CONFIRMING SUBSURFACE INITIATION AT NON-METALLIC INCLUSIONS AS ONE MECHANISM FOR WHITE ETCHING CRACK (WEC) FORMATION

摘要

Various RCF tests and serial sectioning analyses mapping RCF wear volumes have been conducted to investigate WEC formation mechanisms. This includes hydrogen charged, non-hydrogen charged conditions and actual wind turbine gearbox bearings from transient test rigs and the field. The mode of WEC initiation & propagation may vary depending on test condition and application, however the evidence for one WEC mechanism from the authors studies above is summarised in the following. 1. Mapping of WECs in their entirety showed that in both hydrogen charged and non-hydrogen charged testing the majority of WECs were subsurface initiated and propagated to surface to cause WSF. 2. WECs were often found to interact with inclusions that were judged to be crack initiators from the inclusions chemical composition, depth below the contact surface and crack continuity in the near vicinity of the inclusion. Sulfide inclusions, globular manganese sulfide + oxide inclusions and small globular oxide inclusions between ～1 - 20 urn in diameter/length predominated as crack initiators. 3. Subsurface crack initiation and propagation of WECs is at least one of the mechanisms of WSF.