• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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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.

• Smart Structures and Systems
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• v.13 no.3
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• pp.353-374
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• 2014

Recent studies were dedicated to the realization of measurements on stay-cable samples of different geometry and static conditions as available at several facilities. The elaboration of the acquired data showed a a satisfactory efficacy of the dampers made of NiTi wires in smoothing the cable oscillations. A further attempt to investigate the applicability of the achieved results beyond the specific case-studies represented by the tested cable-stayed samples is herein pursued. Comparative studies are carried out by varying the diameter of the NiTi wire so that similar measurements can be taken also from laboratory steel cables of reduced size. Details of the preparation of the Ni-Ti wires are discussed with particular attention being paid to the suppression of the creep phenomenon. The resulting shape of the hysteretic cycle differs according to the wire diameter, which affects the order of the fitting polynomial to be used when trying to retrieve the experimental results by numerical analyses. For a NiTi wire of given diameter, an estimate of the amount of dissipated energy per cycle is given at low levels of maximum strain, which correspond to a fatigue fracture life of the order of millions of cycles. The dissipative capability is affected by both the temperature and the cycling frequency at which the tests are performed. Such effects are quantified and an ageing process is proposed in order to extend the working temperature range of the damper to cold weathers typical of the winter season in Northern Europe and Canada. A procedure for the simulation of the shape memory alloy behavior in lengthy cables by finite element analysis is eventually outlined.

• Journal of the Korean Society of Safety
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• v.19 no.4 s.68
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• pp.1-7
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• 2004

This study investigated the effects of aging on the transformation behavior of $Ti-50.1at\%$ Ni alloy by means of differential scanning calorimetry. It was found that aging in the temperature range of $350^{\circ}C\~550^{\circ}C$ induced complex transformation behavior, involving the R-phase and multiple-stage martensitic transformation. Usually aged Ni-rich NiTi alloys undergo martensitic transformation on cooling from high temperatures in two step : B2 to R and then R to Bl9'(normal behavior). But under certain ageing conditions, the transformation can also occur in three or more step(unusual multiple step behavior). In the present study we use differential seaming calorimetry(DSC) for a systematic investigation of the evolution of transformation behavior with ageing temperature and time.

• Transactions on Electrical and Electronic Materials
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• v.13 no.1
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• pp.19-22
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• 2012

Transformation behavior of rapidly solidified Ti-47.3Ni (at%) alloy ribbons and thermal stability of the R phase in the ribbons were investigated by means of differential scanning calorimetry (DSC), X-ray diffraction, and transmission electron microscopy. Rapidly solidified Ti-47.3Ni alloy ribbons showed the two-stage B2-R-B19' martensitic transformation behavior. The B2-R transformation in the ribbons was observed even after annealing at 1,223 K, which was attributed to the fact that a specific orientation relationship between $Ti_2Ni$ and matrix in the ribbons is maintained after annealing at 1,223 K. The DSC peak temperature of the B2-R transformation ($T_R^*$) decreased with raising annealing temperature, which was attributed to the increased volume fraction of $Ti_2Ni$, thus causing an increased Ni content in the matrix.

• Smart Structures and Systems
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• v.6 no.1
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• pp.73-85
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• 2010

The potential offered by the thermo-mechanical properties of shape memory alloys (SMA) in structural engineering applications has been the topic of many research studies during the last two decades. The main issues concern the long-term predictability of the material behaviour and the fatigue lifetime of the macro structural elements (as different from the one of wire segments). The laboratory tests reported in this paper are carried out on bar specimens and they were planned in order to pursue two objectives. First, the creep phenomenon is investigated for two different alloys, a classical Ni-Ti alloy and a Cu-based alloy. The attention is then focused on the Cu-based alloy only and its fatigue characteristics at given temperatures are investigated. Stress and thermal cycles are alternated to detect any path dependency.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.6
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• pp.368-374
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• 2009

Nickel titanium shape memory alloys (NiTi) have been investigated for applications in the biomedical industry. However, little is known about the influences of surface modifications on the propertise of these alloys. The effect of electropolishing and heat treatments was found to exhibit significant surface roughness. Change of phase was B2, r-phase and B19' by heat treatments. In this study, effect of the electropolishing conditions on surface roughness is investigated in Ni-Ti alloys (Nitinol). Variation in phases with heat treatment temperature is investigated for a Ni-Ti alloy by X-ray diffraction and DSC. Characteristic of the microstructure have been observed by SEM. Surface roughness have been measured by AFM. The results clearly show that significant different in surface property to heat treated at $500^{\circ}C$ (R-phase). $TiO_2$ phases preciritated all of the specimens. It is not good effect of surface roughness because made to surface relief. The surface roughness appears to be important in the property of Ni-Ti alloys for biomedical applications.

