Fatigue susceptibility under contact loading of hardmetals coated with ceramic films

The contact fatigue behavior of a fine-grained hardmetal coated with two distinct ceramic films, either a TiN monolayer or a WC/C multilayer, is studied by means of indentation testing techniques. Spherical indentation tests indicate that the investigated coated systems exhibit different susceptibility to fatigue degradation in terms of emergence of circular cracks at the coating surface. Furthermore, these cracks are found to induce well-defined substrate cracking without any intermediate decohesion. Accordingly, the intrinsic mechanical degradation under cyclic loading of the ceramic films is pointed out as key feature for rationalizing the experimental findings. This is finally sustained by the higher mechanical degradation exhibited by the WC/C film, as compared to the TiN one, on the basis of imprint size and contact stiffness changes with increasing number of cycles under repetitive nanoindentation