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Research Papers

Strengthening Behavior and Tension–Compression Strength–Asymmetry in Nanocrystalline Metal–Ceramic Composites

[+] Author and Article Information
A. M. Dongare1

Department of Materials Science and Engineering,  North Carolina State University, Raleigh, NC 27695amdongare@ncsu.edu

B. LaMattina, A. M. Rajendran

Rutgers,  The State University of New Jersey, Piscataway, NJ 08854 Department of Mechanical Engineering,  University of Mississippi, University, MS 38677

1

Corresponding author.

J. Eng. Mater. Technol 134(4), 041003 (Aug 09, 2012) (8 pages) doi:10.1115/1.4006678 History: Received October 17, 2011; Revised April 16, 2012; Published August 09, 2012; Online August 09, 2012

Metal–ceramic composites are an emerging class of materials for use in the next-generation high technology applications due to their ability to sustain plastic deformation and resist failure in extreme mechanical environments. Large scale molecular dynamics simulations are used to investigate the performance of nanocrystalline metal–matrix composites (MMCs) formed by the reinforcement of the nanocrystalline Al matrix with a random distribution of nanoscale ceramic particles. The interatomic interactions are defined by the newly developed angular-dependent embedded atom method (A-EAM) by combining the embedded atom method (EAM) potential for Al with the Stillinger–Weber (SW) potential for Si in one functional form. The molecular dynamics (MD) simulations are aimed to investigate the strengthening behavior and the tension–compression strength asymmetry of these composites as a function of volume fraction of the reinforcing Si phase. MD simulations suggest that the strength of the nanocomposite increases linearly with an increase in the volume fraction of Si in the Al-rich region, whereas the increase is very sharp in the Si-rich region. The higher strength of the nanocomposite is attributed to the reduced sliding/rotation between the Al/Si and the Si/Si grains as compared to the pure nanocrystalline metal.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Phase diagrams of the Al–Si alloy predicted by the A-EAM potential (a) and obtained experimentally [29] (b). The eutectic temperatures and compositions are 887 K and 21 at. % Si in (a) and 850 K and 12.2 at. % Si in (b).

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Figure 2

The initial configuration of nanocrystalline Al/Si systems with an average grain size of 6 nm and a total of 43 grains and each atom is colored according to the CNA/CN values. The contour for the Al atoms colored according to the CNA/CN characterization is as follows: the yellow atoms represent bulk fcc stacking, the red colored atoms represent local hexagonal close-packed order (stacking faults), the light blue atoms represent a coordination of 12 other than fcc, and the dark blue atoms represent a coordination other than 12. The contour for the Si atoms colored according to the CNA/CN characterization is as follows: The purple atoms represent the tetrahedral bonding in the diamond cubic lattice, the light blue atoms represent a coordination of 4 other than the tetrahedral bonding, the green atoms represent coordination greater than 4, the dark blue atoms represent a coordination of less than 4. See online article for color figure.

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Figure 3

Stress–strain curves for deformation of nanocrystalline Al–Si composites with varying Si volume fractions for conditions of loading in (a) tension and (b) compression. See online article for color figure.

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Figure 4

Stress–strain curves for deformation of nanocrystalline (a) Al, (b) Al/Si composite (volume fraction ∼ 56% Si), and (c) Si with a grain size of 6 nm for conditions of loading in tension (black curve) and compression (red curve). See online article for color figure.

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Figure 5

Calculated flow stress curves for deformation of nanocrystalline Al/Si sample for various volume fractions of Si. The red colored curve (linear fit) corresponds to tensile loading conditions and the black curve (linear fit) corresponds to compressive loading conditions.

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Figure 6

Snapshots of the nanocrystalline Al/Si system corresponding to 15% strain during loading in tension and compression for a volume fraction of: 0% Si in (a) and (b); 28% Si in (c) and (d); 56% Si in (e) and (f); and 100% Si in (g) and (h). The atoms are colored according to the CNA/CN contour as indicated in Fig. 2. See online article for color figure.

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