Microstructural, alloying, and architectural effects on the fracture toughness of hard CrN coatings

Physical vapor-deposited CrN is a well-established protective coating material for tribological applications and is also of interest as a potential alternative to Cr(VI)-based coating routes. However, its fracture toughness remains a critical property for mechanically demanding applications. This study investigates microstructural, alloying, and architectural strategies to modify the mechanical properties of cathodic arc-evaporated CrN-based coatings using nanoindentation and in-situ micromechanical cantilever bending tests. Bias- and temperature-induced microstructural changes in pure CrN led to moderate hardness variations but showed only limited influence on fracture toughness within the investigated range. In contrast, Ce-Si alloying increased the hardness up to 27.5 GPa and improved K IC by approximately 20% at low alloying content, indicating that alloying-induced changes in lattice parameter and boundary constitution can enhance crack resistance. The strongest improvement was achieved by CrN/TiN superlattice coatings, where hardness increased by approximately 40% and K IC by approximately 50% compared with the arithmetic mean of the monolithic constituents. This improvement is attributed to interface-related mechanisms associated with the multilayer architecture. Overall, the results show that alloying and superlattice design are more effective strategies for improving the fracture toughness of CrN-based coatings than microstructure tuning of pure CrN alone.