Does direct metal-to-metal contact in ball bearings cause wear?

Direct metal to metal contact in ball bearings can cause wear.
Under normal circumstances, the design of ball bearings is to avoid direct metal contact through lubricating oil film or other lubrication methods. When there is insufficient lubrication, direct metal to metal contact may occur between the ball and the inner and outer rings.
Once direct metal to metal contact occurs, the following situations can occur that cause to wear. Firstly, the friction coefficient between metals is relatively high, which generates a large amount of frictional heat during relative motion. This not only increases the temperature of the bearing, but also accelerates the wear of the material. High temperature may also cause to a decrease in the hardness of bearing materials, further exacerbating wear. Secondly, direct metal contact will cause surface micro peaks to interact with each other, resulting in adhesive wear. Over time, material transfer and detachment may occur at the adhesive site, forming pits and scratches, seriously affecting the accuracy and lifespan of the bearing. Finally, direct contact between metals may also cause fatigue wear. Under repeated loading, fatigue cracks will appear on the surface of the bearing and gradually propagate, ultimately cause to material peeling and damage.