Effects of segment-structured DLC film on the fretting wear of railway axle journal bearings

Abstract

Fretting wear is surface damage caused by repeated slight relative slips between two contact surfaces. In railway applications, fretting wear can occur between the inner ring and the backing ring of an axle journal tapered roller bearing. The authors supposed that the fretting wear of the backing ring can be prevented by means of hard-film coatings if hard films can follow the deformation of the backing ring. A segment-structured diamond-like carbon (S-DLC) film has been proposed to solve this problem. In this work, the authors investigated the effect of S-DLC film on the fretting wear through rotation tests of full-scale railway axle bearings with the backing ring side face coated with S-DLC film or conventional continuous diamond-like carbon (C-DLC) film. As the result, the S-DLC film coated backing ring demonstrated less wear compared to the C-DLC film coated backing ring. In addition, the iron content of the grease in the bearing with the S-DLC film coated backing ring was lower than that of the grease in the bearing with the C-DLC film coated backing ring. It is conceivable that the relative sliding motion in the radial direction between them may be restrained by the latticed pattern of the S-DLC film being pressed into the inner ring large side face. It is concluded that the S-DLC film is effective in suppressing the fretting wear generated on the contact surfaces between them of the axle bearings.

Influence Factors on Mechanisms of Superlubricity in DLC Films: A Review

“…Since the discovery of DLC films, their application as a selflubricating and protective coating in mechanical engineering is increasingly broadened. For example, their applications in gearings (Michalczewski et al, 2019), bearings (Okamura et al, 2019), engine piston rings (Kumar et al, 2019), oil-well tubings , rubber seals (Liu J. Q. et al, 2019), and friction pairs in spacecraft (Donnet et al, 1999) have been testified to be effective and valuable. Superlubricity achieved with DLC coatings can provide a new concept to meet the increasing demand for lower energy consumption, longer life time, and higher power density of future mechanical systems, which has an enormous potential value from both economic and environmental perspectives.…”

<b>R&D Activities and Future Perspectives in Material Technology</b>

“…9. A segment-structured DLC film that could adhere to the rear lid and reduce the friction coefficient was investigated as a functional coating, and it was confirmed in laboratory tests using actual axle bearings that fretting wear could be suppressed [8].…”

<b>Recent Research and Development Activities in Materials Technology</b>

“…In order to develop preventive measures for fretting wear of axle bearings, elucidation of the fretting wear phenomena caused by repeated slight relative slips between the inner ring and the backing ring, and investigation of the preventive measures have been conducted (Fig. 5) [4]. Many railway materials are required to deal with vibration, but there are influences from these types of smallscale vibrations in addition to larger vibrations, and research and development on these types of micro-vibrations has been carried out.…”