Graphene–aluminum nanocomposites
Highlights
► We investigated the mechanical properties of aluminum and aluminum nanocomposites. ► Graphene composite had lower strength and hardness compared to nanotube reinforcement. ► Processing causes aluminum carbide formation at graphene defects. ► The carbides in between grains is a source of weakness and lowers tensile strength.
Introduction
Graphene has attracted considerable attention in the last several years because of properties such as high mechanical strength and modulus, electrical and thermal conductivity and optical transmittance. Fabrication methods have been devised to create single layer and multilayer graphene and graphene oxide in small quantities, with the intent to find methods that will result in bulk quantities of graphene for use in applications such as composites. There have been a limited amount of studies on the behavior of graphene composites. While studies have primarily been concerned with enhancing the properties of polymer matrices [1], [2], [3], [4], [5], with some results having shown great promise, there has been little to no research in metal matrices. This is likely a result of the greater difficulties in dispersion and fabrication, and the unknown interfacial chemical reactions in metal composites. This disparity in the amount of research given to polymer matrices as compared to metal matrices is seen in carbon nanotube (CNT) composites as well.
Aluminum has been a common material to study in metal–carbon nanotube composites due to the diverse range of technical applications for lightweight alloys. Researchers have seen mixed results with some reporting little or no increase in mechanical strength [6] while others have seen significant increases in strength. Many of these differences are a result of the quality of dispersion, fabrication method, and interfacial reactions that occur. In this study, graphene platelets derived from graphite oxide are combined with aluminum in order to observe the effects on mechanical strength.
Section snippets
Experimental procedure
Valimet H-10 atomized pure aluminum powder with an average particle size of ∼22 μm was used in this study. Graphite oxide was prepared by oxidizing graphite in a solution of sulfuric acid, nitric acid, and potassium chlorate for 96 h [7], [8]. Thermal exfoliation of graphite oxide was achieved by placing the graphite oxide powder in a quartz tube that was sealed at one end. The other end was closed using a rubber stopper and an argon inlet was inserted into the stopper. The sample was flushed
Results and discussion
Table 1 shows the hardness of the various samples after hot isostatic pressing and after extrusion. It is clear from the data that the aluminum reinforced with 1.0 wt% MWNT displays the highest hardness among the materials tested. Pure aluminum showed an increase in hardness after extrusion to a value slightly below the nanotube reinforced material. The increase in hardness is likely due to the formation of a more refined and compacted microstructure. The graphene composite showed high
Conclusions
We have fabricated aluminum nanocomposites by milling, hot isostatic pressing, and hot extrusion. Our results indicate that multiwalled carbon nanotubes can increase the tensile strength of aluminum by up to ∼12%. However we find that graphene is prone to forming aluminum carbide during processing, which lowers the hardness and tensile strength of aluminum. The defective nature of graphene produced by thermal exfoliation/reduction of graphite oxide is likely responsible for promoting aluminum
Acknowledgments
The authors wish to acknowledge Prof. Roger N. Wright at Rensselaer Polytechnic Institute for his assistance in extruding the aluminum billets.
References (19)
- et al.
Mater. Sci. Eng. A
(2011) - et al.
Acta Mater.
(2007) - et al.
Mater. Sci. Eng. A
(2003) - et al.
Acta Mater.
(2006) - et al.
Carbon
(2009) - et al.
Mater. Lett.
(2007) - et al.
Compos. Sci. Technol.
(2010) - et al.
Mater. Sci. Eng. A
(2007) - et al.
J. Alloys Compounds
(2008)