• 한국세라믹학회지
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• 제52권6호
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• pp.429-434
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• 2015

This study investigates the macroscopic wear behaviors of C/C and C/C-SiC composites coated with hafnium carbide (HfC). To improve the wear resistance of C/C composites, low-pressure chemical vapor deposition (LPCVD) was used to obtain HfC coating. The CVD coatings were deposited at various deposition temperatures of 1300, 1400, and $1500^{\circ}C$. The effect of the substrate material (the C/C substrate, the C/C-CVR substrate, or the C/C-SiC substrate deposited by LSI) was also studied to improve the wear resistance. The experiment used the ball-on-disk method, with a tungsten carbide (WC) ball utilized as an indenter to evaluate the wear behavior. The HfC coatings were found to effectively improve the wear resistance of C/C and C/C-SiC composites, compared with the case of a non-coated C/C composite. The former showed lower friction coefficients and almost no wear loss during the wear test because of the presence of hard coatings. The wear scar width was relatively narrower for the C/C and C/C-SiC composites with hafnium coatings. Wear behavior was found to critically depend on the deposition temperature and the material. Thus, the HfC-coated C/C-SiC composites fabricated at deposition temperatures of $1500^{\circ}C$ showed the best wear resistance, a lower friction coefficient, and almost no loss during the wear test.

• KSTLE International Journal
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• 제3권1호
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• pp.43-48
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• 2002

Dry sliding wear and friction test of CrN coaling on two types of aluminum alloy substrates,6061 Al and 7075 Al deposited by arc ion plating, was peformed with a ball-on-disk tribometer. The effects of normal Bead and the mechanical properties of substrate on the friction coefficient and wear-resistance of CrN coating were investigated. The worn surfaces were observed by SEM. The results show that surface micro-hardness of CrN- coated 7075 Al is higher than that of CrN-coated 6061 Al. With an increase in normal lead, wear volume increases, while the friction coefficient decreases. The friction coefficient of CrN-coated 6061 Al is higher than that of CrN-coated 7075 Al, while the wear-resistance of CrN-coated 6061 Al is lower than the CrN-coated 7075 Al's, which indicates that the substrate mechanical properties have strong inf1uences on the friction coefficient and wear of CrN coating. The main wear mechanism was fragments of CrN coating, which were caused by apparent plastic deformation of substrate during wear test.

• KSTLE International Journal
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• 제6권2호
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• pp.45-50
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• 2005

Plasma ceramic spray that is applied on a machine part under severe work conditions has been investigated for tribological behavior. The application of ceramic coatings by plasma spray has become essential in tribosystems to produce wear resistance and long life in severe conditions. The purpose of this study was to investigate the wear characteristics of $8\%Y_{2}O_3-ZrO_2$ coating, in view of the effect of post-spay heat treatment. The plasma-sprayed $8\%Y_{2}O_3-ZrO_2$ coating was studied to know the relationship between phase transformations and wear behavior related to post-spray heat treatment. Wear test was carried out with ball on disk type on normal loads of 50N,70N and 90N under room temperature. The phase transformation of phase and the value of residual stress were measured by X-ray diffraction method(XRD). Tribological characteristics and wear mechanisms of coatings were observed by SEM. The tribological wear performance was discussed in the focusing of residual stress. Consequently, post-spray heat treatment plays an important role in decreasing residual stress. Residual stress in the coating system has a significant influence on the wear mechanism of coating.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.457-458
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• 2002

The fractal dimension is the characteristics that can quantitatively define the irregularity in natural. It is useful in describing the morphology or various rubbed surface for hydraulic piston motor instead of the stylus profiling method. But fractal parameters had not constructed on the morphological characteristic or rubbed surface because of the insufficient knowledge about a conception of fractal dimension. In this study, for the purpose or applying fractal I parameters practically, we have suggested way to establish the morphological characteristic of rubbed surface with fractal parameters, and we carried out an experiment on the lubricant friction and wear by using Ball-ON-Disk type tester. Materials were the brass and the bronze which are used to slipper-pad in the hydraulic piston motor. We searched for fractal parameters or surface structure with the digital image processing, Surface fractal dimension can be determined by sum of intensity difference of surface pixel. Using the image processing and fractal parameters for rubbed surface in the friction and wear test, morphology of rubbed sur race can be effectively obtained by fractal dimensions.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.45-52
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• 2002

The tribological role of mass transfer layer was studied with silver coatings under various ranges of load and sliding speed. Silver coating was performed with a functionally gradient coating method. Tests were performed in dry sliding conditions, using a ball-on-disk contact configuration, at the load of 0.0196-17.64 N and the sliding speed of 20-1,000 mm/s in ambient air. Optical microscope and EPMA analyses showed that contact surfaces were covered with the mass transfer layers of agglomerated wear particles depending upon the contact conditions, and they greatly influenced the tribological characteristics of the surfaces. However, the formation of mass transfer layer was suppressed as the sliding speed increased, and above a critical sliding speed, no mass transfer layer was able to form. For building up a general framework of tribological behavior of the coated silver films, all test data were summarized on a map whose axes are contact pressure and sliding speed.

