Length-scale-dependent deformation and fracture behavior of Cu/X (X=Nb, Zr) multilayers: The constraining effects of the ductile phase on the brittle phase

Length-scale-dependent deformation and fracture behavior of Cu/X (X=Nb, Zr) multilayers: The constraining effects of the ductile phase on the brittle phase

The plastic deformation and fracture behavior of two different types of Cu/X (X=Nb, Zr) nanostructured multilayered films (NMFs) were systematically investigated over wide ranges of modulation period (λ) and modulation ratio (η, the ratio of X layer thickness to Cu layer thickness). It was found tha...

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Bibliographic Details
Published in:Acta materialia 2011-11, Vol.59 (19), p.7368-7379
Main Authors: Zhang, J.Y., Zhang, X., Wang, R.H., Lei, S.Y., Zhang, P., Niu, J.J., Liu, G., Zhang, G.J., Sun, J.
Format: Article
Language:eng
Subjects:
Applied sciences
Constraining
Constraint effects
Copper
Crack propagation
Deformability
Dislocations
Ductile fracture
Exact sciences and technology
Fracture behavior
Fracture mechanics
Fracture toughness
Fractures
Length scale
Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology
Metals. Metallurgy
Modulation
Nanostructured multilayers
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Summary:The plastic deformation and fracture behavior of two different types of Cu/X (X=Nb, Zr) nanostructured multilayered films (NMFs) were systematically investigated over wide ranges of modulation period (λ) and modulation ratio (η, the ratio of X layer thickness to Cu layer thickness). It was found that both the ductility and fracture mode of the NMFs were predominantly related to the constraining effect of ductile Cu layers on microcrack-initiating X layers, which showed a significant length-scale dependence on λ and η. Experimental observations and theoretical analyses also revealed a transition in strengthening mechanism, from single dislocation slip in confined layers to a load-bearing effect, when the Cu layer thickness was reduced to below ∼15nm by either decreasing λ or increasing η. This is due to the intense suppression of dislocation activities in the thin Cu layers, which causes a remarkable reduction in the deformability of the Cu layers. Concomitantly, the constraining effect of Cu layers on microcrack propagation is weakened, which can be used to explain the experimentally observed λ and η-dependent fracture mode transition from shear mode to an opening mode. Furthermore, the fracture toughness of the NMFs is also found to be sensitive to both λ and η. A fracture mechanism-based micromechanical model is developed to quantitatively assess the length-scale-dependent fracture toughness, and these calculations are in good agreement with experimental findings.
ISSN:1359-6454
1873-2453