• Journal of the Korean Society for Heat Treatment
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• v.21 no.1
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• pp.10-19
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• 2008

To investigate the effect of ultrasonic nano-crystalline surface modification (UNSM) treatment on rolling contact fatigue and residual stress properties of bearing steels, this paper carried out a rolling contact fatigue test, measured residual stress and retained austenite, performed a wear test, observed microstructure, measured micro hardness, and analyzed surface topology. After the UNSM treatment, it was found that the surface became minute by over $100{\mu}m$. The micro surface hardness was changed from Hv730~740 of base material to Hv850~880 with about 20% improvement, and hardening depth was about 1.3 mm. The compressive residual stress was measured as high as -700~-900 MPa, and the quantity of retained austenite was reduced to 27% from 34%. The polymet RCF-6 ball type rolling contact fatigue test showed over 4 times longer fatigue lifetime after the UNSM treatment under 551 kgf load and 8,000 rpm. In addition, this paper observed the samples, which went through the rolling contact fatigue test, with OM and SEM, and it was found that the samples had a spalling phenomenon (the race way is decentralized) after the UNSM treatment. However, before the treatment, the samples had excessive spalling and complete exploration. Comparison of the test samples before and after the UNSM treatment showed a big difference in the fatigue lifetime, which seems to result from the complicated effects of micro particles, compressive residual stress, retained austenite, and surface topology.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.3
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• pp.127-132
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• 2011

The silicon-containing Diamond-like Carbon (Si-DLC) film as an low friction coefficient coating has especially treated a different silicon content by plasma-enhanced chemical vapor deposition (PECVD) process at $500^{\circ}C$ on nitrided-STD 11 mold steel with (TMS) gas flow rate. The effects of variable silicon content on the Si-DLC films were tested with relative humidity of 5, 30 and 85% using a ball-on-disk tribometer. The wear-tested and original surface of Si-DLC films were analysed for an understanding of physical and chemical characterization, including a changing structure, via Raman spectra and nano hardness test. The results of Raman spectra have inferred a changing intra-structure from dangling bonds. And high silicon containing DLC films have shown increasing carbon peak ratio ($I_D/I_G$) values and G-peak values. In particular, the tribological tested surface of Si-DLC was shown the increasing hardness value in proportional to TMS gas flow rate. Therefore, at same time, the structure of the Si-DLC film was changed to a different intra-structure and increased hardness film with mechanical shear force and chemical reaction.

• Journal of the Korean institute of surface engineering
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• v.42 no.3
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• pp.109-115
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• 2009

Magnesium is one of the lightest metals, and magnesium alloys have excellent physical and mechanical properties such as high stiffness/weight ratios, good castability, good vibration and shock absorption. However their poor corrosion resistance, wear resistance, hardness and so on, have limited their application. To improve these defects, many techniques are developed. Micro arc oxidation(MAO) is a one of the surface treatments under anodic oxidation in which ceramic coating is directly formed on the surface of magnesium alloy. In this study, the characteristics of anodic film were examined after coating the AZ31B magnesium alloy through the MAO process. MAO was carried out in potassium hydroxide, potassium fluoride, and various concentration of sodium silicate in electrolyte. The morphology and chemical composition of the coating layer were characterized by SEM, XRD, EPMA and EDS. The hardness of anodic films was measured by micro-vickers hardness tester. As a result, the morphology and composition of anodic film were changed by concentration of sodium silicate. Thickness and Si composition of anodic film was increased with increasing concentration of sodium silicate in electrolyte. The hardness of anodic film was highly increased when the concentration of sodium silicate was above 40 g/l in electrolyte.

