• Journal of the Korean Vacuum Society
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• v.10 no.2
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• pp.182-188
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• 2001

Thin films of $SiO_xC_y$ deposited by means of PECVD(plasma enhanced chemical vapor deposition) using HMDSO(hexamethyldisiloxane)/$O_2$ were characterized. The effects of deposition conditions such as RF power, oxygen flow rate and hydrogen flow rate on the chemical bond structure, atomic composition, surface roughness and wear characteristics of the films were investigated by means of FTIR, XPS, AFM and Hazemeter. The deposition rate of $SiO_xC_y$ was greater than 100 nm/min, which is relatively high rate. The XPS results showed that the carbon content in a deposited film was lower than that of previous studies where different organosilicone materials were used. The optimum wear resistance was attained when RF power was 200 Watt and oxygen flow rate was 100 sccm. This study implies that the $HMDSO/O_2$ system is effective in forming a film with a lower carbon content and good abrasion resistance.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.2
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• pp.94-100
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• 2004

In order to improve the wear resistance of Ti-6Al-4V alloy, plasma carburization treatment was newly carried out without consumption of its good specific strength and fatigue life over the temperature. Effect of the plasma carburization was analyzed and compared with the non-treated alloy by microstructural observation, structure characterization and mechanical test. The plasma treated alloy formed a carburized layer of about $150{\mu}m$ in depth from the surface, where a fine and hard particles of TiC and $V_4C_3$ were homogeneously dispersed through the layer. The steady-static creep behaviors of Ti-6Al-4V alloy, using the constant stress creep tester, were investigated over the temperature range of $510{\sim}550^{\circ}C$(0.42~0.44Tm) and the stress range of 200~275 MPa. Stress exponent(n) was decreased from 9.32 of non-treatment specimen to 8.95 of carburized, however, the activation energy(Q) increased from 238 to 250 kJ/mol with the same condition as indicated above. From the above results, it can be concluded that the static creep deformation for Ti-6Al-4V alloy was controlled by the dislocation climb over the ranges of the experimental conditions.

• Journal of Korea Foundry Society
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• v.25 no.2
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• pp.88-94
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• 2005

The microstructure and mechanical property of the ceramic reinforced AC4C matrix composites processed by squeeze casting were investigated. In this study Kaowool and Saffil fiber which are ceramic reinforcements are used as preform materials. As a matrix material, Al-7wt.%Si-0.3wt.%Mg(AC4C) has been used. In case of Kaowool and Saffil/AC4C composites, 7.5 MPa squeezing pressure and minimum 7.0% binder amount are needed to produce sound composite materials. The tensile strength of Kaowool/ AC4C composite is lower than the matrix metal and this can be explained by the melt unfilling due to formed cluster of Kaowool reinforcements. But the mechanical properties of hardness, wear resistance and thermal expansion are better than the matrix materials due to the strengthening effect of ceramic reinforcements.

• Journal of Welding and Joining
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• v.34 no.2
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• pp.30-35
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• 2016

Last few decades have seen a rapid increase in the fabrication and characterization of Al alloys for automobiles, heat exchangers and aerospace industries. Aluminium alloys are popular because of their high specific strength, light weight, excellent wear and high oxidation resistance. The development of aluminium alloys in these applications makes their study and research of utmost importance. Brazing is applied to the aluminium alloys for joining various aluminium parts together in most of the industrial applications. Various parameters affect the joining process of these aluminium alloys. In this article, various types of processing parameters have been discussed, and special attention has been given to the category of aluminium brazing alloys. The article reviews on the various parameters that affect the brazing property in various scientific and technological applications.

• Corrosion Science and Technology
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• v.17 no.2
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• pp.68-73
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• 2018

Substitution of hip and knee joints by CoCr alloys is in great demand due to their high wear resistance and good biocompatibility. Understanding of tribocorrosion in joint replacements requires study of variables such as coefficient of friction and the choice of a proper corrosive medium in wear-corrosion tests carried out in the lab. The objective of this study was to characterize tribocorrosion behaviour of CoCr alloy with low (LCCoCr) and high carbon (HCCoCr) contents in several corrosive media: NaCl, Phosphate Buffer Solution (PBS), and PBS with hyaluronic acid (PBS-HA). Tribocorrosion tests were carried out on a pin-on-disk tribometer with an integrated electrochemical cell. A normal load of 5N was applied on the alumina ball counterpart at a rotation rate of 120 rpm. Coefficient of friction (COF) was measured and tribocorrosion behaviour was characterized by in situ application of electrochemical techniques. HCCoCr alloy immersed in PBS-HA showed the best tribocorrosion behaviour with the lowest COF. In this case, in situ measurement of corrosion potential and the impedance data under wear corrosion process showed an active state while passive film was continuously destroyed without possibility of regeneration.

