Effects of mechanical properties and layer structure on the cyclic dynamic loading of TiN-based coatings

The cyclic dynamic loading behaviour of a multilayer TiAlSiN coating on M2 steel was systematically investigated using repetitive nano-impact over a wide range of impact load. Its behaviour was compared with a monolayer TiN on the same substrate. When the load was increased to 10 mN and 30 mN for the TiN and TiAlSiN coatings, respectively, cracks started to appear during the tests demonstrated as depth steps in the impact depth curves. The improved crack resistance of TiAlSiN coating is consistent with its higher H/Er and H3/Er2 measured by nanoindentation. The impact footprints were studied from both top-view and cross-sectional view using a focused ion beam microscope and SEM. Spallation was observed in both coatings at higher impact loads. TiAlSiN coating shows much less spallation due to its multilayer structure. The cross-sectional study discovered that the cracks were initiated within the coating. A simple model has been used to study the power law relationship between the impact volume loss and the impact velocity.