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Abstract
It is well established that many properties of copper-based composites are far superior to those of conventional copper or its alloys. Examples of such properties include specific strength, high temperature deformation, wear resistance, and have low thermal expansion. In many applications, such as electrical contact devices and substrate for silicon semiconductor elements, controlled thermal expansion is required in order to match other linking components.
In this study, pure calcined alumina particles were chemically coated with Cu, with loading of 80 wt. %. The Cu-coated alumina powders were used to fabricate Cu-alumina composites using conventional powder metallurgy process. For comparison, uncoated alumina powders were dry-mixed with Cu-powder of the same Cu loading as those made from coated composites, and the mixture was then cold pressed and sintered at identical processing conditions which were applied for fabricating Cu-coated alumina composites.
In this investigation, different activation processes were employed for alumina powders in order to enhance the Cu-coating process, namely. Cu-coating inactivated alumina composites, Cu-coating etched alumina composites. Cu-coating Pd-metallized alumina composites, and Cu-coating Ag-metallized alumina composites. The chemical composition of all investigated materials of either coated or uncoated are the same, and differ only from one to another with few decimal percent (less than 0.05 %) which resulted due to the activation process.
Evaluation testing were carried out for both Cu-alumina composites of either coated or uncoated powders, which include: density and porosity measurements, electrical and thermal conductivity, hardness and wear, thermal expansion, and corrosion behaviour. Microstructure observation of Cu-coated alumina particles indicates that all types of different activated alumina were successfully coated with copper up to 80 wt. % Cu. Qualitative description of the compaction and sintering processes were given. It was found that, the green densities of Cu-coated reinforcements compacts were higher than that of uncoated one. The microstructure of Cu-coated sintered composites revealed that less porosity content and good contact between reinforcement and Cu-matrix were observed.
When comparing the measured properties of Cu-coated alumina composites with uncoated one it was found that the properties of Cu-coated composites were superior. Comparing the properties of the Cu-coated composites with different activation processes, it was noted that the best properties observed for the Cu-coated with Pd and Ag metallization composites, and the lowest properties was observed for the Cu-