corrosion resistant characteristics, and broadly used in manufacturing parts for military and aerospace industries. And these alloys also are recognized for organism materials comparatively and used as fixing ones in the human body. Nevertheless thess alloys have excellent properties such as corrosion resistance, heat resistance, and good tensile strength, it is difficult to machine by traditional methods because of high hardness and chemically activated property. So higher tool wear is expected when cutting by tools. Therefore, it is required nontraditional machining process. And the mechanical characteristics such as surface structure and shape, hardness and bending strength are studied for wire electrical discharge machined and surface ground titanium alloys for various heat-treated conditions.

• 대한기계학회논문집A
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• 제27권2호
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• pp.231-238
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• 2003

The fuel of light water reactor is used for several years under high temperature and pressure, so it needs to be clad with high corrosion resistance material. The cladding materials must have the characteristics of low absorption of a neutron and high corrosion resistance. Zircaloy-2 in Boiling Water Reactor, Zircaloy-4 in Pressurized Water Reactor have been used as cladding materials and Zirlo has been developed as the material for preventing the corrosion. If the fracture of the cladding tube occurs during operation, it will cause the economic loss to shut down and replace the system. So it is needed to evaluate the integrity of the cladding materials. In this paper, the tensile characteristics of the cladding materials were investigated for the basic research of fracture characteristics. Also the residual stress was analyzed to compare the tube type(original type) specimen and the flattened type specimen.

• 한국표면공학회지
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• 제49권3호
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• pp.274-279
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• 2016

Stainless steel is widely used in various industries due to its excellent anti-corrosion characteristics. However, if the stainless steel is exposed to high speed fluid flow and chloride ion in the marine environment, corrosion and cavitation damage occurred on the surface easily. Therefore, to prevent these problems, stabilzed stainless steel is applied to offshore and shipbuilding industries. In this study, stabilized stainless steel specimen was made by 19%Cr-9%Ni with different Nb contents (0.29%, 0.46% and 0.71%). And then, their cavitation characteristics were investigated. As a result, the characteristics of cavitation resistance of stainless steel could be improved by increasing Nb contents.

• 한국표면공학회지
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• 제36권4호
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• pp.339-346
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• 2003

Stainless steel wire has been used in industry, dental and medical parts. Especially, it has been used widely for the dental orthodontic materials. The orthodontic wire requires good mechanical properties, such as elastic strength, combined with a high resistance to corrosion. To increase elastic strength and good corrosion resistance, drawing methods(one-step and two-step drawing) have been used and the electrochemical characteristics of drawed wire have been researched using potentiodynamic method in 0.9％NaCl and field emission scanning electron microscope. The one-step drawed wire showed the formation of rough surface. The hardness and tensile strength of two-step drawed wire increased. For the case of two-step drawed wire, the corrosion resistance and pitting potential increased compared with one-step drawed wire due to the drawing induced small surface roughness, such as scratch. The passivation and active current density decreased as the reduction in area for drawing increased.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1062-1067
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• 2003

In this study, corrosion fatigue characteristics of CF8M and CF8A steel were investigated on the simulated PWR condition(Temp.:$316^{\circ}C$, Pres.: 15:MPa). To make the simulated PWR condition. the special test machine consisted of INSTRON, Autoclave, LOOP and Measurement system was developed. As ${\Delta}K$ is ranged from 11 to $20MPa{\sqrt{m}}$, Crack growth rate of PWR condition is faster than air condition. Above $20MPa{\sqrt{m}}$, the crack growth rate of PWR and air condition is similar. Corrosion fatigue characteristics regardless of the ferrite contents($10{\sim}25wt.%$) is not different. After the test, the fracture surface of specimens was examined. It was difficult to verify the fracture modes such as striation, intergranular crack and cleavage and so on. As the ferrite content of CF8M is increased, the more particles covered fracture surface were peeled.

• 비파괴검사학회지
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• 제20권5호
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• pp.397-401
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• 2000

화력발전 플랜트의 터빈 블레이드(blade) 재료인 12Cr 합금강의 고속 열화 시편에 대한 레일리(Rayleigh) 표면탄성파의 산란과 속도의 주파수 의존특성을 액체/고체 경계 면에서 표면파의 발생기구에 의해 나타나는 후방복사 초음파 세기의 입사각 의존성으로 간접 평가하고 부식피로 특성과 비교 분석하였다. 후방복사 현상이 발생하는 입사각 폭은 부식온도와 반비례하였으며 이는 효과적 부식층의 두께 증가로 설명되었다. 이 프로파일의 폭은 피로시험에서 균열성장 관계식인 파리스(Paris) 법칙의 지수 m과 선형적으로 반비례하여 열화시편의 부식 피로 특성의 비파괴적 평가에 있어 후방복사된 초음파를 이용한 기술이 매우 유용함을 보여 보여주었다.

• Corrosion Science and Technology
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• 제14권6호
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• pp.296-300
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• 2015

ALDC8 (Al-Si-Cu) alloy has been often corroded with pattern of intergranular corrosion in corrosive environments. Thus, in order to improve its corrosion resistance, the effect of annealing heat treatment to corrosion resistance and hardness was investigated with parameters of heating temperatures such as $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$, $400^{\circ}C$ and $500^{\circ}C$ for 1hr. The hardness was varied with annealing temperature and slightly decreased with annealing heat treatment. However, the relation between annealing temperature and hardness agreed not well each other. Corrosion potential was shifted to noble direction and corrosion current density was also decreased with increasing annealing temperature. Moreover, both AC impedance at 10 mHz and polarization resistance on the cyclic voltammogram curve were also increased with increasing annealing temperature. Furthermore, intergranular corrosion was somewhat observed in non heat treatment as well as annealing temperatures at $100^{\circ}C$, $200^{\circ}C$ and $300^{\circ}C$, while, intergranular corrosion was not nearly observed at annealing temperature of $400^{\circ}C$, $500^{\circ}C$. Consequently, it is considered that the annealing heat treatment of ALDC8 alloy may be an available method not only to inhibit its intergranular corrosion but also to improve its corrosion resistance.