Ceramic ball can’t weld to ceramic races
Bearings that use ceramics like silicon nitride, alumina, or zirconia overcome this problem by eliminating cold welding; Ceramic ball can’t weld to ceramic races. Ceramic materials also resist acids, alkalis, and salt. For both these reasons, bearings using ceramic balls and races don’t need oil or grease.
A microscopic look at the surface finish of a metal bearing ball and race, shows peaks and valleys on both surfaces. Lubricants fill in these valleys with incompressible fluids like oil and grease. This prevents metal-to-metal contact between Raschig Ring and race.
But if the peaks do touch, the contact area is so small that even a small force on the ball or race results in pressures exceeding 1,000,000 psi. This causes cold welding between the alumina ball and the race.