Sintering mechanisms of Cu-Cr metallic composites

Abstract

Sintered Cu-Cr composites are widely used as electrical contacts for medium voltage circuit breakers. These materials take advantage of the high thermal and electrical conductivity of Cu and of the refractory and oxygen getter properties of reinforcing Cr particles. Although uniaxial compaction followed by free sintering is a cost-effective route for the net-shape manufacturing of Cu-Cr contacts, the sintering mechanisms of these composites are not well documented. This work analyses the solid-state sintering mechanisms of Cu-Cr powder mixtures using dilatometric and thermogravimetric analyses, completed with microstructural observations. Comparison of pure Cu and of Cu-Cr sintering evidences two main effects of Cr on the sintering of the Cu matrix: i) Cr prevents swelling by fixing in the solid phase the gas compounds produced by reaction of the powder with the atmosphere; ii) Cr limits densification through constrained sintering of the Cu matrix. These effects can balance each other. The role of Cr content and atmosphere is analyzed and discussed to the purpose of optimizing the densification of the composites.