EFFECT OF GRAPHITE WITH AND WITHOUT COPPER COATING ON CONSOLIDATION BEHAVIOR AND SINTERING OF COPPER-GRAPHITE COMPOSITE

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 fl ask using a mechanical stirrer at 3600 rev min(-1) for a period of 6 m in. The method of copper coating graphite particles is described. The copper-graphite powder mixture was of nominal composition 8 wt-% graph ite. Small cylindrical specimens of 8 mm diameter and 12 mm length wer e obtained by die compaction using a unidirectional hydraulic press at ambient temperature over a pressure range of 400-1200 MPa. For compar ison, parallel specimens made of pure copper powders were consolidated and pressed under identical conditions. In this investigation, an att empt has been made to study the particle properties and behaviour whic h 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 equati on can be applied to the compaction of copper-graphite powder mixes. W hen sintering at 1000 degrees C, it was found that copper coated graph ite compacts were fully sintered in a shorter time than uncoated compa cts. The sintered specimens were mirror polished using a standard tech nique before being examined metallographically. Copper coated graphite composites possessed high relative density and low electrical resisti vity very close to the corresponding values of pure copper, however un coated graphite composites showed lower relative density and higher el ectrical resistivity values. Compression measurements showed that the yield and ultimate strengths of coated graphite composites were much h igher than those of uncoated specimens.