Length-scale effects on fracture of multilayers

Fracture of Ti/TiN multilayer specimens was studied in situ inside a transmission electron microscope. Fracture toughness for cracks propagating perpendicular to the multilayers is found to be thickness dependent, varying from 1.45 to 2.45 MPa-m0.5 as the specimen thickness increased from 150 to 300 nm. Single-mode crack renucleation was observed in the metals layers, which is anomalous to the continuum-based elastic–plastic multilayer fracture model predictions. This is explained by the ultrafine columnar grain structure in the metal layers.