• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.735-738
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• 2000

The characteristics of wire electrical discharge machining (WEDM) are governed by many factors such as the power supply type, operating condition and electrode material. This work deals with the effect of wire electrode materials on the machining characteristics such as, metal removal rate, surface characteristics and surface roughness during WEDM A wire's thermal physical properties are melting point, electrical conductivity and vapor pressure. One of the desired qualities of wire is a low melting point and high vapor pressure to help expel the contaminants from the gap. They are determined by the mix of alloying elements (in the case of plain brass and coated wire) or the base core material(i.e. molybdenum). Experiments have been conducted regarding the choice of suitable wire electrode materials and influence of the properties of these materials on the machinability and surface characteristics in WEDM, the experimental results are presented and discussed from their metallurgical aspect. And the coating effect of various alloying elements(Au, Ag, Cu, Zn, Cr, Mn, etc.) to the Cu or 65-35 brass core on them was reviewed also. The removal rate of some coated wires are higher than that of 65-35 brass electrode wire because the wire is difficult to break due to the wire cooling effect of Zn evaporation latent heat and the Zn oxide on the surface is effective in preventing short circuit. The removal rate increases with increasing Zn content from 35, 40 and Zn coated wire

• Journal of the Korean institute of surface engineering
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• v.41 no.5
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• pp.181-188
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• 2008

A.C. impedance properties of HA/Ti compound layer coated Ti-30Ta-($3{\sim}15$)Nb alloys have been studied by electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10 and 15 wt% Nb were manufactured by the vacuum furnace system. And then specimen was homogenized at $1000^{\circ}C$ for 24 hrs. The sample was cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The non-coated and coated morphology of Ti alloy were analyzed by X-ray diffractometer (XRD), energy X-ray dispersive spectroscopy (EDX) and filed emission scanning electron microscope (FE-SEM). The corrosion behaviors were investigated using A.C. impedance test (PARSTAT 2273, USA) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Ti-30Ta-($3{\sim}15\;wt%$)Nb alloys showed the ${\alpha}+{\beta}$ phase, and $\beta$ phase peak was predominantly appeared in the case of increasingly Nb contents. The microstructures of Ti alloy were transformed from needle-like structure to equiaxed structure as Nb content increased. From the analysis of coating surface, HA/Ti composite surface uniformed coating layer with 750 nm thickness. The growth directions of film were (211), (112), (300) and (202) for HA/Ti composite coating on the surface after heat treatment at $550^{\circ}C$, whereas, the growth direction of film was (110) for Ti coating. The polarization resistance ($R_p$) of HA/Ti composite coated Ti-alloys were higher than those of the Ti and HA coated samples in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.126-126
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• 2012

In this study, adhesion of plasma spray coated hydroxyapatite film on the two-step anodized dental implant was investigated. The plasma spray was carried out on the dental implant after two step anodization. The adhesion of coated HA film was investigated by FE-SEM after fatigue test. In the case of two-step anodized implant showed a good adhesion between implant and coated film.

• Korean Journal of Materials Research
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• v.33 no.2
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• pp.47-53
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• 2023

When exposed to different types of bacteria in the oral cavity, denture based resins are prone to bacteria attachment. The purpose of this study was to investigate the physical, biological, and antimicrobial properties of denture base resins coated with Peony extract (200, 400, and 600 ㎍/mL). Specifically, the surface properties (microhardness, contact angle, and color change of the coated specimens), cell cytotoxicity (measured using MTT assay), and antimicrobial activity (against S. mutans (Streptococcus mutans) and C. albicans (Candida albicans) using a growth inhibition assay) were evaluated. The polyphenol content was measured using ultraviolet-visible (UV-vis) spectrometry. The experimental groups (specimens coated with Peony extract) and a control group (specimens coated without Peony extract) were statistically compared using a one-way analysis of variance and Tukey's post-hoc tests. No statistically significant differences in surface properties or cell cytotoxicity were observed, which demonstrated their biocompatibility. Conversely, a statistically significant difference in antimicrobial activity was observed between the experimental and control groups after 48 h. This confirms the antimicrobial activity of the denture base resin coated with Peony extract and demonstrates that it is a promising dental material for preventing stomatitis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.874-877
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• 2000

Pre-coated sheet materials are a cost-effective and environmentally attractive alternative to conventional sheet materials coated after forming. At present but the high scratch sensitivity of coating used for pre-coated metal sheet is a major limitation to use of these materials. Because of high scratch sensitivity, products made by pre-coated metal sheet are not formed by conventional design method. This study has been performed to investigate scratch characteristic of non-vinyl pre-coated metal (PCM) sheet. Using the simple U-bending test equipment, three non-vinyls PCM's were tested. This paper provides the results of bending tests showing the influence of sheet surface texture, tool material and process conditions. It was found that the influence of punch, die clearance and tool material had an effect upon the scratch characteristic.

