Adhesion strength of ductile aluminium and brittle TiN coatings on steel, aluminium and copper, measured by fracture mechanics tests

The interface fracture toughness K-c and the fracture energy G(c) of the coating systems of TiN on high speed steel (HSS), and aluminum on austenitic steel, copper and HSS have been measured by the three-point bend test. K-c and especially G(c) can be used to characterize the adhesion strength of a coating system. The coatings are produced by a magnetron sputtering process. The coating thickness and a negative bias voltage are chosen to show the effects of the process parameters on the fracture energy. The fracture mechanics data are compared with microhardness and scratch test data obtained from samples subjected to an identical preparation treatment. The results demonstrate that the trends of the experimental data observed with different testing methods can differ strongly, since the contributions of the interface and bulk properties of the coating and the substrate material are quite different.