Page 329 - Handbook of Materials Failure Analysis

326 CHAPTER 13 A concise filtergram wear particle atlas

50 mm
(a) (b)
FIGURE 13.18
The micropitting and macropitting on a first-stage planet bearing overhauled from a wind
turbine gearbox: (a) the rollers; (b) the inner ring.

WEC

WEC

The fresh spalling surface
The rolled spalling surface on the raceway
(b)
(a)
100µm
FIGURE 13.19
The microstructures of the above bearing inner ring: (a) showing the white etching cracks
(WEC) in the subsurface under optical microscope (200 ); (b) the formation of spalling
as a result of the WEC propagation (ESEM 500 ).

8 THE OXIDE WEAR PARTICLES
Oxide wear particles are referred to the wear particles with oxide scale. There are two
types of oxide scales, red oxide scales and black oxide scales. Red oxide scale is asso-
ciated with the moisture in the oil, whereas black oxide scale is believed to be asso-
ciated with high temperatures due to the improper lubrication.
Iron oxides have deferent crystals and different colors. Hematite (α-Fe 2 O 3 ) and
magnetize (Fe 3 O 4 ) are the most common in nature. Red oxide is believed as hematite
(α-Fe 2 O 3 )[2], which is similar to “rust.” For black oxide wear particles, their oxide
scale has not been studied.
Figure 13.24 shows the typical red oxide wear particles. Both the particles were
found in an oil sample with the extremely high moisture content (24,660 ppm). The
oil sample was taken from a forward drive gearbox in a paper mill.