The Japanese Society of Tribologists organized the international session as one of the sessions held in JAST Tribology Conference, Fukui, September 2010. One part of the boundary lubrication session organized by Professor Shigeyuki Mori from Iwate University and Professor Masabumi Masuko from Tokyo Institute of Technology also joined with the international session.

After the opening remarks, Professor Nicholas D. Spencer from Swiss Federal Institute of Technology gave an invited lecture. Fourteen general presentations followed by two invited speeches by Professor Teruo Murakami from Kyushu University and Dr. Rowena Crockett from Swiss Federal Institute for Materials Research and Technology were contributed in this session. In order to distribute their high-quality research work, JAST invited fourteen presenters who made the general speech to submit their contributions to Tribology Online as peer reviewed papers. the papers submitted subsequently underwent the normal peer review process by multiple reviewers. Among the papers submitted, four papers were selected for publication in this special issue.

The organizing committee wishes to express their sincere appreciation to all the authors and participants at the international session. The guest editor also would like to express his acknowledgement to all the reviewers.

Guest Editor
Tomoaki Iwai

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Real-time visualization of the nm-thick liquid lubricants is useful to clarify the lubrication phenomena using liquid thin films, for example, the lubrication for hard disk drives. In this paper, we present a method of measuing the film thickness using a vertical-objective-based ellipsometric microscope, which is a microscope based on ellipsometry that widely used for the investigation for thin films. In this method, the intensity signal can be directly converted to the thickness and the calibration can also be done by a phase shift method without any other devices. Sub-nm thickness and the sub-μm lateral resolutions were experimentally achieved for the visualization of the nm-thick lubricant films.

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In this work, the influence of maximum normal impact load, absorbed energy, and contact impulse, on the impact crater volume/depth of a hydrogen-free diamond-like carbon coating (commonly known as DLC) has been studied. The tungsten high speed steel (SKH2) specimen discs were coated with DLC using the Physical Vapour Deposition (PVD) method. The 90° impact test was performed using a self-developed impact tester, where the DLC coated disc was impacted by a chromium molybdenum steel (SCM420) pin, at 400 impact cycles, under lubricated conditions. The results show that the most crucial factor, affecting the impact crater volume/depth of DLC coating under impact, is the maximum normal impact load.

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A systematic analysis of the effect of oxygen concentration in inert gas environments on friction and wear properties of carbon nitride (CNx) coatings is discussed in this paper. The friction tests in inert gas environments with constant and increasing oxygen concentration were performed using a ball-on-disk tribometer equipped with a gas blow unit and a ball-on-disk tribometer situated inside a steel chamber, respectively. It is found that the friction coefficients of CNx coatings in inert gas environments increased linearly from 0.04 or less to around 0.10 with the increase of oxygen concentration from 0 to 10 vol.%. Their increased slowly to 0.12 with further increasing oxygen concentration. The specific wear rates of the ball and the disk in the range of friction coefficients less than 0.06 were in the order of 10^-8 mm³/Nm and 10^-7 mm³/Nm, respectively. These wear rates increased almost linearly with the increase of oxygen concentration in inert gas environments, except for the case of CNx coated Si₃N₄ ball. The friction and wear mechanisms of CNx coatings in inert gas environments with different oxygen concentration were discussed according to the composition and structural changes of worn surfaces on disks by using XPS and Raman analysis.

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The authors evaluated the fatigue life using a rolling four ball test with mineral oil samples in which an alkaline metal, a phosphorus system or a sulfur system compound were added. As a result, it was likely that a decrease of the hardness in the vicinity of the ball surface shortened the fatigue life. Moreover, it was found that the larger the corrosion energy in extract water of the oil sample, the shorter the fatigue life. There is a linear relationship between the corrosion energy and the fatigue life. In addition, the technology to extend the fatigue life and the investigation on additive effect are reported.

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