The Effect of Elastic–Plastic Mismatch and Interface Proximity on the Fracture Toughness of Ti-TiN Thin Films

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 bilayer and trilayer architectures has 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 the plastic zone size of 250 nm in Ti layer improves the overall fracture resistance of the architecture by nearly ten times compared to the initiation fracture resistance in TiN, preventing catastrophic fracture of these multilayered films. These results will aid in physics informed design of optimized thickness of metallic interlayers in multilayered thin film architectures.