Page 327 - Handbook of Materials Failure Analysis

324 CHAPTER 13 A concise filtergram wear particle atlas

100µm 100µm
(a) (b)
FIGURE 13.16
The front side and the back side of a fatigue wear particle (200 ): (a) the front side;
(b) the back.

CASE 2: THE WIND TURBINE GEARBOX PREMATURE FAILURES

Wind turbine gearbox premature failures are a tough technical problem worldwide
[15,16]. The gearboxes designed for 20 years of service life, often suffers failures in
between 2 and 11 years [17], mainly occurring in first stage of the planet gear bear-
ings. The failure mode was spalling. The culprit of the spalling was the white etching
cracks (WEC), a kind of microstructural alternation.
Figure 13.18 displays the micropitting and the macropitting on an overhauled
bearing from a wind turbine gearbox. This bearing failed in only 3 years of opera-
tions. Figure 13.19a shows the cross section of the inner ring’s microstructures under
optical microscope, in which the WEC were apparent. Under ESEM, the spalling by
the microcracks is displayed (Figure 13.19b).
In the process of spalling, significant amount of large fatigue wear particles were
generated. Figure 13.20 shows the typical wear particles from a wind turbine gearbox.
In the fatigue crack propagation, some striations can be left on the fatigue wear par-
ticle surface. Figure 13.21a shows a large fatigue wear particle(L870 μm) under stereo-
microscope (45 ). The striations can be distinguished. Under the high resolution and
deep focus of ESEM, the striations can be clearly displayed (Figure 13.21b).

7 SEVERE SLIDING WEAR PARTICLES
Severe sliding wear particles are generated from adhesive wear mode. In the
excessive stress or in the improper lubrication conditions, the lubrication region
would breakdown. The metal to metal contact would generate significant amount
of severe sliding wear particles. Generally speaking, adhesive wear is a catastrophic
wear mode. In extreme cases, the components would seize.
Sliding wear particles feature with the surface striations formed by the sliding metal
contact. As the adhesive wear deteriorates, the striations enlarge and deepen. If the cold
weld occurs, the particle surface features would appear to be torn from the adhesive.
Figure 13.22 displays the severe sliding wear particles from different machines.
Figure 13.22a and b were the severe sliding wear particles from Case Study 2.