The JAST Tribology Conference, Tokyo, May 2008 was held at Tokyo from Monday May 12th to Wednesday May 14th, 2008.

A total of 156 presentations were made with five parallel sessions, and a total of 580 participants took part in the conference. At every Tribology Conference, JAST publishes a bound volume of proceedings, which includes extended abstracts of all the papers presented. Since the pages are limited to two pages for each paper and most of them are written in Japanese, the authors were requested to submit their paper to the JAST's official international journal “Tribology Online.”

The papers submitted to the Tribology Online have subsequently undergone the normal peer review process by multiple reviewers. In this special issue, thirteen papers are published following the decision of authors themselves either not to submit their papers and the process of peer review.

The Editorial Committee wishes to express their appreciation to all the authors who submitted their papers to this International Journal. As the Editor-in-Chief, I would like to express my sincere thanks to the Associate Editors, the Reviewers, and the Publication Coordinators for their effort to complete the peer-review processes and the publication work under the tight schedule.

View full abstract

This study aims to clarify the interaction between a silicon wafer and individual diamond abrasives in grinding to support the estimation of optimal grinding conditions for minimizing the subsurface damages and maximizing the removal rate. In this paper, the effects of adhesion (or lubrication) between a Si wafer and a diamond abrasive on the material removal and tool wear were analyzed by means of the molecular dynamics simulation. A few simulations were performed with changing the dissociation (cohesion) energy of a Morse potential function between a pair of Si and C atoms to evaluate the influence of adhesion on the material removal process. As a result, a trend similar to the actual diamond grinding process of silicon wafer was confirmed, which suggested that the reduction in adhesion (or proper lubrication) is effective for the reduction in subsurface damages, grinding forces, grinding temperature and tool wear, but may lead to reduction in the material removal rate as well.

View full abstract

Silicon-Boron-Carbon-Nitride (SiBCN) thin films were deposited on Si (100) substrates by ECR-type ion beam sputtering at a substrate temperature of 200 ºC, and thermal stability of SiBCN films were investigated at 600 ºC, 700 ºC and 800 ºC in air. A composed Si-B-C (Si plate and B4C target) target was used for the film deposition. The composition and chemical bonding structure of the prepared films were investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. Si-N bonds increased with increasing silicon content. Surface roughness of SiBCN films decreased with increasing Si content. Hardness of SiBCN films exhibited up to 22 GPa with increasing silicon content. SiBCN films showed no changes in chemical bonds after heating at 600 ºC. Even after heating at 700 ºC, SiBCN films maintained relatively high hardness, whereas hardness of SiBCN films was quietly reduced after heating at 800 ºC. Thermal stability of SiBCN films was improved with increasing Si content.

View full abstract

Based on the demand of extremely increased area density for magnetic data storage, the contact recording systems have been proposed, in which stronger and thinner hard coatings and lubricant films for the head disk interface (HDI) are desired. In this study, two lubrication methods, i.e., the vacuum vapor deposition and dip-coating methods are evaluated and compared in order to satisfy the demands from the HDI development. Perfluoropolyether (PFPE) is applied to the diamond-like carbon (DLC) surface. The advantage of the vacuum vapor deposition is to prevent contamination of the DLC surface from the atmosphere because of no exposed samples to the atmosphere. In contrast, the advantage of dip-coating method is to thicken the bonded layer of the PFPE by heat treatment. We discuss the adsorption mechanism between the PFPE molecules and DLC surface for each method. In addition, a simple reaction model based on the Arrhenius equation is developed and compared to the experimental results. We concluded that the reaction will be dominated by covalent bonds and hydrogen bonding. Furthermore, the reaction model can well express the experimental results. The remarkable destruction of the DLC film by the heat treatment are not seen in the samples heat treated at a temperature from 353 to 423 K while the remarkable destruction are seen in the samples treated from 423 to 473 K.

View full abstract

Fractoluminescence (FL) intensity and bending strength were simultaneously measured in silica glass, single crystal and polycrystalline MgO to study dependence of the FL on mechanical properties. In the silica glass, the FL intensity was positively correlated with the bending strength. Also, the positive correlation was found in the single crystal MgO. However, there was not clear dependence in the polycrystalline MgO. This suggests that the FL intensity is connected with the energy released by fracture in glasses and single crystal ceramics, and that grain boundary also contributes to the FL in polycrystalline ceramics.

View full abstract

Under the same EHL contact conditions as in the traction experiments carried out by Wedeven et al., the authors performed a non-Newtonian thermal EHL analysis. In the present analysis, the lubricating oil was assumed to behave as a Maxwell fluid. Lubricating oil is the automotive traction oil with the viscosity grade of ISO VG32. Input parameters are maximum Hertzian pressure P_H=1.5 GPa, entrainment velocity u_e=10 m/s, slide-roll ratio ∑=0%∼4.0% and inlet oil temperature t₀=313 K∼413 K. The Eyring stress, the elastic shear modulus and the limiting shear stress which are needed to calculate the shear stress components were obtained from reference traction curves. The traction coefficients obtained by the numerical analysis agreed well with the measured values in traction experiments. Furthermore, it was found that the shear stress distribution is affected not only by the inlet oil temperature but also by the rolling-sliding conditions.