• Transactions on Electrical and Electronic Materials
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• v.8 no.2
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• pp.67-72
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• 2007

High Pressure Micro Jet (HPMJ) pad conditioning system was investigated as an alternative to diamond disc conditioning in copper CMP. A series of comparative 50-wafer marathon runs were conducted at constant wafer pressure and sliding velocity using Rohm & Haas IC1000 and Asahi-Kasei EMD Corporation (UNIPAD) concentrically grooved pads under ex-situ diamond conditioning or HPMJ conditioning. SEM images indicated that fibrous surface was restored using UNIPAD pads under both diamond and HPMJ conditioning. With IC1000 pads, asperities on the surface were significantly collapsed. This was believed to be due to differences in pad wear rates for the two conditioning methods. COF and removal rate were stable from wafer to wafer using both diamond and HPMJ conditioning when UNIPAD pads were used. Also, HPMJ conditioning showed higher COF and removal rate when compared to diamond conditioning for UNIPAD. On the other hand, COF and removal rates for IC1000 pads decreased significantly under HPMJ conditioning. Regardless of pad conditioning method adopted and the type of pad used, linear correlation was observed between temperature and COF, and removal rate and COF.

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1127-1132
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• 1998

The possibilities of producing Al-10%Ti-4%Fe composites through in-situ processing and thus achieving mechanical property improvements over binary Al-10%Ti to a level or higher exhibited by PM SiC/A12124 composites were explored in this study. The microstructure of in-situ processed Al-10%Ti-4%Fe composites was similar to that of Al matrix composites reinforced with discontinuous SiC particulates(SiC/A12124) and significant enhancements in elastic modulus, tensile strength and wear resistance were observed as compared to Al-10%Ti alloy. These results can be attributed to the in-situ formed Al. Fe by third element addition, leading to additional dispersion strengthening effect over $Al_3Ti$ phase reinforcement in Al-Ti system.

• Asian Journal of Atmospheric Environment
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• v.7 no.1
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• pp.38-47
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• 2013

$PM_{10}$ concentrations were measured at four monitoring sites at the Daechaung station of the Seoul subway. The four locations included two tunnels, a platform, and a waiting room. The outside site of the subway was also monitored for comparison purposes. In addition, the effect of the platform screen doors (PSDs) recently installed to isolate the $PM_{10}$ in a platform from a tunnel were evaluated, and a comparison between $PM_{10}$ levels during rush and non-rush hours was performed. It was observed that $PM_{10}$ levels in the tunnels were generally higher than those in the other locations. This might be associated with the generation of $PM_{10}$ within the tunnel due to the train braking and wear of the subway lines with the motion of the trains, which promotes the mixing and suspension of particulate matter. During this tunnel study, it was observed that the particle size of $PM_{10}$ ranged from 1.8 to 5.6 ${\mu}m$. It was revealed that the $PM_{10}$ levels in the tunnels were significantly increased by the PSDs, while those in the platform and waiting room decreased. As a result, in order to estimate the effect of ventilation system on $PM_{10}$ levels in the tunnels, fans with inverters were operated. It was found that the concentration of $PM_{10}$ was below 150 ${\mu}g/m^3$ when the air flow rate into a tunnel was approximately 210,000-216,000 CMH.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.4
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• pp.305-310
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• 2012

It is a great challenge for dentists to do prosthetic restorations of a patient with reduced occlusal vertical dimension (OVD). Proper determination of the OVD is significant. An 85-year-old male patient came in with missing right maxillary posterior teeth. After diagnostic wax-up, reversible provisional prostheses were used to evaluate the new OVD in the maxilla and mandible. After that, the patient was evaluated clinically based on the criteria of esthetic, phonetic, and OVD. After 8 weeks, teeth with excessive wear were treated with root canal therapy and fiber post and core and irreversible provisional prostheses were done. After 8 weeks of observation period, final restorations with fixed partial dentures and removable partial dentures were made. Throughout the follow-up period of 6 months, no symptoms related with increased OVD and mechanical complications were observed.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.6
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• pp.769-779
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• 2007

