Micropitting
Micropitting turns up in 2 fields: tribology, gears. Here is what it means to the people in each one.
Micropitting in tribology
Fatigue damage made of tiny pits, about 10 to 20 microns deep, that turns gear and bearing surfaces dull gray.
Surface-initiated rolling contact fatigue in which vast numbers of microscopic cracks and pits form on hardened gear teeth or bearing races running in a thin, mixed film. To the eye it shows as dull, satin-gray patches, hence the names gray staining and frosting. Micropitting can stabilize, but it also changes the tooth profile, raises noise and often seeds macropitting. Higher viscosity, smoother surfaces and micropitting-resistant gear oils reduce it.
"High-speed pinion is showing micropitting, those gray bands weren't there at the last borescope."
Micropitting in gears
Very fine surface fatigue pits, too small to see one by one, that give tooth flanks a dull gray look.
A surface fatigue mode in which countless pits around 10 to 20 microns deep form where the oil film is thinner than the surface roughness. The affected area looks matte gray rather than pitted, and under magnification shows tiny cracks and craters. It is common on hardened, ground gears in slow, heavily loaded drives such as wind turbines, and it can remove enough material to change the profile and start macropitting.
"Micropitting band on every tooth at the dedendum, the oil's too thin for this load, talk to the lube supplier."