Fracture toughness trends of modulus-matched TiN/(Cr,Al)N thin film superlattices

J. Buchinger, A. Wagner, Zhuo Chen, Zaoli Zhang, David Holec, Paul Heinz Mayrhofer, Matthias Bartosik

Publikation: Beitrag in FachzeitschriftArtikelForschungBegutachtung

6 Zitate (Scopus)

Abstract

Through superlattice (SL) architectures, the hardness as well as the fracture toughness of ceramic thin films can be enhanced. The hardness-related SL effect is reasonably well understood, however, the mechanisms driving the toughness-enhancing effect are still partially unexplored. To isolate the effect of the lattice mismatch from the elastic moduli mismatch on the toughness-related properties, we designed TiN/Cr 0.37Al 0.63N superlattices, in which the involved layers have effectively identical elastic moduli, but sizeably different lattice parameters. Micromechanical bending tests show an enhanced fracture toughness K IC of the SLs (2.5±0.1 MPa√m) compared with monolithic TiN (2.0±0.1 MPa√m) and Cr 0.37Al 0.63N (1.3±0.1 MPa√m) with only a weak bilayer period (Λ) dependence. Superimposing an analytical model based on continuum mechanics on the experimental data, we demonstrate that, at low Λ, the nanolayers within the SL exhibit strong coherency strains, as misfit dislocation formation is energetically unfavourable. With increasing layer thicknesses, misfit dislocations start to form in the two layer materials – first in Cr 0.37Al 0.63N and slightly Λ-shifted in TiN. The associated evolution of coherency strains in the TiN and Cr 0.37Al 0.63N layers causes the observed bilayer-period-dependent toughness enhancement beyond the constituent materials. Supporting structural, morphological, chemical, and mechanical analyses are provided by X-ray diffraction, electron microscopy techniques, and nanoindentation.

OriginalspracheEnglisch
Seiten (von - bis)376-386
Seitenumfang11
FachzeitschriftActa materialia
Jahrgang202.2021
Ausgabenummer1 January
Frühes Online-Datum1 Nov. 2020
DOIs
PublikationsstatusVeröffentlicht - 1 Jan. 2021

Bibliographische Notiz

Funding Information:
JB, AW, DH, PHM, and MB highly acknowledge the financial support of the Austrian Science Fund (FWF): P30341-N36. The authors acknowledge the use of the facilities of USTEM and XRC at TU Wien. We thank the Institute for Mechanics of Materials and Structures (TU Wien) for providing the PicoIndenter PI-85.

Funding Information:
JB, AW, DH, PHM, and MB highly acknowledge the financial support of the Austrian Science Fund (FWF): P30341-N36. The authors acknowledge the use of the facilities of USTEM and XRC at TU Wien. We thank the Institute for Mechanics of Materials and Structures (TU Wien) for providing the PicoIndenter PI-85.

Publisher Copyright:
© 2020 Acta Materialia Inc.

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