Investigating the high frequency fatigue failure mechanisms of mono and multilayer PVD coatings by the cyclic impact tests

Serrated chips are produced at high frequency in the high-speed machining, which often induce a severe failure of the coated cutting tools. In such case, the high frequency fatigue properties of coatings are pivotal. A monolayer TiAlSiN coating and multilayer TiAlN/TiSiN nano-coating were deposited on the ISO P30 cemented carbide substrate. The cyclic impact tests with high frequency were performed with a developed impact tester, which could generate different oscillation amplitudes by using the ultrasonic actuator. The surface response and fatigue fracture of coatings were analyzed by the measurement of dynamic forces and investigation of SEM images. Besides, the sequential load-indentation tests were performed on these two coatings. These tests would be used as baseline reference for comparison purposes with the ones determined under cyclic loading conditions. The fatigue fracture processes of coatings in the high frequency cyclic impact tests were analyzed, and the crack propagation in the cross-sections of coatings were observed by using focused ion beam (FIB) machine to slot cut the impact imprints. It showed that the interfacial delamination of coating/substrate system was more susceptible to the high frequency cyclic impact tests. Furthermore, the multilayer TiAlN/TiSiN nano-coating exhibited higher cyclic impact resistance at low impact loading conditions, but worse cyclic impact resistance at large impact loading conditions compared to the monolayer TiAlSiN coating.