• Transactions of Materials Processing
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• v.33 no.3
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• pp.200-207
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• 2024

In this study, we developed a semi-analytical approach for the numerical analysis of residual stress in oxide scales formed on hot-rolled steels. The oxide scale, formed during the hot rolling process, experiences complex interactions due to thermal and mechanical influences, significantly affecting the material's integrity and performance. Our research focuses on integrating various stress components such as thermal stress, growth stress, and creep behavior to predict the residual stress within the oxide layer. The semi-analytical method combines analytical expressions for each stress component with numerical integration to account for their cumulative effects. Validation through instrumented indentation tests confirms the reliability of our model, which considers thermal expansion coefficient (CTE) differences, scale growth, and creep-induced stress relaxation. Our findings indicate that thermal stress resulting from CTE differences significantly impacts the overall residual stress, with growth stress contributing a compressive component during cooling, and creep behavior playing a minor role in stress relaxation. This comprehensive approach enhances the accuracy of residual stress prediction, facilitating the optimization of material design and processing conditions for hot-rolled steel products.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.8
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• pp.651-654
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• 2010

This paper describes the thermal and mechanical properties of doped thin film 3C-SiC and porous 3C-SiC. In this work, the in-situ doped thin film 3C-SiC was deposited by using atmospheric pressure chemical vapor deposition (APCVD) method at $120^{\circ}C$ using single-precursor hexamethyildisilane: $Si_2(CH_3)_6$ (HMDS) as Si and C precursors. 0~40 sccm $N_2$ gas was used as doping source. After growing of doped thin film 3C-SiC, porous structure was achieved by anodization process with 380 nm UV-LED. Anodization time and current density were fixed at 60 sec and 7.1 mA/$cm^2$, respectively. The thermal and mechanical properties of the $N_2$ doped porous 3C-SiC was measured by temperature coefficient of resistance (TCR) and nano-indentation, respectively. In the case of 0 sccm, the variations of TCR of thin film and porous 3C-SiC are similar, but TCR conversely changed with increase of $N_2$ flow rate. Maximum young's modulus and hardness of porous 3C-SiC films were measured to be 276 GPa and 32 Gpa at 0 sccm $N_2$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.518-523
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• 1998

The fracture toughness and hardness of 62 %$SiO_2-19%ZrO_2-9%Na_2O-10%B_2O_3$(wt%) glass ceramics system were investigated. As a result of DTA study to find crystallization temperature, an exothermic peak near $820^{\circ}C$ was observed. The optimum nucleation temperature and the optimum crystal growth temperature were determined by XRD and SEM analysis, and were approximately $650^{\circ}C$, $840^{\circ}C$ respectively. The fracture toughness of this zirconia glass ceramics was determined by Vickers Indentation Method. The hardness value was not changed with increasing of the heat treatment temperature, but fracture toughness value was increased up to $1.8 MPa{\cdot}m^{1/2}$ at $840^{\circ}C$, with increasing of heat treatment temperature.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.1
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• pp.169-186
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• 1996

The purpose of this study was to investigate the mechanical properities and biocompatibility with crystallization temperature and time of a bioactive glass-ceramic system $41.4wt%SiO_{2}-35.0wt%CaO-3.0wt%MgO-12.0wt%P_{2}O_{5}-8.6wt%Al_{2}O_{3}$ with same molar percent of $Al_{2}O_{3}\;and\;P_{2}O_{5}$. The crystallization behaviors were investigated with DTA, XRD and SEM. Fracture toughness with the change of crystallization temperature and time was measured by indentation fracture method. Also, biocompatibility was evaluated by culture of mouse fibroblast cell line L929. The results obtained were as follows ; 1. The major crystalline phases were apatite and anorthite, and relative intensity of anorthite phase was increased at $1004^{\circ}C$. 2. The hardness and fracture toughness were gradually increased with the increase in ceraming temperature to $1004^{\circ}C$. 3. When the glass ceramic was heat-treated for 4 hours at ceraming temperature of $1004^{\circ}C$, hardness and fracture toughness showed the maximum values $578.84k/mm^2\;and\;2.07MPa\;m^{1/2}$, respectively. 4. The growth rate and cytotoxic of L929 fibroblast cells for bioactive glass ceramic were better than those of stainless steel and titanium.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.2007-2013
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• 2017

In order to give hydrophobic surface properties on carbon steel, the fluorinated amorphous carbon films were prepared by using linear 2.45GHz microwave PECVD device. Two different process approaches have been tested. One is direct deposition of a-C:H:F films using admixture of $Ar/CH_4/CF_4$ working gases and the other is surface treatment using $CF_4$ plasma after deposition of a-C:H film with $Ar/CH_4$ binary gas system. $Ar/CF_4$ plasma treated surface with high $CF_4$ gas ratio shows best hydrophobicity and durability of hydrophobicity. Nanometer scale surface roughness seems one of the most important factors for hydrophobicity within our experimental conditions. The properties of a-C:H:F films and $CF_4$ plasma treated a-C:H films were investigated in terms of surface roughness, hardness, microstructure, chemical bonding, atomic bonding structure between carbon and fluorine, adhesion and water contact angle by using atomic force microscopy (AFM), nano-indentation, Raman analysis and X-ray photoelectron spectroscopy (XPS).

