Indentation of a hard film on a compliant substrate: film fracture mechanisms to accommodate substrate plasticity

In this paper we discuss various contact damage modes in thin TiN films on steel substrate with increasing load. To understand the displacement at different points along the depth of the film, we have used a TiN–AlTiN multilayered film in which each layer acts as a strain marker and we have also calculated the stresses theoretically using an elastic model of spherical indentation of a bi-layer. The study has helped to understand the physics behind different fracture phenomena, such as confinement of columnar sliding to the middle of the film, the genesis of lateral cracks during unloading, etc. We also emphasize the co-existence and competition of different modes of fracture in the film, rather than a single mode, at a particular combination of film thickness, substrate hardness and load and describe the way different modes interact in the spatial domains when they do coexist.