Deformation mechanisms in TiN/(Ti,Al)N multilayers under depth-sensing indentation

TiN/(Ti,Al)N multilayer coatings prepared by physical vapour deposition onto steel substrates were subjected to depth-sensing indentation testing. The investigation was aimed at predicting their performance by identifying the contact-induced fracture mechanisms. Analysis of the load-displacement curves showed their efficiency in identifying the occurrence of cracking, the mechanisms of which were explored using new techniques based on focused ion beam cross-sectional transmission electron microscopy of the indents. The fracture modes were observed to take place along the columnar boundaries and in the layers parallel to the interfaces. Furthermore, the load capacity and the transitions between the different deformation regimes were controlled by a combination of the properties of the coating material itself, the substrate upon which the coating was deposited, and the interface(s) that bonded the system together. Nanoindentation testing with a continuous stiffness module and a high-load cell was also used to study the variation of hardness and effective modulus between the multilayer system and a monolithic TiN reference coating.