Mechanical properties of silicon nitride rolling elements in dependence of size and shape

Silicon nitride rolling elements for hybrid bearings (rollers, two sizes of balls and plate material as a reference) made from the same material lot and using the same sintering route are investigated in regard to their microstructure and their mechanical properties. For the first time, a direct comparison of the surface strength of the components as well as of their fracture toughness is enabled by recently developed testing methods for balls and rollers.It was found that the microstructure of these material variants influences the fracture toughness up to about 10%. In addition, due to the different surface finish, the surface strength of the different rolling elements (made of the same material) is very different. The differences may reach up to 100% and more.