Microstructure and indentation hardness study of CAE-PVD (Cr,Ti,Al)N solid solution coatings deposited using a combinatorial multitarget approach

Abstract

In this study we have analysed the indentation hardness and modulus of cathodic arc deposited CrTiAlN coatings as a function of the stoichiometric variables Ti/Cr, Al content and cation mix. The coatings have been prepared using a combinatorial cathode composition approach, leading up to 14 different stoichiometries produced in 5 batches. The coatings have been inspected by glow discharge optical emission spectroscopy, scanning electron microscopy, X-ray diffraction and nanoindentation techniques. The coatings develop crystalline structures compatible with solid solutions of face-centered cubic unit cells for all the compositions produced. Such unit cells exhibited a downwards lattice parameter dependency on the aluminum concentration of the coatings (from 0.417 nm down to 0.413 nm). The indentation hardness as a function of the Ti/Cr is compatible with other previous studies reported. The films hardnesses and moduli also increase as the aluminum concentration increases (21 GPa up to 34 GPa). Both indentation responses upon Ti/Cr and Al are attributed to solid solution strengthening. However in order to prove this statement, the indentation hardness and modulus were studied as a function of the mixing term of the cations, as this term is well representative of the solid solution compositional map. The observed results unambiguously evidence that the solid solution strengthening effect is confirmed on the basis of the dependency between the indentation hardness and the so called degree of mixing.