• Tribology and Lubricants
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• 제34권6호
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• pp.235-240
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• 2018

Superlubricity refers to the lubrication phenomenon that occurs when the friction coefficient is lower than 0.01. In recent years, this phenomenon has received a significant amount of attention because it can greatly contribute to the reduction of economic and environmental losses caused by friction and wear. In the case of acid lubricants, only ceramic materials can be used for superlubricity, and it takes a long running-in period to enter the superlubricity regime. In this work, we investigated the superlubricity effect of vitreous enamel coating on SUS304. We also examined the running-in period of vitreous enamel coating under phosphoric acid lubricant condition with respect to surface treatments. Drying and polishing methods were used to treat the vitreous enamel coating on the specimen. The friction experimental results revealed that superlubricity could be achieved with vitreous enamel coating. It was also found that the drying and polishing methods can significantly reduce the running-in period and improve the wear properties of vitreous enamel coating. In particular, the polishing method shortened the running-in period by approximately 99% and reduced the wear rate by approximately 99%, compared to nontreated vitreous enamel coating.

• 한국표면공학회지
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• 제43권2호
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• pp.97-104
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• 2010

In this paper, we conducted MATLAB simulation using the reflectance formula and the Planck's black body radiation principle, for the purpose of identifying the opimum material and thickness of anti-reflective coating from double layered structures. We found that the optimum condition was obtained when refractive index of upper layer is 1.44 and that of lower layer is 2.29. As materials close to these refractive indices, $MgF_2$ as the upper layer and $HfO_2$, ZnS, $TiO_2$ as the lower layer were suggested. The best result in an average reflectance of 2.759% was obtained from a double layered structure of $MgF_2$ 94 nm/ZnS 55 nm.

• 한국재료학회지
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• 제30권11호
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• pp.609-614
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• 2020

3 mol% yttria-doped stabilized zirconia (3YSZ) is synthesized by a solvothermal process, and its characteristics are investigated using various methods. Also, the dispersibility of synthesized 3YSZ nanoparticles is observed with the species of surface modifier. The 3YSZ nano sol prepared with an optimum condition is employed in prism coating and its properties are evaluated. The synthesized 3YSZ nanoparticles show a globular shape with about 10 to 20 nm crystallite size. The mixed phases with the nano sol show a high specific surface of 178 ㎡/g. The prism sheet coated with the 3YSZ nano sol present an excellent refractive index, transmittance, and luminance; refractive index is 1.603, transmittance is 90.2 %, and luminance of coating film is improved by 5.9 % compared to that of the film without 3YSZ nano sol. It is verified that the surface modified 3YSZ is suitable as the prism sheet for optical displays.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.42-48
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• 2001

Chromium carbides have the excellent wear properties as transition metal carbides. Their tribological applications were studied recently. The nano-sized ceramic could enhance the mechanical and electronical properties of materials. In this study, it was observed to test the wear of the coated surface of nano-sized chromium carbides. The nano-sized chromium carbides were produced by sol-gel processing. Coating surface of produced powders was obtained front plasma spraying. Wear test of coating surface was held increasing temperature. The friction coefficient and the wear loss were testified in dry environment. And the worn surfaces were analyzed by XRD and SEM.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.127-134
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• 2001

Nano adhesion and friction between a Sj$_3$N$_4$ AFM tip and thin silver films were experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM(atomic force microscope) and LFM(lateral force microscope) modes in various ranges of normal load. Thin silver films deposited by IBAD (ion beam assisted deposition) on Si-wafer (100) and Si-wafer of different surface roughness were used. Results showed that nano adhesion and friction decreased as the surface roughness increased. When the Si surfaces were coated by pure silver, the adhesion and friction decreased. But the adhesion and friction were not affected by the thickness of IBAD silver coating. As the normal force increased, the adhesion forces of bare Si-wafer and IBAD silver coating film remained constant, but the friction forces increased linearly. Test results suggested that the friction was mainly governed by the adhesion as long as the normal load was low.

• 한국표면공학회지
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• 제40권6호
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• pp.254-257
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• 2007

TiN coating on tool steel has been widely used for the improvement of durability of tools. In this work, radical nitriding(RN) is carried out on SKD61 at $450^{\circ}C$ for 5 hours in the ammonia gas pressure $2.7{\times}10^3\;Pa$. The TiN coating is carried out by arc ion plating(AIP) with the process parameters: arc power 150 A, bias voltage -50V, coating time 40 minutes and nitrogen gas pressure $4{\times}10^3\;Pa$. Hardness, elastic modulus, friction coefficient and adhesion of TiN coating on substrates of both TiN/SKD61 and TiN/RN SKD61 coatings are investigated comparatively. The primary crystalline faces of TiN surface are(200) and(111) for TiN/SKD61 and TiN/RN SKD61 respectively. In addition to the primary phase, Fe phase exists in TiN/SKD61 coating, but not in TIN/RN SKD61. The hardness of TiN/RN SKD61 is about 700 Hv, 250 Hv(56%) higher than that of TiN/SKD61 at the near interface of TiN and substrates. At the TiN surface, hardness of TiN/RN SKD61 is 2,149 Hv, 71 Hv(3%) higher than that of TiN/SKD61. The elastic modulus of TiN coating is improved to 26.7 GPa(6%) by radical nitriding. The adhesion is improved by the RN coating showing no spalling. buckling and chipping on the scratch test track which are shown on the non-RN TiN/SKD61.

