• 대한기계학회논문집
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• 제18권11호
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• pp.2913-2921
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• 1994

In SMA(shape memory alloy), the degradation by fatigue is one of the most important problems to be overcome, when SMA is used for robot-actuator material. The actuator is operated repeatitively for long time and its repeating operation develops the fatigue degradation of SMA. The fatigue degradation changes the transformation temperature and deformation behavior and results in inaccurate operation control of robot. Accordingly, the changing behavior of transformation temperature and deformation which results from repeating operation is to be investigated in advance and the scheme to resolve those problems have to be made for the design of actuator. In this study, the fatigue tests were carried out on SMA specimens prepared to have different condition of aging time and pre-strain with the direct-current heating-cooling method, which was a general method of operation in robot actuators. The behavior of transformation temperature and deformation were examined and analyzed in each specimen and the study was performed to establish the optimistic manufacturing condition of SMA against the fatigue degradation.

• 한국해양공학회지
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• 제9권1호
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• pp.101-110
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• 1995

In SMA(Shape Memory Alloy), the degradation by fatigue is one of the most important problems to be overcome, when SMA is used for robot-actuator materials. The actuator is operated repetitively for long time and its repeating operation develops the fatigue degradation of SMA. The fatigue degradation changes the transformation temperature and deformation behavior and results in inaccurate operation and deformation which results form repeating operation is to be investigated in advance and the scheme to resolve those problems have to be made for the design of actuator. In this paper, for the improvement of the fatigue degradation by repetive movement and better control of the correct movement by the stability of martensite transformation in the development of Robots actuator, Pre-strain(0, 1.5, 5, 8%) are loaded in the specimens and fatigue testing were carried out by the method of heating and cooling in direct condition. From the results of these experiments, the effect on pre-strain which affect the transformation characteristic and fatigue degradation phenomena were correctly investigated.

• 대한금속재료학회지
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• 제47권3호
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• pp.147-154
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• 2009

The effect of carbon addition on the microstructures and mechanical properties of $Ni_3Al$ and TiAl intermetallic alloys have been characterized. It is shown that carbon is not only an efficient solid solution strengthener in $Ni_3Al$ and TiAl, it is also an efficient precipitation strengthener by fine dispersion of carbide. Transmission electron microscope investigation has been performed on the particle-dislocation interactions in $Ni_3Al$ and TiAl intermetallics containing various types of fine precipitates. In an $L1_2$-ordered $Ni_3Al$ alloy with 4 mol.% of chromium and 0.2~3.0 mol.% of carbon, fine octahedral precipitates of $M_{23}C_6$ type carbide, which has the cube-cube orientation relationship with the matrix, appear during aging. Typical Orowan loops are formed in $Ni_3Al$ containing fine dispersions of $M_{23}C_6$ particles. In the L10-ordered TiAl containing 0.1~2.0 mol.% carbon, TEM observations revealed that needle-like precipitates, which lie only in one direction parallel to the [001] axis of the $L1_0$ matrix, appear in the matrix and preferentially at dislocations. Selected area electron diffraction (SAED) patterns analyses have shown that the needle-shaped precipitate is $Ti_3AlC$ of perovskite type. The orientation relationship between the $Ti_3AlC$ and the $L1_0$ matrix is found to be $(001)_{Ti3AlC}//(001)_{L10\;matrix}$ and $[010]_{Ti3AlC}//[010]_{L10\;matrix}$. By aging at higher temperatures or for longer period at 1073 K, plate-like precipitates of $Ti_2AlC$ with a hexagonal structure are formed on the {111} planes of the $L1_0$ matrix. The orientation relationship between the $(0001)_{Ti2AlC}//(111)_{L10\;matrix}$ is and $[1120]_{Ti2AlC}//[101]_{L10\;matrix}$. High temperature strength of TiAl increases appreciably by the precipitation of fine carbide. Dislocations bypass the carbide needles at further higher temperatures.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.29-29
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• 1999

