Ultrathin-film interferometry was used to investigate the developing process of boundary films in a steel-on-silica contact lubricated by a solution of n-hexadecanoic acid dissolved in n-hexadecane. Immersion of the surfaces in the solution is not sufficient to initiate boundary film formation. However, upon a nominally pure rolling contact, boundary film formation is initiated, and, once initiated, the boundary film develops spontaneously. It is believed that the initial monolayer film adsorbed strongly on the solid surface induces subsequent molecular stacking from the solution. The developed boundary film can be partially destroyed by the rolling contact, although the nominally identical rolling contact acts as the trigger of boundary film formation. These findings reveal that the immobile boundary films to reduce friction of solids under high pressure result from the equilibrium of two competing processes: spontaneous development by molecular stacking and mechanical destruction by relative motion of the contact surfaces.

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Frictional force was measured on directional calcite (1 0 -1 4) surface, where triangular carbonate ions are all tilted to [4 2 -1] direction. With the normal load < 49 mN, observed frictional asymmetry, +[4 2 -1] > -[4 2 -1], was the same as that measured in nm-scale. In the higher normal load range, a new component was added to the friction in -[4 2 -1] direction, and the asymmetry was reversed. Only in the direction of stronger friction, characteristic triangular deformation patterns were formed. Microscopic observation after indentation experiments revealed that the patterns were formed by slip on c (0 0 0 1) faces on one side of the stylus, followed by cleavage on r{1 0 -1 4} faces. A mechanical model was proposed to explain why the deformation occurs only in one quadrant of the surface. The result of scratch perpendicularly in [0 1 0] direction, also supports the mechanism of deformation. The results show when and how the contribution of plastic deformation is added to intrinsic surface friction and affects the frictional asymmetry. The frictional force in the -[4 2 -1] scratch increased linearly with the total lengths of the traces of c-slip.

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The optimum texturing pattern for a thrust sliding bearing of a scroll compressor was investigated. As the basis of lubrication analysis for multiple circular bumps pattern, fundamental hydrodynamic lubrication effects of the axisymmetric circular geometry expressed by the power law formula were analyzed using elastohydrodynamic lubrication (EHL) analysis. The optimum geometry to improve the load carrying capacity and reduce frictional force for the model geometry was discussed. Frictional properties of the proposed thrust bearings were experimentally evaluated and compared with numerically predicted properties. In order to clarify the robustness against accidental high load, seizure limits of a circular bump pattern were experimentally evaluated. These results show that the initial frictional properties are able to control by the crowning profile, the proposed pattern has a sufficiently low friction coefficient and quite a high seizure limits.

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The effect of the hardness of a counterface on the sliding wear behavior of SiC whisker or of SiC particle reinforced aluminum matrix composites (designated as MMCw, MMCp) was investigated by pin-on-disk tests. The counterface materials were 0.45% carbon steel and tool steel with a hardness range (HV=180-1000) obtained by different heat treatment. When the MMCw (V_f=29%) and MMCp (V_f=10%, d=5 µm) pins were rubbed against steel disks, their wear rates took constant values below the hardness of the worn surfaces, but the wear rates varied inversely proportional with increasing hardness of the steel counterface. The wear rates of the steel disks varied inversely with their hardness. On the other hand, when a MMC disk was rubbed against a steel pin, the wear rates of MMCp showed an almost constant value regardless of the counterface hardness. The wear rates of MMCw increased slightly for high hardness of the counterface. The wear rates of the steel counterfaces were remarkably small. These phenomena are discussed depending on the characteristics of worn surfaces, the wear debris and tribo-induced layers on the counterface. The findings obtained in this study contribute to the evaluation of tribological properties of aluminum alloys as well as their matrix composites based on a large variety of experimental data obtained with different wear test methods.

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The authors have studied the current density and voltage at which electrical pitting occurs in a small ball bearing. Some current-applying bearing tests in previous studies showed an interesting tendency for the vibration of bearings to increase when they were lubricated with a thicker oil film. In this study, the oil film parameter is intentionally changed, and its effects on the generation of pitting and vibration acceleration are experimentally investigated. Ball bearing endurance tests involving 500 h of operation were performed by applying a direct electric current with various rotational speeds, and with various base oil viscosities of grease and surface roughness of the raceway. The test results clarified that electrical pitting appeared more clearly and the vibration due to damage became severer with increasing oil film parameter. Although a larger oil film parameter is generally advantageous for increasing bearing life, it is undesirable from the standpoint of preventing electrical pitting.

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The thin film properties of some novel branched perfluoropolyether (PFPE) boundary lubricants are investigated as a function of molecular polarity and end-group bonding to the underlying carbon film. The PFPE main chain, comprised of n-perfluoroethylene oxide monomer units, is stiffer than the Fomblin Z main chain that is a copolymer of perfluoro-methylene oxide and -ethylene oxide monomer units. Terraced flow and bonding kinetics show decreased lubricant mobility compared to PFPEs based on a Fomblin Z main chain. Lubricant pick-up is reduced for the tetraol adduct due to the larger Hamaker constant and increased intermolecular cohesion.

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This paper reviews the electrical methods to evaluate lubrication, with the focus on elastohydrodynamic applications. The methods are based on the measurement of the electrical resistance and/or capacitance, and are used to determine the thickness of lubricating films as well as to detect asperity contact in the mixed lubrication regime. The experimental works are introduced in which these methods are used in conventional sliding and rolling/sliding tests and machine component tests including piston ring and cylinder liner, cam and follower, and gears. Also some works on the effect of electric field upon lubrication phenomena are introduced. Advantages and disadvantages of the electrical methods are discussed.

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