Issue 16, 2019

Biomimetic hard and tough nanoceramic Ti–Al–N film with self-assembled six-level hierarchy


Nature uses self-assembly of a fairly limited selection of components to build hard and tough protective tissues like nacre and enamel. The resulting hierarchical micro/nanostructures provide decisive toughening mechanisms while preserving strength. However, to mimic microstructural and mechanical characteristics of natural materials in application-relevant synthetic nanostructures has proven to be difficult. Here, we demonstrate a biomimetic synthesis strategy, based on chemical vapour deposition technology, employed to fabricate a protective high-temperature resistant nanostructured ceramic TiAlN thin film with six levels of hierarchy. By using just two variants of gaseous precursors and through bottom-up self-assembly, an irregularly arranged hard and tough multilayer stack was formed, consisting of hard sublayers with herringbone micrograins, separated by tough interlayers with spherical nanograins, respectively composed of lamellar nanostructures of alternating coherent/incoherent, hard/tough, single-/poly-crystalline platelets. Micro- and nanomechanical testing, performed in situ in scanning and transmission electron microscopes, manifests intrinsic toughening mechanisms mediated by five types of interfaces resulting in intergranular, transgranular and cleavage fracture modes with zigzag-like crack patterns at multiple length-scales. The hierarchical 2.7 μm thick film self-assembled during ∼15 minutes of deposition time shows hardness, fracture stress and toughness of ∼31 GPa, ∼7.9 GPa and ∼4.7 MPa m0.5, respectively, as well as phase/microstructural thermal stability up to ∼950/900 °C. The film's microstructural and mechanical characteristics represent a milestone in the production of protective and wear-resistant thin films.

Graphical abstract: Biomimetic hard and tough nanoceramic Ti–Al–N film with self-assembled six-level hierarchy

Supplementary files

Article information

Article type
21 Dec 2018
20 Mar 2019
First published
10 Apr 2019
This article is Open Access
Creative Commons BY license

Nanoscale, 2019,11, 7986-7995

Biomimetic hard and tough nanoceramic Ti–Al–N film with self-assembled six-level hierarchy

M. Meindlhumer, J. Zalesak, R. Pitonak, J. Todt, B. Sartory, M. Burghammer, A. Stark, N. Schell, R. Daniel, J. F. Keckes, M. Lessiak, A. Köpf, R. Weißenbacher and J. Keckes, Nanoscale, 2019, 11, 7986 DOI: 10.1039/C8NR10339A

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