나노스케일 표면돌기 간의 미세접촉에 대한 해석

안효석,장동영,Ahn, Hyo-Sok,Jang, Dong-Young 한국생산제조학회 2009 한국생산제조학회지 Vol.26 No.3

In micro/nano-scale contacts in MEMS and NEMS, capillary and van der Waals forces generated around contacting micro-asperities significantly influence the performance of concerning device as they are closely related to adhesion and stiction of interacting surfaces. In this regard, it is of prime importance to accurately estimate the magnitude of surface forces so that an optimal solution for reducing friction and adhesion of micro/nano-surfaces may be obtained We introduced an effective method to calculate these surface forces based on topography information obtained from an atomic force microscope. This method was used to calculate surface forces generated in the contact interface formed between diamond-like carbon coating and $Si_3N_4$ ball. This method is shown to effectively demonstrate the influence of capillary force in the contact area, especially in humid atmosphere.

WC/C 박막의 윤활접촉하의 마멸기구

안효석(Hyo-Sok Ahn),김두인(Doo-In Kim) 한국트라이볼로지학회 2008 한국윤활학회지(윤활학회지) Vol.24 No.6

The running-in behaviour of the metal carbon coating (WC/C) was evaluated with regard to its applicability as wear-resistant coating for key components in engines. Reciprocating wear tests under lubricated condition employing an oscillating friction wear tester were performed to investigate the tribological behaviors of the coatings in ambient environment. Confocal microscopy and scanning electron microscopy were used to observe worn surfaces and the wear scars on the steel balls. Elemental composition of the coating and worn surfaces were characterized using Auger electron spectroscopy. The friction behavior of WC/C coating was comparable to common carbon-based coatings. Thin tribofilm was formed on the worn surface of the steel ball due to material transfer and tribochemical reaction whereas there was no evidence of tribofilm generation on the coating surface. indicating the chemical innertness of WC/C coating.

Si 함유량에 따른 Si-DLC/DLC 코팅의 건조마찰 특성

안효석(Hyo-Sok Ahn) 한국생산제조학회 2007 한국생산제조학회지 Vol.16 No.6

Although DLC coatings have good tribological properties, these are dependent on the deposition method, property of contact surface, and test condition. Si-DLC/DLC coatings with various Si content were deposited on Si substrates and tested using a reciprocating friction tester against steel balls. The results revealed that the tribological behavior of Si-DLC/DLC coatings was dependent on the Si content. The formation of transfer film and wear particles on the contact surface was greatly influenced by the Si content in DLC coatings. In particular, silicon oxide transfer film formed by tribochemical reaction contributed to reduce wear and friction.

원자력현미경의 위상차영상을 이용한 나노표면의 미소기계적 특성 평가

안효석(Hyo-Sok Ahn) 한국생산제조학회 2007 한국생산제조학회지 Vol.16 No.5

Phase contrast imaging in atomic force microscopy showed a promise as an effective tool for better understanding of micromechanical properties of surfaces at nano scale. A qualitative estimation model for phase contrast images obtained with a tapping mode AFM was developed. This investigation demonstrated the high efficiency of combined analysis of topography and phase contrast images for characterizing nanosurfaces. Phase contrast images allowed estimation of relative stiffness(elastic modulus) of the sample surface. The phase contrast images revealed a significant inhomogeneity of the nano scale worn surfaces. Phase contrast images are also capable of revealing the formation of tribofilms.

원자력현미경의 위상차영상을 이용한 나노표면의 미소기계적 특성 평가

안효석(Hyo-Sok Ahn) 한국생산제조학회 2007 한국공작기계학회 춘계학술대회논문집 Vol.2007 No.-

Phase contrast imaging in atomic force microscopy showed a promise as an effective tool for better understanding of micromechanical properties of surfaces at nano scale. A qualitative estimation model for phase contrast images obtained with a tapping mode AFM was developed. This investigation demonstrated the high efficiency of combined analysis of topography and phase contrast images for characterizing nanosurfaces. Phase contrast images allowed estimation of relative stiffness (elastic modulus) of the sample surface. The phase contrast images revealed a significant inhomogeneity of the nano scale worn surfaces. Phase contrast images are also capable of revealing the formation of tribofilms.

나노스케일 표면돌기 간의 미세접촉에 대한 해석

안효석(Hyo-Sok Ahn),장동영(Dong-Young Jang) 한국생산제조학회 2009 한국생산제조학회지 Vol.18 No.4

In micro/nano-scale contacts in MEMS and NEMS, capillary and van der Waals forces generated around contacting micro-asperities significantly influence the performance of concerning device as they are closely related to adhesion and stiction of interacting surfaces. In this regard, it is of prime importance to accurately estimate the magnitude of surface forces so that an optimal solution for reducing friction and adhesion of micro/nano-surfaces may be obtained. We introduced an effective method to calculate these surface forces based on topography information obtained from an atomic force microscope. This method was used to calculate surface forces generated in the contact interface formed between diamond-like carbon coating and Si₃N₄ ball. This method is shown to effectively demonstrate the influence of capillary force in the contact area, especially in humid atmosphere.

Si 함유량에 따른 Si-DLC/DLC 코팅의 건조마찰 특성

안효석(Hyo-Sok Ahn) 한국생산제조학회 2007 한국공작기계학회 춘계학술대회논문집 Vol.2007 No.-

Although DLC coatings have good tribological properties, these are dependant on the deposition method, property of contact surface, and test condition. Si-DLC/DLC coatings with various Si content were deposited on Si substrates and tested using a reciprocating friction tester against steel balls. The results revealed that the tribological behavior of Si-DLC/DLC coatings was dependant on the Si content. The formation of transfer film and wear particles on the contact surface was greatly influenced by the Si content in DLC coatings. In particular, silicon oxide transfer film formed by tribochemical reaction contributed to reduce wear and friction.

