• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.3
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• pp.101-105
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• 2006

We fabricated the nano $TiN_x$ by making of reaction between titanium powder and $Si_3N_4$ during planetary milling. The $TiN_x$ powder was sintered by spark plasma sintering machine after mixing with 50 wt% of titanium powder, and the sintered body was heat-treated at $850^{\circ}C$ in order to investigate its hardness property at the elevated temperature. We analyzed crystal structure by XRD. We observed the peaks of $TiN_{0.26}$ and TiN after 10 hours milling, and we observed TiN peak mainly after 20 hours milling. The reacted particle size distribution was investigated by FE-SEM. Increase of milling time, the size of reacted particles was decreased and the $10{\sim}20nm$ size of $TiN_x$ on the surface of titanium and $TiN_x$ was observed after 20 hours milling. The micro-Vickers hardness of mixed sintered body was about $1050kgf/mm^2$.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.877-885
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• 2013

A seawater pipe of the engine room in the ships is being surrounded with severely corrosive environments caused by fast flowing of the seawater, containing aggressive chloride ion and high conductivity etc.. Therefore, the leakage of the seawater from its pipe have been often occurred due to its local corrosion by aggressive chloride ions. Subsequently, its leakage area is usually welded by AC shielded metal arc welding with various electrodes. In this study, when the sea water pipe is welded with several types of electrodes such as E4301, E4311, E4313 and E4316, a difference of the corrosion resistance on the welding metal zones was investigated using an electrochemical method, observing microstructure, measuring polarization behaviors and hardness. The weld metal zone welded with E4313 electrode exhibited the lowest value of hardness compared to other weld metal zones. In addition, its zone indicated also the best corrosion resistance than those of other weld metal zones. Furthermore, all of the weld metal zones revealed a relatively better corrosion resistance than those of the base metal zones. and also showed higher hardness than the base metal zones.

• Journal of Conservation Science
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• v.34 no.5
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• pp.433-442
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• 2018

In this study, metal properties were compared by preparingthree iron knives from steel ingots produced via traditional iron-making, and ingot which jointed the steel of modern times. Metal microscope and SEM-EDS analysis revealed fine ferrite and pearlite structures of the hypo-eutectoid steel of Fe-C alloys. All samples also exhibited martensite on the blade of the knife. By Vicker's hardness analysis, the hardness of the sand iron knife (K1) was 533.38 HV, sand iron-nickel steel knife (K3) was 514.8 HV, and sand iron-carbon steel knife (K2) was 477.02 HV. The mass reduction due to wear was 0.058% for K1, 0.059% for K3, and 0.144% for K2. EPMA(Electron probe micro-analyzer) analysis of the surface pattern of the specimens confirmed that the patterns were exposed due to differences in the content of C or the chemical composition. Additional research on heat treatment processes is needed to increase the abrasion resistance of blades. Traditional steel ingots could produce high-quality steel if combined with nickel steel.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.9
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• pp.4185-4190
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• 2013

We executed the property changes of the sintered MgO (99.9% purity, 300nm size) specimens with addition to CaO content of 0.00wt%, 0.25wt%, and 0.50wt%, processed at 7GPa, for 5min, 600~$800^{\circ}C$. To investigate the micro-structure and physical property changes of the sintered MgO(-CaO), we employed a scanning electron microscopy(SEM), X-ray diffractomerty(XRD), Vickers hardness, and density. The SEM result showed that MgO powder of 300nm size was changed into sintered structure of 520nm by high pressure and low temperature sintering, regardless of the CaO contents. According to the XRD analysis, no CaO phase observed, while MgO peaks shift indicated the existence of CaO in the MgO matrix. The Vickers hardness result showed that hardness of sintered MgO-CaO increased by 12% compared pure MgO under the same temperature conditions. It implied that we can obtain the same hardness with $100^{\circ}C$ lowered sintering temperatures by addition of CaO. The density results showed that it was possible to obtain density of 98%, which is 5% greater than that of pure MgO at low temperature of $600^{\circ}C$.

• Journal of Dental Rehabilitation and Applied Science
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• v.34 no.4
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• pp.290-296
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• 2018

Purpose: The aim of this study was to evaluate the polymerization ability of resin-based materials used for teeth splinting according to the thickness of cure. Materials and Methods: For this study, the Light-Fix and G-FIX developed for resinous splinting materials and the G-aenial Universal Flo, the high-flowable composite resin available as restorative and splinting material, were used. Ten specimens of the thickness of 2, 3, 4 and 5 mm and 5 mm in diameter for each composite resin (total 120) were prepared. The microhardness of top and bottom surfaces for each specimen was measured by the Vickers hardness testing machine. The polymerization ability of the composite resin for each thickness was statistically analyzed using independent T-test at a 0.05 level of significance. Results: There was no difference of polymerization ability regardless of the thickness in the Light-Fix and G-FIX. The G-aenial Universal Flo showed significantly low polymerization ability from the thickness of the 3 mm (P < 0.05). Conclusion: The Light-Fix and G-FIX, which are resin-based materials used for teeth splinting, are expected to be suitable for light curing up to 5 mm in thickness.

