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

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.