나노기공구조를 가진 알루미나필름의 트라이볼로지 특성

김효상(Hyo-Sang Kim),김대현(Dae-Hyun Kim),안효석(Hyo-Sok Ahn),한준희(Junhee Hahn),이우(Lee Woo) 한국트라이볼로지학회 2009 한국트라이볼로지학회 학술대회 Vol.2009 No.11

Tribological properties of nanoporous structured alumina film was investigated. Alumina film (AAO: anodic aluminum oxide) of 2 ㎛ thickness having nanopores of 45 ㎚ diameter with 105 ㎚ interpore-diatance was fabricated by mild anodization process. Reciprocating ball-on-flat sliding friction tests using 1 ㎜ diameter steel ball as a counterpart were carried out with wide range of normal load from 1 mN to 1 N in an ambient environment. The morphology of worn surfaces were analyzed using scanning electron microscopy. The friction coefficient was strongly influenced by the applied normal load. Smooth layer patches were formed on the worn surface of both AAO and steel ball at relatively high load (100 mN and 1 N) due to tribochemical reaction and compaction of wear debris. These tribolayers contributed to the lower friction at high loads. Extremely thin layer patches, due to mild plastic deformation of surface layer, were sparsely distributed on the worn surface of AAO at low loads (1 mN and 10 mN) without the evidence of tribochemical reaction. Delaminated wear particles were generated at high loads by fatigue due to repeated loading and sliding.

MoO₃가 첨가된 Cr₂O₃ 플라즈마 용사코팅의 고온 마찰 마멸 특성

여인웅,안효석,임대순,Lyo, In-Woong,Ahn, Hyo-Sok,Lim, Dae-Soon 한국세라믹학회 2002 한국세라믹학회지 Vol.39 No.9

산화몰리브덴($MoO_3$)이 첨가된 산화크롬 용사코팅층을 제조하여 산화몰리브덴의 첨가에 따른 고온(450$^{\circ}C$)에서의 플라즈마 용사코팅층에 마찰, 마멸특성을 조사하였다. 마찰, 마멸 특성에 대한 실험을 위하여 왕복동 마멸시험장치를 사용하였다. TEM을 이용하여 코팅층의 미세 구조와 각 상들의 조성을 살펴보았다. 분석 결과에 의하면 산화몰리브덴이 입계로 분산되어 있어 코팅층의 경도와 밀도의 증가가 발생하였다. 마멸시험후 마멸면의 물리적 변화와 화학적 조성의 변화를 SEM와 XPS를 통하여 살펴보았다. 산화몰리브덴이 첨가된 코팅층에서 마찰계수의 감소를 관찰할 수 있었다. 산화몰리브덴이 첨가된 코팅의 마멸된 표면에 마찰, 마멸에 유리한 보호막의 형성이 광범위하게 일어남을 알 수 있었다. 이러한 보호막에 몰리브덴이 산화몰리브덴의 형태로 존재하는 것을 XPS 분석을 통하여 알 수 있었다. 보호막에 산화몰리브덴의 존재가 마찰계수를 감소시키는 것으로 생각된다. Tribological behavior of plasma-sprayed $Cr_2O_3$-based coatings containing $MoO_3$ at 450$^{\circ}C$ was investigated to understand the influence of $MoO_3$. A reciprocal disc-on-plate type tribo-tester was employed to examine fricition and wear behavior of the specimens. The microstructure and phase composition of the coating was characterized with Transmission Electron Microscopy(TEM). The TEM analysis indicated that $MoO_3$ was dispersed into the grain boundary, resulting in the increase of the hardness and density of the coating. Worn surfaces were investigated by scanning electron microscopy and chemistry of the worn surfaces was analyzed using a X-ray Photoelectron Spectrometer(XPS). The results showed that the friction coefficient of the $MoO_3$-added coatings was lower than that without $MoO_3$ addition. The larger protecting layers were observed at the worn surface of plasma spray coated specimens with $MoO_3$ composition in the protecting layer appears to be more favorable in reducing the friction.

오일 함침된 나노 기공 산화알루미늄 필름의 마찰 거동

김효상(Hyo-Sang Kim),김대현(Dae-Hyun Kim),한준희(Junhee Hahn),안효석(Hyo-Sok Ahn) 한국트라이볼로지학회 2011 한국윤활학회지(윤활학회지) Vol.27 No.4

Friction behavior of nanoporous anodic aluminum oxide(AAO) film was investigated. A 60 μm thick AAO film having nanopores of 45 nm diameter with 105 nm interpore-diatance was fabricated by mild anodization process. The AAO film was then saturated with paraffinic oil. Reciprocating ball-on-flat sliding friction tests using 1 mm diameter steel ball as the counterpart were carried out with normal load ranging from 0.1 N to 1 N in an ambient environment. The morphology of worn surfaces were analyzed using scanning electron microscopy. The friction coefficient significantly increased with the increase of load. The boundary lubrication layer of paraffinic oil contributed to the lower friction at relatively low load (0.1 N), but it is less effective at high load (1 N). Plastic deformed layer patches were formed on the worn surface of oil-enriched AAO at relatively low load (0.1 N) without evidence of tribochemical reaction. On the other hand, thick tribolayers were formed on the worn surface of both oil-enriched a nd as-prepared AAO at relatively high load (1 N) due to tribochemical reaction and material transfer.