• Korean Journal of Metals and Materials
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• v.46 no.5
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• pp.321-327
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• 2008

Cu based amorphous ($Cu_{54}Zr_{22}Ti_{18}Ni_6$) coating was produced by cold spraying as a new fabrication process. The microstructure and macroscopic properties of amorphous coating layer was investigated and compared with those of cold sprayed pure Cu coating. Amorphous powders were prepared by gas atomization and Al 6061 was used as the substrate plate. X-ray diffraction results showed that Cu based amorphous powder could be successfully deposited by cold spraying without any crystallization. The Cu based amorphous coating layer ($300{\sim}400{\mu}m$ thickness) contained 4.87% porosity. The hardness of Cu based amorphous coating represented $412.8H_v$, which was correspond to 68% of the hardness of injection casted bulk amorphous material. The wear resistance of Cu based amorphous coating was found to be three times higher than that of pure Cu coating. The 3-point bending test results showed that the adhesion strength of Cu based amorphous coating layer was higher than that pure Cu coating. It was also observed that hard Cu base amorphous particle could easily deform soft substrate by particle collisions and thus generated strong adhesion between coating and substrate. However, the amorphous coating layer unexpectedly represented lower corrosion resistance than pure Cu coating, which might be resulted from the higher content of porosity in the cold sprayed amorphous coating.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.1
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• pp.10-14
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• 2014

Niobium nitride coatings have many potential thin film applications due to their chemical inertness, good mechanical properties, temperature stability and superconducting properties. In this study, $NbN_x$ coatings were prepared by inductively coupled plasma (ICP) assisted DC magnetron sputtering method on the surface of AISI 304 austenitic stainless steels. Effects of target power were studied on mechanical and chemical properties of the coatings. The coating structure was analyzed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The coating hardness was measured by micro-knoop hardness tester. The coating thickness was measured using a 3D profiler and wear characteristics were estimated using a ball-on-disk wear tester. The thickness of the $NbN_x$ coatings increased linearly from 300 nm to 2000 nm as the Nb target power increased, and it showed over $HK_{0.005}$ 4000 hardness above Nb target power of 300 W. Hexagonal ${\delta}^{\prime}$-NbN phase and cubic ${\delta}$-NbN phase were observed in the coating films and the hardness of the NbNx coatings was higher when these two peaks were mixed. The corrosion resistance increased with the increase of the Nb target power.

• Composites Research
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• v.33 no.5
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• pp.256-261
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• 2020

In this study, the ignition temperature of the Al-Ti-C reaction system, the microstructure and the mechanical properties of the TiC/Mg composite which produced by the self-propagating high-temperature synthesis (SHS) followed by stir casting process were investigated. Mg based composite with uniformly dispersed 0, 10, 20, and 30 vol.% TiC were fabricated, and higher volume fraction of TiC reinforced composite showed superior compressive strength and wear resistance as compared with Mg matrix. It is attributed to the less contamination, defects, impurities in TiC/Mg composite by the in-situ SHS yield effective load transfer from the matrix to the reinforcement.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1542-1547
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• 2007

Laser surface treatment technologies have been used to improve characteristics of wear and to enhance the fatigue resistance for mold parts. The optical lens with the elliptical profile is designed to obtain a wide surface hardening area with a uniform hardness. The objective of this research work is to investigate the influence of the process parameters, such as power of laser and defocused spot position, on the characteristics of laser surface treatment for the case of SKD61 steel and SCM4 steel. From the results of the experiments, it has been shown that the maximum average hardness is approximatly 700${\sim}$780 Hv when the power, focal position and the travel of laser are 1,095 W, 0mm and 0.3 m/min, respectively. In samples treated with lower scanning speeds, some small carbide particles appear in the interdendritic regions. This region contains fine martensite and carbide in proportions which depend on the local thermal cycle.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2011.05a
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• pp.58-58
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• 2011

Nickel-ceramics nanocomposite coatings can be applied as the wear resistance coating, corrosion protection of underlying materials, and decorative coatings. Hence, Nickel based nanocomposite coatings, especially Ni-SiC, have been extensively studied in recent years. However, more often agglomeration problem of the nanoparticles in the nickel matrix can cause deterioration of the mechanical properties rather than improvement. The homogeneous distribution of the nanoparticles in the matrix coating is still being challenging. In this experiment, electrochemical deposition of Ni-SiC composite coating was done in presence of ultrasound. The effects of different ultrasonic powers and frequencies on the nanoparticle dispersion were studied. The electrodeposition was carried out in nickel sulfamate bath by applying pulse current technique. Compared to the conventional mechanical stirring technique to prevent nanoparticles agglomeration and sedimentation during composite electrodeposition, the aid of ultrasonic dispersion along with mechanical stirring has been found to be more effective not only for the nanoparticles dispersion, but also for the mechanical properties of the electrodeposited coatings. Nanoparticles were found to be distributed homogeneously with reduced agglomeration. The microstructure of the composite coating has also been changed, allowing some random orientations of the nickel crystallite grain growths, smooth surface, and finer grains. As a consequence, better mechanical properties of the composites were observed.