Elsevier

Ceramics International

Volume 46, Issue 9, 15 June 2020, Pages 13569-13579
Ceramics International

Preparation of Ag/reduced graphene oxide reinforced copper matrix composites through spark plasma sintering: An investigation of microstructure and mechanical properties

https://doi.org/10.1016/j.ceramint.2020.02.142Get rights and content

Abstract

The reduced graphene oxide (rGO) decorated with Ag nanoparticles was synthesized by the chemical reduction of graphene oxide in an aqueous solution containing AgNO3, in the presence of hydrazine hydrate as a reducing agent. The reduction of graphene oxide was confirmed by FT-IR and raman spectroscopy analyses. The x-ray diffraction pattern and UV–visible investigations demonstrated the formation of Ag particles on the surface of rGO sheets. After successful decoration, the Ag/rGO nano-composite was used as the reinforcement in the copper matrix composite. Cu–Ag/rGO composites with different percentages of Ag/rGO (0.4, 0.8, 1.6 and 3.2 vol%.) were prepared by mechanical milling and spark plasma sintering (SPS). The effects of the Ag/rGO content on the consolidation process, micro-hardness, bending strength and also, fracture surface of the prepared samples were then investigated. The three-point bending strength of the sintered samples was increased from 285 to 472 MPa by the addition 0.8 vol%. of Ag/rGO, as compared to the pure Cu. Moreover, increasing the reinforcement content to the 3.2 vol%. Ag/rGO led to decreasing the bending strength to 433 MPa. The highest micro-hardness (81 Hv) was obtained for the composite sample containing the 1.6 vol%. Ag/rGO. By increasing Ag/r-GO as the reinforcement (3.2 vol%.), the Vickers hardness was decreased to 69 Hv. Also, investigation of the fracture surface morphology showed transformation of fracture mechanism from plastic changes to brittle ones by raising the Ag/rGO content volume from 0.8 to 1.6 vol %.

Introduction

Copper and its alloys have been widely used in many branches of engineering applications due to such unique properties as high electrical and thermal conductivity and also, good corrosion resistance. These properties make copper and its alloys suitable candidates for use in electrical sliding contacts, resistance welding electrodes, heat sinks, etc, [[1], [2], [3]]. In spite of the above-mentioned advantages, copper has the main problem of low strength in comparison to other structural engineering metal alloys and composites such as Fe and Ti [[4], [5], [6], [7]]. Therefore, numerous investigations have been devoted to enhancing the mechanical properties of copper with the minimum decrease in electrical conductivity, as the main properties of this metal, through making new alloys or composites [[8], [9], [10]].

Graphene and CNTs have gained more attention among other reinforcements in copper metal matrix composites, such as SiC [11], Si3N4 [12], TiC [13], TiB2 [14], B4C [15], etc, due to the low loss of electrical conductivity and proper mechanical properties of these carbon-based components [[16], [17], [18]].

Graphene is a carbon allotrope with sp2 hybrid. It consists of a layer-to- layer structure from carbon atoms. In the recent years, graphene has been considerably noted by researchers due to such unique properties as the Young's modulus of 1 TPa, and remarkable electrical and thermal conductivity (≈5000 W mk−1). Graphene can be considered as a suitable replacement for carbon nanotubes (CNTs) as the reinforcement in metal matrix composites due to its surface area (2630 m2g-1) and 2-D structure, as compared to CNTs (1315 m2g-1 surface area and 1-D structure). Moreover, using graphene instead of ceramic reinforcements, such as Al2O3, SiC, etc., does not seriously reduce electrical and thermal conductivity of the composites, as compared to the pure copper [[19], [20], [21]].

Although extensive studies have been carried out to improve the mechanical properties of metallic materials with addition of graphene, the homogenous distribution of graphene in the metal matrix is still a major challenge in the preparation of metal-graphene composites. This is since graphene nanosheets (GNPs) tend to agglomerate due to their high surface area and van der Waals forces between GNPs. On the other hand, the weak interfacial bond between copper and graphene, which is due to their different thermal expansion coefficients, causes a significant reduction in the mechanical properties of Cu-based composites. To tackle the difficulty of GNPs agglomeration in metal matrix composites, several different methods have been proposed; these include combined liquid state ultrasonic processing and solid state stirring, flake powder metallurgy and molecular-level mixing. The uniform distribution of GNPs as a result of applying the mentioned method leads to improved mechanical properties [[22], [23], [24]].

The molecular-level mixing is a new method preventing the agglomeration of GNPs synthesized on metallic nanoparticles in metal matrix composites (MMCs). One of the most important benefits of metallic nanoparticles attached to GNPs is that a space obstacle is crated, thereby preventing GNPs from joining. Additionally, physical and mechanical properties of MMCs can be improved by correctly selecting metallic nanoparticles located on GNPs, helping to establish strong bonding in the metal-graphene interface.

In the present work, Ag- rGO (reduced graphene oxide) nano-composite was synthesized by some simple chemical reduction. The employed method offered two benefits: (1) Ag-rGO nanocomposite could be easily provided in one post by the reaction between AgNO3 and graphene oxide (GO) under an aqueous solution containing hydrazine hydrate as the reducer factor; (2) faster reaction and time-saving, as compared to the two-post synthesis methods. Moreover, the effect of reinforcement contents on the mechanical properties and microstructure of Cu– Ag/rGO composites prepared via spark plasma sintering could be investigated.

Section snippets

Synthesis of Ag-rGO nanocomposite

Ag- rGO nanocomposite was synthesized by the chemical reduction of silver nitrate and graphene oxide in an aqueous solution, in the presence of hydrazine hydrate as the reducing agent. For this purpose, 100 mg of GO was dispersed in 200 ml of deionized water by ultrasonication for 40 min in order to achieve a stable colloid of GNPs. The obtained colloid of GNPs was stirred for 1h; then 0.1 g of the AgNO3 powder was added under continuous stirring for 1h to form a homogeneous mixture. The

Results and discussion

Fig. 3 shows the X-ray diffraction (XRD) patterns of GO, rGO and Ag- rGO nanocomposites. As can be observed in Fig. 3a, a peak that appeared at 2θ = 11° that belonged to the (002) diffraction plane of GO. As shown in Fig. 3b, a broad peak that appeared at 2θ = 24.2° could be attributed to the (002) diffraction plane of rGO, implying the removal of oxy-containing functional group and reduction of GO [25,26]. Fig. 3c represents the diffraction peaks obtained at 38.1°, 44.3° and 64.5°, which

Conclusions

  • Ag/rGO nanocomposite was synthesized by a chemical reduction of graphene oxide in an aqueous solution under hydrazine hydrate as the reducing agent and silver nitrate. The morphology of the synthesized nanocomposite showed the homogenous distribution of Ag nanoparticles with a size in the range of 40–55 nm on the rGO sheets.

  • An Ag/rGO nanocomposite with different volume contents was used as the second phase in the copper matrix composite. Cu– Ag/rGO composites were prepared by mechanical milling

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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