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Research Papers

Investigation of Thermal Stress Variability Due to Microstructure in Thin Aluminum Films

[+] Author and Article Information
Antoinette M. Maniatty1

Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180maniaa@rpi.edu

G. S. Cargill

Department of Materials Science and Engineering, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015gsc3@lehigh.edu

Laura E. Moyer2

Department of Materials Science and Engineering, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015

Chia-Ju Yang

Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180

1

Corresponding author.

2

Present address: Alcoa Power and Propulsion, Alcoa, Inc., 9 Roy St., Dover, NJ 07801.

J. Appl. Mech 78(1), 011012 (Oct 20, 2010) (8 pages) doi:10.1115/1.4002212 History: Received March 24, 2010; Revised July 08, 2010; Posted July 23, 2010; Published October 20, 2010; Online October 20, 2010

An X-ray microbeam study and a polycrystal finite element model of a 10×10μm2 section of a 1μm thick polycrystalline aluminum film on a silicon substrate are used to investigate the effect of microstructure on thermal stress variability. In the X-ray microbeam study, the grain orientations and deviatoric elastic strain field are measured at the subgrain level in the film during and after two thermal cycles. A finite element model of the observed grain structure is created and modeled with an elastoviscoplastic crystal constitutive model that incorporates film thickness and grain size effects as well as dislocation entanglement hardening. The experimental and simulation results are compared at both the film and subgrain scales. While the experiment and model agree fairly well at the film level, the experimental results show much greater elastic strain variability than the simulations. In considering the grain size effect, the experiment and model both predict a similar Hall–Petch coefficient, which is consistent with literature data on free standing aluminum thin films.

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Figures

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Figure 1

(a) FIB image showing the grain structure of the Al film and (b) pole figure showing the strong ⟨111⟩ fiber texture

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Figure 2

Measured temperature history for the second cooling leg

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Figure 3

[100] inverse pole figure color maps of first three area scans at room temperature after the second thermal cycle. Grain boundaries greater than 5 deg are shown and x and y are the horizontal and vertical directions, respectively.

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Figure 4

[100] inverse pole figure color map of grain structure model used in simulations

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Figure 5

Comparison between the model and the experiment of the average biaxial stress versus temperature

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Figure 6

Average normal deviatoric elastic strain components, (a) showing relaxation and (b) after adjusting to compensate for relaxation

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Figure 7

Comparison of perpendicular deviatoric elastic strain resulting from (a) the simulation and (b) the experiment. The x and y scales are in μm and the color scale is in units of 10−3. For the experimental results, the color scale is cropped to match that of the simulation, i.e., pixels with strains outside of the −2.2×10−3 to 1.7×10−3 range were assigned to corresponding end point strain values in (b).

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Figure 8

Effect of the grain size on the perpendicular deviatoric elastic strain

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Figure 9

Hall–Petch coefficient as a function of biaxial strain

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