Rolling contact fatigue behaviour of thermally sprayed rolling elements

An experimental approach with a modified four-ball machine is used to investigate the rolling contact fatigue (RCF) performance and failure mode of thermally sprayed rolling element bearing steel balls. A superdetonation gun (SDG 2040) is used to deposit a tungsten carbide coating (WC-15%Co) on steel substrate balls. This test configuration has been used to simulate traditional steel and ceramic hybrid rolling element ball-bearings. Microhardness of coating and substrate, scanning electron microscopy (SEM) and finite element modelling (FEM) of the contact problem for coated elements are the key tools in the analysis. The results show that coated specimens do not perform well and the failure is through the coating itself and not at the interface. Results from FEM and SEM of failed areas indicate that the failure of coatings is in plain shear at the edge of the contact area. An improvement is required in the coating technique for rolling contact fatigue application, Advanced processes such as high velocity oxy-fuel (HVOF), etc. may provide different results. The mode of failure in the coated specimens is delamination.