The effect of elastic-plastic mismatch and interface proximity on the fracture toughness of Ti-TiN thin films

TL;DR

This study investigates how elastic-plastic mismatch and interface proximity influence the fracture toughness of Ti-TiN multilayer thin films, revealing that metallic Ti interlayers significantly enhance crack resistance.

Contribution

It quantifies the impact of elastic-plastic mismatch and interlayer thickness on fracture toughness, providing new insights for designing more durable TiN-based coatings.

Findings

Ti interlayers increase crack growth resistance.

A 250 nm Ti layer improves fracture resistance tenfold.

Plastic dissipation in Ti enhances toughness.

Abstract

Magnetron sputtered titanium nitride (TiN) thin films are widely used as protective coatings due to their high hardness, but suffer from inherent brittleness and low fracture toughness, limiting their applicability. The multilayering of TiN films with metallic titanium (Ti) interlayers in the form of bi-layer and tri-layer systems have been studied using microcantilever fracture tests. Plastic dissipation in the Ti layer is shown to lead to an increase in crack growth resistance. The effect of the elastic-plastic mismatch between the two materials on the crack driving force, as well as the size of the fully developed plastic zone in Ti have been quantified in this work for the first time. It is shown that incorporating a Ti layer thickness of 250 nm can improve the fracture resistance by nearly ten times compared to the initiation fracture toughness in TiN, preventing catastrophic fracture of these multi-layered films. These results will aid in physics informed design of optimised thickness of metallic interlayers in multi-layered thin films.