Deformation and Cracking Mechanism in CrN/TiN Multilayer Coatings

In this study, the effects of the microstructural properties on the deformation and damage mechanism of CrN/TiN multilayer coatings deposited on Custom 450 steel using the unbalanced reactive magnetron sputtering PVD process were studied. All coatings were fabricated with an overall thickness of 1.5 µm, but different bilayer periods (Λ). Structural and mechanical properties of coatings were investigated by XRD analysis and nanoindentation experiment, respectively. Indentation tests at three loads of 100, 300, and 450 mN were performed on the coatings’ surface and then, cross-sections of fractured imprints were analyzed with SEM and TEM. Measuring the length of the cracks induced by indentation loads and analyzing the load-displacement curves, apparent fracture energy values of multilayer coatings were calculated. We observed that multilayer systems with bilayer periods of 4.5–15 nm possess superlattice structure, which also results in higher values for Young’s modulus and hardness as well as higher fracture energy. Comparison of cross-sectional SEM and TEM observations showed that coatings with smaller bilayer periods tend to deform by shear sliding mechanism due to the existence of the long-grown columns, while short dispersed grains—growing in the coatings with a larger bilayer period—led to deformation via local grain boundary sliding and grain rotation.