**Author details**

(1–22 μm). But, it is observed that nanoflake size matrix possesses a great compatibility with the graphene and significant improvement in the properties was observed. graphene synthesized through chemically, thermally exfoliated and hummer's method are used to fabricate the composite through hot extrusion. Some of the studies used slurry blending technique in which the ethanol or acetone is used as the medium. Thus processed metal matrix and graphene mixtures are consolidated through hydraulic pressing or hot isostatic pressing (HIP)

The metal (Al, Mg)/graphene composite produced through hot extrusion possess densities close to theoretical densities. Further, nanofiller graphene and the metallic grains are aligned along the direction of extrusion. Most of the graphene-MMCs, synthesized through hot extrusion, exhibit an improvement in strength, fracture toughness and hardness. Al-graphene composites extruded at a temperature less than 500°C possess a drastic improvement in the properties and it was found that they are defect free. Also, optimized graphene content for the aluminum matrix induce the extreme strength and larger grain refinement in the developed composite. Further, optimized graphene content in the matrix prevents the agglomeration

Hot rolling involves a combination of ball milling (high energy) and rolling which was used to fabricate the graphene-metal matrix composite effectively. The metal particle size range of 20–200 μm with 97–99.7% purity was considered in the studies. Thus processed powder mixtures were compacted in a thin copper (Cu) tube and subjected to rolling. Usually high speed differential rolling (HSDR) or equal speed rolling (ESR) is used and HSDR exhibited a larger amount of deformation]. Solid state friction stirring procedure same as friction stir welding. The process uses a non-consumable rotating tool which was hold mechanically by the rotating head and stirs the material. The main challenge in case of graphene/metal matrix system was the huge aspect ratio and small thickness will lead to agglomeration during the surface processing. In addition, a novel combination of liquid state solid stirring followed by friction stir processing to fabricate graphene/metal composite. Lot of agglomeration was found in the current method [58]. Graphene oxide reduction to graphene during chemical mixing was used to form a composite. This method was applied to develop many composite including palladium, platinum, cobalt, gold, etc. In the chemical mixing method solution media was used to disperse GO and metal particles during the synthesis [59]. During the process metal nanoparticles absorbed on the GO flakes and subjected to catalytic reduction reaction of GO with the solution and form a metal-graphene composite. This method enables the metal particle to sit over the reduced graphene nanoflakes and prevents the agglomeration and restacking. Chemical mixing of graphene with metal uses a metallic salts and graphene as a starting material. During the process, metallic salts are reduced in to the solvent and deposited on the graphene sheets to form a composite. The process prevents the agglomeration of the graphene flakes by developing a

Most of the researchers have discussed the positive aspects of graphene reinforced composites, the extensive property of graphene and its huge potential for industrial applications. Due

and sintered at <600°C in argon (Ar) atmosphere followed by extrusion [56].

which helps in preventing the carbide formation sites [57].

nonosized metallic particle between each graphene layers.

**5. Conclusion**

58 Powder Technology

Prashantha Kumar HG\* and Anthony Xavior M

\*Address all correspondence to: prashanthakumar.hg@gmail.com

School of Mechanical Engineering, VIT University, Vellore, TN, India
