3.2. Evaluation of mechanical properties

The results from the characterization of the TiAlN, TiAlN/SiNx, TiAlN + CNx, TiAlN/ CNx + TiAlN, and TiAlN/CNx + CNx films are summarized in Table 1 [4, 7]. The hardness measured for TiAlN was 2590 HV. The hardness values of the multilayer TiAlN/SiNx, TiAlN/ CNx + TiAlN, and TiAlN/CNx + CNx films were higher than those of the monolayer TiAlN and TiAlN + CNx films. The increase in hardness could be attributed to the introduction of a large number of TiAlN/SiNx and TiAlN/CNx interfaces in the cases of the TiAlN/SiNx and TiAlN/CNx films, respectively [4, 7]. The high hardness of the multilayer coatings is related to the role of interfaces as effective obstacles to lattice dislocation slip, which is the dominant deformation mechanism in microscale composite coatings. Owing to these interfacial and nanoscale effects, conventional lattice dislocation slip was prevented in the nanostructure


Table 1. Vickers microhardness, critical load, grain size and roughness (Sy) of monolayer and multilayer films.

coatings [4, 26, 27]. Scratch tests were conducted on the coatings and the results are shown in Table 1. The multilayer TiAlN/SiNx, TiAlN/CNx + TiAlN, and TiAlN/CNx + CNx films showed higher critical load values than the monolayer TiAlN and TiAlN + CNx films. These results suggest that the improved adhesion strength might be attributed to the interfaces of the multilayer preventing extension of fractures and the multilayer structure improving the wear resistance of the coating [4].
