Nanoindentation stress–strain curves as a method for thin-film complete mechanical characterization: application to nanometric CrN/Cr multilayer coatings

Abstract

The mechanical behavior of CrN/Cr multilayer coatings deposited by rf magnetron sputtering has been investigated by nanoindentation measurements performed with indenters of different geometries. Nanoindentation stress–strain curves generated from these measurements allow us to characterize the complete mechanical behavior of these coatings in the elastic, elastoplastic, plastic and fracture deformation regimes. In particular, indentation measurements carried out with a 100-μm-radius spherical indenter allowed us to study the elastic deformation regime and estimate the yield stress parameter through the initial indentation yielding point. The elastoplastic deformation regime has been studied using a 5-μm-radius spherical indenter and the stationary yielding regime (fully plastic regime) has been investigated with a pyramidal indenter of Berkovich geometry. The use of a pyramidal cube-corner indenter allowed us to study coating fracture characteristics. Nanometric CrN/Cr multilayer structures as well as single CrN and Cr coatings have been characterized. The study has shown that multilayered coatings with period thicknesses less than 46 nm present values of yield stress, Young’s modulus, hardness and toughness higher than those for single-layer CrN and Cr coatings.