• Proceedings of the Korean Environmental Sciences Society Conference
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• 2001.05a
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• pp.236-237
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• 2001

In this study, experiments were carried out to measure the variations in the corrosion potential and current density of polarization curves with amorphous $Fe_{70}Cr_5Si_{10}B_{15}$ and $Co_{70}Cr_5Si_{10}B_{15}$ alloy ribbon. The results were particularly examined to identify the influences of corrosion potential including various conditions such as hydrochloric acid, temperature, salt, pH, and oxygen. The optimum conditions were established with variations including temperature, salt, pH, oxygen, corrosion rate, and resistance of corrosion potential. The mass tranfer coefficient(${\alpha}$) value was determined with the Tafel's slope for the anodic dissolution based on the polarization effect with optimum conditions. The second anodic current density peak and maximum passive current density were designated as the critical corrosion sensitivity($I_{r}/I_{f}$).

• Journal of the Korean Society for Precision Engineering
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• v.12 no.7
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• pp.178-188
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• 1995

A study on the temperature distribution of tungsten carbide alloy steel(WC-Co) in surface grinding was conducted to improve the surface finish and to find optimum grinding conditions which would lead to efficient grinding operation by theoretical finite element method analysis and experimental test of workpiece under various conditions. Based on the comparixion of test results and FEM analysis data, it is concluded that the FEM computer simulation of heat transfer is useful in predicting the temperature distribution of test material that the increase of temperature is more infuleneced by the grinding depth than the grinding speed. And that the grinding energy flux of dey grinding is 4 to 6 time greater than wet grinding regardless of grinding speed and finally that the heat transfer does not take place in depth deeper than 3mm from the grinding surface.

• Journal of Power System Engineering
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• v.5 no.2
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• pp.63-70
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• 2001

To obtain the optimal condition of heat treatment of wear-resistant alloy, hardness and Charpy V-notch test have been performed with Co-based Stellite No.4, No.6 and Tribaloy 800 alloys, following by heat treatment at the various conditions. Heat treatment at $1250^{\circ}C$ for 1 hours caused the as-casted Tribaloy 800 with FCC crystal structure to transform to HCP structure and lamellar eutectic structure was disappeared, which did not influence on the hardness. Aging at $800^{\circ}C$ for 20 hours, following by $1250^{\circ}C$ for 2 hours heat treatment has enhanced hardness significantly, which is due to the precipitation of large amounts of Laves-phase. The hardness of Stellite alloys was increased by the aging at $800^{\circ}C$ to 5 hours, and was nearly constant by the aging over 5 hours. The toughness of Stellite alloys was a few influenced by the aging treatment.

• Journal of Welding and Joining
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• v.25 no.1
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• pp.30-36
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• 2007

A joining of dissimilar metal combination faces significant problems such as poor strength and cracking associated with brittle intermetallic compounds(IMC) formed. An application of laser allows low heat input; leading to less dilution and smaller heat affected zone. The $CO_2$ laser overlay was conducted on an AC2B alloy with feeding Fe-based powders. The overlay area was significantly influenced from the travel velocity rather than the powder feeding rate. The interface between the overlay and substrate consisted of the hard and brittle IMC($FeAl_3,\;Fe_3Al,\;Fe_2Al_5$), which initiating and propagating the crack. The reciprocating test for the slide wear was conducted on a multi-pass overlay experiment. Comparing with the multi-pass overlay with no overlap, the overlay with 50% overlap showed better wear resistance.

• Corrosion Science and Technology
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• v.12 no.6
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• pp.295-303
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• 2013

Silane surface treatments have been developed as an alternative for toxic and carcinogenic chromate-based treatments for years. It is consistently observed that ultra-thin films offer excellent corrosion protection as well as paint adhesion to metals. The silane performance is comparable to, or in some cases better than, that of chromate layers. Based on the tetra-ethylorthosilicate(TEOS) and methlyl trieethoxysilane(MTES), inorganic sol was synthesized and formed hybrid networks with $SiO_2$ nano particle and polypropylene glycol(PPG) on Zn alloyed steel surface. According to SST results, addition of 10nm and 50nm $SiO_2$ nanoparticle in synthesized solution improved anti-corrosion property by its shear stress relaxation effect during curing process. Also, SST results were shown that anti-corrosive property was affected by the amounts of organic compounds.

• Journal of Technologic Dentistry
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• v.23 no.1
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• pp.55-64
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• 2001

This study is focusing on the improvement of problems of Ti-6Al-4V alloy. A new Ti based alloy, Ti-15Sn-4Nb, have designed to examine any possibility of improving the mechanical properties and biocompatibility. Specimens of Ti alloys were melted in vacuum arc furnace and homogenized at $100^{\circ}C$ for 24h. All specimens were solution treated at $812^{\circ}C$ and aged at $500^{\circ}C$ for 10h. The corrosion resistance of Ti alloys was evaluated by potentiodynamic polarization test and immersion test inl%Lactic acid solutions. Ti-15Sn-4Nb system alloys showed Widmanstatten microstructure after solution treatment which is typical microstructure of ${\alpha}+{\beta}$ type Ti alloys. Analysing the corrosion resistance of Ti alloys, it was concluded that the passive films of Ti-15Sn-4Nb system alloys are more stable than that of Ti-6Al-4V alloys. Also, the corrosion resistance of Ti-15Sn-4Nb system alloys was improved with adding elements, Hf. It was analysed that the passive film of the Ti-15Sn-4Nb alloy which was formed in air atmosphere was consisted of TiO2, SnO and NbO through X-ray photoelectron spectroscopy(XPS) analysis.