• Journal of Sensor Science and Technology
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• v.7 no.4
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• pp.285-292
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• 1998

Shape Memory Alloy(SMA) has been used in many engineering fields because of its good characteristics of actuator. For example, SMA wire can be embedded easily in the polymer composite laminate and then be used as actuator for structural control. Since the strain have a significant influence on the electrical resistance of SMA wire, It is a possible to use the SMA wire as a sensor of such physical quantities. In this study, the possibility for the application of Ni-Ti SMA wire as a sensor embedded within a composite laminate is investigated.

• Korean Journal of Materials Research
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• v.22 no.2
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• pp.66-70
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• 2012

Ti-Ni alloys are widely used in numerous biomedical applications (e.g., orthodontics, cardiovascular science, orthopaedics) due to their distinctive thermomechanical and mechanical properties, such as the shape memory effect, superelasticity and low elastic modulus. In order to increase the biocompatibility of Ti-Ni alloys, many surface modification techniques, such as the sol-gel technique, plasma immersion ion implantation (PIII), laser surface melting, plasma spraying, and chemical vapor deposition, have been employed. In this study, a Ti-49.5Ni (at%) alloy was electrochemically etched in 1M $H_2SO_4$+ X (1.5, 2.0, 2.5) wt% HF electrolytes to modify the surface morphology. The morphology, element distribution, crystal structure, roughness and energy of the surface were investigated by scanning electron microscopy (SEM), energy-dispersive Xray spectrometry (EDS), X-ray diffractometry (XRD), atomic force microscopy (AFM) and contact angle analysis. Micro-sized pores were formed on the Ti-49.5Ni (at%) alloy surface by electrochemical etching with 1M $H_2SO_4$+ X (1.5, 2.0, 2.5) wt% HF. The volume fractions of the pores were increased by increasing the concentration of the HF electrolytes. Depending on the HF concentration, different pore sizes, heights, surface roughness levels, and surface energy levels were obtained. To investigate the osteoblast adhesion of the electrochemically etched Ti-49.5Ni (at%) alloy, a MTT test was performed. The degree of osteoblast adhesion was increased at a high concentration of HF-treated surface structures.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.1
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• pp.16-20
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• 2008

This paper presents the construction of micro tool clamping device using a Ni-Ti shape memory alloy(SMA) ring. Clamping force of the device is produced by elastic force of the SMA reverted to its original shape in normal temperature. Phase transformation of the SMA was realized by temperature control using a peltier element. Prototype of the SMA tool clamping device was fabricated and examined its clamping force and clamping/unclamping operation.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.1
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• pp.9-15
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• 2002

Deformation behavior of nickel-rich Ti-51.5at.%Ni single crystals was investigated over a wide range of temperatures(77 to 440K) and strain levels(up to 9%) in compression. These alloys combined superior strength with wide range of pseudoelasticity temperature interval(~200K). The slip deformation in [001] orientation did not occur due to the prevailing slip system, and consequently, exhibited pseudoelastic deformation at temperatures ranging from 77 to 283K and 273 to 440K for the solutionized and over-aged cases, respectively. The critical transformation stress levels were in the range of 800 to 1800MPa for the solutionized case, and 200 to 1000MPa for the over-aged case depending on the temperature and specimen orientation. These stress levels are considerably higher compared to these class of alloys having lower Ni contents. The maximum transformation strains, measured from incremental straining experiments in compression, were lower compared to the phenomenological theory with Type II twinning. A compound twinning model depending on the successive austenite(B2) to intermediate phase(R) to martensite(B19') transformation predicts lower transformation strains compared to the Type II twinning case.