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Research Papers

Orientation-Dependent Hardness in As-Deposited and Low-Temperature Annealed Ti/Ni Multilayer Thin Films

[+] Author and Article Information
Zhou Yang

Department of Mechanical Engineering,
University of Washington,
Box 352600,
Seattle, WA 98195

Junlan Wang

Department of Mechanical Engineering,
University of Washington,
Box 352600,
Seattle, WA 98195
e-mail: junlan@u.washington.edu

1Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received September 5, 2014; final manuscript received November 6, 2014; accepted manuscript posted November 13, 2014; published online December 3, 2014. Editor: Yonggang Huang.

J. Appl. Mech 82(1), 011008 (Jan 01, 2015) (7 pages) Paper No: JAM-14-1418; doi: 10.1115/1.4029058 History: Received September 05, 2014; Revised November 06, 2014; Accepted November 13, 2014; Online December 03, 2014

Strong orientation dependent hardness has been observed in both as-deposited and low-temperature annealed Ti/Ni multilayer thin films. The anisotropic hardness of as-deposited films is attributed to dominant deformation mechanism switch from dislocation pile-up against the interfaces to confined layer slip (CLS) within the layers as the loading direction changes from perpendicular to parallel to the interfaces. Additional strengthening of the multilayers is achieved after low-temperature annealing without noticeable microstructure modification due to temperature-induced grain boundary relaxation. This thermal strengthening is found to increase with decreasing layer thickness and increasing annealing temperature, and is more pronounced for loading directions parallel to the interfaces.

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Figures

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Fig. 3

SEM images of cross section morphology for Ti/Ni multilayer films with individual layer thickness: (a) 200 nm; (b) 100 nm; (c) 50 nm; and (d) 25 nm

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Fig. 4

SEM images of 200 °C annealed Ti/Ni multilayer with layer thickness 200 nm: (a) surface morphology and (b) cross section morphology

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Fig. 5

Hardness of Ti/Ni multilayer films for surface indentation and cross section indentation. The hardness is fitted by Hall–Petch model for surface indentation and CLS model for cross section indentation, respectively.

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Fig. 6

Representative SEM (a) and SPM (b), images of polished cross sections of the multilayer thin films after indentation

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Fig. 2

SEM images of surface morphology for Ti/Ni multilayer films with individual layer thickness: (a) 200 nm; (b) 100 nm; (c) 50 nm; and (d) 25 nm

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Fig. 1

XRD spectra for as-deposited and 200 °C annealed Ti/Ni multilayers

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Fig. 7

Hardness of both as-deposited and annealed Ti/Ni multilayer films: (a) surface indentation, (b) cross section indentation, and (c) comparison of surface (S) indentation and cross section (CS) indentation with the annealing induced hardening shown as increment on the bar graph

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