• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.692-696
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• 2001

Thermo-mechanical behavior and mechanical properties of intelligent polymer matrix composite with SMA fiber are experimentally studied. It is found that increments of compressive thermal strain is observed as the pre-strain and TiNi volume fraction increase. The smartness of the SMA is given due to the shape memory effect of the TiNi fiber which generates compressive residual stress in the matrix material when heated after being prestrained. In the paper, alloy is based on the general purpose commercial code ANSYS. And for the purpose of easy and fast user's analysis, it is developed the Graphical User Interface by using Tcl/Tk language.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.185-189
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• 1999

There has been a considerable attention in Invar alloys because of its low thermal expansion property. A low thermal expansion property of Invar alloys, lower than 10-6 near the room temperature, is attractive for precision machine tools. However, the expansion property of Invar alloys is limited below about 520。K, and mechanical properties are relatively low to apply to machine tools. In order to improve mechanical properties in this alloy, Ti alloy element was added to an invar alloy. Microstructure changes and optimum heat-treatment conditions according to Ti addition were discussed in the Ni38-Mo2-Crl-Fe Invar alloy.

• Transactions of Materials Processing
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• v.20 no.6
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• pp.432-438
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• 2011

A method for estimating the shear spinnability is suggested, and it was applied to sheets of Ti-6Al-4V alloy for estimation of shear spinnability at hot working temperature. The effective working temperature was $850^{\circ}C$ or above. The hot spinning operation was carried out in two steps of shear spinning. The reduction of thickness at the first step was 50% and 45% at the second, and the overall reduction of thickness was 72.4%. The cone spinning process could produce a uniform wall thickness with only a few percent tolerance, proving itself appropriate for making cones of Ti-6Al-4V alloy with uniform wall thickness.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.523-524
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• 2006

The $TiB_2$ dispersion strengthened copper alloy was attracted as thermal and electrical functional material for the high mechanical strength, high thermal stability and good conductivity of $TiB_2$. In the present study, the focus is on the synthesis of $TiB_2$ dispersed copper alloy by spark plasma sintering process using copper oxide and titanium diboride as raw materials. The mechanical, thermal and electrical properties of sintered bodies were discussed with the sintering parameters, and developed microstructure and phase of sintered bodies.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.158-163
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• 2009

Titanium alloy sheets have excellent specific strength and corrosion resistance as well as good performance at high temperature. Recently, titanium alloys are widely employed not only aerospace parts but also bio prothesis and motorcycle. However, due to the low formability and large spring back at room temperature, titanium alloy sheets were usually formed by slow forming or hot forming with heating die and specimen. In the sheet metal forming area, FE simulation technique to optimize forming process is widely used. To achieve high accuracy FE simulation results, Identification of material properties and deformation characteristic such as yield function are very important. In this study, uniaxial tensile and biaxial tensile test of Ti-6Al-4V alloy sheet with thickness of 1.0mm were performed at elevated temperature of 873k. Biaxial tensile tests with cruciform specimen were performed until the specimen was breakdown to characterize the yield locus of Ti-6Al-4V alloy sheet. The experimental results for yield locus are compared with the theoretical predictions based on Von Mises, Hill, Logan-Hosford, and Balat's model. Among these Logan-Hosford's yield criterion well predicts the experimental results.

• Journal of Periodontal and Implant Science
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• v.30 no.1
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• pp.187-203
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• 2000

