Development of White Etching Bands under Accelerated Rolling Contact Fatigue.

Abstract

Bearing steel under severe loading condition undergoes substantial subsurface microstructural alterations known as Dark etching regions and white etching bands. White etching bands (WEBs) develop after hundreds of millions of stress cycles in bearing components and have been reported for several decades but the formation mechanism of white bands is not fully elucidated. Current research presents a systematic rolling contact fatigue (RCF) testing in a rotary tribometer under accelerated conditions, where rolling cycles are simulated in a 4-ball test configuration. The post RCF investigations have been carried out to understand the formation mechanism of WEBs in a ball-on-ball point contact load. WEBs have been characterised with the help of nanoindentation and Energy-dispersive X-ray spectroscopy analysis. The quantitative analysis of WEBs growth with subsurface stress field has revealed that the unique orientations of white bands are governed by the plane of maximum relative normal stress along the contact track. Moreover, the accelerated growth and reversal of WEBs sequence at elevated temperature have revealed that the WEBs formation is dependent on temperature/load combination. The observed growth of lenticular carbides in current research is also compared with dislocation gliding model and the role of carbon diffusion within WEBs is highlighted.