• Journal of the Korean Applied Science and Technology
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• v.35 no.1
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• pp.80-88
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• 2018

In this study, we prepared hybrid composites by using low temperature sol-gel process for transparent and hard coating film. The hybrid composites consist of $ZrO_2/TiO_2/organosilane$, of which organosilane was introduced 3-(trimethoxysilyl)propyl methacrylate due to the role of a photocurable ceramic material for low temperature process. The ceramic composites with various composition ratios were coated on a polycarbonate substrate using a sol-gel process of low temperature process, and characterized optical and mechanical properties of coated thin film. The transparencies of coated thin films were 97.5 % or more, and the pencil hardness were 9H or more. In the case of the ZTS-2-1, the nano-indentation hardness was measured at the highest value of 1.14 GPa.

• Journal of Korean Dental Science
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• v.9 no.1
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• pp.19-27
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• 2016

Purpose: Laser treatment has become a popular method in implant dentistry, and lasers have been used for the decontamination of implant surfaces when treating peri-implantitis. This study was performed to evaluate the effects of an Erbium-doped:Yttrium-Aluminum-Garnet (Er:YAG) laser with different settings on machined (MA), sand-blasted and acid-etched (SA), and resorbable blast media (RBM) titanium surfaces using scanning electron microscopy and confocal microscopy. Materials and Methods: Four MA, four SA, and four RBM discs were either irradiated at 40 mJ/20 Hz, 90 mJ/20 Hz, or 40 mJ/25 Hz for 2 minutes. The specimens were evaluated with scanning electron microscopy and confocal microscopy. Result: The untreated MA surface demonstrated uniform roughness with circumferential machining marks, and depressions were observed after laser treatment. The untreated SA surface demonstrated a rough surface with sharp spikes and deep pits, and the laser produced noticeable changes on the SA titanium surfaces with melting and fusion. The untreated RBM surface demonstrated a rough surface with irregular indentation, and treatment with the laser produced changes on the RBM titanium surfaces. The Er:YAG laser produced significant changes on the roughness parameters, including arithmetic mean height of the surface (Sa) and maximum height of the surface (Sz), of the MA and SA surfaces. However, the Er:YAG laser did not produce notable changes on the roughness parameters, such as Sa and Sz, of the RBM surfaces. Conclusion: This study evaluated the effects of an Er:YAG laser on MA, SA, and RBM titanium discs using confocal microscopy and scanning electron microscopy. Treatment with the laser produced significant changes in the roughness of MA and SA surfaces, but the roughness parameters of the RBM discs were not significantly changed. Further research is needed to evaluate the efficiency of the Er:YAG laser in removing the contaminants, adhering bacteria, and the effects of treatment on cellular attachment, proliferation, and differentiation.

• Journal of the Korean institute of surface engineering
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• v.38 no.6
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• pp.207-211
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• 2005

In this work a multi-layered nanostructured TiAIN/CrN superlattice coatings was synthesized using closed-field unbalanced magnetron sputtering method and the relationships between their superlattice period (1), micro-structure, hardness and elastic modulus were investigated. In addition, wear test at $500^{\circ}C$ and oxidation resistance test at $900^{\circ}C$ were performed to investigate high temperature properties of these thin films. The coatings were characterized in terms of microstructure and mechanical properties by transmission electron microscopy (TEM) and nano-indentation test. Results from TEM analysis showed that superlattice periods was inversely proportional to the jig rotation speed. The maximum hardness and elastic modulus of 37 GPa and 375 GPa were observed at superalttice period of 6.1 nm and 4.4 nm, respectively. An higher value of microhardness from TiAIN/CrN thin films than either TiAIN (30 GPa) or CrN (26 GPa) was noted while the elastic modulus was approximately an average of TiAIN and CrN films. These enhancement effects in superlattice films could be attributed to the resistance to dislocation glide across interface between the CrN and TiAIN layers. Much improved plastic deformation resistance ($H^3/E^2$) of 0.36 from TiAIN/CrN coatings was observed, compared with 0.15 and 0.16 from TiAIN and CrN, respectively. Also the wear resistance at $500^{\circ}C$ was largely increased than those of single TiAIN and CrN coatings and TiAIN/CrN coatings showed much reduced weight gain after exposure at $900^{\circ}C$ for 20 hours.

• Journal of the Korean Vacuum Society
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• v.9 no.4
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• pp.328-334
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• 2000

DLC (Diamond-Like Carbon) films were deposited by ECR-PECVD (electron cyclotron resonance plasma-enhanced chemical vapor deposition) method with the variation of substrate bias voltage under the others are constant except it. We have investigated the ion bombardment effect induced by the substrate bias voltage on films during the deposition of film. The characteristics of the film were analyzed using the Dektak surface profiler, SEM, FTIR spectroscopy, Raman spectroscopy and Nano Indentation tester. FTIR spectroscopy analysis shows that the amount of dehydrogenation in films was increased with the increase of substrate bias voltage and films thickness was decreased. Raman scattering analysis shows that integrated intensity ratio $(I_D /I_G)$ of the D and G peak was increased as the substrate bias voltage increased, and films hardness was increased. From these results, it can be concluded that films deposited at this experimental have the enhanced characteristics of DLC because of the ion bombardment effect on films during the deposition of film.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.281-285
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• 2008

Die hobbing is one of the dieblock manufacturing methods of cold forging die, which makes the upper side of dieblock indented using master punch, hobb to produce impression not using cutting work. SKD11, alloy tool steel was used as the material of dieblock and stainless sheet metal was used as product material in cold forging work. The life span of the die was 6,000 strokes. In this research, the material of dieblock was changed into SKH51, the high speed tool steel and the product material was S45C, the carbon steel in the cold forging work. The life span of the die was 21,000 strokes, which is 350% of the life span of the die using the former method.