• 한국재료학회지
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• 제17권11호
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• pp.601-605
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• 2007

The tribological properties of acrylonitrile-butadiene rubber (NBR) filled with two kinds of carbon black filler were examined. Different types of Semi-Reinforcing Furnace (SRF), and High Abrasion Furnace (HAF) blacks were used as filler material to test the influence of carbon black particle size on the friction and wear of NBR. Results from tribological tests using a ball on disk method showed that the smaller HAF particles were more effective for reducing the wear of NBR during frictional sliding. The hardness, elastic modulus at 100% elongation, and elongation at break were measured to examine the correlation between the effects of carbon black on the mechanical and tribological properties of the NBR specimens. The wear tracks of the NBR specimens were observed with scanning electron microscopy (SEM). The wear tracks for NBR with different ratios of SRF and HAF showed clearly different abrasion patterns. Mechanisms for the friction and wear behavior of NBR with different sizes of carbon black filler were proposed using evidence from wear track observation, as well as the mechanical and tribological test results.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.312-315
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• 2004

A lubricated state of an automobile transmission can not be inspected directly with eyes. Thus, it needs to develop a more general method. Wear debris can be collected from the lubricants of operating transmission of an automobile and its morphology is directly related to the fiction condition of the interacting materials from which the wear particles originated in lubricated transmission. In this paper, to identify the friction condition for transmission gear by neural network, the wear test of ball-on-disk type and the analysis of friction state were carried out for carburized SCM420 and nitrocarburized NT100 under different experimental conditions. The four shape parameters($50\%$ volumetric diameter, aspect, roundness and reflectivity) of wear debris were calculated by the image processing system. They were used as input values to identify the moving condition of transmission gear by the neural network.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.748-752
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• 2004

Fluid dynamic bearings (FDBs) have been replacing ball bearings of the HDD spindle motor very rapidly. But there are several demerits of HDB, such as high friction torque, variable viscosity of the fluid lubricant depending on operating temperature, low stiffness, and etc. Eccentricity is one of the major parameters which affects the static and dynamic characteristics. As the static eccentricity is larger, the stiffness and the damping coefficients become bigger. But friction torque is relatively unaffected by the static eccentricity. This research proposes a new type of journal bearing with asymmetric journal grooves which results in better dynamic characteristics. The static and dynamic characteristics of the new journal bearing are investigated by solving the Reynolds' equation with FEM, and the transient analysis is performed to predict the dynamic behavior of rotor by solving the equations of motion of a HDD spindle system with Runge-Kutta method. The result shows that the proposed Journal bearings have much bigger stiffness and damping coefficients compared with the conventional symmetric ones. And consequently, it has smaller whirl radius and tilting angle.

• 한국기계가공학회지
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• 제16권1호
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• pp.149-156
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• 2017

Graphene nanoplatelet (GNP)-reinforced alumina ($Al_2O_3$) is a promising material for micro-partapplications, particularly micro-nozzle shapes, because of its excellent wearresistance. In this study, a $Al_2O_3$/GNPcomposite with 15 vol% graphene nanoplatelets (GNP) was highly densified and fabricated via spark plasma sintering for micro-electrical discharge drilling (Micro-ED drilling) and the wear resistance property of the composite is evaluated via the ball-on-disk method. In addition, the diameter and shape of the micro-electrodes machined by wire electrical discharge grinding (WEDG), block electrical discharge grinding (BEDG), and new linear block moving electrical discharge grinding (LBMEDG) methods are systematically compared and analyzed to observe the micro-hole machining in the micro-ED drilling of the $Al_2O_3$/15vol% GNP composite.

• Tribology and Lubricants
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• 제11권5호
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• pp.59-65
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• 1995

Tribological behaviors of nitrogen incorporated amorphous diamond-like carbon films were experimentally measured under a vacuum ($3 \times 10^{-5}$ Torr) using a ball (AISI 52100 steel)-on-disk wear-rig. Nitrogen incorporated DLC films were deposited by r.f. plasma assisted chemical vapor deposition method. Mixtures of benzene and ammonia or nitrogen gases were used as the reaction gases for the r.f. PACVD, and Si (100) wafer was used as the substrate. In the tribo-test, effects of DLC film thickness and normal load in friction were measured and discussed. Results showed that friction of nitrogen incorporated DLC films from a mixture gas of benzene and ammonia was lower than that of 100% benzene, specially in the measurement of minimum coefficient of friction. Differences in frictional characteristics of nitrogen incorporated DLC films were explained with the changes in chemical structures of the films. Result also showed that friction of DLC films increased with the sliding contact cycle, which remarkably accompanied with roll-shaped wear debris. Mechanisms and roles of the polymer-like wear debris were presented and discussed.