Wear behavior and electrical conductivity study of Cu-graphite MMC prepared by powder metallurgy route

Abstract

We have studied the effect of pitch coke and milling on wear behavior and electrical conductivity of Cu-graphite composite. Copper-graphite MMC containing 1, 3, 5 and 10 vol. % of graphite plus pitch coke were prepared by conventional powder metallurgical route where graphite/pitch coke ratio are 50:50 (by weight) and 30:70 (by weight). The composite powder mixture were cold compacted and sintered in tubular furnace at 900° C for 1h with argon gas. The composites were then characterized by XRD and SEM. It was observed that high hardness values of Cu-graphite metal matrix composite with graphite/pitch coke ratio of 30:70 (by weight) as compared to 50:50. It has also been noticed that MMC with graphite/pitch coke ratio of 30:70 shows higher wear resistance due to higher hardness as compared to 50:50. Wear rate and wear volume was calculated and found that it decreases with increase in vol. % of graphite. Electrical conductivity analysis shows decrease in electrical conductivity with increase in vol. % of graphite plus pitch coke. To study the effect of milling, Cu with 1 & 5 vol. % of graphite powders were milled for 2, 4, 8, 20 and 40h. The milled powder mixture were cold compacted and sintered in tabular furnace at 900° C for 1h with argon gas. It can be seen from the micrographs that initially there is an increase in particle size (flake formation) due to ductile nature of Cu. But in later stage reduction in particle size takes place due to strain hardening during milling. In initial milling period (up to 10 h) hardness trend is decreasing but after that hardness value goes up. Milling of initial Cu and graphite powder mixtures result in higher wear resistance than un-milled powder. Wear rate and wear volume decreases with increase in milling time. It was also observed that high hardness of Cu-graphite MMC (milled) as compared to (un-milled). Electrical conductivity decreases with increase in milling time as milling introduces number of defects and impurity.