Statement of problem. When TiN coating is applied to the abutment screw, occurrence of greater preload and prevention of the screw loosening could be expected due to decrease of frictional resistance. However, the proper thickness of TiN coating on abutment screw has not been yet reported. Purpose. The purpose of this study is to find out the appropriate TiN coating thickness by evaluating the detorque force and the surface change of titanium abutment screw with various TiN coating thickness. Material and methods. 1. Material Thirty five non-coated abutment screws were prepared for TiN coating. TiN coatings were prepared by Arc ion plating method. Depending on the coating deposition time(CDT), experimental groups were divided into 6 groups(CDT 30min, 60min, 90min, 120min, 150min, 180min) and those of 1 group was not coated as a control group. Each group was made up of 5 abutment screws. 2. Methods FE-SEM(Field Emission Scanning Electron Microscoper) and EDX(Energy Dispersive X-ray Spectroscopy) were used to observe the surface of the abutment screw. Electric scales was used to measure the weight of the abutment screw after the repeated closing and opening of 10 trials. Detorque force was measured with digital torque gauge, at each trial. Results. 1. As the coating deposition time increased, the surface became more consistent and smooth. 2. As for the abutment screws that were TiN coated for more than 60 minutes, no surface change was found after the repeated closing and opening. 3. The TiN coated abutment screws showed less weight change than the non-coated abutment screws. 4. The TiN coated abutment screws showed higher mean detorque force than the noncoated abutment screws. 5. The abutment screw coated for 60 minutes showed the highest mean detorque force. Conclusion. The coating layer of proper thickness is demanded to obtain consistent and smooth coating surface, resistance to wear, and increased detorque force of the abutment screw. In conclusion, the coating deposition time of 60 minutes indicated improved mechanical property, when TiN coating was conducted on titanium abutment screw.

• The Journal of Advanced Prosthodontics
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• v.8 no.1
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• pp.21-29
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• 2016

This in vitro study investigated and compared the durability and retention of three types of attachments. MATERIALS AND METHODS. Three commercially available attachments were investigated: $Clix^{(R)}$, Dalbo-$Plus^{(R)}$ and $Locator^{(R)}$. In total, 72 samples of these attachments were placed in the acrylic resin forms and subjected to mechanical testing (5400 cycles of insertion and removal) over the respective ball or Locator abutments immersed in artificial saliva at pH 7 and $37^{\circ}C$. The abutments were placed at angulations of $0^{\circ}$, $10^{\circ}$ and $20^{\circ}$. The retention force was recorded at the beginning and after 540, 1080, 2160, 3240, 4320 and 5400 insertion-removal cycles. RESULTS. The results revealed that there were significant differences in the average values of the insertion/removal force due to angulation ($F_{(2.48)}=343619$, P<.05) and the type of attachment ($F_{(7.48)}=23.220$, P<.05). CONCLUSION. Greater angulation of the abutments was found to influence the retention capacity of the attachments, and the fatigue test simulating 5 years of denture insertion and removal did not produce wear in the metal abutments.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.171-175
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• 2001

Chemical mechanical polishing(CMP) process has been widely used to planarize dielectrics and metal, which can apply to employed in integrated circuits for sub-micron technology. Despite the increased use of CMP process, it is difficult to accomplish the global planarization of free-defects in inter level dielectrics and metal. Especially, defects like (micro-scratch) lead to severe circuit failure, and affects yield. Current conditioning method - bladder type, orbital pad motion - usually provides unsuitable pad profile during ex-situ conditioning near the end of pad life. Since much of the pad wear occurs by the mechanism of bladder tripe conditioning and its orbital motion without rotation, we need to implement new ex-situ conditioner which can prevent abnormal regional force on pad caused by bladder-type and also need to rotate the pad during conditioning. Another important study of ADPC is related to the orbital scratch of which source is assumed as diamond grit dropped from the strip during ex-situ conditioning. Scratch from diamond grit damaged wafer severely so usual1y scraped. Figure 1 shows the typical shape of scratch damaged from diamond. We suspected that intensive forces to the edge area of bladder type stripper accelerated the drop of Diamond grit during conditioning, so new designed Flat stripper was introduced.