• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2003.11a
• /
• pp.355-359
• /
• 2003

In this paper, we investigated the wear lift, wear rate, and its transition on the Hertz pressure. In the experiment, we used TiAlCrN coating deposited by the sputtering technique and ball diameter of 10mm, 7.94mm and 4.76mm for the various Hertz pressure. Ball-on-disk sliding tests wire performed under the unlubricated condition. As the diameter of a ball decreased, the failure load of TiAlCrN coating decreased. However, a good correlation was observed between the wear life and Hertz pressure, and all ball specimens showed the infinite wear life at about 450MPa. In measurement of wear rate, as the diameter of the ball inclosed, the wear transition appeared in bigger load. However, a good correlation was observed between the wear rate and Hertz pressure. The transition appeared in the range from 550MPa to 600MPa at all ball speimens.

• Journal of the Korean Vacuum Society
• /
• v.7 no.1
• /
• pp.59-65
• /
• 1998

Multi-layer diamond-like carbon (DLC) films were deposited by 13.56 MHz r.f. PACVD method. Multi-layer DLC film was composed of 2.5 $mu extrm{m}$ thick pure DLC filml and 0.2$\mu\textrm{m}$ thick Si incorporated DLC (Si-DLC) film as a surface layer. Tribological behaviors of the multi-layer DLC film were investigated with a ball-on-disk type tribometer in ambient atmosphere using AISI 52100 steel ball. Low friction coefficient (<0.1) period increased with increasing the Si content in the surface Si-DLC film. The wear rate after 44,000 cycles and 158,400 cycles were the $2.5\times10^{-8}\sim1.8\times10^{-7}\textrm{mm}^3$/rev. and $7.1\times10^{-9}\sim1.8\times10^{-8}\textrm{mm}^3$/rev.,respectively. The wear rate of the multi-layer DLC film after 158,400 cycles was about 2 times smaller than that of pure DLC films of 2.7 $\mu\textrm{m}$ thickness. This high wear resistance and low friction coefficient was caused by the formation of Si oxide layer on the wear scar surface, as confirmed by the debris composition analysis. It was further shown that this si oxide debris layer on the wear scar surface is formed again even after removing the debris of the steel ball, which maintain the low friction coefficient between multi-layer DLC films and steel ball.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07b
• /
• pp.674-677
• /
• 2002

In this paper, two kinds of windmill type motors which have a disk shape and a ring shape piezoelectric ceramics were studied. And characteristics of two models were compared with each others. A windmill type ultrasonic motor is composed of a stator, a rotor, and a ball bearing. The stator is made of a piezoelectric ceramics and two metals endcaps. When the piezoelectric ceramics vibrate, displacement of torsonal vibration appear at metal endcaps. The motor with 11.0[mm] diameter was studied by finite element analysis. The voltage of 100[V] was supplied at each model. Resonance frequency of 206.875[KHz] was obtained at the disk type, but ring type was 137.562[KHz]. The maximum torsonal displacement of $1.112[{\mu}m]$ was obtained at the disk type, but ring type was $1.698[{\mu}m]$.

• Tribology and Lubricants
• /
• v.23 no.6
• /
• pp.298-300
• /
• 2007

Frictional characteristics of mesoporous $SiO_2$ thin films were evaluated with different pore sizes. The films were manufactured by sol-gel and self-assembly methods to have a porous structure. The pores on the surface may play as the outlet of wear particle and the storage of lubricant so that the surface interactions could be improved. The pores were exposed on the surface by chemical mechanical polishing (CMP) or plasma-etching after forming the porous films. The ball-on-disk tests with mesoporous $SiO_2$ thin films on glass specimen were conducted at sliding speed of 15 rpm and a load of 0.26 N. The results show considerable dependency of friction on pore size of mesoporous $SiO_2$ thin films. The friction coefficient decreased as increasing the pore size. CMP process was very useful to expose the pores on the surface.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.19 no.7
• /
• pp.618-623
• /
• 2006

Hydrogenated Diamond-like carbon (DLC) films were prepared by the radio frequency plasma enhanced chemical vapor deposition (RF PECVD) method on silicon substrates using methane $(CH_4)$ and hydrogen $(H_2)$ gas. The wear track on the DLC films was examined after the ball-on disk (BOD) measurement with a Raman mapping method. The BOD measurement of the DLC films was performed for 1 to 3 hours with a 1-hour step time. The sliding traces on the hydrogenated DLC film after the BOD measurement were also observed using an optical microscope. The surface roughness and cross-sectional images of the wear track were obtained using an atomic force microscope (AFM). The novel Raman mapping method effectively shows the graphitization of DLC films of $300{\mu}m\times300{\mu}m$ area according to the sliding time by G-peak positions (intensities) and $I_D/I_G$ ratios.