• The Journal of Advanced Prosthodontics
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• v.8 no.1
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• pp.1-8
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• 2016

PURPOSE. The purpose of this study was to evaluate the efficacy of two different metal conditioners for non-precious metal alloys for the bonding of porcelain to a cobalt-chromium (Co-Cr) alloy. MATERIALS AND METHODS. Disk-shaped specimens ($2.5{\times}10.0mm$) were cast with Co-Cr alloy and used as adherend materials. The bonding surfaces were polished with a 600-grid silicon carbide paper and airborne-particle abraded using $110{\mu}m$ alumina particles. Bonding specimens were fabricated by applying and firing either of the metal conditioners on the airborne-particle abraded surface, followed by firing porcelain into 5 mm in diameter and 3 mm in height. Specimens without metal conditioner were also fabricated. Shear bond strength for each group (n=8) were measured and compared (${\alpha}=.05$). Sectional view of bonding interface was observed by SEM. EDS analysis was performed to determine the chemical elements of metal conditioners and to determine the failure modes after shear test. RESULTS. There were significant differences among three groups, and two metal conditioner-applied groups showed significantly higher values compared to the non-metal conditioner group. The SEM observation of the sectional view at bonding interface revealed loose contact at porcelain-alloy surface for non-metal conditioner group, however, close contact at both alloy-metal conditioner and metal conditioner-porcelain interfaces for both metal conditioner-applied groups. All the specimens showed mixed failures. EDS analysis showed that one metal conditioner was Si-based material, and another was Ti-based material. Si-based metal conditioner showed higher bond strengths compared to the Ti-based metal conditioner, but exhibited more porous failure surface failure. CONCLUSION. Based on the results of this study, it can be stated that the application of metal conditioner is recommended for the bonding of porcelain to cobalt-chromium alloys.

• Tribology and Lubricants
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• v.36 no.4
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• pp.199-206
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• 2020

CoCr-based alloys have been developed as wear-resistant materials owing to their excellent mechanical properties and strong wear resistance. The purpose of this study is to experimentally assess the frictional and wear characteristics of CoCr-based alloys slid against two different counter materials subjected to various normal forces to determine the expansion applicability of CoCr-based alloys. CoCrMo and CoCr alloys were selected as the target materials and NiCr and NiCrB alloys as counter materials. Experimental tests were performed using a pin-on-reciprocating plate tribo-tester under dry lubrication. Before performing the tests, the surface of the specimens was observed through confocal microscopy and the hardness was measured using a micro-Vickers hardness tester. The wear volume of the plate was calculated at the end of the tests using confocal microscope data, and the wear rate was quantitatively obtained based on Archard's wear law. From the results, the wear rates of the CoCrMo specimens that slid against NiCr and NiCrB are 7.69 × 10^-6 ㎣/Nm and 5.26 × 10^-6 ㎣/Nm, respectively. The wear rates of the CoCr specimens that slid against NiCr and NiCrB were higher than those of the CoCrMo specimens by factors of approximately 4 and 8, respectively. The CoCrMo specimens further exhibited lower friction characteristics than the CoCr specimens. The findings of this study will be useful for expanded applications of CoCr-based alloys as wear-resistant materials for various mechanical parts.

• Nuclear Engineering and Technology
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• v.50 no.1
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• pp.107-115
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• 2018

To ensure the structural integrity of nuclear power plants, it is essential to predict the lifetime of Alloy 182 weld, which is used for welding in nuclear reactors. The lifetime of Alloy 182 weld is directly related to the crack initiation time. Owing to the large time scatter in most crack initiation tests, a probabilistic model, such as the Weibull distribution, has mainly been adopted for prediction. However, since statistically more advanced methods than current typical methods may be applied, we suggest a statistical procedure for parameter estimation of the crack initiation time of Alloy 182 weld, considering right-censored data and the covariate effect. Furthermore, we suggest a procedure for uncertainty evaluation of the estimators based on the bootstrap method. The suggested statistical procedure can be applied not only to Alloy 182 weld but also to any material degradation data set including right-censored data with covariate effect.

• Transactions of Materials Processing
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• v.29 no.3
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• pp.163-171
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• 2020

We present a multi-step cold drawing for a non-equiatomic Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ high entropy alloy (HEA) with a simple face-centered cubic (FCC) crystal structure. The distribution of strain in the cold-drawn Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ HEA wires was analyzed by the finite element method (FEM). The effective strain was expected to be higher as it was closer to the surface of the wire. However, the reverse shear strain acted to cause a transition in the shear strain behavior. The critical effective strain at which the shear strain transition behavior is completely shifted was predicted to be 4.75. Severely cold-drawn Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ HEA wires up to 96% of the maximum cross-sectional reduction ratio were successfully manufactured without breakage. With the assistance of electron back-scattering diffraction and transmission electron microscope analyses, the abundant deformation twins were found in the region of high effective strain, which is a major strengthening mechanism for the cold-drawn Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ HEA wire.