Constitutive analysis for the quantification of hardness decay in a superlattice CrN/NbN hard-coating

Abstract

In the present study, a constitutive analysis of the evolution of the mechanical response of a CrN/NbN superlattice coating exposed to high temperature has been performed. Parametric approaches were used to obtain a single master curve describing the experimental data as well as time–temperature–hardness maps to extrapolate the material response. Although the parametric approaches gave an excellent description of the data, an additional effort was devoted to identifying a constitutive equation similar to the power-law function widely used in creep. An excellent description was obtained for a hardness exponent close to 18 and an apparent activation energy ranging from 400 to 500 kJ/mol. Possible micro-mechanisms giving reason for this value of the apparent activation energy were discussed.