• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.137-138
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• 2002

The benefits of using DLC coatings on steel in dry sliding are well known. The present study has investigated the effects of using the same materials but in a boundary lubricated environment. Tribological tests were performed using a load-scanning device and a lubricant with an extreme-pressure (EP) additive. XPS and grazing incidence XRD are used for chemical analysis. The chemical composition of the resulting tribofilm is correlated to different friction behaviors and contact loads, and indicates that high loads are beneficial for formation of low friction tribofilm.

• Journal of Powder Materials
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• v.26 no.4
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• pp.319-326
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• 2019

Additive manufacturing (AM) is a highly innovative method for joining dissimilar materials for industrial applications. In the present work, AM of STS630 and Ti-6Al-4V powder alloys on medium entropy alloys (MEAs) NiCrCo and NiCrCoMn is studied. The STS630 and Ti64 powders are deposited on the MEAs. Joint delamination and cracks are observed after the deposition of Ti64 on the MEAs, whereas the deposition of STS630 on the MEAs is successful, without any cracks and joint delamination. The microstructure around the fusion zone interface is characterized by scanning electron microscopy and X-ray diffraction. Intermetallic compounds are formed at the interfacial regions of MEA-Ti64 samples. In addition, Vicker's hardness value increased dramatically at the joint interface between MEAs and Ti-6Al-4V compared to that between MEAs and STS630. This result is attributed to the brittle nature of the joint, which can lead to a decrease in the joint strength.

• Journal of Powder Materials
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• v.30 no.3
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• pp.223-232
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• 2023

Metal additive manufacturing (AM) has transformed conventional manufacturing processes by offering unprecedented opportunities for design innovation, reduced lead times, and cost-effective production. Aluminum alloy, a material used in metal 3D printing, is a representative lightweight structural material known for its high specific strength and corrosion resistance. Consequently, there is an increasing demand for 3D printed aluminum alloy components across industries, including aerospace, transportation, and consumer goods. To meet this demand, research on alloys and process conditions that satisfy the specific requirement of each industry is necessary. However, 3D printing processes exhibit different behaviors of alloy elements owing to rapid thermal dynamics, making it challenging to predict the microstructure and properties. In this study, we gathered published data on the relationship between alloy composition, processing conditions, and properties. Furthermore, we conducted a sensitivity analysis on the effects of the process variables on the density and hardness of aluminum alloys used in additive manufacturing.

• Journal of Electrochemical Science and Technology
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• v.7 no.3
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• pp.214-217
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• 2016

In this study, we studied the enhancement of the energy densities of electrochemical capacitors by improving the working voltage range of the electrolyte. To prevent the decomposition of the electrolyte, stable SEI layers were formed by reductive degradation of additive materials such as fluoro-ethylene carbonate (FEC) and vinyl ethylene carbonate (VEC) before degradation of the base electrolyte. As a result, the solution resistance (R_s) of EC:DMC + SL 20 % + VEC 1 % electrolytes observed 1.47 Ω and the charge transfer resistance (R_ct) was 2.64 Ω at the open circuit voltage. Additionally, a cycle retention of 94 % was observed for EC:DMC + SL 20 % + VEC 1 % after 500 cycles at 3.5 V.

• Journal of Electrochemical Science and Technology
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• v.8 no.2
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• pp.162-168
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• 2017

$LiNi_xCo_yMn_zO_2$ cathode materials have been the focus of much attention because of their high specific capacity. However, because of the poor interfacial stability between cathodes and electrolytes, the cycling performance of these materials fades rapidly, especially at high temperatures. In the present paper, we propose the use of tris(trimethylsilyl) phosphate (TMSPO), which contains phosphate and silyl functional groups, as a functional additive in electrolytes. The addition of TMSPO resulted in the formation of cathode electrolyte interphase (CEI) layers on the surfaces of the cathodes and effectively suppressed electrolyte decomposition reactions, even at high temperatures. As a result, cells cycled with TMSPO exhibited remarkable capacity, which remained after 50 cycles (82.0%), compared to cells cycled without TMSPO (64.6%).

