The influence of oil additives on spread cracks in silicon nitride

The properties of ceramic materials (high hardness, high-temperature capability, low coefficient of thermal expansion) are of interest to rolling element materials. One of the most interesting materials is silicon nitride.The paper presents an experimental study of the influence of oil additives (Cl, S, P, cerium dioxide (CeO2)) on spread cracks in silicon nitride. The additives Cl, S, P are bound in molecules in liquid form soluble in the base oil. The CeO2 is purely in powder form in suspension. The use of CeO2 powder was made based on the good results of polishing of silicon nitride. A ceramic angular contact ball bearing was modelled using a four-ball machine. Silicon nitride, 12-in diameters balls were artificially damaged with pre-cracks. Ring formed pre-cracks were propagated on the ball surface by a blunt impact load using a tungsten carbide ball under five various impacts.Rolling contact fatigue failure modes were studied under high contact stresses and speed. The surface of silicon nitride balls before and after failure was examined using scanning electron microscopy.The research of the present paper shows that fatigue failure under rolling contact loading is markedly sensitive on the size of pre-cracks and oil additives. Propagations of surface pre-cracks takes place under fatigue load. Primary and secondary surface crack propagation are described.