On the 50^th anniversary of the technical committee on wear research, its activities are reviewed with a special reference to the major symposiums. As the first technical committee, it started 12 years after the foundation of the Japanese Society of Lubrication, the previous organization of the Japanese Society of Tribologists (JAST). Since it began, the committee has been driven to hold symposiums. During the first decade, the symposium took place every year focusing on a variety of subjects of wear mechanisms and problems. Some of the discussions at the end of the symposiums were recorded on the journals. After the next decades, the symposiums have been devoting much attention on wear fundamentals. The presentations were published in the proceedings of annual conferences or in the special issues of the JAST journals, one of which was entitled “Does tribology describe wear scientifically?”

The paper is the review of mechanism and theory of adhesive wear for the special issue commemorating “The history of wear research group in 50 years and the development of wear research”.

The measurement of wear is a measurement of the surface change caused by friction. It is necessary to measure the change caused during friction with the lapse of time and to compare them in order to perform the evaluation of wear resistance or the life prediction of friction materials. As for the measurements of wear, the measurements of the wear state such as not only the wear volume but also the wear mode and the surface damage become extremely important. Most of the measurements of wear are performed by ex situ measurements measured after taking out the measuring object from a machine that stopped the operation; that is measurements outside the friction system. However, when the measuring object is taken out from the machine, a difference occurs between the actual phenomenon and the measuring result at the frictional interface. Therefore, it is ideal to perform the measurement of wear by in situ measurements; that is in-process measurements in the friction system. This is one of the big issues for the measurements of wear that hasn't changed since a long time ago. In this article, the kind, the feature, and the transition of the measurements of wear are outlined, and the current state of the studies on the in-process measurements of wear and the possibility to the future are described.

Quantitative research on the contribution of chemical reactions to wear is not enough. As a measure to obtain quantitativeness, there is a research example focusing on the formation of ammonia in the wear of nitrides in water. In this report, we introduced an example in which the chemical wear rate was calculated from the amount of ammonia produced and the contribution of chemical reaction to wear was studied. In addition, we introduced an example of the study based on the chemical wear state diagram, which divides wear into regions based on the chemical wear rate, and explained the regions of wear form a chemical view point.

It is well-known that beginning of sliding so-called running-in is an important for stable low friction by formation of wellconformed interface with suitable tribo-chemical product. To form such functional interface, initial wear in the conforming process in the early stages of friction is key to lead for changing in the material, physical and chemical properties of the surface. Further, initial wear during running-in leads to continuous self-formation of low friction interface due to tribo-chemical wear at the stable low friction stage. The running-in control technique for self-forming such low friction interface more surely and stably is a low friction technology. The surface texture that can actively control tribo-chemical reaction introduced in this paper is one of the promising low friction technologies.

The lubricated area can be recognized as “an enclosed space”surrounded by solid surfaces with relative motion. The solid surfaces are separated by thin films such as the hydrodynamic viscous film, absorbed film, and chemical reaction film. The orders of the thicknesses of the films range from nm to μm. In the lubricated area complex and transient phenomena occur based on the physical, chemical and material behaviours. Therefore, it is necessary but significant difficult to extract in situ information from the enclosed space without disturbances. One of ways to access to the lubricated area for in situ extraction of information is to replace one or both of solid surfaces with transparent material to employ optical techniques. So far, many in situ optical observation, measurement, and analysis techniques have been developed for the lubricated area. The author has also developed several in situ optical techniques for a better understanding of “scuffing”, which is a catastrophic failure with a big wear scar as a result of significant increases in friction, wear, temperature, and vibrations. In this paper, developed in situ optical techniques, the scuffing process, and specific phenomena in the scuffing process are introduced.

This paper discusses wear phenomena from an aspect of the atomic interaction. It is demonstrated that the friction coefficient is affected difference in the inter-atomic distances between the mutually rubbed materials. Then, from the relation between the friction coefficient and wear coefficient, it is discussed that progress of wear is strongly affected by the number of atoms subjected sheer force simultaneously. The lager difference in inter-atomic distances represents the lower friction coefficient and the smaller wear. It is almost impossible to remove one atom from the surface during a wear process, because applied force to the atom is much weaker than the supporting force around the atom.