• Journal of the korean academy of Pediatric Dentistry
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• v.46 no.2
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• pp.226-232
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• 2019

The purpose of this study was to investigate the effect of adding a protective coating on the microhardness and wear resistance of glass ionomer cements (GICs). Specimens were prepared from GIC and resin-modified GIC (RMGI), and divided into 3 groups based on surface protection: (1) no coating (NC), (2) Equia coat coating (EC), and (3) un-filled adhesive coating (AD). All specimens were then placed in distilled water for 24 h. Surface hardness (n = 10) was evaluated on a Vickers hardness testing machine. Wear resistance (n = 10) was evaluated after subjecting the specimen to thermocycling for 10,000 cycles using a chewing simulator. Data were analyzed using a one-way ANOVA and the Kruskal-Wallis test. Surface hardness was highest in the NC groups, followed by the EC and AD groups. The wear depth of GI + NC was significantly higher than that of all RMGI groups. EC did not significantly lower the wear depth compared to AD. Based on these results, it was concluded that although EC does not increase the surface microhardness of GIC, it can increase the wear resistance.

• Journal of Korea Foundry Society
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• v.41 no.2
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• pp.127-131
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• 2021

Based on its good compatibility with high-temperature environments, the Ti-48Al-2Cr-2Nb alloy is used for high-temperature materials of industrial equipment. In this study, a Ti-48Al-2Cr-2Nb alloy turbocharger turbine wheel was fabricated by a vacuum centrifugal casting method. The conditions that prevent misrun defects of the turbocharger turbine wheel blade from centrifugal casting using alumina molds were investigated. The microstructure of the alloy prepared by vacuum centrifugal casting was studied by means of optical microscopy (OM), with a micro-Vickers hardness analyzer (HV), by X-ray diffraction (XRD) and by SEM-EDS. The HV and SEM-EDS examinations of the as-cast Ti-48Al-2Cr-2Nb alloy showed that the thickness of the oxide layer (α-case) was typically less than 50 ㎛. At a high preheating temperature of 1,100℃, a moderate RPM of 260, and with an alumina mold with a large gate size, there were almost no misrun defects. Therefore, it was confirmed that a Ti-48Al-2Cr-2Nb alloy turbocharger turbine wheel with fewer misrun defects could be achieved through a high preheating temperature, a moderate RPM, a large gate size and an alumina mold to suppress the formation of alpha-case components.

• Journal of the korean academy of Pediatric Dentistry
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• v.44 no.4
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• pp.412-418
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• 2017

During orthodontic treatment, formation of white spot lesions (WSLs) around brackets has long been recognized as a potential risk. This study performed to investigate effect of preventing enamel demineralization and remineralization by application of fluoride-containing orthodontic primer. Fifty extracted bovine incisors teeth were randomly allocated to 3 groups: (I) Non-preparation specimens, (II) Application of Light Bond$^{TM}$ as fluoride containing orthodontic primer, (III) Application of Transbond$^{TM}$ XT Primer as traditional orthodontic primer without fluoride. Each group is demineralized under artificial carious solution. The demineralization pattern was evaluated using a Q-ray view, Vickers hardness test and polarized light microscope. The remained primer was calculated as 35 - 50%. The highest surface microhardness was shown on Light Bond$^{TM}$ surface. There were statistically significant differences in Vickers microhardness number between adjacent areas of Light Bond$^{TM}$ and non-prepared area. There was almost no demineralization of the enamel surface under the Light Bond$^{TM}$. At the adjacent site of Light Bond$^{TM}$, the shallow caries pattern and remineralization appearance were also observed. These results suggest that the use of fluoride-containing primers may be useful for bracket attachment to reduce enamel demineralization during orthodontic treatment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.3
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• pp.267-272
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• 2011

We analyzed the wear characterization of $Si_3N_4$ ceramics according to the amount of added $SiO_2$ nanocolloid. The test specimen was prepared by hot-press sintering at 35 MPa and 2123 K in an $N_2$ gas atmosphere for 1 h. A wear test was performed with a block-on-ring tester, and the test conditions were as follows: (1) the ring with a diameter of 35 mm had a rotational speed of 50 rpm; (2) the load was 9.8 N; and (3) the temperature was $25^{\circ}C$. The test results show that $Si_3N_4$ ceramics have a friction coefficient of about 1.0 and a wear loss of about 0.02 mm. Of the specimens used this study, the test specimen with 1.3 wt% of added $SiO_2$ nanocolloid has the best wear resistance because it has the lowest friction coefficient and the smallest wear loss. This specimen also has the highest Vickers hardness and bending strength. In this study, the friction coefficient is inversely proportional to the hardness and bending strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.603-611
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• 2020

A porous material which can contain liquid perfume was manufactured by adding 1~4 wt% of polysiloxane into a composite containing 20 ㎛ Ag powder and 30 wt% of 53 ㎛ salt, sintering for 60 min at 750℃, and melting salt selectively. The changes in pore, hardness, and microstructure were confirmed according to the polysiloxane content both before and after sintering. The manufactured silver liquid container was formed with open pores both before and after sintering, and the container shrunk by 2~7 % in both perpendicular and parallel directions after sintering. Vickers hardness was increased after sintering and was doubled when 2 wt% of polysiloxane was added. In case of the microstructure, the surface condition of the silver liquid container became darker according to the polysiloxane content, and the pore size was decreased from 50 ㎛ to under 10 ㎛. The composition distribution result revealed an even distribution when 2 wt% of polysiloxane was added but uneven distribution when over 3 wt% of polysiloxane was added due to decreased hardness by cluster. Therefore, the addition of an appropriate amount of 2 wt% polysiloxane reinforced the porous silver with open pores to offer application for jewelry usage.