Synthesis and Characterization of Cu-graphite-SiC Hybrid Metal Matrix Composite Prepared by Powder Metallurgy Route

Abstract

Copper based hybrid metal matrix composites reinforced with graphite and SiC by powder metallurgy route takes the advantage of both graphite and SiC. Graphite helps in improving the wear resistance as graphite acts as a lubricating film on the contact surface and its having small co-efficient of thermal expansion, but hardness decreases due to softness of graphite. SiC helps in improving the hardness of the composite. Copper based hybrid metal matrix composites are used in many electrical contact applications like contact bushes and bearing materials. Cu based metal matrix composite is also used as heat sink because of its low coefficient of thermal expansion and packaging of microelectronics compact. In our present investigation, attempts have been made to fabricate Copper–graphite-SiC hybrid metal matrix composites by powder metallurgy route. The main aim is to improve the mechanical properties and wear resistance of composite with a minor loss of electrical conductivity. Cu-graphite-SiC hybrid metal matrix composites were fabricated using copper powder reinforced with 1, 3, 5, 10 and 15 vol. % graphite along with 2, 5, 10 wt. % of SiC. Powders were blended in a turbula shaker mixer for 30 minutes. The composite powders were cold compacted by uni-axial pressing upon applying a pressure of 700 MPa for 5 minutes. The compacted samples were sintered in a tubular furnace at 900oC for 1h in argon atmosphere. For comparison, coarse and fine SiC powders were used to study the effect of SiC particle size on the mechanical and electrical conductivity of the fabricated composites. X-ray diffraction (XRD) was used to identify the phases of the composite. Microstructural analysis was carried under optical microscope, SEM (Scanning electron microscope) and FESEM (Field emission SEM), which shows the uniform distribution and good bonding of graphite and SiC reinforcement with copper matrix. Archimedes’ principle was used to determine the relative density of the composites and it was found that relative density increased from 78.0 to 86.5% with increase in the amount of reinforcement for coarse SiC particle. For fine SiC particle, the value of relative density was found around 88.5%. It was observed that hardness of the composites increased with increase in SiC content and it decreased with increase in graphite content. The maximum hardness value was achieved for high content of SiC and low content of graphite as the maximum hardness value of 76.1 VHN for Cu-1 vol. % graphite-10 wt. % SiC whereas for pure Cu hardness value was 32 VHN. It was noticed that hardness of the composites containing fine SiC particle is more as compared to coarse SiC particle. Compressive strength of the composites decreases with increase in the graphite content. iv | P a g e There was an increase in compressive strength with addition of higher amount of SiC for fixed content of graphite. Compressive strength of the composite containing fine SiC particle is more as compared to coarse SiC particle. Non-lubricated sliding wear resistance of the composite increases by addition of graphite and SiC in the hybrid composite as graphite act as lubricating film on contact surface and addition of SiC support the stress on the contact surface which prevent plastic deformation but abrasion takes place on the surface. Electrical conductivity of the composites decreased with the increase in the amount of graphite and SiC. The electrical conductivity value for pure Cu was found to be 4.39×106 Siemens/m and it decreased to 1.93×106 Siemens/m for Cu-15 vol. % graphite-10 wt. % SiC. Electrical conductivity of the composite containing fine SiC particle is lower than coarse SiC.