Deconvolution of fracture properties of TiN films on steels from nanoindentation load–displacement curves

A columnar TiN film under contact loading fails by shear fracture along inter-columnar boundaries. To deconvolute inter-columnar fracture strength from load-displacement curves, nanoindentation experiments were carried out on columnar ~ 1.4 (mu)m thick TiN films deposited on steels of various hardness, using a Berkovich indenter. A model, which is developed based on the shear-fracture driven deformation of the coating, is applied to the load-displacement curves to obtain inter-columnar fracture strength. The correlation between the fracture strength, biaxial residual stress and substrate yield stress is outlined. The result suggests that the presence of a high compressive residual stress substantially improves the shear fracture strength of a columnar TiN film.