An inverse method for extracting the mechanical properties of the constituent materials of a multilayer from nanoindentation data

Abstract

Multilayer thin films have demonstrated enhanced behaviour relative to monolayers of equivalent thickness (e.g. the superlattice effect). However, multilayer constituents can differ considerably in their microstructures (e.g. from interrupted growth and phase suppression), hence mechanical properties, compared to their monolayer or bulk counterparts. Although methods for extracting effective properties of multilayers are well established, identifying the mechanical properties of the individual constituents of a multilayer required for corresponding finite element models remains very difficult. This paper presents an inverse method for identifying the properties of material constituents in their multilayer states from a combination of finite element simulations and indentation data, which is extensible to multilayers containing any number of constituents. The method is demonstrated using simulations and analysis corresponding to nanoindentation experiments on CrN, TiN and NbN monolayers, and TiN/CrN, NbN/CrN and TiN/NbN multilayers. Constituent properties extracted using the method are presented, and FE models using the extracted properties are employed to assess the applicability of a simple relationship between hardness and yield stress for the constituent materials, and a rule of mixtures for the multilayers.