The viscosity of motor oil gets lower in order to decrease resistance at region of the fluid lubrication. On the other hands, this causes increasing of friction at the boundary lubrication region. For this reason, it is required to use a friction modifier to reduce the boundary friction. MoDTC is especially used as friction modifier. Although the decomposition mechanism of MoDTC has been presumed, it is considered only in the case of metal, not hard coatings. So, it is required to understand the effects of hard coatings to friction in motor oils. We tried to clarify the surface and tribofilm changes depending on the kinds of hard coatings by SEM-EDX, TEM and so on. As a result of experiment of hard coatings against metal, we clarified the process as follows when friction of CrN reduces. In the early stage of friction, Fe of the opposite metal transfers to CrN. Mo₂S₂O₂ intermediate product which is formed by MoDTC decomposition is formed on CrN divided into Fe oxide and Mo sulfide. At this time, crystal orientation between Fe oxide and CrN is matching because the lattice constant of Fe oxide is twice that of CrN. These results show that the crystal structure of hard coatings is important for formation of stable interface. And this newly knowledge is necessary to achieve low friction for systems using hard coatings.

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In this work, the viability of Friction Stir Processing (FSP) was explored as a potential method to enhance the tribological properties of aerospace alloy AA2219-T87. The dry sliding wear properties of FSP, and as-received AA2219 alloy in mild and severe wear regimes were studied using a vertical- interaction tribometer by varying contact pressures and sliding speeds. The results show that, FSP samples exhibited an enhanced wear resistance in the severe wear regime and can be attributed to the propensity of FSP aluminium alloy to undergo friction-induced strain hardening in-situ during dry sliding. This recurrent ‘sliding-friction induced strain hardening’ facilitated for an increased hardness towards the sliding-interface, thereby enhancing the wear resistance and this was confirmed through cross sectional nano-indentation studies.

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The tribological enhancement of nano-lubricant that consist of formulated Eichhornia Crassipes carbon nanotubes (EC-CNTs) dispersed in base rapeseed oil using sodium dodecyl sulfate (SDS) and oleic acid (OA) as surfactants was conducted in this study. The experiment was done using high frequency reciprocating rig, applying 0.5 mass%, 1 mass% and 1.5 mass% EC-CNTs alongside 2% and 5% of the various surfactants and sonicated for 25 minutes and 50 minutes respectively. The use of surfactants and sonication was to reduce agglomeration. The outcome showed that SDS yielded better results than OA, further revealed that the use of 2% SDS under sonication time of 50 minutes reduced the solution agglomeration compared to 5% SDS and sonication time of 25 minutes. The tribological test conducted on EC-CNTs concentration effects was based on friction and wear reduction, load carrying ability, lubricant film stability, wear scar micrograph and mechanism of particles. The results indicated that inclusion of nanoparticles substantially enhanced the tribological characteristics. However, pronounced enhancement was recorded with 1 mass% EC-CNT compared to counterpart lubricants. Friction and wear reduction by 1 mass% EC-CNT were 65.4% and 63.6% respectively against base oil. The nanoparticles exhibited excellent mechanism for which the tribological enhancement was achieved.

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To improve the reliability of the design of hard disk drives, this study aims to determine the effective elastic properties of disks with perfluoropolyether lubricant films on the diamond-like carbon overcoats of magnetic disks. However, the determination of the effective elastic modulus of multi-layered film from molecularly thin lubricant films (1.0 nm) and diamond-like carbon overcoats is extremely difficult because these layers are ultra-thin. Therefore, the method of etching in the depth direction with an Ar-gas cluster ion beam is proposed in this study. The lubricants D-4OH and Z-tetraol, comprising different main chains, are applied to the samples at varying thicknesses. Additionally, the D-4OH is UV-treated to vary the bonded film thickness. The effective Young's modulus of disk with D-4OH is approximately 60 and 20 GPa at 1.2 and 2.9 nm film thicknesses, respectively, whereas that of Z-tetraol is approximately 16 GPa at 1.2 nm film thickness, and exhibits less dependence on the film thickness than that of D-4OH. The effective Young's modulus of D-4OH increases with increasing bonded thickness. These results suggest a significant variation in the effective Young's modulus of disks with the lubricant film based on the film thickness, molecular structure, and adsorption state.

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A simulation method taking into account sequential changes of the tooth contact state due to the tooth surface wear was developed in order to evaluate the influence of wear on pitting durability. As a result of calculating the tooth end relief shape as a parameter, the variation in the wear propagation rate was obtained depending on the contact stress distribution. The study also obtained the non-linear wear propagation property, in which the initial wear propagation was rapid and then changed gradually. In order to verify the wear characteristics, gear durability tests were conducted using gears with tooth tip modification and end relief, and sequential changes in the tooth surface wear state were observed. The test results revealed that the non-linear wear propagation property was obtained as in the calculation results. Wear propagation in the tooth lead direction and pitting life were able to be predicted. Using this calculation method and the experimental evaluation, it was made clear that the temporal alteration of contact stress and the non-linear propagation changed the pitting initiation timing and position, and may also have an effect on the pitting durability.

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Tribological properties of tin (Sn)-zinc (Zn) hybrid coating on bronze were evaluated in lubricated condition mating with a chromium alloy steel (Japanese Industrial Standards, JIS SUJ2) flat surface. A shot peening technique using Sn and Zn fine powders as the impact media was applied to the coating process. The resulted coating film thickness was approximately 1-2 µm. Tribological properties of mono-layered coating showed that the friction coefficient and the wear loss were considerably smaller than those of the bronze and that the transfer layer morphology was different depending on the coating material. Further decrease of the friction coefficient was found on the hybrid Sn-Zn coating surface and Zn transfer layer accompanying with oxygen reduced. Therefore, it is concluded that hybrid Sn-Zn coating is effective means to improve the tribological properties of bronze surface.

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In this paper, an investigation has been made to study the dynamic characteristics of porous inclined slider bearing with rough surface lubricated with micropolar fluid lubricant. On the basis of Eringen’s micro-continuum theory, the Reynolds type equation of porous slider bearing is derived by considering rough surface and squeezing action to evaluate dynamic characteristics of slider bearing. Perturbation method has been used for detailed analysis. Reynolds type equations are obtained for steady performance and perturbed characteristics. The solutions of these equations are obtained. According to the results, an increase (decrease) in the load carrying capacity, dynamic stiffness and damping coefficient are observed for the negatively (positively) skewed surface roughness.

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