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Bulk copper, copper-graphene and copper-graphite composites were produced from copper-thermally expanded graphite (TEG) powder mixtures with 0-3 wt.% TEG contents via modified powder metallurgy process that includes powder milling in a planetary mill at 350 rpm for 5 hours, compaction, and vacuum annealing at 1030 °C for 1 hour. Phase composition and microstructure of the composites were analysed by XRD and SEM techniques. According to Raman spectroscopy, TEG transforms into a few layer graphene flakes in case of composites with 0.1-1 wt.% of carbon additive, while for 3 wt.% of carbon additive it remains in the form of graphite. The addition of 0.1 wt.% TEG results in the tensile strength increase up to 160 MPa (from 93 MPa for pure copper specimen synthesized via the similar synthesis route). Vickers hardness obtained for Specimens under the study is independent fromthe composite composition. [ABSTRACT FROM AUTHOR]

This paper presents data on fabrication of "nickel-graphene-graphite" bulk composites using powder metallurgy methods combined with the high energy ball milling. The composites were then processed by high pressure torsion (HPT) at temperatures of 23 and 200 °C. This treatment gives rise to the formation of new "nanostructured nickel-graphene" composites. The phase composition of the new composite specimens was examined by X-ray diffraction. Raman spectroscopy proved graphite-to-graphene conversion under mechanical treatments. The microstructure of the new composite specimens was investigated by scanning electron and transmission electron microscopy methods. Composite specimens after HPT at temperature of 200 °C demonstrate the optimal combination of strength (σ02= 923 MPa; σb= 992 MPa) and ductility (Ϙ = 99%). Composite specimens with 2 wt.% graphene content after HPT at room temperature exhibits superior microhardness Hv = 6.45 GPa. [ABSTRACT FROM AUTHOR]

The present work reports the detailed investigation of graphene-modified bulk nickel composites with graphene+graphite phase content up to 4.7 at.%. The composites were fabricated using ball milling and powder metallurgy methods with nickel nanopowder and exfoliated graphite being starting materials. Phase composition and composites structure were studied via X-ray diffraction technique (XRD), Differential scanning calorimetry (DSC), Raman spectroscopy (RS) and scanning electron microscopy (SEM). The effect of graphene addition on the grains size and orientation was determined from backscattered electrons images (EBSD technique). The effect of graphene-graphite phase content on the mechanical properties of the composite was studied. It was shown that small amounts of this phase result in the graphene formation on the surface of metal grains; in turn, this phenomenon affects the composite mechanical properties: its hardness increases, its plasticity decreases, and the strength value remains on the same level. The increase in the graphene-graphite phase content results in graphene flakes formation and new phase allocation corresponding to graphite, leading to the plasticity recovery and in the significant decrease of hardness and strength. [ABSTRACT FROM AUTHOR]