• 한국정밀공학회지
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• 제19권10호
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• pp.52-59
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• 2002

The thermo-mechanical characteristics of high temperature NITINOL shape memory alloy were evaluated using DSC with small samples and DMA with three-point bending specimens. The shape memory alloy of 54.4Ni/45.5Ti wt.% was used so that the phase transformation temperatures were in the range of 50~11$0^{\circ}C$. Two types of sample were tested in the experiments corresponding to as-received and annealed conditions. Simple beam bending theory was used to calculate the dynamic moduli of the shape memory alloy. According to the results, a large discrepancy in transformation temperatures was found between DSC and DMA techniques. Annealing treatment was found to suppress the R-phase transformation during cooling and the secondary plateau in the austenite transformation. Such a heat treatment was also significantly influenced to raise the transformation temperatures and the moduli of the shape memory alloy.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.426-429
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• 2003

In this study, phase transformation characteristics of Nitinol shape memory alloy with 54.5wt%Ni-45.5wt%Ti were investigated by varying with annealing treatment and cutting conditions through DSC(differential scanning calorimetry). Annealing treatment conditions were considered as heat treated time of 5 min, 15 min, 30 min, and 45 min, heat treated temperature of 40$0^{\circ}C$, 50$0^{\circ}C$, 5$25^{\circ}C$, 55$0^{\circ}C$, 575$^{\circ}C$, $600^{\circ}C$, $700^{\circ}C$, 80$0^{\circ}C$, and 90$0^{\circ}C$, and environmental condition of heat treatment under vacuum or air. Cutting conditions were considered as no cutting, one side cutting, and two side cutting. Tensile test was also conducted on Nitinol shape memory alloy to investigate thermomechanical characteristics by varying with annealing heat treatment histories. According to the results, annealing treatment and cutting conditions were found to significantly affect on phase transformation and thermomechanical characteristics of Nitinol shape memory alloy.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.49-54
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• 2007

Electropolishing, the anodic dissolution process without contact with tools, is a surface treatment method to make a surface planarization using an electrochemical reaction with low current density. Nitinol is a metal alloy composed of Ni and Ti around 50% respectively which has shape memory effect. Nitinol can be put various applications which require purity and high pricision surface of products. The aim of this study is to investigate the characteristic of electropolishing effect for nitinol workpieces. In order to analyze the characteristics of electropolishing effect, surface roughness and micro-burr size were measured in terms of machining conditions such as current density, machining time and electrode gap. The tendencies about improvement of surface roughness and deburring effect by electropolishing for nitinol workpieces were determined.

• International Journal of Korean Welding Society
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• 제3권1호
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• pp.39-44
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• 2003

The welded specimens were made by butt welding of the 2 wires of 50mm length using the pulsed YAG laser. The laser welded wires were tested for investigating the shape memory effect and the ability of super elasticity. The fatigue properties of the welded wires were investigated using the rotary bending fatigue tester specially designed for wires. Moreover, the effect of defocusing distance during laser welding on the static and fatigue properties was Investigated. The shape memory effect and super elasticity of the laser welded wires were approximately identical with that of base metal at the test temperature below 353K. However, the welded wires were broken within elastic limit at the test temperature above 353k. Under the cyclic bending loading conditions, the welded wires could be useful only below the elastic limit, while the base metal had sufficient fatigue life even the stress induced M-phase region. The fatigue strength of the welded wires was about half of that of the base metal. The deterioration of the static and fatigue properties in the welded wires was proven to be from the large difference of the transformation behavior between the base metal and welded part that is caused by vaporization of Ni-content at the welded part during the welding process. The defocusing distance below 3mm acted more largely on lowering the strength of the welded wires than that of 6mm or 8mm.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.139-144
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• 2002

Ti-50.9at%Ni wires were welded using pulsed YAG laser. The laser welded wires were tested for investigating the shape memo교 effect and the ability of super elasticity. The fatigue properties of the welded wires were investigated using the rotary bending fatigue tester specially designed for wires. Moreover, the effect of defocusing distance during laser welding on the static and fatigue properties was investigated. The shape memory effect and super elasticity of the laser welded wires were approximately identical with that of base metal at the test temperature below 353K. However, the welded wires were broken within elastic limit at the test temperature above 353k. Under the cyclic bending loading conditions, the welded wires could be useful only below the elastic limit, while the base metal had sufficient fatigue life even the stress induced M-phase region. The fatigue strength of the welded wires was about half of that of the base metal. The deterioration of the static and fatigue properties in the welded wires was proven to be from the large difference of the transformation behavior between the base metal and welded part that is caused by vaporization of Ni-content at the welded part during the welding process. The defocusing distance below 3mm acted more largely on lowering the strength of the welded wires than that of 6mm or 8mm.

• 한국진공학회지
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• 제16권2호
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• pp.116-121
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• 2007

Ti-50 at. % Ni 합금 타깃으로 PLD(pulsed laser deposition)방법을 사용하여 TiNi 형상기억합금 박막을 제작하였다. Ar분위기(200 mTorr)와 고진공분위기($5{\times}10^{-6}\;Torr$)에서 제작한 TiNi 박막의 조성 및 결정성의 변화를 조사했으며, 박막의 조성은 에너지 분산 엑스선 분광 분석(EDXS)을 이용하여 조사하였고, 박막의 결정성은 엑스선 회절장치(XRD)를 이용하여 조사하였다. 박막의 조성은 기판과 타깃의 거리에 의존되었지만, 기판의 온도와는 무관함을 알 수 있었으며, Ar 분위기에서 플룸 안쪽에 기판이 위치하였을 때 조성 제어가 용이함을 알 수 있었다. 또한, Ar 가스 분위기에서 증착 된 TiNi 박막은 고진공분위기에서 증착된 박막보다 더 낮은 온도(약 $400^{\circ}C$)에서 in situ로 결정화됨을 알 수 있었다. 이들 결과는, PLD방법으로 TiNi 형상기억합금 박막을 제작할 때 분위기 가스의 압력이 결정화 온도를 낮추어 주는 중요한 역할을 할 수 있음을 시사한다.

• 한국산업안전학회:학술대회논문집
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• 한국안전학회 2003년도 추계 학술논문발표회 논문집
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• pp.107-112
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• 2003

형상기억합금(shape memory alloy; SMA)은 소성가공을 통하여 원하는 형태로 변형시킨 이후에도(현재로서는 최대 10%미만의 변형) 일정조건의 열을 가하면 원래의 형상으로 복원되는 합금을 말한다. 형상기억효과는 고상(solid state)에서의 금속조직이 오스테나이트(austenite: 이하 A 또는 B2상)로부터 마르텐사이트(martensite: 이하 M 또는 B19'상)로, 다시 역으로 마르텐사이트에서 오스테나이트로의 변태에 기인되는 것으로 밝혀지고 있으며 이러한 변태는 온도유기변태(temperature induced transformation)와 응력유기변태(stress induced transformation)로 분류할 수 있다.(중략)