Understanding white etching cracks in rolling element bearings: Formation mechanisms and influent tribochemical drivers

Abstract

Among prevalent tribological failures in rolling element bearings, a peculiar rolling contact fatigue mode has been defined as white etching cracks, which correspond to broad subsurface three-dimensional branching crack networks bordered by white etching microstructure. White etching cracks tend to appear before other conventional rolling contact fatigue microstructural alterations and eventually lead to premature flaking or radial cracking that remains unpredictable using fatigue life estimations. Even though they have been reported for several decades, occurrences present no common evident denominator and are delicate to reproduce on laboratory test rigs without artificial hydrogen charging. In this study, white etching crack reproductions on two different standard endurance test rigs are compared and analyzed in order to, firstly, propose, an update of the understanding of white etching crack surface affected tribochemical formation mechanisms, and secondly, to identify influent tribochemical and mechanical drivers. If white etching cracks are associated to different combinations of specific non-self-sufficient macroscopic drivers depending on the application or the test rig, evidences demonstrate that they often come down to similar phenomena at a microscopic tribological scale that should all be mastered for efficient white etching crack reproduction and countermeasure design.