Micro pitting

Micro pitting is a fatigue failure of the surface of a material commonly seen in rolling bearings and gears.

Micropits are originated from the local contact of asperities produced by improper lubrication.

In a normal bearing the surfaces are separated by a layer of oil, this is known as elastohydrodynamic (EHD) lubrication.

Water in the oil can make micro pitting worse by causing hydrogen embrittlement of the surface.

So high surface roughness decreases the stability on heavy stressed parts.