• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.137-137
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• 2015

The purposed of this work was to observe hydroxyapatite precipitation phenomena on micro-pore formed Ti-Nb alloy by PEO technique. The Ti-30Nb and Ti-30Ta alloys were remelted at least ten times in order to avoid inhomogeneity, and then cylindrical specimens (diameter 10 mm, thickness 4 mm) were cut by using laser from cast ingots of the Ti alloys. Heat treatment was carried out at $1050^{\circ}C$ for 2 h for homogenization in argon atmosphere. The morphologic change of the alloys were examined by X-ray diffractometer (XRD) and field emission scanning electron microscopy (FE-SEM).

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.138-138
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• 2015

In this study, highly ordered nanotubular surface of Ti-25Ta-xHf alloys for dental applications was researched. Ti-25Ta-xHf alloys were contained from 0% to 15% Hf content. Formation of nanotubular structure was achieved by an electrochemical method in 1M $H_3PO_4$ electrolytes containing 0.8%wt. % NaF.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.185-185
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• 2014

In this study, we investigated surface characteristics of hydroxyapatite coated surface on nano/micro pore structured Ti-35Ta-xNb alloys. This paper was focus on morphology and corrosion resistance of Anodic oxidation. To prepare the samples, Ti-35Ta-xNb (x= 0, 10 wt. %) alloys were manufactured by arc melting and heat-treated for 12 h at $1050^{\circ}C$ in Ar atmosphere at $0^{\circ}C$ water quenching. Micro-pore structured surface was performed using anodization with a DC power supply at 280 V for 3 min, nanotube formed on Ti-35Ta-xNb alloys was performed using DC power supply at 30 V in 60 min at room temperature. Surface morphology and structure were examined by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.186-186
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• 2014

In this study, corrosion behaviors of Ti-xNb alloys for biomaterials. The Ti-xNb binary alloys contained from 10 wt. % to 50 wt. % contents were manufactured by vacuum arc-melting furnace. Microstructures of the alloys were examined by optical microscope (OM) and field emission scanning electron microscope (FE-SEM). In order to identify the phase constitutents of the Ti-xNb alloys, X-ray diffractometer (XRD) with a Cu K radiation was used. The corrosion behaviors were investigated using potentiostat (Model2273,EG & GCo, USA) in NaCl solution at $(36.6{\pm}1.0)^{\circ}C$.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.194-194
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• 2013

In order to investigate nanotube morphology change of Ti-6Al-4V alloys by heat treatments, the Ti-6Al-4V alloys were used in this study. In non-treated Ti-6Al-4V alloy case, nanotubes only exhibited at ${\alpha}$ phase region with dissolved V-oxide area of ${\beta}$ phase. However, in Ti-6Al-4V alloy at $800^{\circ}C$ WQ case, nanotubes exhibited at both ${\alpha}$ and ${\beta}$ phase region. Electrochemical corrosion studies showed that the nanotubular alloy at $800^{\circ}C$WQ possesses slightly higher corrosion resistance than non-treated nanotubular alloy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.63-66
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• 1999

The effects of UV and ozone on the weathershed materials for 5 polymer insulators were investigated. This study was carried by material characterizations such as surface microstructure, thermal property, chemical structure and contact angle. The aged specimens are compared with new ones. In case of UV, the chalking of fillers and cracking of surface were increased with the increase of UV radiation time. In case of ozone, aged specimens are not different from new ones. From this study, It can be concluded that UV has more effect on the surface properties of weathershed materials than ozone.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.4
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• pp.217-222
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• 2009

The effects of severe plastic deformation by equal channel angular pressing (ECAP) and subsequent heat treatment on the low cycle fatigue behaviors of Al-Mg-Si alloy were investigated. The specimens which were peak aged at $175^{\circ}C$ after solution treatment showed cyclic hardening at all strain amplitudes, while the specimens ECAPed after solution treatment showed cyclic softening at all strain amplitudes during fatigue. The specimens aged at $100^{\circ}C$ after ECAP showed slight cyclic hardening. Various changes of cyclic fatigue behavior after severe plastic deformation and/or heat treatment were discussed in terms of the microstructural changes and precipitation conditions.

• Korean Journal of Metals and Materials
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• v.47 no.11
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• pp.694-698
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• 2009

The $Co_{3}Ti$ phase hardens appreciably by the fine precipitation of disordered fcc Co-rich phase upon aging after quenching from solution annealing temperature. Transmission electron microscope (TEM) observations revealed that the precipitates are platelet in shape, lying nearly parallel to the {100} planes of the $Ll_{2}$-ordered matrix, and perfectly coherent with the matrix lattice at the beginning of aging. The high temperature strength increases appreciably with the fine precipitation of disordered Co-rich phase over the whole temperature range investigated. TEM observations of the under-aged and deformed alloys revealed that superdislocations are pinned by precipitates indicating an attractive interaction between dislocations and precipitates. In the over-aged state, thin twins are introduced in the fcc Co-rich precipitates during deformation.

• Nuclear Engineering and Technology
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• v.54 no.4
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• pp.1167-1174
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• 2022

Cast austenitic stainless steels (CASSs) are widely used as structural materials in the nuclear industry. The main drawback of CASSs is the reduction in fracture toughness due to long-term exposure to operating environment. Even though ultrasonic non-destructive testing has been conducted in major nuclear components and pipes, the detection of cracks is difficult due to the scattering and attenuation of ultrasonic waves by the coarse grains and the inhomogeneity of CASS materials. In this study, the ultrasonic signals measured in thermally aged CASS were discriminated for the first time with the simple ultrasonic technique (UT) and machine learning (ML) models. Several different ML models, specifically the K-nearest neighbors (KNN), Support Vector Machine (SVM), and Multi-Layer Perceptron (MLP) models, were used to classify the ultrasonic signals as thermal aging condition of CASS specimens. We identified that the ML models can predict the category of ultrasonic signals effectively according to the aging condition.

• Proceedings of the Korean Society of Crop Science Conference
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• 1999.05a
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• pp.150-151
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• 1999