When the bearing load exceeds the designed load, the raceways "spall," eventually failing from fatigue stress. Fatigue stress failure can occur from misalignment, excessive loading, spalling, poor lubrication, or incorrect operating conditions. Spalling on the surface of a ball increases wear to the raceway, noise, and bearing vibration. Typically, spalling can be observed first as pitting in the inner raceway.

One of the most frequently discussed issues associated with hybrid bearings and silicon nitride balls is the failure mode. A properly engineered silicon nitride bearing ball fails in the same manner as a steel ball; through spalling of the ball surface. There are many case examples where failed bearings have been examined and the silicon nitride balls have shown no effects from operation.

In the 1990's, less than 3% of bearings suffer fatigue failures. This is primarily due to vast improvements in the quality of steels.

Machine Tool Bearings

Machine tool bearings are relatively lightly loaded, thus the problem of load is insignificant. Most machine tool bearings fail due to contamination, lack of lubrication, improper lubrication, or failure from excessive heat generation. For machine tool applications today, there is no risk in using a hybrid bearing.