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Since it was first isolated in 2004, graphene has been extensively investigated and has become one of the most exciting materials discovered in decades. This sp2 hybridized, two-dimensional (2D), single atom thick carbon (C) alloy possesses incredible physicochemical properties. Therefore, the thermal, electrical and mechanical properties of graphene, alone and in combination with other materials, have been an area of intense research in various avenues, such as within the alloy industry.
Methods such as mechanical exfoliation, epitaxial growth, chemical vapor deposition (CVD), thermal reduction of graphene oxide (GO) and chemical reduction of GO in colloidal suspensions are used to make graphene. While there are several methods available for the production of graphene, those that are suitable for large scale production of graphene are still lacking.
Incorporation of Graphene in Composite Materials
Scientists have been investigating the feasibility of using graphene in conjugation with other 2D and 3D materials to achieve similar physicochemical properties to those exhibited by graphene.
Previous studies have shown that the tensile strength of polyvinyl alcohol (PVA) composites can be increased 76% by incorporating 0.7 wt% graphene. Similarly, a 53% increase in fracture toughness has been achieved in graphene reinforced epoxy composites. Another study has shown that incorporation of 0.78 vol% of graphene platelets in Al2O3 ceramic matrix led to a 31% increase in flexural strength and 27% increase in fracture toughness.
Aluminum Alloy Reinforced by Graphene Nanoflakes (GNFs)
As a result of their low density, superior strength and excellent ductility properties, aluminum (Al) alloys are commonly used in the aeronautical, aerospace and electronics industries. The strength of Al alloys can further be improved by reinforcing the Al with other material of high strength. However, the biggest challenge lies in the successful integration and uniform dispersion of materials, such as carbon fibers or graphene, with Al without compromising the intrinsic structures of Al matrix.
GNFs can be produced by the chemical reduction of GO in colloidal suspensions. Due to the hydrophilic nature of GNFs this material can be used for composite applications. GNFs have been shown to retain the mechanical properties of graphene, despite being comprised of multiple layers of graphene. Although the mechanical properties of GNFs are significantly lower than that of graphene, it is estimated that their tensile strength is still 100 times higher than that of structural steel1. As a result of this exceptional strength, the superior elongation and larger specific surface area of GNFs/Al alloy nanocomposites exhibit great potential for use in next generation metal matrix nanocomposites.
Researchers from the Beijing Institute of Aeronautical Materials, in collaboration with the Aviation Industry Corporation of China, have successfully prepared graphene reinforced Al nanocomposites using powder metallurgy process. This group of researchers has discovered that GNFs/Al alloy nanocomposites demonstrate significantly superior mechanical properties with an increase in GNFs content. In addition, this team found that the incorporation of 0.50 wt% GNFs to the Al alloys increased the yield strength by nearly 50% without decreasing elongation of the Al alloy.
Carbon Fibers Coated with Graphene Reinforced Titanium Aluminide (TiAl) Alloy Composite
As a result of its lightweight and superior strength properties, TiAl alloys are extensively used within the aerospace industry. Several efforts have been made to further improve the strength and toughness of TiAl alloys without increasing the density of the material.
Researchers at the Hebei University of Technology’s School of Material Science and Engineering have used powder metallurgy, melt spun and vacuum melting technologies to produce TiAL alloy reinforced with carbon fibers coated with graphene. The resulting material displayed a prominent reduction in density while also exhibiting extraordinary mechanical properties. Compared to a fracture strain of 16% and average strength of 1801 Mpa in pure TiAl alloys, TiAl alloys reinforced with graphene coated carbon fibers showed improvements in fracture strain to 26.27% and average strength to 2312 Mpa.
As predicted, graphene has emerged as a wonder material with a wide variety of applications. While more work is still required for the large-scale use of graphene and exploitation of its full potential, recent discoveries are pointing towards an optimistic future for graphene-based industries.
Sources and Further Reading
- Liang, J., Huang, Y., Zhang, L., Wang, Y., Ma, Y., Guo, T., & Chen, Y. (2009). Molecular-Level Dispersion of Graphene into Poly(vinyl alcohol) and Effective Reinforcement of their Nanocomposites. Advanced Functional Materials 19(14). DOI: 10.1002/adfm.200801776.
- Rafiee, M. A., Rafiee, J., Wang, Z., Song, H., Yu, Z., Koratkart, N. (2009). Enahnced Mechanical Proeprties of Nanocomposites at Low Graphene Content. ACS Nano 3(12); 3884-3890. DOI: 10.1021/nn9010472.
- Cui, S., Cui, C., Xie, J., Liu, S., & Shi, J. (2018). Carbon fibers coated with graphene reinforced TiAl alloy composite with high strength and toughness. Scientific Reports 8. DOI: 10.1038/s41598-018-20799-y.