White Etching Cracks

White etching cracks is a type of subsurface initiated pitting failure of hardened steels.  These are commonly observed in wind turbine bearings.  A subsurface crack is usually initiated on a metal inclusion, which then grows until it reaches the surface.  They are characterised by early failure by pitting and can be viewed directly with subsurface analysis – viewing below the surface area using a sectioning, grinding and etching procedure.  The WECs are cracks surround by a white etched area.

We generate WECs on small rollers and conduct subsurface analysis to confirm their presence.

The surface of a roller showing the presence of axial cracks and pits:

WEC surface axial cracks
WEC surface axial cracks

These axial cracks can then progress into a full subsurface pit.  Examples are shown below from three repeat tests with a bad reference oil:

WEC pit example
WEC pit example

Sectioning the roller then reveals a network of cracks surrounded by white etching areas.

Subsurface WEC network
Subsurface WEC network

Any spalls found are associated with WEC networks:

Spall with WEC example
Spall with WEC example
Spall with WEC example 2
Spall with WEC example 2