Alumina particulate/Cu matrix composites prepared by powder metallurgy

Abstract

Two Cu-20 wt-% alumina composites were fabricated by powder metallurgy (PM), one was prepared from Cu coated alumina powders and the second was consolidated from a mixture of Cu and alumina powders. Both composites were cold pressed at different pressures, ranging from 150 to 600 MPa, in a floating die using a hydraulic press, and only compacts pressed at 600 MPa were sintered in pure hydrogen atmosphere at 900°C. The effect of consolidation parameters on powder compressibility was also studied.

Microstructure investigation revealed that a continuous uniform Cu layer was precipitated around each alumina powder. When the investigated powders were cold pressed, it was noted that compacts made from Cu coated alumina have higher green density than those fabricated from mixed powders. Moreover, the sintered Cu coated alumina composites showed higher density and more uniform alumina distribution, and continuous interconnected Cu skeletal structure. However, in the case of sintered composites made from powder mixture, the Cu skeletal structure was broken and the alumina particles were inhomogenously distributed within the Cu matrix. The electrical resistivity and coefficient of thermal expansion of composites made from Cu coated alumina exhibited much lower values than those made from mixed powders, whereas hardness measurements of the latter showed lower values.