Yoshitsugu Kimura

Boron nitride as a lubricant additive

Hexagonal boron nitride (BN) has a graphite-like lamellar structure, but has been considered less effective than other solid lubricants except for high-temperature applications. The present paper describes a series of sliding experiments which show somewhat curious behavior of BN when added to lubricating oil, and discusses their results by comparing with the results of observation and analysis of sliding surfaces. In the case of sliding of bearing steel vs. itself, BN slightly increased the coefficient of friction, but dramatically decreased wear. Boron was found to remain on the surfaces, but the remnant was almost oxidized; it was some sort of oxide but not stoichiometric. If bearing steel was slid against cast iron, BN decreased the coefficient of friction, but the decrease in wear was less marked, and the remnant in this case was mostly BN. These results show that BN is effective in reducing wear if used as a lubricant additive.

Wear and fatigue in rolling contact

Researches on wear and fatigue in rolling contact from a tribological viewpoint are introduced. Transmission of traction and accompanying microslip in the contact region play critical roles in these phenomena. First, a quantitative analysis of wear in rolling contact with microslip is introduced, and it is shown that a simplified microslip theory can explain its behavior. Second, a marked change in contact fatigue life with traction is demonstrated, and a theory is introduced which relates the fatigue life with cumulative shear strain in the subsurface.

Life improvement of TiN-duplex-treated tool steel by tempering

Effects of tempering the nitrided substrate on the life of TiN-duplex-treated tool steel are studied as a potential tool material for plasticity processes. Ring-on-block sliding tests are carried out against aluminum alloy without lubrication to evaluate the life of the TiN coating film under a high-load, low-speed condition where wear takes place predominantly. Results show that the tempering prolongs the TiN coating film life more than twofold. This is due to an increased fracture toughness of the substrate and improved adhesive strength of the coating-substrate interface, both suppressing wear of the TiN layer by scratching.

Thinning films and design of lubricated components - A state-of-the-art report from Japan

A brief survey is presented of the trends of reduction of lubricating film thickness in several components which has taken place in recent decades, and of the operation of certain components in the presence of extremely thin lubricating films from birth. New technologies are introduced which have been developed to ensure their successful operation.