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Research Papers

Direct Observation of Crack Propagation in Copper–Niobium Multilayers

[+] Author and Article Information
K. Hattar1

Materials Science and Engineering, University of Illinois; Sandia National Laboratories, Albuquerque, NM 87185-1056

A. Misra

Los Alamos National Laboratory, Los Alamos, NM 87545

M. R. F. Dosanjh

Sandia National Laboratories, Albuquerque, NM 87185-1056,  New Mexico Institute of Mining and Technology, Socorro, NM 87801

P. Dickerson, R. G. Hoagland

 Los Alamos National Laboratory, Los Alamos, NM 87545

I. M. Robertson

Materials Science and Engineering,  University of Illinois, Urbana, IL 61801

1

Corresponding author.

J. Eng. Mater. Technol 134(2), 021014 (Mar 27, 2012) (5 pages) doi:10.1115/1.4005953 History: Received September 30, 2011; Revised January 05, 2012; Published March 26, 2012; Online March 27, 2012

The failure of a cross-sectional 65 nm-thick copper and 150 nm-thick niobium multilayer thin film was investigated via an in situ transmission electron microscopy straining experiment. The fracture of the free-standing multilayer films was associated with confined dislocation slip within layers containing and preceding the crack tip. Four crack hindrance mechanisms were observed to operate during crack propagation: microvoid formation, crack deviation, layer necking, and crack blunting. Failure was observed to occur across and through the copper and niobium layers but never within the interfaces or grain boundaries. These results are discussed relative to the length-scale-dependent deformation mechanisms of nanoscale metallic multilayers.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) SEM micrograph of the Cu–Nb film mounted in a TEM straining structure. (b) TEM micrograph of the initial laminar microstructure including selected-area diffraction pattern.

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Figure 2

(a) Dominant crack after minor loading. (b) Identical crack after additional loading. (c) Fracture surface after in situ straining.

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Figure 3

A series of micrographs illustrating the development of microcracks in the nanolayered film. (a) Development of a microcrack. (b) Development of a second microcrack underneath the first. (c) Crack deviation. (d) Crack growth. (e) Final separation.

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Figure 4

Crack hindrance mechanisms in isostrained Cu–Nb films. (a) Layer necking. (b) Crack blunting.

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Figure 5

(a) Location of final fracture before dislocation motion. (b) Layer thinning. (c) Layer thinning with crack motion. (d) Final fracture in a Cu layer.

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