Early stages of micropitting were examined on experimental gears designed for surface fatigue studies by the AGMA
Helical Gear Rating Committee. Optical profilometer, SEM and metallographic examinations were conducted on the
first prototype gearset tested. The gearset was tested in an FZG test rig. To evaluate tooth bending fatigue strength, the
gears were loaded to load stage 12. A tooth broke from bending fatigue in .88 hours (the expected time). This short run
time allowed for the examination of micropitting at an early stage of development. The distribution and morphology of
micropitting over the tooth face and associated relationships to surface micro and macro geometry features and traction
are examined. Micropitting was primarily associated with finish geometry. A few pits were associated with sulfide
inclusions and one pit was possibly initiated by a small non-metallic inclusion. Metallographic examinations revealed
asperity related lines of dark etching alterations (DEA) caused by high asperity contact and traction stresses.

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