• 한국결정성장학회지
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• 제17권4호
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• pp.172-178
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• 2007

수평회전식 수열법에 의해 운모 분말을 합성하였다. 수열조건은 출발원료로 $K_2O,\;Al(OH)_3$ 그리고 $SiO_2$의 비는 1 : 3 : 3mol%로 하고 수열용매로 8mol%의 KOH를 함께 추가하여 $260^{\circ}C$에서 72시간 동안 반응시켰다. 합성한 분말은 수직형 수열처리법에 의한 은나노 코팅 운모 제조를 위해 사용하였다. 은나노 코팅의 처리를 위한 수열조건은 출발원료로 합성한 분말로 하고, 수열용매로 $0.5{\ell}$ 3차 증류수, 그리고 1,000ppm의 은나노 졸을 코팅원료로 사용하여 $160{\sim}260^{\circ}C$ 범위에서 72시간 동안 반응시켰다. 처리 후 결정구조, 은나노 코팅 여부 및 코팅된 운모의 특성은 XRD, SEM, TEH-EDX 및 shake plask법을 통해 분석하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.202.1-202.1
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• 2013

ZnO nanostructure was fabricated on a Si substrate using two-step growth. The seed layer was grown on the Si substrate by a sol-gel spin-coating. In the first step, ZnO nanorods were grown by a hydrothermal method at $140^{\circ}C$ for 5 min. In the second step, a ZnO thin film was grown on the ZnO nanorods by spin-coating. After growth, these films were annealed at $800^{\circ}C$ for 10 min. Electrical and optical properties of ZnO nanostructures have modified by plasma-assisted molecular beam epitaxy (PA-MBE) regrowth. The carrier concentration and resistivity increased by PA-MBE regrowth. In the photoluminescence, the full width at half maximum and intensity were decreased and increased, respectively, by PA-MBE regrowth.

• 한국정밀공학회지
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• 제24권3호
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• pp.91-99
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• 2007

Fractures of galvannealed coating layer during actual press forming in automotive applications were observed by scanning electron microscopy in order to understand fracture mechanism. Fracture behaviors of galvannealed coating layer in extra deep drawing quality steels and high strength steels have been studied by performing the tests describing the representative plastic deformation in sheet metal forming such as uni-axial tensile test, compression test, bi-axial test and plane strain test. Growth and direction of cracks were deeply related to the plastic deformation modes and history. The material properties of galvannealed coating layer were investigated by nano-indentation test equipped with Berkovich diamond indentor for the specimens. Hardness and elastic modulus of the coating layer were higher than bared steels and that was the reason for crack of coating layer. Flat friction test and drawbead friction test were performed to observe the effect of the surface morphology on the frictional characteristics. The micro-plasto hydrodynamic lubrication were appeared and played an important role in reducing the coefficient of friction.

• Tribology and Lubricants
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• 제35권2호
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• pp.106-113
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• 2019

We investigated the application of tetrahedral amorphous carbon (ta-C) coatings to fabricate a glass lens manufactured using a glass molding process (GMP). In this work, ta-C coatings with different thickness (50, 100, 150 and 200 nm) were deposited on a tungsten carbide (WC-Co) mold using the X-bend filter of a filtered cathode vacuum arc. The effects of thickness on mechanical and tribological properties of the coating were studied. These ta-C coatings were characterized by atomic force microscopy, scanning electron microscopy, nano-indentation measurements, Raman spectrometry, Rockwell-C tests, scratch tests and ball on disc tribometer tests. The nano-indentation measurements showed that hardness increased with an increase in coating thickness. In addition, the G-peak position in the Raman spectra analysis was right shifted from 1520 to $1586cm^{-1}$, indicating that the $sp^3$ content increased with increasing thickness of ta-C coatings. The scratch test showed that, compared to other coatings, the 100-nm-thick ta-C coating displayed excellent adhesion strength without delamination. The friction test was carried out in a nitrogen environment using a ball-on-disk tribometer. The 100-nm-thick ta-C coating showed a low friction coefficient of 0.078. When this coating was applied to a GMP, the life time, i.e., shot counts, dramatically increased up to 2,500 counts, in comparison with Ir-Re coating.