• Tribology and Lubricants
• /
• v.22 no.3
• /
• pp.127-130
• /
• 2006

DLC (Diamond Like Carbon) films show very desirable surface interactions with high hardness, low friction coefficient, and good wear-resistance properties. The friction behavior of hydrogenated DLC film is dependent on tribological environment, especially surrounding temperature. In this work, the tribological behaviors of DLC (Diamond-like carbon) films, prepared by the radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method, were studied in elevated temperatures. The ball-on-disk tests with DLC films on steel specimens were conducted at a sliding speed of 60 rpm, a load of 10N, and surrounding various temperatures of $25^{\circ}C,\;40^{\circ}C,\;55^{\circ}C\;and\;75^{\circ}C$. The results show considerable dependency of DLC tribological parameters on temperature. The friction coefficient decreased as the surrounding temperature increased. After tests the wear tracks of hydrogenated DLC film were analyzed by optical microscope, scanning electron spectroscopy (SEM) and Raman spectroscopy. The surface roughness and 3-D images of wear track were also obtained by an atomic force microscope (AFM).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.05a
• /
• pp.930-935
• /
• 2001

The experimental characterization of hydrodynamic bearing spindle motor is performed for the practical implementation of high-performance hard disk drive system. Firstly, the design concept of hydrodynamic bearing for the disk drive system is addressed including the herringbone grooved journal bearing, the spiral grooved thrust bearing, capillary seal design, and the viscous pumping of fluid. Secondly, the experimental evaluation is performed for the disk drive system in which the hydrodynamic bearing spindle motor is implemented and its dynamic performances are compared with conventional ball-bearing spindle motor. The key parameters include NRRO(Non Repeatable Run-Out), disk dynamics, acoustics, and resultant PES (Position Error Signal). Finally, the external gyro-exciting test results including 200k CSS(Continuous Start-Stop) on three angular attitudes(0,90, 180 degree) are presented in order to verify the practical reliability of disk drive system subject to the gyro-motion of hydrodynamic bearing spindle motor.

• Tribology and Lubricants
• /
• v.14 no.2
• /
• pp.35-41
• /
• 1998

The $WS_2$ solid lubricant synthesized through the vapour phase transport method was coated on the commercial bearing steel (SUJ 2) substrate, and the tribological behaviour of the lubricant was investigated using a ball-on-disk type tester. The $WS_2$ powder was spray-coated at room temperature using compressed air, and the change of friction coefficient was examined in various conditions, i.e., specimen configuration, atmosphere (air and nitrogen), applied load and rotating speed. $WS_2$ coated ball and disk showed the optimum friction coefficient of 0.07 and wear life of 45,000 cycles in the nitrogen atmosphere under 0.3 kgf and 100 rpm, whereas relatively high coefficient of 0.13 and reduced wear life of 4,000 cycles were observed in air atmosphere. The effect of rotating speed on the friction coefficient was not observed both in nitrogen and in air atmospheres. This confirmed that the spray-coated $WS_2$ solid lubricant was effective in reducing the friction coefficient and improving wear life in nitrogen atmosphere, and the oxygen and moisture existing in air could seriously deteriorate the lubrication effect of $WS_2$ coating layer.

• Journal of the Korean Society for Heat Treatment
• /
• v.27 no.2
• /
• pp.65-71
• /
• 2014

SMF9060 material is a Fe-based powder sintered alloy that is used for several automobile components such as Synchronize Hub, oil pump and transmission. These components are required excellent wear resistance and durability. In this study, we have performed a dry wear test at the ambient air and Ar gas conditions in the room temperature, and a lubricant wear test at the room temperature and engine oil temperature of $100^{\circ}C$. The amount of wear volume and coefficient friction are measured by a Profilometer and a Ball on disk type wear tester. The wear volume in Ar gas condition was a little higher than that in the ambient air condition. However the wear volume in the lubricant wear condition was much lower than in the dry wear condition. XRD analysis of the debris in Ar gas condition showed that the oxide film was not formed.

• Tribology and Lubricants
• /
• v.30 no.5
• /
• pp.291-294
• /
• 2014

Multiple additives can help improve the performance of generally used lubricants. These additives include MoS2, cadmium, chloride, indium, sulfide, and phosphide, which are harmful to both humans and the environment. Thus, researchers in this industry have been trying to reduce the use of these additives by finding alternatives. Nanodiamonds are one of these candidates. Nanodiamond particles are very hard, chemically stable, and highly heat-conductive. This research involved uniformly dispersing nanodiamond particles in marine engine oils via a matrix synthesis method at various concentrations (0, 0.1, 0.3, 0.5, and 1.0 wt). Friction and wear tests involved constant loads on ball-on-disk specimens, where the ball was AISI 51200 steel, the disk was AISI 1020 steel, and the sliding speed was 0.217 m/s. The lowest wear occurred at a suitable concentration of nanodiamonds (0.3 wt). However, excessive amounts of nanodiamonds caused them to act as abrasive debris because of their hardness, which increased the wear amount. The friction coefficient decreased as the nanodiamond concentration increased because their octagonal, almost spherical shape caused them to act as rolling contact elements between two surfaces.