TY - JOUR

T1 - Fracture toughness trends of modulus-matched TiN/(Cr,Al)N thin film superlattices

AU - Buchinger, J.

AU - Wagner, A.

AU - Chen, Zhuo

AU - Zhang, Zaoli

AU - Holec, David

AU - Mayrhofer, Paul Heinz

AU - Bartosik, Matthias

N1 - Publisher Copyright: © 2020 Acta Materialia Inc.

PY - 2021/1/1

Y1 - 2021/1/1

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85096192228&partnerID=8YFLogxK

U2 - 10.1016/j.actamat.2020.10.068

DO - 10.1016/j.actamat.2020.10.068

M3 - Article

VL - 202.2021

SP - 376

EP - 386

JO - Acta materialia

JF - Acta materialia

SN - 1359-6454

IS - 1 January

ER -