Effect of Graphite with and Without Copper Coating on Consolidation Behaviour and Sintering of Copper–Graphite Composite

Abstract

Copper-graphite composites were made by a powder metallurgical method. Two starting graphite powders, either with or without copper coating, were each mixed individually with copper metal powder in a conical flask using a mechanical stirrer at 3600 rev min⁻¹ for a period of 6 min. The method of copper coating graphite particles is described. The copper-graphite powder mixture was of nominal composition 8 wt-% graphite. Small cylindrical specimens of 8mm diameter and 12mm length were obtained by die compaction using a unidirectional hydraulic press at ambient temperature over a pressure range of 400-1200 MPa. For comparison, parallel specimens made of pure copper powders were consolidated and pressed under identical conditions. In this investigation, an attempt has been made to study the particle properties and behaviour which influence the consolidation of mixes of copper and graphite (coated or uncoated) powders. The green density values of compacts at various pressures are reported. It was found that the Konopicky-Shapiro equation can be applied to the compaction of copper-graphite powder mixes. When sintering at 1000°C, it was found that copper coated graphite compacts were fully sintered in a shorter time than uncoated compacts. The sintered specimens were mirror polished using a standard technique before being examined metallographically. Copper coated graphite composites possessed high relative density and low electrical resistivity very close to the corresponding values of pure copper, however uncoated graphite composites showed lower relative density and higher electrical resistivity values. Compression measurements showed that the yield and ultimate strengths of coated graphite composites were much higher than those of uncoated specimens. PM/0745