Research ArticleMATERIALS SCIENCE

Bioinspired, graphene-enabled Ni composites with high strength and toughness

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Science Advances  31 May 2019:
Vol. 5, no. 5, eaav5577
DOI: 10.1126/sciadv.aav5577
  • Fig. 1 Ni/graphene powders after shear mixing and freeze drying.

    (A) SEM image of Ni/graphene powders, showing no noticeable aggregation of graphene sheets. (B) TEM image of the surface of a Ni/graphene powder, showing that few-layered graphene closely coated around the Ni particle. (C) In situ heating observation of a Ni/graphene powder. Graphene gradually dissolved into Ni with increasing temperature.

  • Fig. 2 Microstructure of the graphene-enabled Ni/Ni3C composite.

    (A) SEM image of cold-rolled Ni/Ni3C composite, showing brick-and-mortar structures. (B) Fracture surface of Ni/Ni3C composite, showing laminated structure constructed by elongated dimples. (C) Low-magnification TEM image, showing a large second-phase particle embedded in the Ni matrix. (D) After cold rolling, Ni grains were deformed into long stripes with the thickness ranging from 100 to 300 nm. (E) Two-beam diffraction dark-field image of the Ni matrix, showing a high concentration of dislocations. (F) Close-up observation of the Ni/Ni3C boundary. (G) HRTEM image of the interface between Ni and a second-phase particle, revealing a transition zone. (H) Ni3C crystal on [−110] plane. (I) HRTEM image of the [−110] plane of Ni3C particle, showing identical atomic arrangement as in the Fig. 2H. (J) Schematic illustration of the formation of Ni/Ni3C composite with a brick-and-mortar structure.

  • Fig. 3 Mechanical properties of graphene-enabled Ni/Ni3C composite with a brick-and-mortar structure.

    (A) Tensile stress-strain curves of Ni, Ni produced by powder metallurgy, and Ni/Ni3C composite (inset shows the size of tensile specimen). (B) Comparative bar chart of mechanical properties of Ni and Ni/Ni3C composite. (C) Elongation versus yield strength plot showing that the as-fabricated Ni/Ni3C composite had an outstanding combination of strength and ductility (mechanical properties of nacre-like composites were derived from (1127, 2934).

  • Fig. 4 Strengthening and toughening mechanisms of graphene-derived Ni/Ni3C composite with brick-and-mortar structure.

    (A) Nanoindentation load-displacement curves of Ni and Ni3C platelet. (B) Hardness map derived from nanoindentation tests. (C) Reduced modulus map derived from nanoindentation tests. (D) Finite element simulation of the Ni/Ni3C composite under tension. (E) APT map of Ni and C atom distribution. (F) APT map of C atom distribution. (G) In situ tensile test with strain map. (H) In situ three-point bending test under SEM.

  • Fig. 5 Microstructure of Ni-Ti-Al/Ni3C composite and high-temperature Vickers hardness of Ni, graphene-derived Ni/Ni3C composite, Ni-Ti-Al/Ni3C composite, and HR-224 superalloy.

    (A) SEM image of Ni-Ti-Al/Ni3C composite after chemical etching. (B) High-angle annular dark-field (HAADF) image of the Ni-Ti-Al/Ni3C composite. (C to F) High-resolution EDS of Ni, Ti, Al, and C maps. (G) Hardness values from high-temperature Vickers hardness tests. (H) Room temperature Vickers hardness indentation impression on Ni-Ti-Al/Ni3C composite (the edge length of the inset image is 180 μm). (I) High-temperature (1000°C) Vickers hardness indentation impression on Ni-Ti-Al/Ni3C composite (the edge length of the inset image is 180 μm).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/5/eaav5577/DC1

    Fig. S1. Graphene sheets produced by shear mixing.

    Fig. S2. Microstructure of Ni/graphene particles without shear mixing or without freeze drying.

    Fig. S3. SEM images of sintered Ni/graphene and Ni sample produced by powder metallurgy after chemical etching.

    Fig. S4. Ni with 4 and 6 wt % graphene after sintering.

    Fig. S5. XRD and EDS spectra of Ni/Ni3C composite and Ni produced by powder metallurgy.

    Fig. S6. Crystal structure and FFT pattern of Ni3C particle.

    Fig. S7. Strengthening of Ni/Ni3C composite.

    Fig. S8. SAED patterns of the Ni matrix.

    Fig. S9. Close-up observation of the crack initiation at the artificial notch.

    Fig. S10. Close-up inspection of the crack propagation of the three-point bending Ni/Ni3C sample.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Graphene sheets produced by shear mixing.
    • Fig. S2. Microstructure of Ni/graphene particles without shear mixing or without freeze drying.
    • Fig. S3. SEM images of sintered Ni/graphene and Ni sample produced by powder metallurgy after chemical etching.
    • Fig. S4. Ni with 4 and 6 wt % graphene after sintering.
    • Fig. S5. XRD and EDS spectra of Ni/Ni3C composite and Ni produced by powder metallurgy.
    • Fig. S6. Crystal structure and FFT pattern of Ni3C particle.
    • Fig. S7. Strengthening of Ni/Ni3C composite.
    • Fig. S8. SAED patterns of the Ni matrix.
    • Fig. S9. Close-up observation of the crack initiation at the artificial notch.
    • Fig. S10. Close-up inspection of the crack propagation of the three-point bending Ni/Ni3C sample.

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