Effect of grinding direction on rolling performance of silicon nitride ceramics using a new device with a ball on flat testing principle

Engineering ceramics have a good potential for increasing applications in various types of modern machinery. For rolling applications silicon nitride is already widely accepted as the best ceramic material due to its relatively high toughness and is successfully applied in all-ceramic and hybrid rolling bearings. However, one of important factors which still limits the use of silicon nitride and other ceramics is the cost of the final surface finishing method. This is critical also for rolling experiments. All presently used testers for rolling contact fatigue are designed in a way that the specimen or counter material revolves around an axis. Complex geometry of the machine and specimens is therefore unavoidable and fine tolerances are needed. This makes rolling fatigue tests of ceramics quite expensive. In our work, a new rolling contact fatigue device named CTD-ROL, which work on the Ball-on-Flat testing principle, was used. Instead of expensive discs, rods or similar specimens, flats were used to study the effect of grinding direction on the dry rolling fatigue of silicon nitride. Such specimens are small and could be relatively easily machined due to their simple geometry. The effect of two grinding directions on rolling behaviour was investigated and compared to the rolling behaviour of polished surfaces. The advantages of the new device and the consistency of the results are presented.