View full abstract

From the viewpoint of natural environmental requirement, the applications of biodegradable lubricants are growing. Most of vegetable oils are biodegradable and have good lubricating performance even at high contact pressure conditions in spite of their lower pressure-viscosity coefficient. In vegetable oils, however, the optimum suppression of oxidative degradation is required to improve the longevity of vegetable oils. Therefore, it is required to clarify the actual lubrication mechanism in vegetable oils with appropriate antioxidant additives. In this study, the tribological properties of four kinds of vegetable oils of different composition were evaluated in four-ball tests at different sliding speed conditions. As an antioxidant additive, α-tocopherol was used. The types of fatty acids in triglycerides appeared to control the lubricating performance through adsorbed film and friction polymer formation, depending on the operating conditions. Therefore, the paraffinic oils containing fatty acid were tested. It was shown that the influences of fatty acid types on lubricating performance were different depending on sliding speeds. These differences are discussed from the viewpoints of the role of friction polymer and oxidation of oils evaluated by FTIR analyses. Finally, effective application of various vegetable oils is discussed on the basis of relationship between tribological behaviors and operating conditions.

View full abstract

We developed a novel ultra-accelerated quantum chemical molecular dynamics simulator and applied it to adsorption dynamics of a diphenyldisulphide molecule on Fe(001) surface. As a result, we observed formation of two Fe-S bonds among the diphenyldisulphide molecule and the Fe(001) surface. In the adsorption state of the molecule on the Fe surface, it was found that two phenyl groups of the molecule were faced parallel to the Fe surface. From the electronic structure analysis, it was clarified that the parallel configuration was induced by the interaction of the 3d atomic orbitals of Fe atoms with the 2p atomic orbitals of carbon atoms as well the formation of Fe-S bonds.

View full abstract

This paper describes an investigation on improvement of lubrication performance by incorporating micropits on a surface with special focus on the arrangement of the micropits. Water lubricated experiments were conducted using a test rig in which parallel conformal sliding motion was produced between mechanical seal faces. Micropits were patterned on the stationary face ring by a Nd:YVO₄ laser and two arrangements of the micropits were tested. It was found that the micropits of the same diameter, depth and area density provide different friction coefficient depending on their arrangement. The difference in friction coefficient between the two arrangements sometimes achieves greater than twice.

View full abstract

We conducted experiments on Burridge-Knopoff model. Ten blocks connected to each other and also to a rest ceilings with springs were placed on a moving belt conveyor. Surfaces of the blocks and the belt conveyor were covered with sandpapers in order to cause stick-slip motions easily. The sum of kinetic energy of slipping blocks in a series was defined as the size of a slip event and its logarithm as the magnitude. The magnitude distribution of slip events was examined. It was clarified that the features of the magnitude-frequency plots depend on the grade of sandpapers used in the experiments.

View full abstract

The wetting and adhesion properties of undulated a-C:H surfaces were investigated. The nano-undulated a-C:H films were prepared by radio frequency plasma enhanced chemical vapor deposition (r.f. PECVD) using nanoscale Cu dots surface on a Si (100) substrate. FE-SEM and AFM analysis showed that the surface had nanoscale undulations. Raman spectra of film showed that the plasma induced damage with Ar ions significantly suppressed the graphitization of a-C:H structure. Also, it was observed that the untreated flat a-C:H surfaces had a water wetting angle of 72° and adhesion force of 333 nN. After the treatment for the undulated a-C:H surfaces whose surface morphologies change to an array of pillar asperities, its wetting angle of water increased up to 104° and adhesion force decreased down to 11 nN. These results agree with the estimation of real area of contact on the basis of Hertz and JKR adhesion models. The effect of the surface undulation treatment was discussed with the following factors: the surface morphology affinity to pillar shape, a reduction of the real area of contact and air pockets trapped in pillar double asperities of the surface.

View full abstract

The relationship between acoustic emission (AE) signals and wear phenomena in severe-mild wear transition is discussed on the basis of the results of observations of wear particles and worn surfaces of steel. Each wear mode, severe wear or mild wear, is reproduced for a different sliding velocity. The influence of relative humidity on mild wear is examined. We found a reduction in the true area of contact and the size of wear particles decreases the AE signal level in severe-mild wear transition. In the mild wear mode, an increase in the number of transfer particles lying between the sliding surfaces decreases the AE signal level. Further, a linear relationship is observed between the AE mean value and the specific wear rate, regardless of the wear mode. This is because the AE signals generated by the formation and removal of transfer particles mainly originate under conditions of repeated dry rubbing.

View full abstract

In this paper, the friction characteristics of microgrooved bearings are examined experimentally and theoretically. The microgrooved bearings have an advantage of suppressing the oil film temperature rises under the heavy loaded conditions. Therefore, this type of bearings are effectively used for automotive engines, for example. However, with the trends of severe operating conditions using very low viscosity oils for the requirements of energy saving, the bearings are increasingly operated under the mixed lubrication conditions. To protect the bearing surface from damage such as seizure and fatigue, it is strongly needed to know the friction characteristics of microgrooved bearings operated under the mixed lubrication conditions. In the experiments, the bearing backside temperature, friction force, friction coefficient and bearing surface topography were measured by changing the applied unit load step by step, and the measured results were compared with the predicted results calculated by the mixed lubrication model. There were good agreements between them and the friction characteristics of microgrooved bearings were clarified experimentally and theoretically.

View full abstract

The effects of metals such as cobalt (Co), cerium (Ce), magnesium (Mg), nickel (Ni) and titanium (Ti) added to diamond-like carbon (DLC) films on boundary lubrication properties were investigated using a ball-on disk tribometer. The boundary lubrication properties of metal-containing DLC films are improved compared with those of DLC films without metal under poly alpha olefin (PAO) lubricant with and without glycerol mono-oleate (GMO) additives. Moreover, under boundary lubrication using PAO with GMO, DLC films with an appropriate quantity of Co-added show the lowest friction coefficient of μ= 0.02 among all the tested metal-containing DLC films. The friction product layers were formed on the sliding surface of Co-containing DLC films. Lower-nanofriction layers formed on the sliding surface were observed by force modulation methods of atomic force microscopy (AFM).

View full abstract