Multi-scale interface design of strong and damage resistant hierarchical nanostructured materials

Abstract

Synthesis of damage resistant nanostructured materials with high strength and fracture toughness is a challenging task. In this work, multi-scale interfaces were implemented into a hierarchical TiN/SiOx microstructure to mimic stepwise crack growth behaviour of the hard and damage resistant bivalve mollusc Saxidomus purpuratus shell. In situ micromechanical testing in scanning and transmission electron microscopes revealed multi-scale crack deflection events at grain boundaries of individual alternately-tilted TiN crystallites, at kinks of their repeatedly tilted columnar grains as well as crack interaction with perpendicular interfaces of elastic amorphous SiOx layers. These events induced an increase in the crack surface area, reduction of the crack driving force and dissipation of local stress and energy at the crack tip with subsequent crack slow-down or arrest, resulting in fracture toughness exceeding by ~200% the toughness of monolithic TiN nanoceramics. By this perspective biomimetic microstructural design, catastrophic failure of brittle ceramics may be turned into a predictable and controllable process increasing reliability of strong materials in various challenging safety-critical engineering applications. It also shows potential paths for the development of strong and simultaneously tough materials with high mechanical and thermal stability.