A study on the three key concepts of White Etching Crack failure mode in its very early stages - Contrast with different testing methods

Abstract

Despite the great attention that WECs have received from researchers over the last few years, the earliest stages of this failure are still under debate. The wide variety of drivers studied, and the different methodologies employed to reproduce this failure mode, raise the question; do different methodologies lead to different initiation mechanisms? The present work aims to understand the most premature stages of WEC formation in 100Cr6 steel discs tested under RCF conditions and pre-charged with hydrogen. Firstly, three key aspects in the WEC formation process were identified, which have been extensively studied by other authors, but at intermediate or late stages of formation. These aspects are, (1) microstructural alteration formation first steps, (2) newly formed grain growth and (3) carbide dissolution. Secondly, samples representative of early stages were analysed by SEM/EDX/EBSD. The results of this research suggest that the early stages of these aspects are in agreement with the intermediate and late stages presented by other authors in the case of both WEC critical oil lubricated bearings and failed field bearings. Therefore, tribometer tests preceded by hydrogen uptake seem to recreate the tribological conditions found in wind turbine bearings. In addition, a very detailed failure initiation mechanism is proposed in this work.