The precipitation of calcium phosphate on implant surface has been known to accelerate osseointegration and to enhance osseous adaptation. The present study was performed to examine whether the precipitation of calcium phosphate on Ti-6Al-4V alloy could be affected by the immersion in NaOH solution and heat treatment. Ti-6Al-4V alloy plates of $15{\times}3.5{\times}1mm$ in dimension were polished sequentially from #240 to #2,000 emery paper and one surface of each specimen was additionally polished with $0.1{\mu}m$ alumina paste. Polished specimens were soaked in various concentrations of NaOH solution(0.1, 1.0, 3.0, 5.0, 7.0, 10.0 M) at $60^{\circ}C$ for 24 hours for alkali treatment, and 5.0 M NaOH treated specimens were heated for 1 hour at each temperature of 400, 500, 600, 700, $800^{\circ}C$. After the alkali and heat treatments, specimens were soaked in the Hank's solution with pH 7.4 at $36.5^{\circ}C$ for 30days.The surface ingredient change of Ti-6Al-4V alloy was evaluated by thin-film X-ray diffractometer(TF-XRD) and the surface microstructure was observed by scanning electron microscope(SEM), and the elements of surface were analyzed by X-ray photoelectron spectroscopy(XPS). The results were obtained as follows ; 1. The precipitation of calcium phosphate on Ti-6Al-4V alloy was accelerated by the immersion in NaOH solution and heat treatment. 2. In Alkali treatment for the precipitation of calcium phosphate on Ti-6Al-4V alloy, the optimal concentration of NaOH solution was 5.0 M. 3. In heat treatment after alkali treatment in 5.0 M NaOH solution, the crystal formation on alloy surface was enhanced by increasing temperature. In heat treated alloys at $600^{\circ}C$, latticed structure and prominences of calcium phosphate layer were most dense. On heat treated alloy surface at the higher temperature(${\geq}700^{\circ}C$), main crystal form was titanium oxide rather than apatite. The above results suggested that the precipitation of calcium phosphate on the surface of Ti-6Al-4V alloy could be induced by alkali treatment in 5.0 M-NaOH solution and by heat treatment at $600^{\circ}C$.

• The Journal of the Korea Contents Association
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• v.14 no.4
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• pp.237-242
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• 2014

In this study, surface characteristics and corrosion behaviors have been investigated in addition to Zr elements on the low elastic modulus Ti-30Ta alloy. Low elastic modulus Ti-30Ta-xZr(x : 3, 7 and 15 wt %) alloys were prepared by arc melting and then heat treated at $1000^{\circ}C$ for 24 hrs in an argon atmosphere. Microstructures of the alloys were examined by field emission scanning electron microscope(FE-SEM) and X-ray diffractometer(XRD). Electrochemical experiments were performed using a conventional three-electrode configuration with a sample working electrode, a high density carbon counter electrode and a saturated calomel reference electrode. According to the result of polarization behavior in the Ti-30Ta-xZr alloys, the current density of homogenized Ti-30Ta-15Zr in the passive region was lower than the other alloys.

• Journal of Electrochemical Science and Technology
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• v.7 no.4
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• pp.269-276
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• 2016

Carbon-supported ordered Pt-Ti alloy nanoparticles were prepared as a durable and efficient oxygen reduction reaction (ORR) electrocatalyst for polymer electrolyte membrane fuel cells (PEMFCs) via wet chemical reduction of Pt and Ti precursors with heat treatment at $800^{\circ}C$. X-ray diffraction analysis confirmed that the prepared electrocatalysts with Ti precursor molar compositions of 40% (PtTi40) and 25% (PtTi25) had ordered $Pt_3Ti$ and $Pt_8Ti$ structures, respectively. Comparison of the ORR polarization before and after 1500 electrochemical cycles between 0.6 and 1.1 V showed little change in the ORR polarization curve of the electrocatalysts, demonstrating the high stability of the PtTi40 and PtTi25 alloys. Under the same conditions, commercial carbon-supported Pt nanoparticle electrocatalysts exhibited a negative potential shift (10 mV) in the ORR polarization curve after electrochemical cycling, indicating degradation of the ORR activity.

• 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 Mechanical Engineers A
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• v.26 no.9
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• pp.1787-1794
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• 2002

TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress in the matrix using shape memory effect. In order to generate compressive residual stress in TiNi/Al6061 shape memory alloy(SMA) composite, 1, 3 and 5% pre-strains were applied to the composite in advance. It was also evaluated the effect of compressive residual stress corresponding to the pre-strain variation and the volume fraction of TiNi alloy. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain in TiNi/Al6061 SMA composite. The results of the microscopic damage evaluation of TiNi/Al6061 SMA composite under various pre-strain using AE technique can be divided into three stage corresponding to the AE signals. AE counts and events were useful parameters to evaluate the fracture mechanism according to the variation of pre-strain. In addition, two dimensional AE source location technique was applied for monitoring the crack initiation and propagation in composite.