The synthesis of layered structures on the nanometer scale has become essential for continued improvements in the operation of various electronic and magnetic devices. Abrupt metal-metal interfaces are desired for applications ranging from metallization in semiconductor devices to fabrication of magnetoresistive tunnel junctions for read heads on magnetic disk drives. In particular, characterizing the interface structure between various transition metals (TM) and aluminum is desirable. We have used the techniques of MeV ion backscattering and channeling (HEIS), x-ray photoemission (ZPS), x-ray photoelectron diffraction(XPD), low-energy ion scattering (LEIS), and low-energy electron diffraction(LEED), together with computer simulations using embedded atom potentials, to study solid-solid interface structure for thin films of Ni, Fe, Co, Pd, Ti, and Ag on Al(001), Al(110) and Al(111) surfaces. Considerations of lattice matching, surface energies, or compound formation energies alone do not adequately predict our result, We find that those metals with metallic radii smaller than Al(e.g. Ni, Fe, Co, Pd) tend to form alloys at the TM-Al interface, while those atoms with larger atomic radii(e.g. Ti, Ag) form epitaxial overlayers. Thus we are led to consider models in which the strain energy associated with alloy formation becomes a kinetic barrier to alloying. Furthermore, we observe the formation of metastable fcc Ti up to a critical thickness of 5 monolayers on Al(001) and Al(110). For Ag films we observe arbitrarily thick epitaxial growth exceeding 30 monolayers with some Al alloying at the interface, possible driven by interface strain relief. Typical examples of these interface structures will be discussed.

• JSTS:Journal of Semiconductor Technology and Science
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• 제17권2호
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• pp.277-282
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• 2017

Nickel germanide (NiGe) is one of the most promising alloy materials for source/drain (S/D) of Ge MOSFETs. However, NiGe has limited thermal stability up to $450^{\circ}C$ which is a challenge for fabrication of Ge MOSFETs. In this paper, a novel method is proposed to improve the thermal stability of NiGe using Co interlayer. As a result, we found that the thermal stability of NiGe was improved from $450^{\circ}C$ to $570^{\circ}C$ by using the proposed Co interlayer. Furthermore, we found that current-voltage (I-V) characteristic was improved a little by using Co/Ni/TiN structure after post-annealing. Therefore, NiGe formed by the proposed Co interlayer that is, Co/Ni/TiN structure, is a promising technology for S/D contact of Ge MOSFETs.

• 대한치과교정학회지
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• 제31권2호통권85호
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• pp.271-281
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• 2001

치아에 부착된 bracket이 교정선을 따라 이동할때 필연적으로 bracket과 교정선, 결찰재 사이에 마찰력이 발생된다. 이에 저자는 동일한 bracket내에서 교정선의 종류, 결찰방법, 건조와 타액상태에 따른 마찰력 차이, 타액의 윤활제로서의 기능을 살펴보기 위해 본 연구를 시행하게 되었다. 본 실험에 사용된 bracket은 .18" ${\times}$ .025" slot의 상악 견치용 standard edgewise bracket(RMO. USA)이며, 교정선은 .016" , .016" ${\times}$ .022" 크기의 Cobalt-chromium(Elgiloy : RMO. USA), Nickel-titanium(Ni-Ti) (ORTHOLLOY : Goldstar Cable Co. KOREA), Beta- titanium(TMA : ORMCO Co., USA)의 2가지 형태의 3종을 이용하여 활주할 때의 마찰력을 만능시험기(Instron, M 1000 EC)를 사용하여 계측하여 다음과 같은 결론을 얻었다. 1. 각각의 동일조건하에서 교정선의 재질에 따른 마찰력은 Co-Cr, Ni-Ti, ${\beta}$-Ti순으로 증가하였다. 단, 타액상태에서 elastomeric으로 결찰한 .016" 군에서는 예외이다. 2. 각 조건하(건조/타액상태, .016" /.016" ${\times}$.022" ) 에서 결찰방법에 따른 마찰력은 elastomeric보다 stainless steel결찰에서 더 크게 나타났다(p<0.05). 3. 각각의 교정선과 결찰방법에서 타액 유무에 따른 마찰력은 stainless steel로 결찰한 .016" Co-Cr, Ni-Ti, ${\beta}$-Ti는 타액상태에서 감소하나, stainless steel로 결찰한 .016" ${\times}$.022" Co-Cr, Ni-Ti, ${\beta}$-Ti는 타액상태에서 증가하였다(p<0.05). 4. 각 조건하(건조/타액상태, elastomeric/stainless steel 결찰) .016" 과 .016" ${\times}$.022" 교정선 사이의 마찰력은 .016" ${\times}$.022" 교정선에서 증가하였다(p<0.05).

• 대한치과보철학회지
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• 제31권3호
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• pp.423-446
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• 1993

