Understanding white etching cracks in rolling element bearings: The effect of hydrogen charging on the formation mechanisms

Abstract

Among prevalent tribological failures, notably in rolling element bearings for wind turbines, an unusual rolling/sliding contact fatigue failure mode has been identified as white etching cracks. White etching cracks are broad subsurface three-dimensional branching crack networks bordered by white etching microstructure, eventually leading to flaking. Reproduction of the failure mode on standard rolling element bearings test rigs has not been mastered yet except with artificial hydrogen charging. Even though these failures have been reported for several decades, there is no evident common denominator in different occurrences. Hence, initiation and propagation mechanisms are not yet fully understood in application. Analyses of the contact conditions of a standard rolling element bearings test rig reproducing white etching cracks on standard and hydrogen precharged inner rings reveal that hydrogen charging seems to modify the white etching cracks initiation mechanism. Based on fractographs, serial sectioning, and scanning electron microscopic analyses, surface initiation and propagation mechanisms are proposed, including influent drivers and possible preventive techniques.