• Journal of Ocean Engineering and Technology
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• v.22 no.3
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• pp.71-75
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• 2008

This paper illustrates haw $Y_2O_3$ contributes to crack-healing strengths as a function of crack-healing temperature and the additive amount. In investigating mechanical properties, the indentation fracture method is very simple and useful, but careful attention must be paid to the statistical data processing because data may be scattered excessively, especially for brittle materials. To estimate accurate AE signal properties we applied the useful time-frequency method with a discrete wavelet analysis algorithm. In experiments, three kinds of specimens were prepared. After the specimens were indented by a Vickers indentor, they were heat-treated and crack-healed to evaluate bending strength and the AE signal. With higher amounts of the additive powder, as 1, 3, or 5% wt. of $Y_2O_3$, the concentrative tendency of dominant frequency trended toward lower frequency groups. The $Al_2O_3$ ceramic with 3% wt. of $Y_2O_3$ was judged most suitable because it demonstrated superior crack-healing ability and relative concentration on the highest frequency group.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.364-371
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• 2013

The sintering behavior of monolithic SiC is examined using the binary sintering additive of $Al_2O_3$-rare earth oxide ($RE_2O_3$, where RE = Sc, Nd, Dy, Ho, or Yb). Through hot pressing at 20 MPa and $1750^{\circ}C$ for 1 h in an Ar atmosphere for 52 nm fine ${\beta}$-SiC powder added with 5 wt% sintering additive, a SiC density of > 97% is achieved, which indicates the effectiveness of $Al_2O_3-RE_2O_3$ system as a sintering of additive for SiC. Based on this result, 7 wt% of $Al_2O_3-Sc_2O_3$ is tested as an additive system for the fabrication of a continuous SiC fiber-reinforced SiC-matrix composite ($SiC_f$/SiC). Electrophoretic deposition combined with the application of ultrasonic pulses is used to efficiently infiltrate the matrix phase into the voids of $Tyranno^{TM}$-SA3 fabric. After hot pressing, a composite density of > 97% is obtained, along with a maximum flexural strength of 443 MPa.

• Journal of Powder Materials
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• v.29 no.5
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• pp.363-369
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• 2022

AlSi10Mg alloys are being actively studied through additive manufacturing for application in the automobile and aerospace industries because of their excellent mechanical properties. To obtain a consistently high quality product through additive manufacturing, studying the flowability and spreadability of the metal powder is necessary. AlSi10Mg powder easily forms an oxide film on the powder surface and has hydrophilic properties, making it vulnerable to moisture. Therefore, in this study, AlSi10Mg powder was hydrophobically modified through silane surface treatment to improve the flowability and spreadability by reducing the effects of moisture. The improved flowability according to the number of silane surface treatments was confirmed using a Carney flowmeter. In addition, to confirm the effects of improved spreadability, the powder prior to surface treatment and that subjected to surface treatment four times were measured and compared using s self-designed recoating tester. The results of this study confirmed the improved flowability and spreadability based on the modified metal powder from hydrophilic to hydrophobic for obtaining a high-quality additive manufacturing product.

• Journal of the Korean Society of Food Science and Nutrition
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• v.41 no.12
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• pp.1842-1846
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• 2012

The effects of hurdle techniques on the reduction of Bacillus cereus spores in Doenjang and Gochujang were investigated. In our system, Bacillus cereus spores were artificially inoculated into Doenjang and Gochujang. Hurdle techniques used in this study were additives (3% ethyl alcohol-0.03% oregano extract), Joule heating ($95^{\circ}C$ for 5 min), and hydrostatic pressure (500 MPa for 5 min at $45^{\circ}C$). Additive-Joule (AJ) and additive-Joule-pressure (AJP) treatments for Doenjang resulted in a 2.80 log and 3.74 log reduction, respectively, while treatments for Gochujang resulted in a 4.71 log and 5.60 log reduction, respectively. This suggests a high synergistic effect of Joule heating with additive treatment in Doenjang and Gochujang. A combination ofg hurdles such as additives, Joule heating, and hydrostatic pressure also kept Bacillus cereus spore counts low during storage at $30^{\circ}C$. Therefore, Bacillus cereus spores inoculated into Doenjang and Gochujang can be effectively reduced through combined treatments, including AJ or AJP.

• Journal of the Korean institute of surface engineering
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• v.53 no.4
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• pp.138-143
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• 2020

In this study, we produced a coil of micro-pattern that can be used for electromagnetic wave absorber, heating material, wireless charging, sensor, antenna, etc. by using electrochemical additive manufacturing method. Currently, it contains research contents for manufacturing a micro pattern coil having practicality through control of process control variables such as applied voltage, distance between electrode, and nozzle injection. Circulation of the electrolyte through the nozzle injection control can significantly contribute to improving the surface characteristics of the coil because of minimizing voltage fluctuations that may occur during the additive manufacturing process. In addition, by applying the pulse method in the application of voltage, the lamination characteristics of the plated body were improved, which showed that the formation of a fine line width plays an important role in the production of a micro pattern coil. By applying the pulse signal to the voltage application, the additive manufacturing characteristics of the produced product were improved, and it was shown that the formation of a fine line width plays an important role in the production of a micro pattern coil.