الفهرس 
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Abstract
Copper is widely used in many applications, such as electrical sliding contacts in motor/generator, bush and heat sink applications. Copper has good electrical and thermal conductivities in addition to its availability and good mechanical properties. Nevertheless, the most important disadvantages of copper are the high density, the high coefficient of thermal expansion , the low wear resistance and high coefficient of friction and low thermal stability applications. This study focuses on how to solve such problems by using powder metallurgy technique, in which a reinforcement material is mixed with pure copper in different percentages for improving wear ,reduce coefficient of friction and improve the mechanical properties.
Graphene and tungsten (Cu-W ) are the most common reinforcements added to copper for these purposes. The effect of processing parameters, physical, mechanical and tribological properties of Cu-W/GNPs and Cu/graphene nano-composites synthesized by powder metallurgy (PM) route were discussed. Nano copper composite reinforced with Cu-W or graphene by 0,0.2,0.4,0.6,0.8 and 1 wt.% was prepared by powder metallurgy technique. The samples were fabricated by mixing Cu powder with W and graphene individually in a mixer mill for 24 hr, then the mixed powders were compacted at 700 MPa and sintered in a gas furnace at 1000 oC for 2hrs. Phase identification and microstructure investigations have been established using X-ray diffraction and field emission scanning electron microscope (FE-SEM). The density and mechanical properties of the prepared composites such as hardness, compression and wear behavior were estimated. Both the electrical and thermal conductivities and coefficient of thermal expansion (CTE) were investigated.
The results of XRD for Cu-W/GNPs composites showed that revealing that no solid .state reaction has occurred between W and GNPs . The microstructure investigation indicated that graphene or Cu- W particles are well dispersed in the copper matrix in which a uniform distribution was established. It was found that the graphene or Cu- W free copper sample compacted at 700 MPa and sintered at 1000°C for 2 hrs recorded the lowest relative density due to the generation of micro pores during consolidation, in addition to mechanical, physical and tribological properties when compared to graphene or Cu- W free copper sample compacted at 700 MPa and sintered at 900°C and 1000 °C for 2 hrs. Nano-Cu/graphene composites fabricated under 700 MPa and 1000°C for 2 hrs recorded the lowest relative density and highest hardness,the highest electrical conductivity in 1%GNPs, but exhibited the lowest wear rate, and coefficient of friction. On increasing graphene content, the thermal conductivity and coefficient of thermal expansion decreased. The wear rate and coefficient of friction were also decreased by increasing graphene content. Cu-W/GNPs composites formed under 700 MPa and sintered at 1000 oC for 2 hrs recorded the lowest relative density,highest hardness and compression strength.the wear rate and coefficient of friction is rduced for samples contain 0.8%GNPs for CU-W dual matrix tested at 10 N load. By increasing Cu- W content the hardness. The results also showed that the sample containing 1wt.% Cu- W is of the highest microhardnessand mechanical properties, but the sample containing 1 wt.% Cu- W has the highest electrical conductivity and the lowest coefficient of thermal expansion.