• Computers and Concrete
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• v.29 no.4
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• pp.255-262
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• 2022

The present study investigates the effects of Cattaneo-Christov thermal effects of stagnation point in Walters-B nanofluid flow through lubrication of power-law fluid by taking the slip at the interfacial condition. The impacts of thermophoresis and Brownian motions are further accounted. The fluid impinging orthogonally on the surface is due to power-law slim coating liquid. The generalized newtonian fluid equation is used that obeys the power law constitutive equation to model our problem. The effect of velocity profiles, temperature for different values of n are investigated. The prandtl on the temperature distribution for partial slip and no slip cases is also observed. It is found that for larger values of prandtl number thermal diffusivity of fluid reduces and it enhance the decrease in temperature and boundary layer thickness.

• Transactions on Electrical and Electronic Materials
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• v.8 no.1
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• pp.5-10
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• 2007

Using a reference slurry, ammonium dodecyl sulfate (ADS), an anionic and environmentally friendly surfactant, was investigated as an alternative to BTA for its inhibition and lubrication characteristics. Results demonstrated that the inhibition efficiency of ADS was superior to that of BTA. Coefficient of friction (COF) was the lowest when the slurry contained ADS. This suggested that adsorbed ADS on the surface provided lubricating action thereby reducing the wear between the contacting surfaces. Temperature results were consistent with the COF and removal rate data. ADS showed the lowest temperature rise again confirming the softening effect of the adsorbed surfactant layer and less energy dissipation due to friction. Spectral analysis of shear force showed that increasing the pad-wafer sliding velocity at constant wafer pressure shifted the high frequency spectral peaks to lower frequencies while increasing the variance of the frictional force. Addition of ADS reduced the fluctuating component of the shear force and the extent of the pre-existing stick-slip phenomena caused by the kinematics of the process and collision event between pad asperities with the wafer. By contrast, in the case of BTA, there were no such observed benefits but instead undesirable effects were seen at some polishing conditions. This work underscored the importance of real-time force spectroscopy in elucidating the adsorption, lubrication and inhibition of additives in slurries in CMP.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.625-630
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• 2013

The friction behavior of a 60-${\mu}m$-thick anodic aluminum oxide (AAO) film having cylindrical nanopores of 45-nm diameter was investigated as a function of impregnated oil viscosity ranging from 3.4 to 392.6 cSt. Reciprocating ball-on-flat sliding friction tests using a 1-mm-diameter steel ball as the counterpart were carried out with normal load ranging from 0.1 to 1 N in an ambient environment. The friction coefficient significantly decreased with an increase in the oil viscosity. The boundary lubrication film remained effectively under all test conditions when high-viscosity oil was impregnated, whereas it was easily destroyed when low-viscosity oil was impregnated. Thin plastic deformed layer patches were formed on the worn surface with high-viscosity oil without evidence of tribochemical reaction and transfer of counterpart material.

• Korean Journal of Metals and Materials
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• v.46 no.11
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• pp.737-746
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• 2008

Mechanisms of sticking phenomena occurring during hot rolling of a modified STS 430J1L ferritic stainless steel have been investigated in this study by using a pilot-plant-scale rolling machine. As the rolling pass proceeds, the Fe-Cr oxide layer formed in a reheating furnace is destroyed, and the destroyed oxides penetrate into the rolled steel to form a thin oxide layer on the surface region. The sticking does not occur on the surface region containing oxides, whereas it occurs on the surface region without oxides by the separation of the rolled steel at high temperatures. This indicates that the resistance to sticking increases by the increase in the surface hardness when a considerable amount of oxides are formed on the surface region, and that the sticking can be evaluated by the volume fraction and distribution of oxides formed on the surface region. The lubrication and the increase of the rolling speed and rolling temperature beneficially affect to the resistance to sticking because they accelerate the formation of oxides on the steel surface region. In order to prevent or minimize the sticking, thus, it is suggested to increase the thickness of the oxide layer formed in the reheating furnace and to homogeneously distribute oxides along the surface region by controlling the hot-rolling process.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2003.11a
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• pp.313-323
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• 2003

The sliding wear behaviors of Zircaloy-4 nuclear fuel rod were investigated using two support springs with convex and concave shapes in room temperature air and water. The main focus is to compare the wear behavior of various test variables such as slip amplitude, environment, contact contours with different spring shape and a number of cycles. The results indicated that wear volume and maximum wear depth increased with slip amplitude in both air and water, but their trends tended to change according to the spring shapes and test environments. In air condition, the wear volume was controlled by wear debris behavior generated on worn surface. As a result, final wear volume and maximum wear depth decreased if a ratio of protruded wear volume to worn area $(D_p)$ would be saturated to specific value. This is because wear particle layer could accommodate large strain by accumulating and transforming wear particle layer. However, in water condition, metal-to metal contact was more dominant and wear volume was greatly affected by changed mechanical behavior between contact surfaces since wear debris should be generated after repeated plastic deformation and fracture. After wear test, worn surfaces were examined using optical microscope and SEM and details of wear mechanism were discussed using a ratio of wear volume to worn area $(D_e)$ at each test condition.

