Nature of contact deformation of TiN films on steel

Nanoindentation experiments were carried out on a columnar ∼1.5-μm-thick TiN film on steel using a conical indenter with a 5-μm tip radius. Microstructural examination of the contact zone indicates that after initial elastic deformation, the deformation mechanism of the TiN is dominated by shear fracture at inter-columnar grain boundaries of the TiN film. A simple model is proposed whereby the applied load is partitioned between a deforming TiN annulus and a central expanding cavity in the steel substrate. It is possible to obtain a good fit to the experimental load–displacement curves with only one adjustable parameter, namely the inter-columnar shear fracture stress of the TiN film. The implication of results in the context of the performance of TiN films in service is also discussed.