Quantitative evaluation of bonding strength for hard coatings by interfacial fatigue strength under cyclic indentation

The adhesion of coating to substrate is an important factor governing the performance and durability of coated engineering components. Existing evaluation methods cannot produce quantitative measurement of bonding strength for strong adherent coating. This paper proposes a novel evaluation method based on the cyclic spherical indentation (CSI) test, which uses successive indentations of a spherical ball onto a coated specimen to induce the detachment of the coatings along the interface. Compared with earlier methods, this method creates only adhesive failures, which only occur during elastic deformation of the substrate, yet it is applicable to coating with strong bonding. The evaluation method creates a curve of shear stress range versus failure cycles for each coating/substrate system. These curves can be used directly to compare the bonding strength of hard coatings.