• Journal of the Korean Society of Safety
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• v.9 no.4
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• pp.58-68
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• 1994

A miniature size electrostatic induction motor has been fabricated and studied parameters Influencing dominantly to the motor speed, such as a voltage and frequency of the 3 phase ac power source supplied to the stator of fabricated motor, the surface resistivity and relative dielectric constant of the rotor surface materials and the concurrently calculated relaxation time constants. It is found that the higher resitivity and/or the higher relative dielectric constant, concurrently the longer relaxation time constant of the rotor surface materials make the motor speed get higher speed. In case of discrete coated rotor surface it is found that the motor speed was increased logarithmically as narrow as width of the discrete coated Ti. And the degree of width of discrete coated Ti to the axial direction of the rotor was 60$^{\circ}$ and 150$^{\circ}$, the motor has got a 125% higher than that at the degree of 0$^{\circ}$.

• Journal of Radiation Industry
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• v.5 no.4
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• pp.371-376
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• 2011

The surface property of the materials used in tissue engineering application has been essential to regulate cellular behaviors by directing their adhesion on the materials. To modulate surface property of the synthetic biodegradable materials, a variety of surface modification techniques have used to introduced surface functional groups or bioactive molecules, recently polydopamine coating method have been introduce as a facile modification method which can be coated on various materials such as polymers, metals, and ceramics regardless of their surface property. However, there are no reports about the degree of polydopamine coating on the materials with different hydrophilicity. In the present study, we prepared acrylic acid grafted nanofibrous meshes using electron-beam irradiation, and then coated meshes with polydopamine. Polydopamine successfully coated on the all meshes, both properties of acrylic acid and polydopamine were detected on the meshes. In addition, the degree of polydopamine deposition on the materials has been altered according to surface hydrophilicity, which was approximately 8-times greater than those on the non-modified materials. In conclusion, dual effect from the acrylic acid grafting and polydopamine may give a chance as a alternative tool in tissue engineering application.

• Bulletin of the Korean Chemical Society
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• v.32 no.5
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• pp.1483-1490
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• 2011

The protection effect of a $ZrO_2$ coating layer on a $LiCoO_2$ thin film was characterized. A wide and smooth $LiCoO_2$ thin film offers sufficient opportunity for careful observation of the reaction at the interface between cathode (coated and uncoated) and electrolyte. The formation of a $ZrO_2$ coating on a $LiCoO_2$ thin film was confirmed by secondary ion mass spectrometry. Scanning electron and atomic force microscopy were used to characterize the surface morphologies of coated and uncoated films before and after cycling. A $ZrO_2$-coated $LiCoO_2$ film showed a higher discharge capacity and rate capability than an uncoated film. This may be associated with a surface protection effect of the coating. The surface of a pristine film was damaged during cycling, whereas the coated film maintained a relatively clear surface under the same measurement conditions. This result clearly demonstrates the protection effect of a $ZrO_2$ coating on a $LiCoO_2$ thin film.

• Journal of the Korean institute of surface engineering
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• v.56 no.1
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• pp.69-76
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• 2023

The effects of hairline treatment on surface blackening and thermal diffusion behaviors of Zn-Al-Mg alloy coated steel sheet were evaluated by the three-dimensional surface profiler and laser-flash technique. The metallographic observation of coating damages by hairline treatments showed that several cracks were initiated and propagated along the interface between primary Zn/eutectic phases. As the hairline processing became more severe, the crack occurrence frequency in eutectic phase of coating layer and the surface roughness increased, which had a proportional relationship with the level of blackening on the coating surface. In addition, the higher interfacial areas of the blackened coating surface, caused by the hairline process, led to an increase in thermal diffusivity and conductivity of the coated steel sheet. On the other hand, when the coating damage by hairline treatment was excessive and the steel substrate was exposed, there was little difference between the thermal diffusivity/conductivity of the untreated sample though the blackening degree was higher than that of untreated sample. This work suggests that the increase in the surface areas of the coating layer without exposure to steel substrate through hairline treatment can be one of the effective technical strategies for the development of Zn-Al-Mg alloy coated steel sheets with higher blackening level and thermal diffusivity.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.268-268
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• 2015

The corrosion protection behavior of AZ31 magnesium alloy (Mg alloy) with cathodic electrophoretic coating (E-coating) pretreated by cerium-based conversion coatings at various pH was investigated in this study. Cerium-based conversion coatings (CeCCs) were deposited on AZ31 Mg alloy by immersion treatment in the nitrate-based cerium salt solution. The morphology and composition of the CeCCs were analyzed using scanning electron microscopy and energy dispersive X-ray spectroscopy. The corrosion properties of the AZ31 Mg alloy pretreated with cerium coating and subsequently E-coated were studied during salt-spray testing. The surface morphologies of the E-coated Mg alloy were examined in detail after different testing times using digital photography. It was found that the protective properties of the E-coating on AZ31 Mg alloy generated are heavily dependent upon the CeCC factors such as treatment time, coating thickness and pH of the solution.