FORMATION OF A GRAPHITE-RICH ZONE IN CENTRIFUGALLY CAST-COPPER ALLOY GRAPHITE COMPOSITES

The formation of the graphite-rich zone in centrifugally cast copper a lloy containing originally 7 and 13 vol % graphite particles, cast at 800 and 1900 r.p.m. was studied as a function of the rotational speed of the mould and the volume fraction of graphite particles. The calcul ated recovery of graphite particles in copper alloys was found to be a round 99% and 95%, for 7 and 13 vol% graphite particles originally add ed to the melts, respectively. The ratio of the thickness of graphite- rich zone to the casting thickness was observed to increase with incre asing volume fraction of graphite particles and with decreasing rotati onal speed of the mould. These ratios were found to be between 0.56 an d 0.76 for centrifugal casting of copper alloy containing 7 and 13 vol % graphite particles, respectively, cast at 800 r.p.m.; the correspond ing ratios were between 0.42 and 0.71, respectively, for the alloys ca st at 1900 r.p.m. The ratio of the thickness of the graphite-rich zone to the casting thickness has been discussed in terms of the velocity of the particle and the solid/liquid interface. (C) 1998 Chapman and H all.