The Influence of Graphite Content and Milling Time on Hardness, Compressive Strength and Wear Volume of Copper - Graphite Composites Prepared Via Powder Metallurgy

Abstract

Copper – graphite composites are widely used in sliding bearings and brushes due to their excellent thermal and electrical conductivities and high wear resistance. The aim of this research is to study the Influence of graphite content and milling time on hardness, compressive strength, wear volume and friction coefficient of copper - graphite composites prepared via powder metallurgy. A powder mixture containing 0,5,10,15,20 and 25 vol% graphite was milled for 1,3,5,7 and 9 hours. The milled mixture was cold pressed at 700 MPa for 30 second, followed by sintering at 900 oC for one hour. It was found through this work that increasing milling time results an appreciate increase in hardness and radial compressive strength, slight reduction in wear volume and slight increase in the coefficient of friction for all compositions except that for pure copper in which a considerable increase in wear volume and decrease in the coefficient of friction was observed. On the other hand, increasing the graphite volume fraction increases the composite hardness, till an optimum value, and decreases the radial compressive strength. A great decrease in both wear volume and coefficient of friction was observed on increasing graphite content up to 25 vol%. Finally, a graphite, cast iron chips and fireclay sintering configuration was found to be an effective procedure which minimize oxidation to levels comparative with those observed previously by sintering in argon or hydrogen atmospheres.