Titanium and its alloys are finding increasing use in medical devices and dental implants. The strong selling point of titanium is its resistance to the highly corrosive body fluids in which an implant must survive. This corrosion resistance is due to a tenacious passive oxide or film which exists on the metal's surface and renders it passive. Potentiodynamic polarization measurement is one of the most commonly used electro-chemical methods that have been applied to measure corrosion rates. And the potentiodynamic polarization test supplies detailed information such as open circuit, rupture, and passivation potential. Furthermore, it indicates the passive range and sensitivity to pitting corrosion. This study was designed to compare the corrosion resistance of the commonly used dental implant materials such as CP Ti, Ti-6A1-4V, Co-Cr-Mo alloy, and 316L stainless steel. And the effects of galvanic couples between titanium and the dental alloys were assessed for their useful-ness-as. materials for superstructure. The working electrode is the specimen , the reference electrode is a saturated calomel electrode (SCE), and the counter electrode is made of carbon. In $N_2-saturated$ 0.9% NaCl solutions, the potential scanning was performed starting from -800mV (SCE) and the scan rate was 1 mV/sec. At least three different polarization measurements were carried out for each material on separate specimen. The galvanic corrosion measurements were conducted in the zero-shunt ammeter with an implant supraconstruction surface ratio of 1:1. The contact current density was recorded over a 24-hour period. The results were as follows : 1. In potential-time curve, all specimens became increasingly more noble after immersion in the test solution and reached between -70mV and 50mV (SCE) respectively after 12 hours. 2. The Ti and Ti alloy in the saline solution were most resistant to corrosion. They showed the typical passive behavior which was exhibited over the entire experimental range. Therefore no breakdown potentials were observed. 3. Comparing the rupture potentials, Ti and Ti alloy had the high(:st value (because their break-down potentials were not observed in this study potential range ) followed by Co-Cr-Mo alloy and stainless steel (316L). So , the corrosion resistance of titanium was cecellent, Co-Cr-Mo alloy slightly inferior and stainless steel (316L) much less. 4. The contact current density sinks faster than any other galvanic couple in the case of Ti/gold alloy. 5. Ag-Pd alloy coupled with Ti yielded high current density in the early stage. Furthermore, Ti became anodic. 6. Ti/Ni-Cr alloy showed a relatively high galvanic current and a tendency to increase.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 춘계학술대회
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• pp.265-268
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• 2007

플렉서블 태양전지용 연성기판재에는 플라스틱재와 금속재가 있다. 기존의 연성기판인 플라스틱의 경우 열과, 내구성, 화학약품에 약하다는 단점이 있으며, 금속기판은 높은 생산원가, 박판화의 어려움 등의 문제를 안고 있다. 상업적으로 응용되거나 연구에 활용되는 플렉서블 기판재의 단점을 보완할 수 있는 가능성을 밝혀보기 위해 전주성형법으로 합금 금속 포일을 제조하여 상용 금속 기판재의 열팽창 거동과 비교해 보았다. 본 연구에서는 플렉서블 태양전지용으로 적용되거나 연구되고 있는 금속 기판 재료인 두께 50 ${\mu}m$인 Ti, Mo, Al 포일을 선택하여 열팽창거동을 조사하였고 이를 전주성형법으로 제조한 두께 10 ${\mu}m$인 Fe-40Ni, Fe-45Ni, Fe-52Ni 합금포일의 열팽창 거동과 비교 분석하였다. 금속 및 합금 포일의 열팽창 거동은 TMA 장비를 사용하여 조사하였다.

• 연구논문집
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• 통권22호
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• pp.127-139
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• 1992

The mechnial properties such as fracture strength, ductility and fatigue strength of Cu shape memory alloy are lower than those of Ti-Ni SMA, because of their high elastic anisotropy and large grain size. And in order to improve the mechanical property of Cu SMA, some techniques such as casting method by addition of refining element, powder metallurgy and rapid solidification process have been studied on the refinement of the grain size of Cu SMA. This study was carried out to refine the grain size of CuAlNi SMA by applying the melt spinning method. According to this study, the conclusions are as follows; - grain size of the melt-spun ribbon was about $1\mum$ - there was not change in grain size, although increasing of hot pressing temperature -grain size of the hot-extruded specimen was about $30-40\mum$, it is more refiner than that of castings

• Journal of Welding and Joining
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• 제15권4호
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• pp.78-89
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• 1997

This study has evaluated the weld metal solidification cracking behavior of several Ni base superalloys (Incoloy 825, Inconel 718 and Inconel 600). Austenitic stainless steels(304, 310S) were also included for comparison. In addition, a possible mechanism of solidification cracking in the fusion zone was suggested based on the extensive microstructural examinations with SEM, EDAX, TEM, SADP and AEM. The solidification cracking resistance of Ni base superalloys was found to be far inferior to that of austenitic stainless steels. The solidification cracking of Incoloy 825 and Inconel 718 was believel to be closely related with the Laves-austenite (Ti rich in 825 and Nb rich in 718) and MC-austenite eutectic phases formed along the grain boundaries during solidification. Cracking in Inconel 600 was always found along the grain boundaries which were enriched with Ti and P. Further, solidifidcation cracking resistance was dependent not only upon the type of love melting phases but also on the amount of the phases along the solidification grain boundaries.