Dislocation entangled mechanisms in cu-graphene nanocomposite fabricated by high-pressure sintering

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Highlights

  • Mechanical attrition followed by high pressure sintering (HPS) was significantly fabricates Cu-Gr-NCs with improved mechanical and electrical properties.

  • Cu-Gr NCs shows significantly higher H and E than NC-Cu

  • The stacking faults and twin boundaries formation leads to damage initiation in NC Cu concurrently; the graphene is ruptured by wrinkling.

Abstract

Graphene reinforced Cu-based nanocomposite (Cu-Gr), synthesized using high-pressure forming (∼8 GPa) route at 300 °C, achieved 96% of relative density and 84% IACS improvement in electrical conductivity, along with a significant increase in hardness and Young's modulus up to ∼94 GPa. The structure and defects evolution of NC-Cu and Cu-Gr nanocomposites were investigated using nanoindentation approach, and then backed up computationally. Molecular dynamics (MD) simulations results are well agreed with experimental data, which significantly reveled that grain growth and grain boundary sliding (GBS) are dominant deformation mechanism involves grain boundary movement through dislocation motion, stacking faults (SFs) and twin boundary (TBs) formation, along with matrix failure through grain growth and GBS with an increase in loading, and subsequently bending (bow shape) processes.

Introduction

Recently 2-D structured graphene has been studied intensively due to its unique mechanical strength [1], high elastic modulus (∼1 TPa) [2], and high electrical conductivity (106 S m−1) [3]. After the noble method developed by Novoselov et al., graphene's commercial viability significantly reduced its manufacturing cost [4]. Further, the 2-D structure offers ease in dispersion into the metallic phase such as copper (Cu) [5]. Cu is a widely accepted material for electrical and thermal conductors owing to its low intrinsic resistivity [6]. Therefore, the development of metal matrix composites through graphene dispersion has drawn attention in recent years for applications like heat sinks, electrodes, and chips [7]. More recently, these composites have contributed towards promising strength and toughness [8]. For instance, Rashad et al. have reported a 131% increase in Young's modulus and a ∼ 50% increase in yield strength while fabricating graphene reinforced magnesium composite [9]. Similarly, 10 wt% graphene-reinforced copper matrix composite, fabricated using hot pressure torsion, exhibited 118% and 101% increase in hardness and Young's modulus, respectively [7]. Homogeneous dispersion and poor interfacial bonding are the major challenge in developing such graphene-based composites [10]. In this aspect, the energized ball milling process is a promising route for dispersing graphene into a metallic matrix. Therefore, powder metallurgy route followed by further consolidation process is mostly favored for developing graphene-based composites [[11], [12], [13]]. Chen et al. prepared graphene-based composites using in-situ growth of graphene over flaky copper powders via milling of Cu powders with PMMA [14]. Intriguing mechanical properties were reported with dispersing 0.95 wt% graphene. The composite reported tensile strength of 274 MPa and yield strength of 144 MPa. Similarly, Yang et al. fabricated graphene-nanoribbon (GNR) reinforced Cu matrix composites via spark plasma sintering at 600 °C followed by hot rolling at 800 °C [14]. The work reports a ∼ 1.3% increase in yield strength of Cu with reinforcing 3 vol% GNR. Sadoun et al. fabricated Al-Al2O3-Ag coated graphene hybrid nanocomposite following powder metallurgy route, where hardness and wear properties were improved with the amount of graphene nanosheets (GNs) [13].

In our earlier study, graphene reinforced Cu matrix nanocomposites were consolidated using HPT [6]. The improved strength was attributed to the microstructural refinement and dislocation pinning at the strong matrix-reinforcement interface, and dependence of grain refinement on applied pressure. Present investigation deals with fabrication of Cu-graphene nanocomposites via hot pressure sintering (HPS) and analyze their structure-property correlation. The microstructural analysis was studied using transmission electron microscopy (STEM) investigation and mechanical properties were correlated using nanoindentation, which were backed up computationally using molecular dynamic simulation.

Section snippets

Experimental details

First, the preforms were prepared through mixing powders of Cu (Alfa Aesar, 99.9 wt% pure), and 2, 6 and 8 wt% graphene powders (Alfa Aesar, 99.9 wt% pure) at appropriate proportion, followed by mechanical alloying using a Retsch PM400 high-energy planetary ball mill. The milling was performed in wet (toluene) medium using a tungsten carbide (WC) coated vial and balls (10 mm diameter) with a 10:1 ball to powder weight ratio, operated at 300 rpm, followed by room temperature green compaction at

Results and discussion

The relative densities of the alloys, as shown in Table 1, were calculated using φ = ρexptth equation, where ρexpt and ρth are the experimental and theoretical densities. Theoretical density is calculated using ρth = 1/(mGrGr + mGrGr) [31], where, mGr and mCu are the mass fractions of graphene and Cu, respectively, while ρGr and ρCu are the densities of graphene and Cu of 1.06 g/cc and 8.31 g/cc, respectively [29,30]. It can be observed from Table 1 that almost complete densification was

Conclusions

In conclusion, we have been observed the following key points from the copper-graphene nanocomposite through HPS and nanoindentation processes using experimental followed by computational approaches:

  • 1.

    Mechanical attrition followed by HPS was significant in the fabrication of pure Cu, Cu/2 wt% graphene, Cu/6 wt% graphene, and Cu/8 wt% graphene.

  • 2.

    TEM reveals no trace of week interface between the graphene and Cu matrix. The SAED investigation in the Cu matrix reveals nano-crystalline grain boundaries

Declaration of Competing Interest

The authors declare that they have no Conflict of interests in this paper.

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