• Journal of Welding and Joining
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• v.35 no.2
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• pp.58-62
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• 2017

A319 aluminum alloy containing 6.5% Si and 3.5% Cu as major alloying elements has been widely used in machinery parts because of its excellent castability and crack resistance. However it needs more wear resistance to extend its usage to the severe wear environments. It has been known that hyper-eutectic Al-Si alloy having more than 12.6% Si contains pro-eutectic Si particles, which give better wear resistance and lubrication characteristics than hypo-eutectic Al-Si alloy like A319 alloy. In this study, it was tried to clad hyper-eutectic Al-Si alloy on the surface of A319 alloy. In the experiments, Al-36%Si alloy powder was mixed with organic binder to make a fluidic paste. The paste was screen-printed on the A319 alloy surface, melted by pulsed Nd:YAG laser and alloyed with the A319 base alloy. As experimental parameters, the average laser power was changed to 111 W, 202 W and 280 W. With increasing the average laser power, the melting depth was changed to $142{\mu}m$, $205{\mu}m$ and $245{\mu}m$, and the dilution rate to 67.2 %, 72.4 % and 75.7 %, and the Si content in the cladding layer to 16.2 %, 14.6 % and 13.7 %, respectively. The cross-section of the cladding layer showed very fine eutectic microstructure even though it was hyper-eutectic Al-Si alloy. This seems to be due to the rapid solidification of the melted spot by single laser pulse. The average hardness for the three cladding layers was HV175, which was much higher than HV96 of A319 base alloy. From the block-on-roll wear tests, A319 alloy had a wear loss of 5.8 mg, but the three cladding layers had an average wear loss of 3.5 mg, which meant that an increase of 40 % in wear resistance was obtained by laser cladding.

• Korean Journal of Metals and Materials
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• v.50 no.3
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• pp.206-211
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• 2012

Graphene has recently received high attention as a promising material for various applications, and many related studies have been undertaken to reveal its basic mechanical properties. However, the tribological properties of graphene film fabricated by the chemical vapor deposition (CVD) method are barely known. In this study, the contact angle and frictional wear characteristics of graphene coated copper film were investigated under room temperature, normal air pressure, and no lubrication condition. The contact angle was measured by sessile drop method and the wear test was carried out under normal loads of 660 mN and 2940 mN, respectively. The tribological behaviors of a graphene coating layer were also examined. Compared to heat treated bare copper foil, the graphene coated one shows a higher contact angle and lower friction coefficient.

• Corrosion Science and Technology
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• v.18 no.5
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• pp.212-219
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• 2019

This paper reviews recent approaches to develop composite polymer-containing coatings by plasma electrolytic oxidation (PEO) using various low-molecular fractions of superdispersed polytetrafluoroethylene (SPTFE). The features of the unique approaches to form the composite polymer-containing coating on the surface of MA8 magnesium alloy were summarized. Improvement in the corrosion and tribological behavior of the polymer-containing coating can be attributed to the morphology and insulating properties of the surface layers and solid lubrication effect of the SPTFE particles. Such multifunctional coatings have high corrosion resistance ($R_p=3.0{\times}10^7{\Omega}cm^2$) and low friction coefficient (0.13) under dry wear conditions. The effect of dispersity and ${\xi}$-potential of the nanoscale materials ($ZrO_2$ and $SiO_2$) used as electrolyte components for the plasma electrolytic oxidation on the composition and properties of the coatings was investigated. Improvement in the protective properties of the coatings with the incorporated nanoparticles was explained by the greater thickness of the protective layer, relatively low porosity, and the presence of narrow non-through pores. The impedance modulus measured at low frequency for the zirconia-containing layer (${\mid}Z{\mid}_{f=0.01Hz}=1.8{\times}10^6{\Omega}{\cdot}cm^2$) was more than one order of magnitude higher than that of the PEO-coating formed in the nanoparticles-free electrolyte (${\mid}Z{\mid}_{f=0.01Hz}=5.4{\times}10^4{\Omega}{\cdot}cm^2$).

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

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.180-186
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• 2000

Friction materials with four different sizes of zircon - l${\mu}{\textrm}{m}$, 6${\mu}{\textrm}{m}$, 75${\mu}{\textrm}{m}$, 140${\mu}{\textrm}{m}$- were investigated to evaluate the size effects of abrasive particles used in the automotive brake pads on brake performance. Although the brake pads with the largest size of zircon showed a good frictional stability and low wear, rotors were severely abraded due to the aggressiveness of coarse Bircon. As the siBe of zircon decreased. friction force and the amplitude of friction coefficient increased. Considering the above results, abrasive materials were thought to destroy transfer film and the extent of the destruction depends on the size of zircon. The small size zircon was not effective in developing a transfer layer on the rotor surface while minimizing the damage on the counter surface.