Deformation Behaviour Study of Cu-graphite, Cu-graphite-SiC Metal Matrix Composite Prepared by Powder Metallurgy

Abstract

Copper is used in many industrial applications like electronic application, automobile industries, and heat sink due to its high electrical conductivity but due to its low strength and wear resistance, its use has been restricted. Addition of graphite into copper reduces the coefficient of friction and but improves wear resistance due to its solid lubricating property but it reduces the mechanical properties like strength and hardness. Addition of SiC on the other hand, increases the hardness and strength of composite and increases the wear resistance of composite but high amount of SiC makes the material brittle. The present research deals with the fabrication of Cu-graphite-SiC hybrid metal matrix composite and deformation behaviour study of Cu-graphite-SiC MMC prepared by powder metallurgy route. Cu-graphite-SiC MMC was prepared by powder metallurgy process by taking different percentage of graphite (5 and 10 vol. %) and SiC (5 and 8 wt. %). The composite powder mixture was cold compacted by uniaxial pressing at a pressure of 700 MPa. Sintering of compacted sample was carried out in tubular furnace under argon gas at a temperature of 900C for 1 hour. The composites were characterized by XRay diffraction, optical microscopy and scanning electron microscopy (SEM). The fabricated composites were cold rolled by single pass (around 50% reduction), then subsequently annealed at 300C. The change in hardness, wear depth and microstructure before and after cold rolling were evaluated. The hardness value increases from 65 VHN to 123 VHN after rolling for Cu-5 vol. % graphite-5 wt. % SiC. A maximum relative density of 95% was achieved for Cu-5 vol. % graphite-8 wt. % SiC composite. Wear depth of Cu-5 vol. % graphite increases from 59 µm to 124 µm after cold rolling. In addition, the residual strain changes form 0.412% to 0.425 % after rolling for the same composite. It has also been observed grains are oriented along the direction of rolling.
Non lubricating sliding wear resistance of the composite increases with increase in graphite and SiC content in the composite as graphite act as a lubricating film on the contact surface and SiC prevent the plastic deformation. Electrical conductivity of pure Cu was found to be 4.5×106 S/m and it decreases to 1.68×106 S/m for Cu-10 vol. % graphite and 2.9×106 S/m for Cu-5 vol.% graphite-5 wt.% SiC which decreases with increase in SiC.