Abstract
Axle journal bearings composed of an inner ring, a backing ring, etc. are used in railway applications. The bearing often show fretting wear due to slight relative slip between the inner ring and the backing ring. In this work, the authors have investigated the effects of hard films coated on the backing ring on the fretting wear. Rotational tests using full-scale railway axle bearings with backing rings of side faces which are coated with either of three hard films (titanium nitride (TiN), chromium nitride (CrN) and diamond-like carbon (DLC)) were conducted. It was found that the fretting wear with the TiN film is the worst as a result of the decohesion of whole TiN film, and the fretting wear of the backing ring coated with the CrN film is slight, although the film was not able to follow the deformation of the base material. It was also found that the fretting wear of the backing ring coated with the DLC film which is the thinnest and the hardest among the three films is as slight as that of the backing ring coated with the CrN film, though some of the DLC film left. Accordingly, it is supposed that the fretting wear of the backing ring can be suppressed, if the film coating has a lower friction coefficient, higher hardness and higher bonding strength with the base material.
