Continuous multi cycle nanoindentation studies on compositionally graded Ti_1-xAl_xN multilayer thin films

Abstract

Two types of Compositionally Graded Multilayer (CGM) films of Ti_1-xAl_xN consisting of 21 layers were synthesized by reactive magnetron co-sputtering technique. The first one begins with a layer of Ti_0.4Al_0.6N from substrate and ends with TiN, whereas exactly a reverse order has been followed in the second one. As deposited CGM films are poly-crystalline with rocksalt structure similar to stoichiometric TiN. Secondary Ion Mass Spectrometry (SIMS) depth profile of the films showed the presence of 21 layers of equal thickness (50 nm) with varying aluminum content in steps. Continuous Multi-Cycle (CMC) nanoindentation technique was used to analyze the failure modes of these films. Topographic examination of the indented zone revealed the presence of edge cracks inside and outside the indentation area when the load exceeds beyond 90 mN. The Load-displacement profiles of CMC and single indentations exhibited the onset of pop-ins at a depth of ~200 nm.